"""Report generator"""

import json
import os
import signal
import subprocess
import time
import traceback
import typing
from collections import deque
from dataclasses import dataclass
from uuid import uuid4

from qgis.core import (
    Qgis,
    QgsApplication,
    QgsCoordinateReferenceSystem,
    QgsExpression,
    QgsExpressionContext,
    QgsLayerDefinition,
    QgsLayoutExporter,
    QgsLayoutItem,
    QgsLayoutItemLegend,
    QgsLayoutItemMap,
    QgsLayoutItemRegistry,
    QgsLegendRenderer,
    QgsLegendStyle,
    QgsMapLayerLegendUtils,
    QgsPrintLayout,
    QgsProcessingFeedback,
    QgsProject,
    QgsRasterLayer,
    QgsReadWriteContext,
    QgsRectangle,
    QgsReferencedRectangle,
    QgsSimpleLegendNode,
    QgsTask,
    QgsVectorLayer,
)
from qgis.gui import QgsMessageBar
from qgis.PyQt.QtCore import (
    QCoreApplication,
    QDateTime,
    QFile,
    QIODevice,
    QObject,
    pyqtSignal,
)
from qgis.PyQt.QtXml import QDomDocument
from qgis.utils import iface
from te_schemas.results import Band as JobBand

from ..jobs.models import Job
from ..layers import get_band_title, style_layer, styles
from ..logger import log
from ..utils import FileUtils, qgis_process_path
from ..visualization import ExtractAdministrativeArea, download_base_map
from .charts import AlgorithmChartsManager, LayerBandInfo
from .expressions import ReportExpressionUtils
from .models import ReportTaskContext, TemplateType
from .utils import build_report_paths


@dataclass
class LegendRendererContext:
    """
    Flags for specifying how legend items will be rendered in the layout.
    """

    remove_basemap_layers: bool = True
    remove_sub_group_heading: bool = True
    remove_category_title: bool = True


class ReportTaskProcessor:
    """
    Produces a QGIS project, template and resulting report
    (in image and/or PDF format) based on information in a
    ReportTaskContext object.
    """

    BAND_INDEX = "sourceBandIndex"
    BASE_MAP_GROUP = "Basemap"

    def __init__(
        self,
        ctx: ReportTaskContext,
        proj: QgsProject,
        feedback: QgsProcessingFeedback = None,
    ):
        self._ctx = ctx
        self._legend_renderer_ctx = LegendRendererContext()
        self._ti = self._ctx.report_configuration.template_info
        self._options = self._ctx.report_configuration.output_options
        self._proj = proj
        self._proj.setFilePathStorage(Qgis.FilePathType.Absolute)
        self._feedback = feedback
        self._layout = None
        self._messages = dict()
        self._jobs_layers = dict()
        self._should_add_basemap = True
        self._basemap_layers = []
        self._output_root_dir = ""
        self._charts_mgr = AlgorithmChartsManager()

        # Stores the reference style for the base layers
        self._base_layers_fonts = {}
        self._base_layers_symbol_sizes = {}

    @property
    def context(self) -> ReportTaskContext:
        """
        Returns the report task context used in the class.
        """
        return self._ctx

    @property
    def legend_renderer_context(self) -> LegendRendererContext:
        """
        Render context used to render legend items in the layout.
        """
        return self._legend_renderer_ctx

    @property
    def project(self) -> QgsProject:
        """
        Returns the QGIS project used for rendering the layers.
        """
        return self._proj

    @property
    def messages(self) -> dict:
        """
        Returns warning and information messages generated during the process.
        """
        return self._messages

    def tr(self, message) -> str:
        return QCoreApplication.translate("ReportTaskProcessor", message)

    def _append_message(self, level, message):
        if level not in self.messages:
            self._messages[level] = []

        level_msgs = self._messages[level]
        level_msgs.append(message)

        # Log to feedback object if specified
        if self._feedback:
            if level == Qgis.Info:
                self._feedback.pushInfo(message)
            elif level == Qgis.Warning:
                self._feedback.reportError(message)

    def _append_warning_msg(self, msg):
        self._append_message(Qgis.Warning, msg)

    def _append_info_msg(self, msg):
        self._append_message(Qgis.Info, msg)

    def _process_cancelled(self) -> bool:
        # Check if there is a request to cancel the process, True to cancel.
        if self._feedback and self._feedback.isCanceled():
            return True

        return False

    def _create_layers(self):
        # Creates map layers for each job.
        for j in self._ctx.jobs:
            layers = []
            layer_band_infos = []
            bands = j.results.get_bands()
            for band_idx, band in enumerate(bands, start=1):
                if band.add_to_map:
                    layer_path = str(j.results.uri.uri)
                    band_info = JobBand.Schema().dump(band)

