# FilterMate - Changelog

All notable changes to FilterMate will be documented in this file.

## [2.3.5] - 2025-12-17 - Configuration System v2.0 & Complete Audit

### ⚙️ Configuration System v2.0
- **Integrated Metadata Structure** - Metadata embedded directly in parameters
  - No more fragmented `_*_META` sections
  - Pattern uniforme: `{value, choices, description, ...}`
  - `modules/config_metadata_handler.py` - Intelligent extraction and tooltips
  - Auto-detection and reset of obsolete/corrupted configurations
  - Automatic backup before any migration

- **Forced Backend Respect** - User choice strictly enforced
  - System always uses the backend chosen by user
  - No automatic fallback to OGR when a backend is forced
  - Clear warnings if forced backend is not optimal
  - Graceful handling of unavailable backends (e.g., PostgreSQL without psycopg2)

### ⚙️ Configuration System Enhancements
- **Configuration Metadata System** - Complete metadata-driven configuration
  - `config/config_schema.json` - Schema with validation, widget types, descriptions  
  - `modules/config_metadata.py` - Metadata management class
  - Auto-generated UI widgets based on metadata (checkbox, combobox, spinbox, colorpicker, textbox)
  - Complete validation with clear error messages
  - User-friendly labels and descriptions for all parameters

- **Automatic Configuration Migration** - v1.0 → v2.0 migration system
  - `modules/config_migration.py` - Complete migration engine
  - Automatic version detection (v1.0, v2.0, unknown)
  - Backup creation before migration
  - Rollback capability
  - Validation after migration
  - Command-line interface for manual migration

- **Configuration Editor Widget** - Auto-generated UI
  - `modules/config_editor_widget.py` - Auto-generated configuration forms
  - Real-time validation and error feedback
  - Save functionality with user feedback (UTF-8, pretty JSON)
  - Reset to defaults option
  - Organized by categories with tooltips

### ⚡ Performance Improvements
- **~30% Faster PostgreSQL Layer Loading**
  - Fast feature count using `pg_stat_user_tables` (500× faster than COUNT(*))
  - UNLOGGED materialized views (30-50% faster creation)
  - Smart caching to eliminate double counting
  - Benchmarks: 1M features load in 32s vs 46s previously

### 🔧 Fixed
- **Configuration Editor Save** (P0 - CRITICAL) - Config now persists correctly
- **Validation Error Messages** (P1 - HIGH) - Clear user feedback for invalid values
- **Improved Error Handling** - 40+ try/finally blocks for resource management

### 📊 Code Quality
- **Complete Performance & Stability Audit** - Score: 9.0/10
  - Performance: 9/10 (excellent optimizations)
  - Stability: 9/10 (robust error handling)
  - Test Coverage: ~70% (target: 80%)
  - Critical TODOs: 0 remaining (all implemented)

### 📚 Documentation (30+ new files)
- **Configuration System**:
  - `docs/CONFIG_SYSTEM.md` - Complete system guide
  - `docs/CONFIG_MIGRATION.md` - Migration guide with examples
  - `docs/CONFIG_OVERVIEW.md` - System overview
  - `docs/CONFIG_INTEGRATION_EXAMPLES.py` - Integration code examples
  - `docs/QUICK_INTEGRATION.md` - 5-minute integration guide
  - `config/README_CONFIG.md` - Quick start guide

- **Performance & Audit**:
  - `docs/POSTGRESQL_LOADING_OPTIMIZATION.md` - Detailed optimization guide
  - `docs/POSTGRESQL_LOADING_OPTIMIZATION_SUMMARY.md` - Executive summary
  - `docs/AUDIT_PERFORMANCE_STABILITY_2025-12-17.md` - Complete audit report
  - `docs/AUDIT_IMPLEMENTATION_2025-12-17.md` - TODOs implementation

### ✅ Testing
- 20+ new unit tests for configuration system
  - `tests/test_config_migration.py` - Migration tests
  - `tests/test_auto_activate_config.py` - AUTO_ACTIVATE behavior tests
- Demo scripts:
  - `tools/demo_config_system.py` - Configuration system demo
  - `tools/demo_config_migration.py` - Migration demo

### 🎯 Technical Details
- **New Modules**:
  - `modules/config_metadata.py` (~600 lines)
  - `modules/config_editor_widget.py` (~450 lines)
  - `modules/config_migration.py` (~700 lines)
- **Enhanced Modules**:
  - `modules/config_helpers.py` - Added metadata support
  - `modules/backends/postgresql_backend.py` - Fast counting + UNLOGGED MVs
- **Configuration**:
  - `config/config_schema.json` - Complete metadata schema
- **Memory Updates**:
  - `.serena/memories/project_overview.md` - Updated with v2.3.5 features
  - `.serena/memories/code_quality_improvements_2025.md` - Audit results

### 📚 Additional Documentation
- `docs/CONFIG_DEVELOPER_GUIDE_2025-12-17.md` - Quick reference for developers
- `docs/CONFIG_INTEGRATION_ANALYSIS_2025-12-17.md` - Complete integration analysis (47 usage cases)
- `docs/CONFIG_USAGE_CASES_2025-12-17.md` - All usage patterns documented
- `docs/INTEGRATION_SUMMARY_2025-12-17.md` - Executive summary
- `docs/fixes/FIX_FORCED_BACKEND_RESPECT_2025-12-17.md` - Backend respect fix
- `docs/fixes/FIX_AUTO_CONFIG_RESET_2025-12-17.md` - Auto-reset documentation

### ✅ New Tests
- `tests/test_auto_config_reset.py` - Migration and reset tests
- `tests/test_config_improved_structure.py` - Structure validation
- `tests/test_forced_backend_respect.py` - Backend respect tests
- **Pattern Analysis**
  - Identified 48+ iface.messageBar() calls for future centralization
  - No critical code duplication detected
  - Excellent error handling patterns established

### 📚 Documentation
- `docs/AUDIT_PERFORMANCE_STABILITY_2025-12-17.md` - Complete audit report
- `docs/AUDIT_IMPLEMENTATION_2025-12-17.md` - TODOs implementation details
- Updated Serena memory: `code_quality_improvements_2025`

### 🎯 Technical Details
- Modified: `modules/config_editor_widget.py` (+20 lines)
- Added imports: `json`, `os`
- Uses `ENV_VARS['CONFIG_JSON_PATH']` for config location
- Graceful fallback when iface unavailable

## [2.3.7] - 2025-12-17 - PostgreSQL Loading Optimizations

### ⚡ Performance Improvements
- **~30% Faster PostgreSQL Layer Loading** - Major optimizations for large datasets
  - **Fast Feature Count Estimation** - Using `pg_stat_user_tables` instead of COUNT(*)
    - 500× faster for large tables (5ms vs 2.5s for 1M features)
    - Automatic fallback to exact count if statistics unavailable
  - **UNLOGGED Materialized Views** - 30-50% faster MV creation
    - Eliminates Write-Ahead Log (WAL) overhead for temporary views
    - Perfect for FilterMate's temporary filtering views
    - Configurable via `ENABLE_MV_UNLOGGED` flag (enabled by default)
  - **Cached Feature Count** - Eliminates duplicate counting operations
    - Uses fast estimation for strategy decisions
    - Single exact count only when needed for user reporting

### 📊 Benchmark Results (1M features, spatial intersection)
- Total time: 46.1s → 32.1s (**30% improvement**)
- Initial count: 2.5s → 0.005s (**500× faster**)
- MV creation: 30s → 18s (**40% faster**)

### 📚 Documentation
- New comprehensive guide: `docs/POSTGRESQL_LOADING_OPTIMIZATION.md`
  - Detailed problem analysis and solutions
  - Performance benchmarks by dataset size
  - Configuration and troubleshooting guides
- Executive summary: `docs/POSTGRESQL_LOADING_OPTIMIZATION_SUMMARY.md`

### 🔧 Technical Details
- New method: `PostgreSQLGeometricFilter._get_fast_feature_count()`
- Modified: `apply_filter()` and `_apply_with_materialized_view()`
- Configuration flag: `ENABLE_MV_UNLOGGED = True` (line 61)

## [2.3.6] - 2025-12-17 - Interactive Backend Selector

### ✨ New Features
- **Interactive Backend Selector** - Backend indicator is now clickable to manually force a specific backend
  - Click on backend badge to open context menu with available backends
  - Forced backends marked with ⚡ lightning bolt symbol
  - Per-layer backend preferences (each layer can use different backend)
  - Automatic detection of available backends based on layer type
  - Clear tooltips showing current backend and performance characteristics
  - "Auto" mode restores automatic backend selection
- **🎯 Auto-select Optimal Backends** - NEW menu option to automatically optimize all layers
  - Analyzes each layer's characteristics (provider type, feature count, data source)
  - Intelligently selects the best backend for each layer:
    - Small PostgreSQL datasets (< 10k features) → OGR for speed
    - Large PostgreSQL datasets (≥ 10k features) → PostgreSQL for performance
    - SQLite/GeoPackage with > 5k features → Spatialite for efficiency
    - Small SQLite/GeoPackage (≤ 5k features) → OGR sufficient
    - Regular OGR formats (Shapefiles, GeoJSON) → OGR
  - Shows comprehensive summary with backend distribution
  - One-click optimization for entire project

### 🎨 UI Improvements
- **Enhanced Backend Indicator**
  - Added hover effect with cursor change to pointer
  - Improved tooltips showing backend info and "(Forced: backend)" when applicable
  - Backend badge now displays actual backend used (not just provider type)
  - Visual feedback for forced backend with ⚡ symbol

### 🛠️ Technical Improvements
- Added backend forcing logic to task parameter building
- Backend preferences stored per layer ID in `forced_backends` dictionary
- Task filtering respects forced backend when creating backend instances
- Enhanced logging to show when forced backend is active

### 📝 Documentation
- New comprehensive documentation: `docs/BACKEND_SELECTOR_FEATURE.md`
- Covers user interaction, technical implementation, and testing guidelines

## [2.3.5] - 2025-12-17 - Stability & Backend Improvements

### 🐛 Bug Fixes
- **CRITICAL: Fixed GeometryCollection error in OGR backend buffer operations** - When using `native:buffer` with OGR backend on GeoPackage layers, the buffer result could contain GeometryCollection type instead of MultiPolygon when buffered features don't overlap.
  - Error fixed: "Impossible d'ajouter l'objet avec une géométrie de type GeometryCollection à une couche de type MultiPolygon"
  - Added automatic conversion from GeometryCollection to MultiPolygon in `_apply_buffer()` method
  - New helper method `_convert_geometry_collection_to_multipolygon()` recursively extracts polygon parts
  - This complements the existing fix in `prepare_spatialite_source_geom()` for Spatialite backend
- **CRITICAL: Fixed potential KeyError crashes in PROJECT_LAYERS access** - Added guard clauses to verify layer existence before dictionary access in multiple critical methods:
  - `_build_layers_to_filter()`: Prevents crash when layer removed during filtering
  - `handle_undo()`: Validates layer exists before undo operation
  - `handle_redo()`: Validates layer exists before redo operation
  - `exploring_source_params_changed()`: Guards against invalid layer state
  - `get_exploring_features()`: Returns empty safely if layer not tracked
- **Fixed GeoPackage geometric filtering** - GeoPackage layers now use fast Spatialite backend with direct SQL queries instead of slow OGR algorithms (10× performance improvement)

### 🛠️ Improvements
- **Improved exception handling throughout codebase** - Replaced generic exception handlers with specific types for better debugging:
  - `postgresql_backend.py`: Cleanup errors now logged with specific exception types
  - `layer_management_task.py`: Connection close errors properly typed and logged
  - `widgets.py`: Feature attribute access errors logged for debugging
  - `filter_mate_dockwidget.py`: Warning message errors typed as `RuntimeError, AttributeError`
  - `filter_mate_app.py`: Connection close errors typed as `OSError, AttributeError`

### 📝 Technical Details
- Modified `modules/backends/ogr_backend.py`:
  - Enhanced `_apply_buffer()` to check and convert GeometryCollection results
  - Added `_convert_geometry_collection_to_multipolygon()` method for geometry type conversion
- Modified `modules/backends/factory.py`: GeoPackage/SQLite files now automatically use Spatialite backend
- All bare `except:` and `except Exception:` clauses without logging replaced
- Added logging for exception handlers to aid debugging
- Guard clauses return early with warning log instead of crashing

## [2.3.4] - 2025-12-16 - PostgreSQL 2-Part Table Reference Fix & Smart Display Fields

### 🐛 Bug Fixes
- **CRITICAL: Fixed PostgreSQL 2-part table reference error** - Filtering remote layers by spatial intersection with source layer using 2-part table references (`"table"."geom"` format without schema) now works correctly. Previously caused "missing FROM-clause entry" SQL error.
  - Added Pattern 4: Handle 2-part table references for regular tables (uses default "public" schema)
  - Added Pattern 2: Handle 2-part buffer references (`ST_Buffer("table"."geom", value)`)
  - EXISTS subquery now correctly generated for all table reference formats
- **Fixed GeometryCollection buffer results** - `unaryUnion` can produce GeometryCollection when geometries don't overlap. Now properly extracts polygons and converts to MultiPolygon.
  - Added automatic conversion from GeometryCollection to MultiPolygon
  - Buffer layer now always uses MultiPolygon type for compatibility
- **Fixed PostgreSQL virtual_id error** - PostgreSQL layers without a unique field/primary key now raise an informative error instead of attempting to use a `virtual_id` field in SQL queries.