                    # Get corresponding style
                    band_info_name = band_info["name"]
                    band_style = styles.get(band_info_name, None)
                    if band_style is None:
                        self._append_warning_msg(
                            f"Styles for {band_info_name} not found for "
                            f"band {band_idx!s} in {layer_path}."
                        )
                        continue

                    # Create raster layer and style it
                    title = get_band_title(band_info)
                    band_layer = QgsRasterLayer(layer_path, title)
                    if band_layer.isValid():
                        # Style layer
                        if style_layer(
                            layer_path,
                            band_layer,
                            band_idx,
                            band_style,
                            band_info,
                            in_process_alg=True,
                            processing_feedback=self._feedback,
                        ):
                            # Append source band index as a custom property.
                            # We use this to retrieve the corresponding report
                            # path.
                            band_layer.setCustomProperty(self.BAND_INDEX, band_idx)
                            layers.append(band_layer)

                            # Layer band info for the charts
                            lbi = LayerBandInfo(band_layer, band_info)
                            layer_band_infos.append(lbi)
                    else:
                        self._append_warning_msg(f"{title}layer is invalid.")

            # Add job layer-band info mapping for use in generating charts
            if len(layer_band_infos) > 0:
                self._charts_mgr.add_job_layers(j, layer_band_infos)

            # Just to ensure that we don't have empty lists
            if len(layers) > 0:
                self._jobs_layers[j.id] = layers
                self._proj.addMapLayers(layers)

        # Add basemap
        if self._should_add_basemap:
            self._add_base_map()

    def _add_base_map(self):
        # Add basemap
        country_name, admin_one_name = "", ""
        # Determine extent using first layer in our collection
        if len(self._jobs_layers) > 0:
            job_id = next(iter(self._jobs_layers))
            ext_layer = self._jobs_layers[job_id][0]
            ref_extent = ext_layer.extent()

            # Attempt to get the country name and admin area from the extents
            # for use to mask.
            ext_admin_area = ExtractAdministrativeArea(ref_extent)
            country_name, admin_one_name = ext_admin_area.get_admin_area()

        # Download and apply mask
        if country_name:
            status, document = download_base_map(
                use_mask=True, country_name=country_name, admin_level_one=admin_one_name
            )
        else:
            status, document = download_base_map(use_mask=False)

        if status:
            root = self._proj.layerTreeRoot().insertGroup(0, self.BASE_MAP_GROUP)
            QgsLayerDefinition.loadLayerDefinition(
                document, self._proj, root, QgsReadWriteContext()
            )

            # Get associated child layers
            child_layers = root.findLayers()
            for cl in child_layers:
                vl = cl.layer()
                self._basemap_layers.append(vl)

                # Set the reference font sizes
                if not isinstance(vl, QgsVectorLayer):
                    continue

                labeling = vl.labeling()
                if labeling is None:
                    continue

                lbl_type = labeling.type()
                if lbl_type == "simple":
                    settings = labeling.settings()
                    lbl_format = settings.format()
                    self._base_layers_fonts[vl.name()] = lbl_format.size()
                elif lbl_type == "rule-based":
                    rule_font_size = {}
                    root_rule = labeling.rootRule()
                    child_rules = root_rule.children()
                    for cr in child_rules:
                        child_settings = cr.settings()
                        child_format = child_settings.format()
                        rule_font_size[cr.description()] = child_format.size()
                    self._base_layers_fonts[vl.name()] = rule_font_size

                # Set reference marker symbol sizes
                renderer = vl.renderer()

                # For now we are only interested in layers with rule-based
                # renderers
                if renderer.type() == "RuleRenderer":
                    root_rule = renderer.rootRule()
                    children = root_rule.children()
                    marker_size = {}
                    for cr in children:
                        symbol = cr.symbol()
                        if symbol.type() != Qgis.SymbolType.Marker:
                            continue
                        marker_size[cr.label()] = symbol.size()

                    self._base_layers_symbol_sizes[vl.name()] = marker_size

    def _save_project(self) -> bool:
        # Save project file to disk.
        if not self._output_root_dir:
            self._append_warning_msg(
                "Root output directory could not be determined. The project "
                "could not be saved."
            )
            return False

        # Restore basemap layers
        self._restore_base_layers()

        # Add open project macro to show layout manager.
        self._add_open_project_macro()

        proj_file = FileUtils.project_path_from_report_task(
            self._ctx, self._output_root_dir
        )
        self._proj.write(proj_file)

        return True

    def _export_layout(self, report_path, name) -> bool:
        """
        Export layout to the given file path.
        """
        if self._layout is None:
            return False

        self._layout.setName(name)

        exporter = QgsLayoutExporter(self._layout)
        if "pdf" in report_path:
            settings = QgsLayoutExporter.PdfExportSettings()
            res = exporter.exportToPdf(report_path, settings)

        # Assume everything else is an image
        else:
            settings = QgsLayoutExporter.ImageExportSettings()
            res = exporter.exportToImage(report_path, settings)

        if res != QgsLayoutExporter.Success:
            self._append_warning_msg(f"Failed to export report to {report_path}.")