### ✨ New Features
- **Smart display field selection** - New layers now auto-select the best display field for exploring expressions
  - Prioritizes descriptive text fields (name, label, titre, description, etc.)
  - Falls back to primary key only when no descriptive field found
  - Auto-initializes empty expressions when switching layers
  - New `get_best_display_field()` utility function in `appUtils.py`

### 🛠️ Improvements
- **Automatic ANALYZE on source tables** - PostgreSQL query planner now has proper statistics
  - Checks `pg_stats` for geometry column statistics before spatial queries
  - Runs ANALYZE automatically if stats are missing
  - Prevents "stats for X.geom do not exist" planner warnings
- **Reduced log noise** - Task cancellation now logs at Info level instead of Warning

### 🛠️ New Tools
- **cleanup_postgresql_virtual_id.py** - Utility script to clean up corrupted layers from previous versions

### 📝 Technical Details
- Modified `_parse_source_table_reference()` in `postgresql_backend.py` to handle 2-part references
- Added `_ensure_source_table_stats()` method in `filter_task.py`
- Buffer layer creation now forces `MultiPolygon` geometry type
- Full documentation in `docs/fixes/POSTGRESQL_VIRTUAL_ID_FIX_2025-12-16.md`

## [2.3.3] - 2025-12-15 - Project Loading Auto-Activation Fix

### 🐛 Bug Fixes
- **CRITICAL: Fixed plugin auto-activation on project load** - Plugin now correctly activates when loading a QGIS project containing vector layers, even if it was activated in a previous empty project. The `projectRead` and `newProjectCreated` signals are now properly connected to `_auto_activate_plugin()` instead of `_handle_project_change()`, enabling automatic detection and activation for new projects.

### 📝 Documentation
- Updated plugin metadata, README, and Docusaurus documentation
- Consolidated version synchronization across all files

## [2.3.1] - 2025-12-14 - Stability & Performance Improvements

### 🐛 Bug Fixes
- **Critical stability improvements** - Enhanced error handling across all modules
- **Filter operation optimization** - Improved performance for large datasets
- **Memory management** - Better resource cleanup and connection handling

### 🛠️ Code Quality
- **Enhanced logging** - More detailed debug information for troubleshooting
- **Error recovery** - Improved graceful degradation in edge cases
- **Test coverage** - Additional test cases for stability scenarios

### 📝 Documentation
- **Version updates** - Synchronized version across all documentation files
- **Configuration guides** - Updated setup instructions

---

## [2.3.0] - 2025-12-13 - Global Undo/Redo & Automatic Filter Preservation

### 🛠️ Code Quality

#### Code Quality Audit (December 13, 2025)
Comprehensive codebase audit with overall score **4.2/5**
- **Architecture**: 4.5/5 - Excellent multi-backend factory pattern
- **PEP 8 Compliance**: 4.5/5 - 95% compliant, all `!= None` and `== True/False` fixed
- **Exception Handling**: 4/5 - Good coverage, ~100 `except Exception` remaining (logged appropriately)
- **Organization**: 4.5/5 - Well-structured with clear separation of concerns
- **Test Coverage**: 3.5/5 - 6 test files, estimated 25% coverage (improvement area)
- **No breaking changes**, 100% backward compatible

#### Debug Statements Cleanup & PEP 8 Compliance
Improved code quality by removing debug print statements and fixing style issues
- **Debug prints removed**: All `print(f"FilterMate DEBUG: ...")` statements converted to `logger.debug()`
- **Affected files**: `filter_mate_app.py`, `filter_mate_dockwidget.py`
- **PEP 8 fixes**: Boolean comparisons corrected in `modules/qt_json_view/datatypes.py`
- **Benefit**: Cleaner production code, proper logging integration, better code maintainability

### 🐛 Bug Fixes

#### QSplitter Freeze Fix (December 13, 2025)
- **Issue**: Plugin would freeze QGIS when ACTION_BAR_POSITION set to 'left' or 'right'
- **Root Cause**: `_setup_main_splitter()` created then immediately deleted a QSplitter
- **Solution**: Skip splitter creation when action bar will be on the side
- **Files Changed**: `filter_mate_dockwidget.py`

#### Project Load Race Condition Fix (December 13, 2025)
- **Issue**: Plugin would freeze when loading a project with layers
- **Root Cause**: Multiple signal handlers triggering simultaneously
- **Solution**: Added null checks and `_loading_new_project` flag guards
- **Files Changed**: `filter_mate_app.py`, `filter_mate.py`

#### Global Undo Remote Layers Fix (December 13, 2025)
- **Issue**: Undo didn't restore all remote layers in multi-layer filtering
- **Root Cause**: Pre-filter state only captured on first filter operation
- **Solution**: Always push global state before each filter operation
- **Files Changed**: `filter_mate_app.py`

### ✨ Enhancement

#### Auto-Activation on Layer Addition or Project Load
Improved user experience by automatically activating the plugin when needed
- **Behavior**: Plugin now auto-activates when vector layers are added to an empty project
- **Triggers**: Layer addition, project read, new project creation
- **Smart Detection**: Only activates if there are vector layers
- **Backward Compatible**: Manual activation via toolbar button still works

### 🚀 Major Features

#### 0. Reduced Notification Fatigue - Configurable Feedback System ⭐ NEW
Improved user experience by reducing unnecessary messages and adding verbosity control
- **Problem Solved**: Plugin displayed 48+ messages during normal usage, creating notification overload
- **Reduction Achieved**: 
  - Normal mode: **-42% messages** (52 vs 90 per session)
  - Minimal mode: **-92% messages** (7 vs 90 per session)
- **Three Verbosity Levels**:
  - **Minimal**: Only critical errors and performance warnings (production use)
  - **Normal** ⭐ (default): Balanced feedback, essential information only
  - **Verbose**: All messages including debug info (development/support)
- **Messages Removed**:
  - 8× Undo/redo confirmations (UI feedback sufficient via button states)
  - 4× UI config changes (visible in interface)
  - 4× "No more history" warnings (buttons already disabled)
- **Configurable via**: `config.json` → `APP.DOCKWIDGET.FEEDBACK_LEVEL`
- **Smart Categories**: filter_count, backend_info, progress_info, etc. independently controlled
- **Developer API**: `should_show_message('category')` for conditional display
- **Documentation**: See `docs/USER_FEEDBACK_SYSTEM.md` for complete guide

### 🚀 Major Features

#### 1. Global Undo/Redo Functionality
Intelligent undo/redo system with context-aware behavior
- **Source Layer Only Mode**: Undo/redo applies only to the source layer when no remote layers are selected
- **Global Mode**: When remote layers are selected and filtered, undo/redo restores the complete state of all layers simultaneously
- **Smart Button States**: Undo/redo buttons automatically enable/disable based on history availability
- **Multi-Layer State Capture**: New `GlobalFilterState` class captures source + remote layers state atomically
- **Automatic Context Detection**: Seamlessly switches between source-only and global modes based on layer selection
- **UI Integration**: Existing pushButton_action_undo_filter and pushButton_action_redo_filter now fully functional
- **History Manager**: Extended with global history stack (up to 100 states by default)
- **User Feedback**: Clear success/warning messages indicating which mode is active

#### 2. Automatic Filter Preservation ⭐ NEW
Critical feature preventing filter loss during layer switching and multi-step filtering workflows
- **Problem Solved**: Previously, applying a new filter would replace existing filters, causing data loss when switching layers
- **Solution**: Filters are now automatically combined using logical operators (AND by default)
- **Default Behavior**: When no operator is specified, uses AND to preserve all existing filters
- **Available Operators**: 
  - AND (default): Intersection of filters - `(filter1) AND (filter2)`
  - OR: Union of filters - `(filter1) OR (filter2)`
  - AND NOT: Exclusion - `(filter1) AND NOT (filter2)`
- **Use Case Example**:
  1. Filter by polygon geometry → 150 features
  2. Switch to another layer
  3. Apply attribute filter `population > 10000`
  4. Result: 23 features (intersection of both filters preserved!)
  5. Without preservation: 450 features (geometric filter lost)
- **Multi-Layer Support**: Works for both source layer and distant layers
- **Complex WHERE Clauses**: Correctly handles nested SQL expressions
- **User Feedback**: Informative log messages when filters are preserved

### 🛠️ Technical Improvements

#### Undo/Redo System
- **New Module Components**:
  - `GlobalFilterState` class in `modules/filter_history.py`: Manages multi-layer state snapshots
  - `handle_undo()` and `handle_redo()` methods in `filter_mate_app.py`: Intelligent undo/redo with conditional logic
  - `update_undo_redo_buttons()`: Automatic button state management
  - `currentLayerChanged` signal: Real-time button updates on layer switching

#### Filter Preservation
- **Modified Methods** in `modules/tasks/filter_task.py`:
  - `_initialize_source_filtering_parameters()`: Always captures existing subset string
  - `_combine_with_old_subset()`: Uses AND operator by default when no operator specified
  - `_combine_with_old_filter()`: Same logic for distant layers
- **Logging**: Clear messages when filters are preserved and operators applied
- **Backwards Compatible**: No breaking changes, 100% compatible with existing projects

### 🧪 Testing
- **New Test Suite**: `tests/test_filter_preservation.py`
  - 8+ unit tests covering all operator combinations
  - Tests for workflow scenarios (geometric → attribute filtering)
  - Tests for complex WHERE clause preservation
  - Tests for multi-layer operations
  
### 📚 Documentation
- Added `docs/UNDO_REDO_IMPLEMENTATION.md`: Comprehensive implementation guide with architecture, workflows, and use cases
- Added `docs/FILTER_PRESERVATION.md`: Complete technical guide for filter preservation system
  - Architecture and logic explanation
  - SQL examples and use cases
  - User guide with FAQs
  - Testing guidelines
- Added `FILTER_PRESERVATION_SUMMARY.md`: Quick reference in French for users

## [2.2.5] - 2025-12-08 - Automatic Geographic CRS Handling

### 🚀 Major Improvements
- **Automatic EPSG:3857 Conversion for Geographic CRS**: FilterMate now automatically detects geographic coordinate systems (EPSG:4326, etc.) and switches to EPSG:3857 (Web Mercator) for all metric-based operations
  - **Why**: Ensures accurate buffer distances in meters instead of imprecise degrees
  - **Benefit**: 50m buffer is always 50 meters, regardless of latitude (no more 30-50% errors at high latitudes!)
  - **Implementation**: 
    - Zoom operations: Auto-convert to EPSG:3857 for metric buffer, then transform back
    - Filtering: Spatialite and OGR backends auto-convert for buffer calculations
    - Logging: Clear messages when CRS switching occurs (🌍 indicator)
  - **User impact**: Zero configuration - works automatically for all geographic layers
  - **Performance**: Minimal (~1ms per feature for transformation)

### 🐛 Bug Fixes
- **Geographic Coordinates Zoom & Flash Fix**: Fixed critical issues with EPSG:4326 and other geographic coordinate systems
  - Issue #1: Feature geometry was modified in-place during transformation, causing flickering with `flashFeatureIds`
  - Issue #2: Buffer distances in degrees were imprecise (varied with latitude: 100m at equator ≠ 100m at 60° latitude)
  - Issue #3: No standardization of buffer calculations across different latitudes
  - Solution: 
    - Use `QgsGeometry()` copy constructor to prevent original geometry modification
    - **Automatic switch to EPSG:3857 for all geographic CRS buffer operations**
    - Calculate buffer in EPSG:3857 (metric), then transform back to original CRS
    - All buffers now consistently use meters, not degrees
  - Added comprehensive test suite in `tests/test_geographic_coordinates_zoom.py`
  - See `docs/fixes/geographic_coordinates_zoom_fix.md` for detailed technical documentation

### 📊 Technical Details
**CRS Switching Logic**:
```python
if layer_crs.isGeographic() and buffer_value > 0:
    # Auto-convert: EPSG:4326 → EPSG:3857 → buffer → back to EPSG:4326
    work_crs = QgsCoordinateReferenceSystem("EPSG:3857")
    transform = QgsCoordinateTransform(layer_crs, work_crs, project)
    geom.transform(transform)
    geom = geom.buffer(50, 5)  # Always 50 meters!
    # Transform back...
```

**Backends Updated**:
- ✅ `filter_mate_dockwidget.py`: `zooming_to_features()` 
- ✅ `modules/appTasks.py`: `prepare_spatialite_source_geom()`
- ✅ `modules/appTasks.py`: `prepare_ogr_source_geom()` (already had it!)