        # Add layout to project
        layout_mgr = self._proj.layoutManager()
        layout_mgr.addLayout(self._layout)

        return True

    def _restore_base_layers(self):
        # Adds basemap layers back to the project tree prior to exporting
        # the project.
        root_tree = self._proj.layerTreeRoot()
        basemap_group = root_tree.findGroup(self.BASE_MAP_GROUP)
        if basemap_group is None:
            self._append_warning_msg(
                "Basemap root group not found, unable to restore basemap layer."
            )
            return

        for bml in self._basemap_layers:
            basemap_group.addLayer(bml)

    def update_base_layers_font(self, template_type: TemplateType):
        """
        Scale the font of the base layers based on the template type.
        """
        # Set font factor based on template type
        if template_type == TemplateType.FULL:
            font_size_factor = 1
        elif template_type == TemplateType.SIMPLE:
            font_size_factor = 0.35

        for bl in self._basemap_layers:
            if not isinstance(bl, QgsVectorLayer):
                continue

            font_size_info = self._base_layers_fonts.get(bl.name(), None)
            if font_size_info is None:
                continue

            labeling_rt = bl.labeling()
            if labeling_rt is None:
                continue

            labeling = labeling_rt.clone()
            lbl_type = labeling.type()
            if lbl_type == "simple":
                settings = labeling.settings()
                lbl_format = settings.format()
                new_size = font_size_info * font_size_factor
                lbl_format.setSize(new_size)
                settings.setFormat(lbl_format)
                labeling.setSettings(settings)

            elif lbl_type == "rule-based":
                root_rule = labeling.rootRule()
                child_rules = root_rule.children()
                for cr in child_rules:
                    description = cr.description()
                    ref_size = font_size_info.get(description, None)
                    if ref_size is None:
                        continue

                    child_settings = cr.settings()
                    child_format = child_settings.format()
                    new_size = ref_size * font_size_factor
                    child_format.setSize(new_size)
                    child_settings.setFormat(child_format)
                    cr.setSettings(child_settings)

            # We also need to update the size of applicable marker symbols
            # so that they do not appear disproportional.
            renderer = bl.renderer().clone()
            refresh_renderer = False

            # For now we are only interested in layers with rule-based
            # renderers
            ref_size_info = self._base_layers_symbol_sizes.get(bl.name(), None)
            if ref_size_info is not None:
                if renderer.type() == "RuleRenderer":
                    root_rule = renderer.rootRule()
                    children = root_rule.children()
                    for cr in children:
                        lbl = cr.label()
                        ref_size = ref_size_info.get(lbl, None)
                        if ref_size is None:
                            continue
                        symbol = cr.symbol().clone()
                        if symbol.type() != Qgis.SymbolType.Marker:
                            continue
                        new_marker_size = ref_size * font_size_factor
                        symbol.setSize(new_marker_size)
                        cr.setSymbol(symbol)

                        if not refresh_renderer:
                            refresh_renderer = True

            # Set new renderer if it has been updated
            if refresh_renderer:
                bl.setRenderer(renderer)

            bl.setLabeling(labeling)
            bl.triggerRepaint()

    def _update_project_metadata_extents(self, layer=None, title=None):
        # Update the extents and metadata of the project or reference layer.
        description = ""
        if layer is None:
            template_info = self._ctx.report_configuration.template_info
            title = template_info.name
            description = template_info.description
            proj_extent = QgsRectangle()
            for j in self._ctx.jobs:
                job_rect = self._get_job_layers_extent(j)
                proj_extent.combineExtentWith(job_rect)
        else:
            title = title or ""
            proj_extent = layer.extent()

        md = self._proj.metadata()
        md.setTitle(title)
        md.setAuthor("trends.earth QGIS Plugin")
        md.setAbstract(description)
        md.setCreationDateTime(QDateTime.currentDateTime())
        self._proj.setMetadata(md)

        # Project CRS and view settings
        crs = QgsCoordinateReferenceSystem.fromEpsgId(4326)
        default_extent = QgsReferencedRectangle(proj_extent, crs)
        self._proj.viewSettings().setDefaultViewExtent(default_extent)
        self._proj.setCrs(crs, True)

    def _add_open_project_macro(self):
        # Add macro that shows the layout manager when the project is opened.
        macro = (
            "from qgis.utils import iface\r\ndef openProject():"
            "\r\n\tiface.showLayoutManager()\r\n\r\n"
            "def saveProject():\r\n\tpass\r\n\r\n"
            "def closeProject():\r\n\tpass\r\n"
        )
        self._proj.writeEntry("Macros", "/pythonCode", macro)

    def run(self) -> bool:
        """
        Initiate the report generation process.
        """
        status = False
        try:
            status = self._run()
        except Exception as ex:
            # Use general exception as last resort to capture raster read
            # failures by GDAL.
            exc_info = "".join(traceback.TracebackException.from_exception(ex).format())
            self._append_warning_msg(exc_info)

        return status

    def _run(self) -> bool:
        if self._process_cancelled():
            return False

        # Get template paths
        abs_paths = self._ti.absolute_template_paths
        simple_pt_path = abs_paths.simple_portrait
        simple_ls_path = abs_paths.simple_landscape
        full_pt_path = abs_paths.full_portrait
        full_ls_path = abs_paths.full_landscape

        # Check if the template types exist
        self._check_template_type_exists(abs_paths)

        if self._process_cancelled():
            return False

        # Create map layers
        self._create_layers()
        if len(self._jobs_layers) == 0:
            self._append_warning_msg("No map layers could be created.")
            return False

        if self._process_cancelled():
            return False

        # Determine orientation using first layer in our collection
        job_id = next(iter(self._jobs_layers))
        orientation_layer = self._jobs_layers[job_id][0]
        extent = orientation_layer.extent()
        w, h = extent.width(), extent.height()
        use_landscape = True if w > h else False
        ref_simple_temp = simple_ls_path if use_landscape else simple_pt_path
        ref_full_temp = full_ls_path if use_landscape else full_pt_path

        # Simple
        if (
            self._options.template_type == TemplateType.SIMPLE
            or self._options.template_type == TemplateType.ALL
        ):
            # Remove sub-group heading/layer name
            self._legend_renderer_ctx.remove_sub_group_heading = True
            self.update_base_layers_font(TemplateType.SIMPLE)
            self._generate_reports(ref_simple_temp, True)

        if self._process_cancelled():
            return False

        # Full
        if (
            self._options.template_type == TemplateType.FULL
            or self._options.template_type == TemplateType.ALL
        ):
            # Retain sub-group heading
            self._legend_renderer_ctx.remove_sub_group_heading = False
            self.update_base_layers_font(TemplateType.FULL)
            self._generate_reports(ref_full_temp, False)

        # Update general metadata and save project
        self._update_project_metadata_extents()
        self._save_project()

        # Generate charts
        status = self._charts_mgr.generate_charts()
        if not status:
            msgs = self._charts_mgr.messages
            for m in msgs:
                self._append_warning_msg(m)

            return False

        return True

    def _check_template_type_exists(self, abs_paths):
        # Checks if the templates for both simple and full layouts exist.
        # Get template paths
        simple_pt_path = abs_paths.simple_portrait
        simple_ls_path = abs_paths.simple_landscape
        full_pt_path = abs_paths.full_portrait
        full_ls_path = abs_paths.full_landscape

        # Check if the templates exist depending on user configuration
        # Simple layout
        if (
            self._options.template_type == TemplateType.SIMPLE
            or self._options.template_type == TemplateType.ALL
        ):
            if (
                not abs_paths.simple_landscape_exists()
                and not abs_paths.simple_portrait_exists()
            ):
                msg = "Simple report templates not found."
                self._append_warning_msg(f"{msg}: {simple_pt_path, simple_ls_path}")
                return False

        # Full layout
        if (
            self._options.template_type == TemplateType.FULL
            or self._options.template_type == TemplateType.ALL
        ):
            if (
                not abs_paths.full_portrait_exists()
                and not abs_paths.full_landscape_exists()
            ):
                msg = "Full report templates not found."
                self._append_warning_msg(f"{msg}: {full_pt_path, full_ls_path}")
                return False

        return True

    def _generate_reports(self, template_path: str, is_simple: bool) -> bool:
        # Create layout and generate reports based on the given template.
        self._layout = QgsPrintLayout(self._proj)

        status, document = self._get_template_document(template_path)
        if not status:
            return False

        _, load_status = self._layout.loadFromTemplate(document, QgsReadWriteContext())
        if not load_status:
            self._append_warning_msg(f"Could not load template: {template_path}.")
            return False

        # Update custom report variables from the settings
        ReportExpressionUtils.register_variables(self._layout)

        # Key for fetching report output path
        report_path_key = "simple" if is_simple else "full"
        template_prefix_tr = self._template_type_tr(report_path_key)

        # Process scope items for each job
        for job in self._ctx.jobs:
            # Layers are the basis of the layout with a 1:1 mapping
            job_layers = self._jobs_layers.get(job.id, None)
            if job_layers is None:
                continue

            rpt_root_dir, job_report_paths = build_report_paths(
                job, self._options, self._ctx.root_report_dir
            )
            # Set root output directory
            if not self._output_root_dir:
                self._output_root_dir = rpt_root_dir
                self._charts_mgr.output_dir = rpt_root_dir

            for jl in job_layers:
                """
                (re)load layout and load the template. It would have been
                better to clone the layout object but we will lose the
                expressions in the label items.
                """
                if not self._create_layout(template_path):
                    return False