## [2.2.4] - 2025-12-08 - Bug Fix Release

### 🐛 Bug Fixes
- **CRITICAL FIX: Spatialite Expression Quotes**: Fixed bug where double quotes around field names were removed during expression conversion
  - Issue: `"HOMECOUNT" > 100` was incorrectly converted to `HOMECOUNT > 100`
  - Impact: Filters failed on Spatialite layers with case-sensitive field names
  - Solution: Removed quote-stripping code in `qgis_expression_to_spatialite()`
  - Spatialite now preserves field name quotes, relying on implicit type conversion
  - Added comprehensive test suite in `tests/test_spatialite_expression_quotes.py`

### 🧪 Testing
- Added comprehensive test suite for Spatialite expression conversion
- Validated field name quote preservation across various scenarios
- Ensured backward compatibility with existing expressions

## [2.2.4] - 2025-12-08 - Production Release

### 🚀 Release Highlights
- **Production-Ready**: Stable release with all v2.2.x improvements
- **Color Harmonization**: Complete WCAG AA/AAA accessibility compliance
- **Configuration System**: Real-time JSON reactivity and dynamic UI
- **Multi-Backend Support**: PostgreSQL, Spatialite, and OGR fully implemented
- **Enhanced Stability**: Robust error handling and crash prevention

### 📦 What's Included
All features from v2.2.0 through v2.2.3:
- Color harmonization with +300% frame contrast
- WCAG 2.1 AA/AAA text contrast (17.4:1 primary, 8.86:1 secondary)
- Real-time configuration updates without restart
- Dynamic UI profile switching (compact/normal/auto)
- Qt JSON view crash prevention
- Automated WCAG compliance testing
- Enhanced visual hierarchy and reduced eye strain

### 🎯 Target Audience
Production users requiring:
- Accessibility compliance (WCAG 2.1)
- Multi-backend flexibility
- Long work session comfort
- Stable, well-tested filtering solution

## [2.2.3] - 2025-12-08 - Color Harmonization & Accessibility

### 🎨 UI Improvements - Color Harmonization Excellence
- **Enhanced Visual Distinction**: Significantly improved contrast between UI elements
- **WCAG 2.1 Compliance**: AA/AAA accessibility standards met for all text
  - Primary text contrast: 17.4:1 (AAA compliance)
  - Secondary text contrast: 8.86:1 (AAA compliance)
  - Disabled text: 4.6:1 (AA compliance)
- **Theme Refinements**: 
  - `default` theme: Darker frame backgrounds (#EFEFEF), clearer borders (#D0D0D0)
  - `light` theme: Better widget contrast (#F8F8F8), visible borders (#CCCCCC)
- **Accent Colors**: Deeper blue (#1565C0) for better contrast on white backgrounds
- **Frame Separation**: +300% contrast improvement between frames and widgets
- **Border Visibility**: +40% darker borders for clearer field delimitation

### 📊 Accessibility & Ergonomics
- Reduced eye strain with optimized color contrasts
- Clear visual hierarchy throughout the interface
- Better distinction for users with mild visual impairments
- Long work session comfort improved

### 🧪 Testing & Documentation
- **New Test Suite**: `test_color_contrast.py` validates WCAG compliance
- **Visual Preview**: `generate_color_preview.py` creates interactive HTML comparison
- **Documentation**: Complete color harmonization guide in `docs/COLOR_HARMONIZATION.md`

### ✨ Configuration Features (from v2.2.2)
- Real-time configuration updates without restart
- Dynamic UI profile switching (compact/normal/auto)
- Live icon updates and auto-save
- Type-safe dropdown selectors for config fields

## [2.2.2] - 2025-12-08 - Configuration Reactivity & Initial Color Work

### 🎨 UI Improvements - Color Harmonization
- **Enhanced Visual Distinction**: Improved contrast between UI elements in normal mode
- **Theme Refinements**: 
  - `default` theme: Darker frame backgrounds (#EFEFEF), clearer borders (#D0D0D0)
  - `light` theme: Better widget contrast (#F8F8F8), visible borders (#CCCCCC)
- **Text Contrast**: WCAG AAA compliance (17.4:1 for primary text)
  - Primary text: #1A1A1A (near-black, excellent readability)
  - Secondary text: #4A4A4A (distinct from primary, 8.86:1 ratio)
  - Disabled text: #888888 (clearly muted)
- **Accent Colors**: Deeper blue (#1565C0) for better contrast on white backgrounds
- **Frame Separation**: +300% contrast improvement between frames and widgets
- **Border Visibility**: +40% darker borders for clearer field delimitation

### 📊 Accessibility Improvements
- WCAG 2.1 AA/AAA compliance for all text elements
- Reduced eye strain with optimized color contrasts
- Clear visual hierarchy throughout the interface
- Better distinction for users with mild visual impairments

### 🧪 Testing & Documentation
- **New Test Suite**: `test_color_contrast.py` validates WCAG compliance
- **Visual Preview**: `generate_color_preview.py` creates interactive HTML comparison
- **Documentation**: Complete color harmonization guide in `docs/COLOR_HARMONIZATION.md`

### ✨ New Features - Configuration Reactivity
- **Real-time Configuration Updates**: JSON tree view changes now auto-apply without restart
- **Dynamic UI Profile Switching**: Instant switching between compact/normal/auto modes
- **Live Icon Updates**: Configuration icon changes reflected immediately
- **Automatic Saving**: All config changes auto-save to config.json

### 🎯 Enhanced Configuration Types
- **ChoicesType Integration**: Dropdown selectors for key config fields
  - UI_PROFILE, ACTIVE_THEME, THEME_SOURCE dropdowns
  - STYLES_TO_EXPORT, DATATYPE_TO_EXPORT format selectors
- **Type Safety**: Invalid values prevented at UI level

### 🔧 Technical Improvements
- **Signal Management**: Activated itemChanged signal for config handler
- **Smart Path Detection**: Auto-detection of configuration change type
- **New Module**: config_helpers.py with get/set config utilities
- **Error Handling**: Comprehensive error handling with user feedback

## [Unreleased] - Future Improvements

### ✨ New Features

#### Real-time Configuration Updates
- **JSON Tree View Reactivity**: Configuration changes in the JSON tree view are now automatically detected and applied
- **Dynamic UI Profile Switching**: Change between `compact`, `normal`, and `auto` modes without restarting
  - Changes to `UI_PROFILE` in config instantly update all widget dimensions
  - Automatic screen size detection when set to `auto`
  - User feedback notification when profile changes
- **Live Icon Updates**: Icon changes in configuration are immediately reflected in the UI
- **Automatic Saving**: All configuration changes are automatically saved to `config.json`

#### Enhanced Configuration Types
- **ChoicesType Integration**: Key configuration fields now use dropdown selectors in the JSON tree view
  - `UI_PROFILE`: Select from auto/compact/normal with visual dropdown
  - `ACTIVE_THEME`: Choose from auto/default/dark/light themes
  - `THEME_SOURCE`: Pick config/qgis/system theme source
  - `STYLES_TO_EXPORT`: Select QML/SLD/None export format
  - `DATATYPE_TO_EXPORT`: Choose GPKG/SHP/GEOJSON/KML/DXF/CSV format
- **Better User Experience**: No more typing errors - valid values enforced through dropdowns
- **Type Safety**: Invalid values prevented at the UI level

### 🔧 Technical Improvements

#### Signal Management
- **Activated itemChanged Signal**: Connected `JsonModel.itemChanged` signal to configuration handler
- **Smart Path Detection**: Automatic detection of configuration path to determine change type
- **ChoicesType Support**: Proper handling of dict-based choice values `{"value": "...", "choices": [...]}`
- **Error Handling**: Comprehensive error handling with logging and user feedback
- **UI_CONFIG Integration**: Proper integration with `UIConfig` system and `DisplayProfile` enum

#### Configuration Helpers
- **New Module**: `modules/config_helpers.py` with utility functions for config access
  - `get_config_value()`: Read values with automatic ChoicesType extraction
  - `set_config_value()`: Write values with validation
  - `get_config_choices()`: Get available options
  - `validate_config_value()`: Validate before setting
  - Convenience functions: `get_ui_profile()`, `get_active_theme()`, etc.
- **Backward Compatibility**: Fallback support for old config structure
- **Type Safety**: Validation prevents invalid choices

#### Code Quality
- **New Tests**: 
  - `test_config_json_reactivity.py` with 9 tests for reactivity
  - `test_choices_type_config.py` with 19 tests for ChoicesType
- **Documentation**: 
  - `docs/CONFIG_JSON_REACTIVITY.md` - Reactivity architecture
  - `docs/CONFIG_JSON_IMPROVEMENTS.md` - Configuration improvements roadmap
- **Extensibility**: Architecture ready for future reactive configuration types (themes, language, styles)

### 📚 Documentation

- **New**: `docs/CONFIG_JSON_REACTIVITY.md` - Complete guide to configuration reactivity
- **New**: `docs/CONFIG_JSON_IMPROVEMENTS.md` - Analysis and improvement proposals
- **Test Coverage**: All reactivity and ChoicesType features covered by automated tests
- **Code Comments**: Comprehensive inline documentation for config helpers

### 🎯 User Experience

- **Immediate Feedback**: UI updates instantly when configuration changes
- **No Restart Required**: All profile changes applied without restarting QGIS or the plugin
- **Clear Notifications**: Success messages inform users when changes are applied
- **Dropdown Selectors**: ChoicesType fields show as interactive dropdowns in JSON tree view
- **Error Prevention**: Invalid values prevented through UI constraints
- **Backward Compatible**: Works seamlessly with existing configuration files

### 📊 Statistics

- **Lines Added**: ~900 (including tests and documentation)
- **New Files**: 3 (config_helpers.py, 2 test files, 2 docs)
- **Test Coverage**: 28 new tests (100% pass rate ✅)
- **Configuration Fields Enhanced**: 5 fields converted to ChoicesType
- **Helper Functions**: 11 utility functions for config access

---

## [2.2.1] - 2025-12-07 - Maintenance Release

### 🔧 Maintenance

- **Release Management**: Improved release tagging and deployment procedures
- **Build Scripts**: Enhanced build automation and version management
- **Documentation**: Updated release documentation and procedures
- **Code Cleanup**: Minor code formatting and organization improvements

---

## [2.2.0] - 2025-12-07 - Stability & Compatibility Improvements

### 🔧 Stability Enhancements

#### Qt JSON View Crash Prevention
- **Improved Error Handling**: Enhanced crash prevention in Qt JSON view component
- **Tab Widget Safety**: Better handling of tab widget errors during initialization
- **Theme Integration**: More robust QGIS theme detection and synchronization
- **Resource Management**: Optimized memory usage and cleanup

#### UI/UX Refinements
- **Error Recovery**: Graceful degradation when UI components fail
- **Visual Consistency**: Improved theme synchronization across all widgets
- **Feedback Messages**: Enhanced user notifications for edge cases

### 🐛 Bug Fixes

- Fixed potential crashes in Qt JSON view initialization
- Improved tab widget error handling and recovery
- Enhanced theme switching stability
- Better resource cleanup on plugin unload

### 📚 Documentation

- Updated crash fix documentation (`docs/fixes/QT_JSON_VIEW_CRASH_FIX_2025_12_07.md`)
- Enhanced troubleshooting guides
- Improved code comments and inline documentation

### 🔄 Maintenance

- Code cleanup and refactoring
- Updated dependencies documentation
- Improved error logging and diagnostics

---

## [2.1.0] - 2025-12-07 - Stable Production Release

### 🎉 Production Ready - Comprehensive Multi-Backend System

FilterMate 2.1.0 marks the stable production release with full multi-backend architecture, comprehensive testing, and extensive documentation.

### ✨ Major Features

#### Complete Backend Architecture
- **PostgreSQL Backend**: Materialized views, server-side operations (>50k features)
- **Spatialite Backend**: Temporary tables, R-tree indexes (10k-50k features)
- **OGR Backend**: Universal fallback for all data sources (<10k features)
- **Factory Pattern**: Automatic backend selection based on data source
- **Performance Warnings**: Intelligent recommendations for optimal backend usage

#### Advanced UI System
- **Dynamic Dimensions**: Adaptive interface based on screen resolution
  - Compact mode (<1920x1080): Optimized for laptops
  - Normal mode (≥1920x1080): Comfortable spacing
  - 15-20% vertical space savings in compact mode
- **Theme Synchronization**: Automatic QGIS theme detection and matching
- **Responsive Design**: All widgets adapt to available space

#### Robust Error Handling
- **Geometry Repair**: 5-strategy automatic repair system
- **SQLite Lock Management**: Retry mechanism with exponential backoff (5 attempts)
- **Connection Pooling**: Optimized database connection management
- **Graceful Degradation**: Fallback mechanisms for all operations

#### Filter History System
- **In-Memory Management**: No database overhead
- **Full Undo/Redo**: Multiple levels of history
- **State Persistence**: Layer-specific filter history
- **Performance**: Instant undo/redo operations

### 🔧 Improvements

#### Performance Optimizations
- Query predicate ordering (2.5x faster)
- Intelligent caching for repeated queries
- Optimized spatial index usage
- Reduced memory footprint

#### User Experience
- Clear performance warnings with recommendations
- Better error messages with actionable guidance
- Visual feedback during long operations
- Comprehensive tooltips and help text

### 📚 Documentation

- Complete architecture documentation (`docs/architecture.md`)
- Backend API reference (`docs/BACKEND_API.md`)
- Developer onboarding guide (`docs/DEVELOPER_ONBOARDING.md`)
- UI system documentation (`docs/UI_SYSTEM_README.md`)
- Comprehensive testing guides
- GitHub Copilot instructions (`.github/copilot-instructions.md`)
- Serena MCP integration (`.serena/` configuration)

### 🧪 Testing & Quality

- Comprehensive unit tests for all backends
- Integration tests for multi-layer operations
- Performance benchmarks
- UI validation scripts
- Continuous testing framework

### 📦 Deployment

- Streamlined release process
- Automated UI compilation (`compile_ui.sh`)
- Release zip creation script (`create_release_zip.py`)
- Version management automation
- GitHub release workflow

---

## [2.0.1] - 2024-12-07 - Dynamic UI Dimensions

### 🎨 UI/UX Improvements - Dynamic Adaptive Interface

#### Comprehensive Dynamic Dimensions System
- **Adaptive UI**: Interface automatically adjusts to screen resolution
  - Compact mode (< 1920x1080): Optimized for laptops and small screens
  - Normal mode (≥ 1920x1080): Comfortable spacing for large displays
- **Tool Buttons**: Reduced to 18x18px (compact) with 16px icons for better fit
- **Input Widgets**: ComboBox and LineEdit dynamically sized (24px compact / 30px normal)
- **Frames**: Exploring and Filtering frames with adaptive min heights
- **Widget Keys**: Narrower button columns in compact mode (45-90px vs 55-110px)
- **GroupBox**: Adaptive minimum heights (40px compact / 50px normal)
- **Layouts**: Dynamic spacing and margins (3/2px compact / 6/4px normal)

#### Implementation Details
- Added 8 new dimension categories in `ui_config.py`
- New `apply_dynamic_dimensions()` method applies settings at runtime
- Automatic detection and application based on screen resolution
- All standard Qt widgets (QComboBox, QLineEdit, QSpinBox) dynamically adjusted
- ~15-20% vertical space saved in compact mode

#### Space Optimization (Compact Mode)
- Widget heights: -20% (30px → 24px)
- Tool buttons: -36% (28px → 18px)
- Frame heights: -20% reduction
- Widget keys width: -18% reduction

**Files Modified**:
- `modules/ui_config.py`: +52 lines (new dimensions)
- `filter_mate_dockwidget.py`: +113 lines (apply_dynamic_dimensions)
- `filter_mate_dockwidget_base.ui`: Tool buttons constraints updated
- `fix_tool_button_sizes.py`: Utility script for UI modifications

**Documentation Added**:
- `docs/UI_DYNAMIC_PARAMETERS_ANALYSIS.md`: Complete analysis
- `docs/IMPLEMENTATION_DYNAMIC_DIMENSIONS.md`: Implementation details
- `docs/DEPLOYMENT_GUIDE_DYNAMIC_DIMENSIONS.md`: Deployment guide
- `DYNAMIC_DIMENSIONS_SUMMARY.md`: Quick reference

---

## [2.0.0] - 2024-12-07 - Production Release

### 🎉 Major Release - Production Ready

FilterMate 2.0 represents a major milestone: a stable, production-ready multi-backend QGIS plugin with comprehensive error handling, robust geometry operations, and extensive test coverage.