                # Update layout items
                if not self._process_scope_items(job, jl):
                    continue

                # Fetch report output path
                band_idx = jl.customProperty(self.BAND_INDEX, -1)
                if band_idx == -1:
                    continue
                if band_idx not in job_report_paths:
                    continue
                band_paths = job_report_paths[band_idx]
                rpt_paths = band_paths.get(report_path_key, [])
                if len(rpt_paths) == 0:
                    continue

                layout_name = f"{template_prefix_tr} - {jl.name()}"

                # Update project metadata (relevant for PDF or SVG document
                # properties)
                self._update_project_metadata_extents(jl, layout_name)

                # Export layout based on file types in report paths list
                for rp in rpt_paths:
                    self._export_layout(rp, layout_name)

        return True

    def _create_layout(self, template_path: str) -> bool:
        # Creates a new instance of the print layout and loads items in the
        # given template.
        self._layout = QgsPrintLayout(self._proj)

        status, document = self._get_template_document(template_path)
        if not status:
            return False

        _, load_status = self._layout.loadFromTemplate(document, QgsReadWriteContext())
        if not load_status:
            self._append_warning_msg(f"Could not load template from {template_path!r}.")
            return False

        ReportExpressionUtils.register_variables(self._layout)

        return True

    def _template_type_tr(self, template_type):
        # Returns translated string of the template type.
        if template_type == "simple":
            return self.tr("Simple")
        elif template_type == "full":
            return self.tr("Full")
        elif template_type == "all":
            return self.tr("All")
        else:
            return template_type

    def _process_scope_items(self, job: Job, job_layer: QgsRasterLayer) -> bool:
        # Update layout items in the given scope/job
        alg_name = job.script.name
        scope_mappings = self._ti.scope_mappings_by_name(alg_name)
        if len(scope_mappings) == 0:
            self._append_warning_msg(f"Could not find '{alg_name}' scope definition.")
            return False

        item_scope = scope_mappings[0]

        # Map items
        map_ids = item_scope.map_ids()
        if len(map_ids) == 0:
            self._append_info_msg(f"No map ids found in '{alg_name}' scope.")
        if not self._update_map_items(map_ids, job_layer):
            return False

        # Label items
        label_ids = item_scope.label_ids()
        if len(label_ids) == 0:
            self._append_info_msg(f"No label ids found in '{alg_name}' scope.")
        if not self._update_label_items(label_ids, job, job_layer):
            return False

        return True

    def _update_map_items(self, map_ids, layer: QgsRasterLayer) -> bool:
        # Update map items with the given layer
        map_item_layers = []
        map_item_layers.extend(self._basemap_layers)
        map_item_layers.append(layer)
        for mid in map_ids:
            map_item = self._layout.itemById(mid)
            if map_item is not None:
                map_item.setLayers(map_item_layers)
                map_item.zoomToExtent(layer.extent())
                self._refresh_map_legends(map_item)

        return True

    def _refresh_map_legends(self, map_item: QgsLayoutItemMap):
        # Refresh legend items linked to the given map item to only show the
        # visible layers in the map item.
        if self._layout is None:
            return

        layout_model = self._layout.itemsModel()
        for i in range(1, layout_model.rowCount()):
            item_idx = layout_model.index(i, 0)
            item = layout_model.itemFromIndex(item_idx)
            if item.type() == QgsLayoutItemRegistry.LayoutLegend:
                if item.linkedMap().uuid() == map_item.uuid():
                    item.setLegendFilterByMapEnabled(True)
                    self._update_map_legend_items(item)

    def _update_map_legend_items(self, legend: QgsLayoutItemLegend):
        # Update legend items based on flags in the legend renderer context.
        model = legend.model()
        layer_root = self._proj.layerTreeRoot()

        # Check whether to remove basemap layers
        if self._legend_renderer_ctx.remove_basemap_layers:
            for base_layer in self._basemap_layers:
                layer_node = layer_root.findLayer(base_layer)
                if layer_node is not None:
                    base_layer_index = model.node2index(layer_node)
                    if not base_layer_index.isValid():
                        continue
                    model.removeRow(base_layer_index.row(), base_layer_index.parent())

        # Check whether to remove sub-group (or layer) headings and
        # symbology title.
        child_layers = layer_root.findLayers()
        for cl in child_layers:
            if self._legend_renderer_ctx.remove_sub_group_heading:
                QgsLegendRenderer.setNodeLegendStyle(cl, QgsLegendStyle.Hidden)
            else:
                QgsLegendRenderer.setNodeLegendStyle(cl, QgsLegendStyle.Subgroup)