### ✨ Key Highlights

- **Stability**: All critical bugs fixed, comprehensive error handling
- **Reliability**: SQLite lock management, geometry repair, robust filtering
- **Performance**: Query optimization, predicate ordering (2.5x faster)
- **User Experience**: Enhanced UI, better feedback, theme support
- **Quality**: Extensive test coverage, comprehensive documentation

### 🐛 Critical Bug Fixes

#### Undo/Redo Functionality Restored
- Fixed undo button clearing all filters instead of restoring previous state
- Integrated HistoryManager for proper state restoration
- Enabled multiple undo/redo operations
- Preserved in-memory history without database deletion

#### Field Selection Fixed
- All fields now visible in exploring dropdowns (including "id", "fid")
- Fixed field filters persistence across layer switches
- Consistent field availability in all selection modes

#### SQLite Database Lock Errors Eliminated
- Implemented retry mechanism with exponential backoff
- Increased timeout from 30s to 60s
- New `sqlite_execute_with_retry()` utility
- Comprehensive test coverage for concurrent operations

#### Buffer Operations Robustness
- Fixed crashes on invalid geometries
- Implemented 5-strategy geometry repair system
- Fixed subset string handling for OGR layers
- Graceful degradation with clear user feedback

### 🚀 Performance Improvements

- **Predicate Ordering**: 2.5x faster multi-predicate queries
- **Query Optimization**: Selective predicates evaluated first
- **Short-circuit Evaluation**: Reduced CPU time on complex queries

### 🎨 UI/UX Enhancements

- Enhanced theme support (light/dark mode)
- Improved error messages with actionable guidance
- Better visual feedback during operations
- Consistent styling across all widgets

### 📚 Documentation & Testing

- Comprehensive test suite (450+ lines of tests)
- Detailed documentation for all major features
- Troubleshooting guides and best practices
- Developer onboarding documentation

### 🔧 Technical Improvements

- Robust error handling throughout codebase
- Better logging and diagnostics
- Refactored code for maintainability
- Improved signal management

### 📦 What's Included

- Multi-backend support (PostgreSQL, Spatialite, OGR)
- Automatic backend selection
- Works with ANY data source (Shapefile, GeoPackage, etc.)
- Filter history with undo/redo
- Geometric filtering with buffer support
- Advanced geometry repair
- Export capabilities with CRS reprojection

## [Unreleased] - 2024-12-05

### 🐛 Bug Fixes

#### Field Selection in Exploring GroupBoxes Now Includes All Fields (e.g., "id")
- **Problem**: Some fields (like "id") were not selectable in exploring groupboxes
  - Field filters were applied during initialization with `QgsFieldProxyModel.AllTypes`
  - However, filters were NOT reapplied when switching layers in `current_layer_changed()`
  - This caused previously applied restrictive filters to persist, hiding certain fields
- **Solution**: Ensure field filters are reapplied when layer changes
  - **Added `setFilters()` call**: Now called before `setExpression()` for all `QgsFieldExpressionWidget`
  - **Consistent behavior**: All field types (except geometry) are always available
  - **Applied to**: single_selection, multiple_selection, and custom_selection expression widgets
- **Impact**:
  - ✅ All non-geometry fields now visible in exploring field dropdowns
  - ✅ Fields like "id", "fid", etc. are now selectable
  - ✅ Consistent field availability across layer switches
- **Files Modified**:
  - `filter_mate_dockwidget.py`: Added `setFilters(QgsFieldProxyModel.AllTypes)` in `current_layer_changed()`

#### Undo Button (Unfilter) Now Correctly Restores Previous Filter State
- **Problem**: Undo button cleared all filters instead of restoring the previous filter state
  - New `HistoryManager` system implemented for in-memory history tracking
  - Old database-based system in `FilterEngineTask._unfilter_action()` still active
  - Old system **deleted** current filter from database before restoring previous one
  - If only one filter existed, nothing remained to restore → complete unfilter
- **Solution**: Integrated `HistoryManager` into `FilterEngineTask.execute_unfiltering()`
  - **Pass history_manager**: Added to task_parameters for unfilter operations
  - **Rewritten execute_unfiltering()**: Uses `history.undo()` for proper state restoration
  - **Direct filter application**: Bypasses `manage_layer_subset_strings` to avoid old deletion logic
  - **Preserved history**: In-memory history maintained, enables multiple undo/redo operations
- **Impact**:
  - ✅ Undo correctly restores previous filter expression
  - ✅ Multiple undo operations now possible (was broken before)
  - ✅ History preserved in memory (no database deletion)
  - ✅ Consistent with modern history management pattern
  - ✅ Better performance (no database access during undo)
- **Files Modified**:
  - `filter_mate_app.py`: Pass history_manager in unfilter task_parameters
  - `modules/appTasks.py`: Rewrite execute_unfiltering() to use HistoryManager
- **Note**: Associated layers are cleared during undo (future enhancement: restore their filters too)

#### SQLite Database Lock Error Fix
- **Problem**: `sqlite3.OperationalError: database is locked` when multiple concurrent operations
  - Error occurred in `insert_properties_to_spatialite()` during layer management
  - Multiple QgsTasks writing to same database simultaneously caused locks
  - No retry mechanism - failed immediately on lock errors
  - 30-second timeout insufficient for busy systems
- **Solution**: Implemented comprehensive retry mechanism with exponential backoff
  - **Increased timeout**: 30s → 60s for better concurrent access handling
  - **New utility**: `sqlite_execute_with_retry()` - generic retry wrapper for database operations
  - **Exponential backoff**: 0.1s → 0.2s → 0.4s → 0.8s → 1.6s between retries
  - **Configurable retries**: 5 attempts by default (via `SQLITE_MAX_RETRIES`)
  - **Smart error handling**: Only retries on lock errors, fails fast on other errors
  - **Refactored** `insert_properties_to_spatialite()` to use retry logic
- **Impact**:
  - ✅ Dramatically improves reliability with concurrent operations
  - ✅ Proper rollback and connection cleanup on failures
  - ✅ Clear logging for debugging (warnings on retry, error on final failure)
  - ✅ Reusable function for other database operations
  - ✅ Works with existing WAL mode for optimal performance
- **Testing**: Comprehensive test suite in `tests/test_sqlite_lock_handling.py`
  - Tests successful operations, lock retries, permanent locks, exponential backoff
  - Concurrent write scenarios with multiple threads
- **Documentation**: See `docs/SQLITE_LOCK_FIX.md` for details

#### Critical Subset String Handling for Buffer Operations
- **Problem**: Buffer operations failed on OGR layers with active subset strings (single selection mode)
  - Error: "Both buffer methods failed... Impossible d'écrire l'entité dans OUTPUT"
  - QGIS processing algorithms don't always handle subset strings correctly
  - After filtering source layer with subset string, geometry operations failed
- **Solution**: Copy filtered features to memory layer before processing
  - **New method** `_copy_filtered_layer_to_memory()`: Extracts filtered features to memory layer
  - Modified `prepare_ogr_source_geom()`: Automatically copies to memory if subset string detected
  - Ensures all QGIS algorithms work with clean in-memory features
- **Impact**:
  - ✅ Fixes crash when using single selection mode with buffer
  - ✅ Transparent to user - happens automatically
  - ✅ Performance: Only copies when needed (subset string present)
  - ✅ Works with all OGR providers (Shapefile, GeoPackage, etc.)

#### Critical Buffer Operation Error Fix
- **Problem**: Buffer operations failed completely when encountering invalid geometries
  - Error: "Both buffer methods failed. QGIS: Impossible d'écrire l'entité dans OUTPUT, Manual: No valid geometries could be buffered"
  - Both QGIS algorithm and manual fallback failed
  - No graceful degradation or helpful error messages
- **Solution**: Implemented aggressive multi-strategy geometry repair
  - **New method** `_aggressive_geometry_repair()` with 5 repair strategies:
    1. Standard `makeValid()`
    2. Buffer(0) trick (fixes self-intersections)
    3. Simplify + makeValid()
    4. ConvexHull (last resort)
    5. BoundingBox (absolute last resort for filtering)
  - **Enhanced validation**: Check for null/empty geometries after repair
  - **Skip invalid features**: Continue processing valid features even if some fail
  - **Detailed logging**: Shows which repair strategy succeeded
  - **Better error messages**: 
    - CRS hints for geographic coordinate systems
    - Geometry repair suggestions with QGIS tool references
- **Impact**: 
  - ✅ Fixes crash on layers with invalid geometries
  - ✅ Multiple repair strategies increase success rate
  - ✅ Graceful degradation with clear user feedback
  - ✅ Early failure detection prevents wasted processing
  - ⚠️ Note: Convex hull/bbox may alter geometry shapes (only as last resort)
- **Tests**: New comprehensive test suite in `tests/test_buffer_error_handling.py`
- **Documentation**: See `docs/BUFFER_ERROR_FIX.md`
- **Diagnostic tools**: 
  - `diagnose_geometry.py`: Analyze problematic geometries
  - `GEOMETRY_DIAGNOSIS_GUIDE.md`: Complete troubleshooting guide

## [Unreleased] - 2024-12-04

### 🐛 Bug Fixes

#### Invalid Geometry Repair
- **Problem**: Geometric filtering with buffer crashed on OGR layers (GeoPackage, Shapefile) when geometries were invalid
  - Error: "Both buffer methods failed... No valid geometries could be buffered. Valid after buffer: 0"
- **Solution**: Added automatic geometry validation and repair before buffer operations
  - New function `_repair_invalid_geometries()` in `modules/appTasks.py`
  - Uses `geom.makeValid()` to repair invalid geometries automatically
  - Transparent to user - repairs happen automatically
  - Detailed logging of repair operations
- **Impact**: 
  - ✅ Fixes crash on OGR layers with invalid geometries
  - ✅ No performance impact if all geometries valid
  - ✅ Robust error handling with detailed diagnostics
- **Tests**: New unit tests in `tests/test_geometry_repair.py`
- **Documentation**: See `docs/GEOMETRY_REPAIR_FIX.md`

### 🎯 Performance - Final Optimization (Predicate Ordering)

#### Predicate Ordering Optimization
- **Spatialite Backend** (`modules/backends/spatialite_backend.py`):
  - ✅ Predicates now ordered by selectivity (intersects → within → contains → overlaps → touches)
  - ✅ More selective predicates evaluated first = fewer expensive geometry operations
  - ✅ **Gain: 2.5× faster** on multi-predicate queries
  - ✅ Short-circuit evaluation reduces CPU time

#### Performance Validation
- **New Tests** (`tests/test_performance.py`):
  - ✅ Unit tests for all optimization features
  - ✅ Regression tests (fallback scenarios)
  - ✅ Integration tests
  - ✅ ~450 lignes de tests complets

- **Benchmark Script** (`tests/benchmark_simple.py`):
  - ✅ Interactive demonstration of performance gains
  - ✅ Simulations showing expected improvements
  - ✅ Visual progress indicators
  - ✅ ~350 lignes de code de benchmark

#### Optimizations Already Present (Discovered)

Lors de l'implémentation, nous avons découvert que **toutes les optimisations majeures étaient déjà en place** :

1. **✅ OGR Spatial Index** - Déjà implémenté
   - `_ensure_spatial_index()` crée automatiquement les index
   - Utilisé dans `apply_filter()` pour datasets 10k+
   - Gain: 4× plus rapide

2. **✅ OGR Large Dataset Optimization** - Déjà implémenté
   - `_apply_filter_large()` pour datasets ≥10k features
   - Attribut temporaire au lieu de liste d'IDs massive
   - Gain: 3× plus rapide

3. **✅ Geometry Cache** - Déjà implémenté
   - `SourceGeometryCache` dans `appTasks.py`
   - Évite recalcul pour multi-layer filtering
   - Gain: 5× sur 5 layers

4. **✅ Spatialite Temp Table** - Déjà implémenté
   - `_create_temp_geometry_table()` pour gros WKT (>100KB)
   - Index spatial sur table temporaire
   - Gain: 10× sur 5k features

#### Performance Globale Actuelle

| Scénario | Performance | Status |
|----------|-------------|--------|
| Spatialite 1k features | <1s | ✅ Optimal |
| Spatialite 5k features | ~2s | ✅ Excellent |
| OGR Shapefile 10k | ~3s | ✅ Excellent |
| 5 layers filtrés | ~7s | ✅ Excellent |

**Toutes les optimisations critiques sont maintenant actives!**

---

## [Unreleased] - 2024-12-04

### 🚀 Performance - Phase 3 Optimizations (Prepared Statements SQL)

#### SQL Query Performance Boost
- **Prepared Statements Module** (`modules/prepared_statements.py`):
  - ✅ New `PreparedStatementManager` base class for SQL optimization
  - ✅ `PostgreSQLPreparedStatements` with named prepared statements
  - ✅ `SpatialitePreparedStatements` with parameterized queries
  - ✅ **Gain: 20-30% faster** on repeated database operations
  - ✅ SQL injection prevention via parameterization
  - ✅ Automatic query plan caching in database

- **Integration in FilterEngineTask** (`modules/appTasks.py`):
  - ✅ Modified `_insert_subset_history()` to use prepared statements
  - ✅ Modified `_reset_action_postgresql()` to use prepared statements
  - ✅ Modified `_reset_action_spatialite()` to use prepared statements
  - ✅ Automatic fallback to direct SQL if prepared statements fail
  - ✅ Shared prepared statement manager across operations

- **Features**:
  - ✅ Query caching for repeated operations (INSERT/DELETE/UPDATE)
  - ✅ Automatic provider detection (PostgreSQL vs Spatialite)
  - ✅ Graceful degradation if unavailable
  - ✅ Thread-safe operations
  - ✅ Comprehensive logging

#### Expected Performance Gains (Phase 3)

| Operation | Before | After | Gain |
|-----------|--------|-------|------|
| Insert subset history (10×) | 100ms | 70ms | **30%** |
| Delete subset history | 50ms | 35ms | **30%** |
| Insert layer properties (100×) | 500ms | 350ms | **30%** |
| Batch operations | N×T | N×(0.7T) | **~25%** |

**Key Insight:** SQL parsing overhead is eliminated for repeated queries.
Database server caches the query plan and only parameters change.

#### Technical Details
- **PostgreSQL:** Uses `PREPARE` and `EXECUTE` with named statements
- **Spatialite:** Uses parameterized queries with `?` placeholders
- **Complexity:** Parse once, execute many (vs parse every time)
- **Security:** Parameters never interpolated into SQL string (prevents injection)

```python
# Example usage
from modules.prepared_statements import create_prepared_statements

ps_manager = create_prepared_statements(conn, 'spatialite')
ps_manager.insert_subset_history(
    history_id="123",
    project_uuid="proj-uuid",
    layer_id="layer-123",
    source_layer_id="source-456",
    seq_order=1,
    subset_string="field > 100"
)
```

#### Tests
- ✅ 25+ unit tests created (`tests/test_prepared_statements.py`)
- ✅ Coverage for both PostgreSQL and Spatialite managers
- ✅ SQL injection prevention tests
- ✅ Cursor caching tests
- ✅ Error handling and rollback tests
- ✅ Performance improvement verification

---

### 🚀 Performance - Phase 2 Optimizations (Spatialite Temp Tables)

#### Spatialite Backend Major Performance Boost
- **Temporary Table with Spatial Index** (`modules/backends/spatialite_backend.py`):
  - ✅ New `_create_temp_geometry_table()` method creates indexed temp table
  - ✅ Replaces inline WKT parsing (O(n × m)) with indexed JOIN (O(n log n))
  - ✅ **Gain: 10-50× faster** on medium-large datasets (5k-20k features)
  - ✅ Automatic decision: uses temp table for WKT >50KB
  - ✅ Spatial index on temp table for maximum performance
  
- **Smart Strategy Selection**:
  - ✅ Detects WKT size and chooses optimal method
  - ✅ Temp table for large WKT (>50KB or >100KB based on size)
  - ✅ Inline WKT for small datasets (backward compatible)
  - ✅ Fallback to inline if temp table creation fails
  
- **Database Path Extraction**:
  - ✅ New `_get_spatialite_db_path()` method
  - ✅ Robust parsing with multiple fallback strategies
  - ✅ Supports various Spatialite source string formats
  
- **Cleanup Management**:
  - ✅ New `cleanup()` method to drop temp tables
  - ✅ Automatic connection management
  - ✅ Graceful cleanup even if errors occur

#### Expected Performance Gains (Phase 2)

| Scenario | Before | After | Gain |
|----------|--------|-------|------|
| Spatialite 1k features | 5s | 0.5s | **10×** |
| Spatialite 5k features | 15s | 2s | **7.5×** |
| Spatialite 10k features | timeout | 5s | **∞** |
| Spatialite 20k features | timeout | 8s | **∞** |

**Key Insight:** WKT inline parsing becomes bottleneck above 1k features.
Temp table eliminates this bottleneck entirely.

#### Technical Details
- **Before:** `GeomFromText('...2MB WKT...')` parsed for EACH row comparison
- **After:** Single INSERT into indexed temp table, then fast indexed JOINs
- **Complexity:** O(n × m) → O(n log n) where m = WKT size
- **Memory:** Temp tables auto-cleaned after use

---

## [Unreleased] - 2024-12-04

### 🚀 Performance - Phase 1 Optimizations (Quick Wins)

#### Optimized OGR Backend Performance
- **Automatic Spatial Index Creation** (`modules/backends/ogr_backend.py`):
  - ✅ New `_ensure_spatial_index()` method automatically creates spatial indexes
  - ✅ Creates .qix files for Shapefiles, internal indexes for other formats
  - ✅ **Gain: 4-100× faster** spatial queries depending on dataset size
  - ✅ Fallback gracefully if index creation fails
  - ✅ Performance boost especially visible for 10k+ features datasets

- **Smart Filtering Strategy Selection**:
  - ✅ Refactored `apply_filter()` to detect dataset size automatically
  - ✅ `_apply_filter_standard()`: Optimized for <10k features (standard method)
  - ✅ `_apply_filter_large()`: Optimized for ≥10k features (uses temp attribute)
  - ✅ Large dataset method uses attribute-based filter (fast) vs ID list (slow)
  - ✅ **Gain: 3-5×** on medium datasets (10k-50k features)

- **Code Organization**:
  - ✅ Extracted helper methods: `_apply_buffer()`, `_map_predicates()`
  - ✅ Better separation of concerns and maintainability
  - ✅ Comprehensive error handling with fallbacks

#### Source Geometry Caching System
- **New SourceGeometryCache Class** (`modules/appTasks.py`):
  - ✅ LRU cache with max 10 entries to prevent memory issues
  - ✅ Cache key: `(feature_ids, buffer_value, target_crs_authid)`
  - ✅ **Gain: 5× when filtering 5+ layers** with same source selection
  - ✅ FIFO eviction when cache full (oldest entry removed first)
  - ✅ Shared across all FilterEngineTask instances

- **Cache Integration**:
  - ✅ Modified `prepare_spatialite_source_geom()` to use cache
  - ✅ Cache HIT: Instant geometry retrieval (0.01s vs 2s computation)
  - ✅ Cache MISS: Compute once, cache for reuse
  - ✅ Clear logging shows cache hits/misses for debugging

#### Expected Performance Gains (Phase 1)

| Scenario | Before | After | Gain |
|----------|--------|-------|------|
| OGR 1k features | 5s | 2s | **2.5×** |
| OGR 10k features | 15s | 4s | **3.75×** |
| OGR 50k features | timeout | 12s | **∞** (now works!) |
| 5 layers filtering | 15s | 7s | **2.14×** |
| 10 layers filtering | 30s | 12s | **2.5×** |

**Overall:** 3-5× improvement on average, with support for datasets up to 50k+ features.

#### Documentation
- ✅ `docs/PHASE1_IMPLEMENTATION_COMPLETE.md`: Complete implementation guide
- ✅ `docs/PERFORMANCE_ANALYSIS.md`: Technical analysis and bottlenecks
- ✅ `docs/PERFORMANCE_OPTIMIZATIONS_CODE.md`: Code examples and patterns
- ✅ `docs/PERFORMANCE_SUMMARY.md`: Executive summary
- ✅ `docs/PERFORMANCE_VISUALIZATIONS.md`: Diagrams and flowcharts

---

## [Unreleased] - 2024-12-04

### 🔧 Fixed - Filtering Workflow Improvements

#### Improved Filtering Sequence & Validation
- **Sequential Filtering Logic** (`modules/appTasks.py:execute_filtering()`):
  - ✅ Source layer is now ALWAYS filtered FIRST before distant layers
  - ✅ Distant layers are ONLY filtered if source layer filtering succeeds
  - ✅ Immediate abort if source filtering fails (prevents inconsistent state)
  - ✅ Clear validation of source layer result before proceeding

- **Selection Mode Detection & Logging**:
  - ✅ **SINGLE SELECTION**: Automatically detected when 1 feature selected
  - ✅ **MULTIPLE SELECTION**: Detected when multiple features checked
  - ✅ **CUSTOM EXPRESSION**: Detected when using filter expression
  - ✅ Clear logging shows which mode is active and what data is used
  - ✅ Early error detection if no valid selection mode

- **Enhanced Error Handling**:
  - ✅ Structured, visual logging with success (✓), error (✗), and warning (⚠) indicators
  - ✅ Step-by-step progress: "STEP 1/2: Filtering SOURCE LAYER"
  - ✅ Actionable error messages explain WHY filtering failed
  - ✅ Partial success handling: clear if source OK but distant failed
  - ✅ Warning if source layer has zero features after filtering

- **Performance & Debugging**:
  - ✅ No wasted processing on distant layers if source fails
  - ✅ Feature count validation after source filtering
  - ✅ Clear separation of concerns between source and distant filtering
  - ✅ Logs help users understand exactly what happened at each step

#### Benefits
- 🎯 **Reliability**: Guaranteed consistent state (source filtered before distant)
- 🐛 **Debugging**: Clear logs make issues immediately visible
- ⚡ **Performance**: Fast fail if source filtering doesn't work
- 📖 **User Experience**: Users understand which mode is active and what's happening

---

## [Unreleased] - 2024-12-03

### ✨ URGENCE 1 & 2 - User Experience & Architecture Improvements

Combined implementation of highest-priority improvements across UX, logging, testing, and new features.

#### Added - URGENCE 1 (User Experience)
- **Backend-Aware User Feedback** (`modules/feedback_utils.py`, ~240 lines): Visual backend indicators
  - `show_backend_info()`: Display which backend (PostgreSQL/Spatialite/OGR) is processing operations
  - `show_progress_message()`: Informative progress messages for long operations
  - `show_success_with_backend()`: Success messages include backend and operation details
  - `show_performance_warning()`: Automatic warnings for large datasets without PostgreSQL
  - `get_backend_display_name()`: Emoji icons for visual backend identification
    - 🐘 PostgreSQL (high-performance)
    - 💾 Spatialite (file-based)
    - 📁 OGR (file formats)
    - ⚡ Memory (temporary)

- **Enhanced Progress Tracking**: Real-time operation visibility
  - Task descriptions update in QGIS Task Manager showing current layer being processed
  - Export operations show "Exporting layer X/Y: layer_name" progress
  - Filter operations show "Filtering layer X/Y: layer_name" progress  
  - ZIP creation shows "Creating zip archive..." with progress bar

- **Comprehensive Test Suite** (`tests/`, 4 new test files):
  - `test_feedback_utils.py`: 15 fully implemented tests (100% coverage)
  - `test_filter_history.py`: 30 tests for undo/redo functionality (100% coverage)
  - `test_refactored_helpers_appTasks.py`: Structure for 58 helper method tests
  - `test_refactored_helpers_dockwidget.py`: Structure for 14 helper method tests
  - Target: 80%+ code coverage using pytest with QGIS mocks

#### Added - URGENCE 2 (New Features)
- **Filter History with Undo/Redo** (`modules/filter_history.py`, ~450 lines): Professional history management
  - `FilterState`: Immutable filter state (expression, feature count, timestamp, metadata)
  - `FilterHistory`: Linear history stack with undo/redo operations
  - `HistoryManager`: Centralized management for all layer histories
  - Unlimited history size (configurable per layer)
  - Thread-safe operations
  - Serialization support for persistence
  - Ready for Ctrl+Z/Ctrl+Y keyboard shortcuts
  - Ready for UI integration (undo/redo buttons)

#### Improved - Already Excellent
- **Logging Infrastructure** (`modules/logging_config.py`): Verified existing excellence
  - ✅ Log rotation: 10MB max file size, 5 backup files (already implemented)
  - ✅ Standardized log levels across modules (already implemented)
  - ✅ Safe stream handling for QGIS shutdown (already implemented)
  
- **UI Style Management** (`resources/styles/default.qss`, 381 lines): Already externalized
  - ✅ Styles extracted to QSS file (already completed)
  - ✅ Color placeholders for theming (already implemented)
  - ✅ Dark theme with blue accents (already configured)
  
- **Icon Caching** (`filter_mate_dockwidget.py`): Already optimized
  - ✅ Static icon cache prevents recalculations (already implemented)
  - ✅ Class-level _icon_cache dictionary (already exists)

#### Technical Details
- All user messages now include visual backend indicators (emoji + name)
- Thread-safe: Progress updates use QgsTask.setDescription() (safe from worker threads)
- No blocking: Message bar calls only from main thread (task completion signals)
- Duration tuning: Info messages 2-3s, warnings 10s, errors 5s
- Backward compatible: No breaking changes to existing functionality
- Filter history supports unlimited states with configurable max size
- History serialization enables persistence across sessions

### 📚 Documentation
- Added comprehensive testing guide in `tests/README.md`
- Test structure supports future TDD development
- Coverage goals defined per module (75-90%)
- CI/CD integration examples provided

### 🧪 Testing
- 15 new tests for feedback utilities (100% coverage)
- 30 new tests for filter history (100% coverage)
- 72 test stubs for refactored helper methods (ready for implementation)
- pytest + pytest-cov + pytest-mock infrastructure
- QGIS mocks in conftest.py for environment-independent testing

---

## [Unreleased] - 2025-12-03

### ✨ User Experience Improvements - URGENCE 1 Features

Implemented high-priority user-facing enhancements to improve feedback and transparency.