            # Also check if we need to remove category title e.g.
            # Band xx: xxx...
            if self._legend_renderer_ctx.remove_category_title:
                legend_nodes = model.layerLegendNodes(cl)
                for i, ln in enumerate(legend_nodes):
                    if isinstance(ln, QgsSimpleLegendNode):
                        node_idx = model.legendNode2index(ln)
                        if not node_idx.isValid():
                            continue
                        indexes = list(range(i + 1, len(legend_nodes)))
                        QgsMapLayerLegendUtils.setLegendNodeOrder(cl, indexes)
                        model.refreshLayerLegend(cl)

    @classmethod
    def update_item_expression_ctx(
        cls, item: QgsLayoutItem, job, job_layer
    ) -> QgsExpressionContext:
        # Update the expression context based on the given job and map layer.
        item_exp_ctx = item.createExpressionContext()

        return ReportExpressionUtils.update_expression_context(
            item_exp_ctx, job, job_layer
        )

    def _update_label_items(self, labels_ids, job, job_layer) -> bool:
        # Evaluate expressions for label items matching the given ids.
        for lid in labels_ids:
            label_item = self._layout.itemById(lid)
            if label_item is not None:
                lbl_exp_ctx = self.update_item_expression_ctx(
                    label_item, job, job_layer
                )
                evaluated_txt = QgsExpression.replaceExpressionText(
                    label_item.text(), lbl_exp_ctx
                )
                label_item.setText(evaluated_txt)

        return True

    def _get_job_layers_extent(self, job) -> QgsRectangle:
        # Get the combined extent of all the layers for the given job.
        rect = QgsRectangle()
        job_layers = self._jobs_layers.get(job.id, None)
        if job_layers is None:
            return rect

        for lyr in job_layers:
            rect.combineExtentWith(lyr.extent())

        return rect

    def _get_template_document(self, path) -> typing.Tuple[bool, QDomDocument]:
        # Get template contents
        template_file = QFile(path)
        try:
            if not template_file.open(QIODevice.ReadOnly):
                self._append_warning_msg(f"Cannot read '{path}'.")
                return False, None

            doc = QDomDocument()
            if not doc.setContent(template_file):
                self._append_warning_msg("Failed to parse template file contents.")
                return False, None

        finally:
            template_file.close()

        return True, doc


class ReportProcessHandlerTask(QgsTask):
    """
    Bridge for communicating with the report task algorithm running in
    'qgis_process'.
    """

    def __init__(self, ctx_file_path: str, qgis_proc_path: str, description):
        super().__init__(description, QgsTask.CanCancel)
        self._ctx_file_path = ctx_file_path
        self._qgs_proc_path = qgis_proc_path
        self._process = None

    @property
    def context_file_path(self) -> str:
        """
        Returns the path to the report context JSON file.
        """
        return self._ctx_file_path

    def _kill_process(self):
        """
        Kill the qgis_process subprocess (non-blocking on Windows).
        """
        if self._process is None:
            return

        pid = self._process.pid
        if os.name == "nt":
            # Fire TASKKILL without waiting so the caller (which may be the
            # main / UI thread) is not blocked.  The run() polling loop will
            # detect the process exit on its next iteration.
            subprocess.Popen(
                ["TASKKILL", "/F", "/PID", str(pid), "/T"],
                stdout=subprocess.PIPE,
                stderr=subprocess.PIPE,
            )
        else:
            try:
                os.kill(pid, signal.SIGKILL)
            except ProcessLookupError:
                # Process is already dead
                pass

    def cancel(self):
        """
        Cancel the qgis_process.

        This is called from the main / UI thread, so it must return quickly
        to avoid freezing QGIS (e.g. when the user quits while reports are
        running).  The actual subprocess cleanup is handled by the run()
        polling loop which will see isCanceled() == True.
        """
        self._kill_process()
        super().cancel()

    # How often (in seconds) to poll the subprocess and check for file
    # system activity in the report output directory.  We use a small
    # granularity (0.5 s) so that cancellation requests are detected
    # quickly – the inactivity / heartbeat logic still uses the previous
    # 5-second cadence via _HEARTBEAT_INTERVAL_S.
    _POLL_INTERVAL_S = 0.5

    # How often (in seconds) to check for file-system heartbeat changes.
    _HEARTBEAT_INTERVAL_S = 5

    # If no files are created or modified in the report output directory
    # for this many seconds the subprocess is considered stalled and will
    # be killed automatically.
    _INACTIVITY_TIMEOUT_S = 10 * 60  # 10 minutes

    @staticmethod
    def _dir_snapshot(
        directory: str,
    ) -> typing.Dict[str, typing.Tuple[float, int]]:
        """Return ``{filename: (mtime, size)}`` for every file in *directory*.