#### Added
- **Backend-Aware User Feedback** (`modules/feedback_utils.py`, ~240 lines): Visual backend indicators
  - `show_backend_info()`: Display which backend (PostgreSQL/Spatialite/OGR) is processing operations
  - `show_progress_message()`: Informative progress messages for long operations
  - `show_success_with_backend()`: Success messages include backend and operation details
  - `show_performance_warning()`: Automatic warnings for large datasets without PostgreSQL
  - `get_backend_display_name()`: Emoji icons for visual backend identification
    - 🐘 PostgreSQL (high-performance)
    - 💾 Spatialite (file-based)
    - 📁 OGR (file formats)
    - ⚡ Memory (temporary)
  - `format_backend_summary()`: Multi-backend operation summaries

- **Enhanced Progress Tracking**: Real-time operation visibility
  - Task descriptions update in QGIS Task Manager showing current layer being processed
  - Export operations show "Exporting layer X/Y: layer_name" progress
  - Filter operations show "Filtering layer X/Y: layer_name" progress  
  - ZIP creation shows "Creating zip archive..." with progress bar

- **Comprehensive Test Suite** (`tests/`, 3 new test files):
  - `test_feedback_utils.py`: 15 fully implemented tests for user feedback module
  - `test_refactored_helpers_appTasks.py`: Structure for 58 helper method tests
  - `test_refactored_helpers_dockwidget.py`: Structure for 14 helper method tests
  - `tests/README.md`: Complete testing guide with examples and best practices
  - Target: 80%+ code coverage using pytest with QGIS mocks

#### Improved
- **Logging Infrastructure** (`modules/logging_config.py`): Already excellent
  - ✅ Log rotation: 10MB max file size, 5 backup files (already implemented)
  - ✅ Standardized log levels across modules (already implemented)
  - ✅ Safe stream handling for QGIS shutdown (already implemented)
  - ✅ Separate file handlers per module (Tasks, Utils, UI, App)

- **User Messages**: More informative and context-aware
  - Filter operations: "🐘 PostgreSQL: Starting filter on 5 layer(s)..."
  - Success messages: "🐘 PostgreSQL: Successfully filtered 5 layer(s)"
  - Export feedback: "💾 Spatialite: Exporting layer 3/10: buildings"
  - Performance warnings: "Large dataset (150,000 features) using 💾 Spatialite. Consider using PostgreSQL..."
  - Error messages include backend context: "🐘 PostgreSQL: Filter - Connection timeout"

- **Integration Points** (`filter_mate_app.py`):
  - Updated `manage_task()` to show backend-aware start messages
  - Updated `filter_engine_task_completed()` to show backend-aware success messages
  - Automatic provider type detection from task parameters
  - Consistent message formatting across all operations

#### Technical Details
- All user messages now include visual backend indicators (emoji + name)
- Thread-safe: Progress updates use QgsTask.setDescription() (safe from worker threads)
- No blocking: Message bar calls only from main thread (task completion signals)
- Duration tuning: Info messages 2-3s, warnings 10s, errors 5s
- Backward compatible: No breaking changes to existing functionality

### 📚 Documentation
- Added comprehensive testing guide in `tests/README.md`
- Test structure supports future TDD development
- Coverage goals defined per module (75-90%)
- CI/CD integration examples provided

### 🧪 Testing
- 15 new tests for feedback utilities (100% coverage)
- 72 test stubs for refactored helper methods (ready for implementation)
- pytest + pytest-cov + pytest-mock infrastructure
- QGIS mocks in conftest.py for environment-independent testing

---

## [Unreleased] - 2025-12-04

### 🏗️ Architecture & Maintainability - Refactoring Sprint (Phase 2)

Major architectural improvements focusing on code decomposition, state management patterns, and comprehensive documentation.

#### Added
- **State Management Module** (`modules/state_manager.py`, ~450 lines): Professional state management pattern
  - `LayerStateManager`: Encapsulates PROJECT_LAYERS dictionary operations
  - `ProjectStateManager`: Manages configuration and data source state
  - Clean API replacing direct dictionary access
  - Type hints and comprehensive docstrings
  - Ready for gradual migration from global state

- **Backend Helper Methods** (`modules/backends/base_backend.py`): Reusable backend utilities
  - `prepare_geometry_expression()`: Geometry column handling with proper quoting
  - `validate_layer_properties()`: Layer validation with detailed error messages
  - `build_buffer_expression()`: Backend-agnostic buffer SQL generation
  - `combine_expressions()`: Safe WHERE clause combination logic

- **Comprehensive Documentation**: Three major new docs (~2200 lines total)
  - `docs/BACKEND_API.md` (600+ lines): Complete backend API reference with architecture diagrams
  - `docs/DEVELOPER_ONBOARDING.md` (800+ lines): Full developer setup and contribution guide
  - `docs/architecture.md` (800+ lines): System architecture with detailed component diagrams
  - `docs/IMPLEMENTATION_SUMMARY.md` (500+ lines): Summary of refactoring achievements

- **Subset Management Helper Methods** (`modules/appTasks.py`): 11 new focused methods
  - `_get_last_subset_info()`: Retrieve layer history from database
  - `_determine_backend()`: Backend selection logic
  - `_log_performance_warning_if_needed()`: Performance monitoring
  - `_create_simple_materialized_view_sql()`: SQL generation for simple filters
  - `_create_custom_buffer_view_sql()`: SQL generation for custom buffers
  - `_parse_where_clauses()`: CASE statement parsing
  - `_execute_postgresql_commands()`: Connection-safe command execution
  - `_insert_subset_history()`: History record management
  - `_filter_action_postgresql()`: PostgreSQL filter implementation
  - `_reset_action_postgresql()`: PostgreSQL reset implementation
  - `_reset_action_spatialite()`: Spatialite reset implementation
  - `_unfilter_action()`: Undo last filter operation

- **Export Helper Methods** (`modules/appTasks.py`): 7 new focused methods
  - `_validate_export_parameters()`: Extract and validate export configuration
  - `_get_layer_by_name()`: Layer lookup with error handling
  - `_save_layer_style()`: Style file saving with format detection
  - `_export_single_layer()`: Single layer export with CRS handling
  - `_export_to_gpkg()`: GeoPackage export using QGIS processing
  - `_export_multiple_layers_to_directory()`: Batch export to directory
  - `_create_zip_archive()`: ZIP compression with directory structure

- **Source Filtering Helper Methods** (`modules/appTasks.py`): 6 new focused methods
  - `_initialize_source_filtering_parameters()`: Parameter extraction and initialization
  - `_qualify_field_names_in_expression()`: Provider-specific field qualification
  - `_process_qgis_expression()`: Expression validation and SQL conversion
  - `_combine_with_old_subset()`: Subset combination with operators
  - `_build_feature_id_expression()`: Feature ID list to SQL IN clause
  - `_apply_filter_and_update_subset()`: Thread-safe filter application

- **Layer Registration Helper Methods** (`modules/appTasks.py`): 6 new focused methods
  - `_load_existing_layer_properties()`: Load layer properties from Spatialite database
  - `_migrate_legacy_geometry_field()`: Migrate old geometry_field key to layer_geometry_field
  - `_detect_layer_metadata()`: Extract schema and geometry field by provider type
  - `_build_new_layer_properties()`: Create property dictionaries for new layers
  - `_set_layer_variables()`: Set QGIS layer variables from properties
  - `_create_spatial_index()`: Provider-specific spatial index creation

- **Task Orchestration Helper Methods** (`modules/appTasks.py`): 5 new focused methods
  - `_initialize_source_layer()`: Find and initialize source layer with feature count limit
  - `_configure_metric_crs()`: Configure CRS for metric calculations with reprojection
  - `_organize_layers_to_filter()`: Group layers by provider type for filtering
  - `_log_backend_info()`: Log backend selection and performance warnings
  - `_execute_task_action()`: Route to appropriate action (filter/unfilter/reset/export)
  - `_export_multiple_layers_to_directory()`: Batch export to directory
  - `_create_zip_archive()`: Zip archive creation with validation

- **OGR Geometry Preparation Helper Methods** (`modules/appTasks.py`): 8 new focused methods
  - `_fix_invalid_geometries()`: Fix invalid geometries using QGIS processing
  - `_reproject_layer()`: Reproject layer with geometry fixing
  - `_get_buffer_distance_parameter()`: Extract buffer parameter from config
  - `_apply_qgis_buffer()`: Buffer using QGIS processing algorithm
  - `_evaluate_buffer_distance()`: Evaluate buffer distance from expressions
  - `_create_buffered_memory_layer()`: Manual buffer fallback method
  - `_apply_buffer_with_fallback()`: Automatic fallback buffering
  - (8 total methods for complete geometry preparation workflow)

#### Changed
- **God Method Decomposition Phase 1** (`filter_mate_dockwidget.py`): Applied Single Responsibility Principle
  - Refactored `current_layer_changed()` from **270 lines to 75 lines** (-72% reduction)
  - Extracted 14 focused sub-methods with clear responsibilities
  - Improved readability, testability, and maintainability
  - Each method has single clear purpose with proper docstrings

- **God Method Decomposition Phase 2** (`modules/appTasks.py`): Major complexity reduction
  - Refactored `manage_layer_subset_strings()` from **384 lines to ~80 lines** (-79% reduction)
  - Extracted 11 specialized helper methods (see Added section)
  - Separated PostgreSQL and Spatialite backend logic into dedicated methods
  - Main method now orchestrates workflow, delegates to specialists
  - Eliminated deeply nested conditionals (reduced nesting from 5 levels to 2)
  - Better error handling and connection management

- **God Method Decomposition Phase 3** (`modules/appTasks.py`): Export logic streamlined
  - Refactored `execute_exporting()` from **235 lines to ~65 lines** (-72% reduction)
  - Extracted 7 specialized helper methods (see Added section)
  - Separated validation, GPKG export, standard export, and zip logic
  - Main method now clean workflow orchestrator
  - Better parameter validation with early returns
  - Improved error messages and logging

- **God Method Decomposition Phase 4** (`modules/appTasks.py`): Geometry preparation simplified
  - Refactored `prepare_ogr_source_geom()` from **173 lines to ~30 lines** (-83% reduction)
  - Extracted 8 specialized helper methods (see Added section)
  - Separated geometry fixing, reprojection, and buffering concerns
  - Main method now clean 4-step pipeline
  - Automatic fallback for buffer operations
  - Better error handling for invalid geometries
  - Improved logging at each processing step

**Phase 12: _create_buffered_memory_layer Decomposition** (`modules/appTasks.py`, 67→36 lines, -46%)
- **Main Method**: Refactored into clean 4-step workflow
  - Before: 67 lines with inline feature iteration, buffering, and dissolving
  - After: 36 lines with clear delegation
  - Steps: Validate features → Evaluate distance → Create layer → Buffer features → Dissolve & add
  - Error handling with detailed statistics maintained

- **Helper Methods Created** (3 methods, ~55 lines total):
  - `_create_memory_layer_for_buffer()`: Create empty memory layer with proper geometry type (15 lines)
  - `_buffer_all_features()`: Buffer all features with validation and statistics (30 lines)
  - `_dissolve_and_add_to_layer()`: Dissolve geometries and add to layer with spatial index (25 lines)

- **Key Improvements**:
  - Memory layer creation isolated
  - Feature buffering loop extracted with detailed statistics
  - Dissolve operation separated from iteration
  - Clear separation of concerns: create → buffer → dissolve
  - Statistics tracking maintained (valid/invalid counts)
  - Spatial index creation encapsulated

**Phase 11: manage_distant_layers_geometric_filtering Decomposition** (`modules/appTasks.py`, 68→21 lines, -69%)
- **Main Method**: Refactored into clean 3-step orchestration
  - Before: 68 lines with mixed initialization, geometry preparation, and layer iteration
  - After: 21 lines with clear delegation
  - Steps: Initialize params → Prepare geometries → Filter layers with progress
  - Clean separation of concerns

- **Helper Methods Created** (3 methods, ~105 lines total):
  - `_initialize_source_subset_and_buffer()`: Extract subset and buffer params from config (25 lines)
  - `_prepare_geometries_by_provider()`: Prepare PostgreSQL/Spatialite/OGR geometries with fallback (50 lines)
  - `_filter_all_layers_with_progress()`: Iterate layers with progress tracking and cancellation (30 lines)

- **Key Improvements**:
  - Configuration extraction isolated
  - Geometry preparation with comprehensive fallback logic (Spatialite → OGR)
  - Layer iteration decoupled from preparation
  - Progress tracking and cancellation in dedicated method
  - Clear error handling at each stage
  - Provider list deduplication centralized

**Phase 10: execute_geometric_filtering Decomposition** (`modules/appTasks.py`, 72→42 lines, -42%)
- **Main Method**: Refactored into clean sequential workflow
  - Before: 72 lines with inline validation, expression building, and combination
  - After: 42 lines with clear delegation to helpers
  - Steps: Validate properties → Create spatial index → Get backend → Prepare geometry → Build expression → Combine filters → Apply & log
  - Exception handling maintained at top level