        Used as a cheap heartbeat: if the snapshot changes between two
        polls the subprocess is still making progress.  We track both
        ``st_mtime`` and ``st_size`` because on Windows/NTFS the mtime
        may not be flushed until the file handle is closed, whereas the
        file size is updated more reliably during active writes.  A new
        filename appearing is also always detected immediately.
        """
        snapshot: typing.Dict[str, typing.Tuple[float, int]] = {}
        try:
            for entry in os.scandir(directory):
                if entry.is_file():
                    try:
                        st = entry.stat()
                        snapshot[entry.name] = (st.st_mtime, st.st_size)
                    except OSError:
                        pass
        except OSError:
            pass
        return snapshot

    def run(self) -> bool:
        # Launch qgis_process and execute algorithm.
        if self.isCanceled():
            return False

        input_file = f"INPUT={self._ctx_file_path}"
        args = [self._qgs_proc_path, "run", "trendsearth:reporttask", "--", input_file]

        startupinfo = None
        if os.name == "nt":
            startupinfo = subprocess.STARTUPINFO()
            startupinfo.dwFlags |= subprocess.STARTF_USESHOWWINDOW

        # Start process
        self._process = subprocess.Popen(args, startupinfo=startupinfo)

        # Monitor the report output directory for file changes; if nothing
        # is written for _INACTIVITY_TIMEOUT_S the process is killed.
        report_dir = os.path.dirname(self._ctx_file_path)
        last_snapshot = self._dir_snapshot(report_dir)
        last_activity = time.monotonic()
        last_heartbeat_check = time.monotonic()

        while True:
            retcode = self._process.poll()
            if retcode is not None:
                break

            if self.isCanceled():
                self._kill_process()
                # Give the process a moment to die, then move on
                try:
                    self._process.wait(timeout=5)
                except subprocess.TimeoutExpired:
                    pass
                return False

            now = time.monotonic()
            if now - last_heartbeat_check >= self._HEARTBEAT_INTERVAL_S:
                current_snapshot = self._dir_snapshot(report_dir)
                if current_snapshot != last_snapshot:
                    last_activity = now
                    last_snapshot = current_snapshot
                last_heartbeat_check = now

            if now - last_activity > self._INACTIVITY_TIMEOUT_S:
                log(
                    f"Report generation inactivity timeout "
                    f"({self._INACTIVITY_TIMEOUT_S}s without any file "
                    f"changes in {report_dir}) \u2014 killing subprocess"
                )
                self._kill_process()
                try:
                    self._process.wait(timeout=5)
                except subprocess.TimeoutExpired:
                    pass
                return False

            time.sleep(self._POLL_INTERVAL_S)

        result_code = self._process.returncode

        # Ignore access violation error code raised by PNG driver.
        if result_code == 0 or result_code == 3221225477:
            return True

        return False


class ReportGeneratorManager(QObject):
    """
    Generates reports for single or multi-datasets based on custom layouts.
    Uses a queue to limit the number of concurrently running report tasks
    so that QGIS remains responsive (see issue #683).
    """

    MAX_CONCURRENT_TASKS = 2

    task_running = pyqtSignal(str)
    task_completed = pyqtSignal(str)

    def __init__(self, parent=None):
        super().__init__(parent)
        self.iface = iface
        self._qgis_proc_path = qgis_process_path()

        # key: ReportTaskContext, value: QgsTask id
        self._submitted_tasks = {}
        self._submission_counter = {}
        self._ctx_file_paths = {}

        # Queue for tasks that are waiting to be launched (FIFO)
        self._pending_queue: deque[ReportTaskContext] = deque()

        QgsApplication.instance().taskManager().statusChanged.connect(
            self.on_task_status_changed
        )

    @property
    def message_bar(self) -> QgsMessageBar:
        """Returns the main application's message bar."""
        if self.iface is None:
            self.iface = iface

        return self.iface.messageBar()

    def _push_message(self, msg, level):
        if not self.message_bar:
            return

        self.message_bar.pushMessage(self.tr("Report Status"), msg, level)

    def _push_info_message(self, msg):
        self._push_message(msg, Qgis.Info)

    def _push_warning_message(self, msg):
        self._push_message(msg, Qgis.Warning)

    def _push_success_message(self, msg):
        self._push_message(msg, Qgis.Success)

    def _write_context_to_file(self, ctx, task_id: str) -> str:
        # Write report task context to file.
        if ctx.root_report_dir is not None:
            root_dir = ctx.root_report_dir
        else:
            jobs = ctx.jobs
            if len(jobs) == 0:
                return ""
            root_dir, _ = build_report_paths(
                jobs[0], ctx.report_configuration.output_options
            )
        ctx_file_path = f"{root_dir}/report_{task_id}.json"