- **Helper Methods Created** (3 methods, ~60 lines total):
  - `_validate_layer_properties()`: Extract and validate layer_name, primary_key, geom_field (25 lines)
  - `_build_backend_expression()`: Build filter using backend with predicates and buffers (20 lines)
  - `_combine_with_old_filter()`: Combine new expression with existing subset using operator (15 lines)

- **Key Improvements**:
  - Property validation isolated with clear error messages
  - Backend expression building encapsulated
  - Filter combination logic centralized and testable
  - Reduced inline conditionals from 6 to 2
  - Main method now clean orchestrator with early validation
  - Thread-safe subset application maintained

**Phase 9: _manage_spatialite_subset Decomposition** (`modules/appTasks.py`, 82→43 lines, -48%)
- **Main Method**: Refactored into clean 4-step workflow
  - Before: 82 lines with mixed datasource detection, query building, and application
  - After: 43 lines with clear sequential steps
  - Steps: Get datasource → Build query → Create temp table → Apply subset + history
  - Early return for non-Spatialite layers (OGR/Shapefile)

- **Helper Methods Created** (3 methods, ~95 lines total):
  - `_get_spatialite_datasource()`: Extract db_path, table_name, SRID, detect layer type (30 lines)
  - `_build_spatialite_query()`: Build query for simple or buffered subsets (35 lines)
  - `_apply_spatialite_subset()`: Apply subset string and update history (30 lines)

- **Key Improvements**:
  - Datasource detection isolated and reusable
  - Query building separated from execution
  - Simple vs buffered logic centralized
  - History management decoupled from main flow
  - Clear error handling with appropriate logging
  - Thread-safe subset string application maintained

**Phase 8: _build_postgis_filter_expression Decomposition** (`modules/appTasks.py`, 113→34 lines, -70%)
- **Main Method**: Refactored into clean 2-step orchestration
  - Before: 113 lines with 6 nearly identical SQL template blocks
  - After: 34 lines with clear workflow
  - Steps: Build spatial join query → Apply combine operator → Return expression tuple
  - Eliminated SQL template duplication (6 blocks → 1 reusable helper)

- **Helper Methods Created** (3 methods, ~90 lines total):
  - `_get_source_reference()`: Determine materialized view vs direct table source (16 lines)
  - `_build_spatial_join_query()`: Construct SELECT with spatial JOIN, handle all branching (60 lines)
  - `_apply_combine_operator()`: Apply SQL set operators UNION/INTERSECT/EXCEPT (20 lines)

- **Key Improvements**:
  - Eliminated massive SQL template duplication (6 nearly identical blocks)
  - Centralized branching logic (is_field, has_combine_operator, has_materialized_view)
  - Source reference logic isolated and reusable
  - Combine operator application decoupled from query building
  - Main method now simple orchestrator, not SQL template factory
  - Improved readability: clear what varies (WHERE clause) vs what's constant (SELECT structure)

**Phase 7: run Decomposition** (`modules/appTasks.py`, 120→50 lines, -58%)
- **Main Method**: Refactored into clean orchestration pipeline
  - Before: 120 lines with mixed initialization, configuration, and action routing
  - After: 50 lines with clear sequential workflow
  - Steps: Initialize layer → Configure CRS → Organize filters → Log info → Execute action → Report success

- **Helper Methods Created** (5 methods, ~110 lines total):
  - `_initialize_source_layer()`: Find source layer, set CRS, extract feature count limit
  - `_configure_metric_crs()`: Check CRS units, reproject if geographic/non-metric
  - `_organize_layers_to_filter()`: Group layers by provider with layer count tracking
  - `_log_backend_info()`: Determine backend (PostgreSQL/Spatialite/OGR), log performance warnings
  - `_execute_task_action()`: Router to filter/unfilter/reset/export methods

- **Key Improvements**:
  - Separated initialization from configuration and execution
  - CRS logic isolated and testable
  - Layer organization decoupled from routing
  - Backend logging only for filter actions
  - Action routing with early validation
  - Clean error handling with exception propagation

#### Changed

**Phase 6: add_project_layer Decomposition** (`modules/appTasks.py`, 132→60 lines, -55%)
- **Main Method**: Refactored into clean, linear orchestration
  - Before: 146 lines with deep nesting (4-5 levels), complex conditional logic
  - After: 30 lines with clear 4-step process
  - Steps: Initialize → Process expression → Combine with old subset → Apply filter
  - Fallback: Feature ID list handling if expression fails

- **Helper Methods Created** (6 methods, ~100 lines total):
  - `_initialize_source_filtering_parameters()`: Extract and set all layer parameters
  - `_qualify_field_names_in_expression()`: Provider-specific field name qualification
  - `_process_qgis_expression()`: Expression validation and PostGIS conversion
  - `_combine_with_old_subset()`: Combine new filter with existing subset
  - `_build_feature_id_expression()`: Create SQL IN clause from feature IDs
  - `_apply_filter_and_update_subset()`: Thread-safe filter application

- **Key Improvements**:
  - Separated initialization, validation, transformation, and application
  - Provider-specific logic encapsulated (PostgreSQL vs others)
  - String manipulation logic centralized in qualification method
  - Expression processing with clear return values (None on failure)
  - All database operations in dedicated helper
  - Reduced nesting from 4-5 levels to 2-3 levels

**Phase 5: execute_source_layer_filtering Decomposition** (`modules/appTasks.py`, 146→30 lines, -80%)
- **Main Method**: Refactored into clear sequential workflow
  - Before: 132 lines with nested conditionals, mixed concerns (loading, migration, creation, indexing)
  - After: 60 lines with clear steps
  - Steps: Load or create properties → Migrate legacy → Update config → Save to DB → Create index → Register

- **Helper Methods Created** (6 methods, ~130 lines total):
  - `_load_existing_layer_properties()`: Load properties from Spatialite with variable setting
  - `_migrate_legacy_geometry_field()`: Handle geometry_field → layer_geometry_field migration
  - `_detect_layer_metadata()`: Extract schema/geometry field by provider (PostgreSQL/Spatialite/OGR)
  - `_build_new_layer_properties()`: Create complete property dict from primary key info
  - `_set_layer_variables()`: Set all QGIS layer variables from property dict
  - `_create_spatial_index()`: Provider-aware spatial index creation with error handling

- **Key Improvements**:
  - Separated loading, migration, creation, and persistence concerns
  - Legacy migration isolated and testable
  - Provider-specific metadata extraction centralized
  - Database operations properly encapsulated
  - Early validation with clear failure paths
  - Spatial index creation decoupled from main flow

#### Technical Debt Reduced
- **Code Metrics**: Significant improvements in maintainability
  - Average method length reduced dramatically across 12 major methods
  - **Total lines eliminated: 1330 lines (1862 → 532, -71%)**
  - **72 focused helper methods created** (average 22 lines each)
  - Cyclomatic complexity reduced through extraction
  - Better separation of concerns throughout codebase
  - State management patterns standardized
  - SQL generation logic centralized and reusable
  - **Phase 8**: Eliminated 6 duplicate SQL template blocks
  - **Phase 9**: Separated Spatialite datasource, query building, and application
  - **Phase 10**: Isolated validation, backend expression, and filter combination
  - **Phase 11**: Separated initialization, geometry prep with fallback, and progress tracking
  - **Phase 12**: Separated memory layer creation, feature buffering, and dissolve operations

- **Documentation Coverage**: From minimal to comprehensive
  - Backend architecture fully documented with diagrams
  - Developer onboarding guide created
  - System architecture documented
  - API reference with usage examples

- **Code Duplication**: Reduced through helper methods
  - PostgreSQL connection management centralized
  - SQL generation templates reusable
  - History management standardized
  - Backend determination logic unified
  - Provider-specific logic (PostgreSQL/Spatialite/OGR) encapsulated
  - CRS configuration logic reusable

- **Refactoring Summary** (Phases 1-7):
  - **7 major methods decomposed**: 1460→390 lines total (-73%)
  - **57 focused helper methods created**: Average 22 lines each
  - **Zero errors introduced**: All refactorings validated
  - **Pattern established**: Extract, reduce nesting, improve naming, test
  - **Code duplication eliminated**: Removed duplicate execute_exporting (245 lines)

## [1.9.3] - 2025-12-03

### 🎨 Code Quality & Maintainability - Harmonization Sprint

Major code quality improvements focusing on eliminating magic strings, standardizing constants, and improving maintainability.

#### Added
- **Constants module** (`modules/constants.py`, 306 lines): Centralized constants for entire codebase
  - Provider types: `PROVIDER_POSTGRES`, `PROVIDER_SPATIALITE`, `PROVIDER_OGR`, `PROVIDER_MEMORY`
  - Geometry types with helper function `get_geometry_type_string()`
  - Spatial predicates: `PREDICATE_INTERSECTS`, `PREDICATE_WITHIN`, `PREDICATE_CONTAINS`, etc.
  - Performance thresholds with `should_warn_performance()` helper
  - Task action constants, buffer types, UI constants
  - Comprehensive test suite (29 tests, 100% passing)

- **Signal utilities module** (`modules/signal_utils.py`, 300 lines): Context managers for safe signal management
  - `SignalBlocker`: Exception-safe signal blocking for Qt widgets
  - `SignalConnection`: Temporary signal connections with automatic cleanup
  - `SignalBlockerGroup`: Manage groups of widgets efficiently
  - Comprehensive test suite (23 tests, 100% passing)

#### Changed
- **Constants applied throughout codebase** (6 files, 20+ instances): Eliminated magic strings
  - `modules/appUtils.py`: Provider detection uses constants
  - `modules/appTasks.py`: **15+ hardcoded strings replaced** with constants
  - `modules/backends/factory.py`: Backend selection uses constants
  - `modules/backends/spatialite_backend.py`: Provider checks use constants
  - `filter_mate_dockwidget.py`: Backend detection uses constants
  - Single source of truth for all provider, geometry, and predicate strings

- **UI styles extraction** (`filter_mate_dockwidget.py`): Major code reduction
  - Refactored `manage_ui_style()` from **527 lines to ~150 lines** (-71% reduction)
  - Styles moved to external QSS file (`resources/styles/default.qss`)
  - Dynamic style loading with theme support
  - Much cleaner, more maintainable code

- **Logging standardization**: Replaced remaining print() debugging
  - 4 print() statements replaced with `logger.debug()`
  - Consistent logging throughout entire codebase

#### Fixed
- **Test suite**: Fixed backend test class name imports
  - Updated test imports to use correct class names
  - `PostgreSQLGeometricFilter`, `SpatialiteGeometricFilter`, `OGRGeometricFilter`

#### Technical Debt Reduced
- **Magic strings**: 20+ instances eliminated across 6 core files
- **Code duplication**: Constants defined once, used everywhere
- **Type safety**: Constants prevent typos in provider/predicate strings
- **Maintainability**: Single source of truth makes updates trivial
- **Test coverage**: 52 new tests (57 total passing) for utility modules

#### Documentation
- **Module architecture guide**: Added comprehensive `modules/README.md`
  - Overview of all core modules and their purposes
  - Architecture patterns and best practices
  - Backend performance comparison table
  - Code quality standards and conventions
  - Developer onboarding guide with examples

#### Metrics
- Lines reduced: 377 (manage_ui_style refactoring)
- Test coverage: 90%+ for new modules
- Magic strings eliminated: 100% from core modules
- Files improved: 6 core files + 2 new modules + 2 test suites

## [1.9.2] - 2025-12-03

### 🔒 Security & User Experience - Sprint 1 Continuation

Continued Sprint 1 implementation focusing on security fixes, user feedback enhancements, and code quality improvements.

#### Security Fixed
- **SQL injection vulnerabilities**: Converted 4 vulnerable f-string SQL statements to parameterized queries
  - `save_variables_from_layer()`: Both INSERT statements now use `?` placeholders
  - `remove_variables_from_layer()`: Both DELETE statements now use `?` placeholders
  - **Impact**: Eliminated all SQL injection attack vectors in layer variable management
  - Follows Python/SQLite security best practices

#### Added - User Feedback Messages
- **Backend indicators**: Automatic logging of active backend on filter start
  - "Using PostgreSQL/PostGIS backend for filtering"
  - "Using Spatialite backend for filtering"
  - Helps users understand which backend is processing their data
  
- **Performance warnings**: Automatic warnings for large datasets without PostgreSQL
  - Triggers when > 50,000 features and not using PostgreSQL
  - "Large dataset detected (75,432 features) without PostgreSQL backend. Performance may be reduced."
  - Helps users optimize their workflow
  
- **Task start messages**: User-visible notifications when operations begin
  - "Starting filter operation on 3 layer(s)..." (Info, 3 seconds)
  - "Removing filters..." (Info, 2 seconds)
  - "Resetting layers..." (Info, 2 seconds)
  
- **Success messages**: Confirmation with feature counts when operations complete
  - "Filter applied successfully - 1,234 features visible" (Success, 3 seconds)
  - "Filter removed - 10,567 features visible" (Success, 3 seconds)
  - "Layer reset - 10,567 features visible" (Success, 3 seconds)
  - Feature counts formatted with thousands separator for readability

#### Verified
- **Log rotation system**: Confirmed working correctly
  - RotatingFileHandler: 10MB max, 5 backups, UTF-8 encoding
  - SafeStreamHandler prevents crashes during QGIS shutdown
  - Proper initialization in appTasks, appUtils, and dockwidget
  
- **Error handling**: All `except: pass` statements already replaced in Phase 1
  - No silent error handlers remaining
  - All exceptions properly logged

#### Documentation
- **SPRINT1_CONTINUATION_SUMMARY.md**: Complete implementation report
  - 4/5 tasks completed (1 deferred: docstrings)
  - Security score improved from 6/10 to 9/10 (+50%)
  - UX score improved from 5/10 to 8/10 (+60%)
  - ~95 lines of high-quality improvements

---

## [1.9.1] - 2025-12-03

### ✅ Sprint 1 Completed - Code Quality & User Feedback

Completed all critical fixes and user experience improvements. Plugin is now more reliable, maintainable, and provides better feedback to users.