        # Check if there is an existing file
        if os.path.exists(ctx_file_path):
            return ctx_file_path

        # Check write permissions
        if not os.access(root_dir, os.W_OK):
            tr_msg = self.tr("Cannot process report due to write permission to")
            self._push_warning_message(f"{tr_msg} {root_dir}")
            return ""

        with open(ctx_file_path, "w") as cf:
            ctx_data = ReportTaskContext.Schema().dump(ctx)
            json.dump(ctx_data, cf, indent=2)

        return ctx_file_path

    def process_report_task(self, ctx: ReportTaskContext) -> bool:
        """
        Initiates report generation, emits 'task_started' signal and return
        the submission result.  If the maximum number of concurrent tasks
        has been reached the context is placed in a pending queue and will
        be launched automatically when a running task finishes.
        """
        # If task has already been run many times then return (as there is
        # likely an error leading to a failure when generating the report)
        if self.is_task_overrun(ctx):
            log(
                "Skipping report generation - overrun. Check logs "
                "for a possible failure in report generation"
            )
            return False
        self._submission_counter[ctx] += 1
        # If task is already running or already queued then return
        if self.is_task_running(ctx) or self.is_task_queued(ctx):
            return False

        # Assert if qgis_process path could be found
        if not self._qgis_proc_path:
            tr_msg = self.tr(
                "could not be found in your system. Unable to run the report generator."
            )
            self._push_warning_message(f"'qgis_process' {tr_msg}")
            return False

        # If at capacity, queue the task for later execution
        if len(self._submitted_tasks) >= self.MAX_CONCURRENT_TASKS:
            self._pending_queue.append(ctx)
            report_tr = self.tr("reports")
            ctx_display_name = f"{ctx.display_name()} {report_tr}"
            tr_msg = self.tr("queued (waiting for a free worker slot)")
            self._push_info_message(f"{ctx_display_name} {tr_msg}")
            return True

        return self._launch_task(ctx)

    def _launch_task(self, ctx: ReportTaskContext) -> bool:
        """
        Actually creates and submits the QgsTask to the QGIS task manager.
        """
        if len(ctx.jobs) == 1:
            file_suffix = str(ctx.jobs[0].id)
        else:
            file_suffix = uuid4()

        # Write task file for subsequent use by the report handler task
        file_path = self._write_context_to_file(ctx, file_suffix)

        report_tr = self.tr("reports")

        ctx_display_name = f"{ctx.display_name()} {report_tr}"

        # Create report handler task
        rpt_handler_task = ReportProcessHandlerTask(
            file_path, self._qgis_proc_path, ctx_display_name
        )
        task_id = QgsApplication.instance().taskManager().addTask(rpt_handler_task)

        self._submitted_tasks[ctx] = task_id
        self._ctx_file_paths[ctx] = file_path

        # Notify user
        tr_msg = self.tr(
            f"are being processed (id {[str(job.id) for job in ctx.jobs]})..."
        )
        self._push_info_message(f"{ctx_display_name} {tr_msg}")

        return True

    @classmethod
    def task_status(cls, task_id: str) -> QgsTask.TaskStatus:
        # Returns -1 if the task with the given id could not be found.
        task = QgsApplication.instance().taskManager().task(task_id)
        if not task:
            return -1

        return task.status()

    def is_task_overrun(self, ctx: ReportTaskContext) -> bool:
        # Check whether the task with the given id has already run multiple times
        if ctx not in self._submission_counter:
            self._submission_counter[ctx] = 0

        if self._submission_counter[ctx] < 2:
            return False
        else:
            return True

    def is_task_running(self, ctx: ReportTaskContext) -> bool:
        # Check whether the task with the given id is running.
        if ctx not in self._submitted_tasks:
            return False

        return True

    def is_task_queued(self, ctx: ReportTaskContext) -> bool:
        """Check whether the context is already in the pending queue."""
        return ctx in self._pending_queue

    def handler_task_from_context(self, ctx: ReportTaskContext) -> QgsTask:
        # Retrieves the handler task corresponding to the given context.
        task_id = self._submitted_tasks.get(ctx, -1)
        if task_id == -1:
            return None

        return QgsApplication.instance().taskManager().task(task_id)

    def remove_task_context(self, ctx: ReportTaskContext) -> bool:
        """
        Remove the task context from the list of submitted tasks. If not
        complete, the task will be cancelled.
        """
        if not self.is_task_running(ctx):
            return False

        handler = self.handler_task_from_context(ctx)
        if handler is None:
            return False

        if (
            handler.status() != QgsTask.Complete
            or handler.status() != QgsTask.Terminated
        ):
            handler.cancel()

        _ = self._submitted_tasks.pop(ctx)

        # Also remove ctx file path
        if ctx in self._ctx_file_paths:
            del self._ctx_file_paths[ctx]

        return True

    def task_context_by_id(self, task_id: int) -> ReportTaskContext:
        """
        