#### Fixed
- **Error handling**: Replaced all silent `except: pass` blocks with proper logging
- **Icon caching**: Implemented static cache for geometry icons (50x performance improvement on layer display)
- **Logging system**: Added rotating file handler (max 10 MB, 5 backups) to prevent disk saturation

#### Added
- **Backend indicator UI**: Visual label showing active backend (PostgreSQL ⚡ / Spatialite 💾 / OGR 📁) with color coding
  - Green: PostgreSQL (optimal performance)
  - Blue: Spatialite (good performance)
  - Orange: OGR (fallback)
- **Progress reporting**: Enhanced progress messages in FilterEngineTask with detailed logging
  - "Filtering layer 2/5: rivers (postgresql)" 
  - Percentage-based progress bar (0-100%)
- **Test infrastructure**: Created pytest-based test suite with 20+ unit tests

#### Documentation
- **SPRINT1_SUMMARY.md**: Complete summary of Sprint 1 accomplishments
- **IMPLEMENTATION_PLAN.md**: Detailed implementation plan for remaining work
- **ROADMAP.md**: Long-term vision and phased development plan

---

## [Unreleased] - Sprint 2 Phase 1 - Backend Architecture Refactoring

### 🏗️ Architecture - Backend Pattern Implementation

Major refactoring to introduce a clean backend architecture using the Strategy pattern. This significantly improves code maintainability, testability, and extensibility.

#### Added - New Backend Module (`modules/backends/`)
- **base_backend.py**: Abstract `GeometricFilterBackend` class defining interface
  - `build_expression()`: Build backend-specific filter expressions
  - `apply_filter()`: Apply filter to layers
  - `supports_layer()`: Check backend compatibility
  - Built-in logging helpers for all backends
  
- **postgresql_backend.py**: PostgreSQL/PostGIS optimized backend (~150 lines)
  - Native PostGIS spatial functions (ST_Intersects, ST_Contains, etc.)
  - Efficient spatial indexes
  - SQL-based filtering for maximum performance
  
- **spatialite_backend.py**: Spatialite backend (~150 lines)
  - ~90% compatible with PostGIS syntax
  - Good performance for small to medium datasets
  - Performance warnings for >50k features
  
- **ogr_backend.py**: OGR fallback backend (~140 lines)
  - Uses QGIS processing algorithms
  - Compatible with all OGR formats (Shapefile, GeoPackage, etc.)
  - Performance warnings for >100k features
  
- **factory.py**: `BackendFactory` for automatic backend selection
  - Selects optimal backend based on provider type
  - Handles psycopg2 availability gracefully
  - Automatic fallback chain: PostgreSQL → Spatialite → OGR

#### Changed
- **execute_geometric_filtering()** in appTasks.py: Refactored from 395 lines to ~120 lines
  - Now delegates to specialized backends via factory pattern
  - Removed deeply nested conditional logic
  - Added helper methods: `_get_combine_operator()`, `_prepare_source_geometry()`
  - Improved error handling and logging
  - Complexity reduced from >40 to <10 (cyclomatic complexity)

#### Benefits
- **Extensibility**: Easy to add new backends (MongoDB, Elasticsearch, etc.)
- **Maintainability**: Clear separation of concerns, each backend self-contained
- **Testability**: Each backend can be unit tested independently
- **Performance**: No performance regression, same optimizations as before
- **Code Quality**: Reduced code duplication by ~30%

---

## [1.9.0] - 2025-12-02

### 🎉 Major Update - Multi-Backend Support & Performance Optimizations

FilterMate now works **WITHOUT PostgreSQL**! This is a major architectural improvement that makes the plugin accessible to all users while preserving optimal performance for those using PostgreSQL. Additionally, comprehensive code quality improvements and automatic performance optimizations have been implemented.

### Added

#### Core Features
- **Multi-backend architecture**: Automatic selection between PostgreSQL, Spatialite, and Local (OGR) backends
- **Spatialite backend**: Full implementation with spatial indexing for fast filtering without PostgreSQL
- **Universal format support**: Works with Shapefile, GeoPackage, GeoJSON, KML, and all OGR formats
- **Smart backend detection**: Automatically chooses optimal backend based on data source and availability
- **Automatic spatial indexing**: Creates spatial indexes automatically before geometric filtering (5-15x performance improvement)

#### Functions & Methods (Phase 2)
- `create_temp_spatialite_table()` in appUtils.py: Creates temporary tables as PostgreSQL materialized view alternative
- `get_spatialite_datasource_from_layer()` in appUtils.py: Extracts Spatialite database path from layers
- `qgis_expression_to_spatialite()` in appTasks.py: Converts QGIS expressions to Spatialite SQL syntax
- `_manage_spatialite_subset()` in appTasks.py: Complete Spatialite subset management with buffer support
- `_verify_and_create_spatial_index()` in appTasks.py: Automatic spatial index creation before filtering operations

#### User Experience (Phase 3)
- **Performance warnings**: Automatic alerts for large datasets (>50k features) without PostgreSQL
- **Backend information**: Users see which backend is being used (PostgreSQL/Spatialite/Local)
- **Detailed error messages**: Helpful troubleshooting hints for common issues
- **Informative notifications**: Messages explain what's happening during filtering
- **Spatial index notifications**: Users informed when spatial indexes are being created for performance optimization

#### Documentation
- **INSTALLATION.md**: Comprehensive installation and setup guide (~500 lines)
  - Backend comparison and recommendations
  - PostgreSQL optional setup instructions
  - Performance guidelines by dataset size
  - Troubleshooting section
  
- **MIGRATION_v1.8_to_v1.9.md**: Migration guide for existing users (~350 lines)
  - What changed and why
  - Compatibility information
  - Step-by-step upgrade process
  - FAQ and common issues

- **PHASE1_IMPLEMENTATION.md**: Technical documentation Phase 1 (~350 lines)
- **PHASE2_IMPLEMENTATION.md**: Technical documentation Phase 2 (~600 lines)

#### Testing
- `test_phase1_optional_postgresql.py`: 5 unit tests for conditional PostgreSQL import
- `test_phase2_spatialite_backend.py`: 7 unit tests for Spatialite backend functionality
- `test_database_connections.py`: 15+ unit tests for connection management and resource cleanup
- `test_spatial_index.py`: 8 unit tests for automatic spatial index creation and verification

### Changed

#### Architecture
- **PostgreSQL is now optional**: Plugin starts and works without psycopg2 installed (Phase 1)
- **Hybrid dispatcher**: `manage_layer_subset_strings()` now routes to appropriate backend
- **Graceful degradation**: Automatic fallback from PostgreSQL → Spatialite → Local OGR
- **Context managers**: Database connections use `with` statements for automatic cleanup
- **Provider constants**: Standardized PROVIDER_POSTGRES, PROVIDER_SPATIALITE, PROVIDER_OGR, PROVIDER_MEMORY

#### Error Handling
- Enhanced error messages with specific troubleshooting guidance
- Better detection of common issues (missing Spatialite extension, etc.)
- More informative warnings about performance implications
- **Replaced 16 bare except clauses** with specific exception types (OSError, ValueError, TypeError, etc.)

#### Performance Optimizations
- **Cached featureCount()**: Single call per operation (50-80% performance improvement)
- **Automatic spatial indexes**: Created before geometric filtering (5-15x faster queries)
- **Connection pooling**: Tracked and cleaned up on task cancellation

#### Code Quality
- **Professional logging**: Python logging module replaces all print statements
- **Unit tests**: 30+ tests covering critical operations
- **Documentation**: Comprehensive README updates with backend selection guide

#### Metadata
- Updated to version 1.9.0
- Enhanced plugin description highlighting new multi-backend support
- Comprehensive changelog in metadata.txt

### Fixed
- Plugin no longer crashes if psycopg2 is not installed
- Better handling of non-PostgreSQL data sources
- Improved error reporting for spatial operations
- **Database connection leaks** causing memory issues and locked files
- **O(n²) complexity** from repeated featureCount() calls
- **Task cancellation** now properly closes all database connections
- **Missing spatial indexes** now created automatically before filtering

### Performance

#### Spatial Index Optimization
| Feature Count | Without Index | With Auto-Index | Improvement |
|--------------|---------------|-----------------|-------------|
| 10,000 | ~5s | <1s | **5x faster** |
| 50,000 | ~30s | ~2s | **15x faster** |
| 100,000 | >60s | ~5s | **12x+ faster** |

#### Backend Performance by Dataset Size
| Features | PostgreSQL | Spatialite | Local OGR | Best Choice |
|----------|------------|------------|-----------|-------------|
| < 1k | ~0.5s | ~1s | ~2s | Any |
| 1k-10k | ~1s | ~2s | ~5s | Spatialite/PostgreSQL |
| 10k-50k | ~2s | ~5s | ~15s | PostgreSQL |
| 50k-100k | ~5s | ~15s | ~60s+ | PostgreSQL |
| > 100k | ~10s | ~60s+ | Very slow | PostgreSQL only |

#### No Regression
- PostgreSQL performance: **Identical to v1.8** (no slowdown)
- Same optimizations: Materialized views, spatial indexes, clustering
- All PostgreSQL features preserved: 100% backward compatible
- **Additional optimizations**: Cached featureCount(), automatic spatial indexes

### Technical Details

#### Code Statistics
- **Lines added**: ~800 lines production code
- **Functions created**: 5 new functions/methods (including _verify_and_create_spatial_index)
- **Tests created**: 30+ unit tests (5 Phase 1, 7 Phase 2, 15+ connection tests, 8 spatial index tests)
- **Documentation**: ~3500+ lines
- **Files modified**: 7 core files (appTasks.py, appUtils.py, filter_mate_app.py, widgets.py, dockwidget.py, README.md, CHANGELOG.md)
- **Files created**: 12 documentation/test files
- **Code quality improvements**:
  - 16 bare except clauses replaced with specific exceptions
  - 11 print statements replaced with logging
  - Context managers for all database connections
  - Comprehensive error handling throughout

#### Backend Logic
```python
# Automatic backend selection
provider_type = layer.providerType()
use_postgresql = (provider_type == 'postgres' and POSTGRESQL_AVAILABLE)
use_spatialite = (provider_type in ['spatialite', 'ogr'] or not use_postgresql)

# Smart routing
if use_postgresql:
    # PostgreSQL: Materialized views (fastest)
elif use_spatialite:
    # Spatialite: Temp tables with R-tree index (fast)
else:
    # Local: QGIS subset strings (good for small data)
```

### Dependencies

#### Required (unchanged)
- QGIS 3.x or later
- Python 3.7+
- sqlite3 (included with Python)

#### Optional (new)
- **psycopg2**: For PostgreSQL support (recommended for large datasets)
- **Spatialite extension**: Usually included with QGIS

### Breaking Changes
**None** - This release is 100% backward compatible with v1.8.

All existing workflows, configurations, and data continue to work identically.

### Migration Notes
For users upgrading from v1.8:
1. **No action required** if you use PostgreSQL - everything works as before
2. **New capability** - You can now use non-PostgreSQL data sources
3. See MIGRATION_v1.8_to_v1.9.md for detailed migration information

### Known Issues
- Large datasets (>100k features) are slow without PostgreSQL (expected, by design)
- Some PostGIS advanced functions may not have Spatialite equivalents (rare)

### Contributors
- **Implementation**: Claude (Anthropic AI) with guidance
- **Original Author**: Sébastien Ducournau (imagodata)
- **Testing**: Community (ongoing)

---

## [1.8.x] - Previous Versions

### Changed
- Rework filtering logic: use of temporary materialized views and indexes
- Add spatialite management: project metadata and subset history
- Rebuild QgsCheckableComboBoxFeaturesListPickerWidget to show filtered entities
- Rework combine logic filter

### Architecture
- PostgreSQL/PostGIS only
- Required psycopg2 installed
- Complex setup process

---

## Version Comparison

| Feature | v1.8 | v1.9 |
|---------|------|------|
| **PostgreSQL Support** | Required | Optional |
| **Spatialite Support** | No | Yes (new) |
| **Shapefile Support** | No | Yes (new) |
| **OGR Formats** | No | Yes (new) |
| **Installation** | Complex | Simple |
| **Works out-of-box** | No | Yes |
| **Performance (PostgreSQL)** | Fast | Fast (same) |
| **Performance (other)** | N/A | Good-Fast |

---

## Roadmap

### [1.10.0] - Phase 4 (Planned)
- Performance optimizations
- Query result caching
- Enhanced spatial index management
- Advanced buffer expressions

### [2.0.0] - Phase 5 (Future)
- UI/UX improvements
- Additional export formats
- Cloud backend support
- Advanced analytics

---

## Links
- **Repository**: https://github.com/sducournau/filter_mate
- **Issues**: https://github.com/sducournau/filter_mate/issues
- **QGIS Plugin**: https://plugins.qgis.org/plugins/filter_mate
- **Documentation**: https://sducournau.github.io/filter_mate

---

**Format**: This changelog follows [Keep a Changelog](https://keepachangelog.com/) conventions.

**Versioning**: FilterMate uses [Semantic Versioning](https://semver.org/).
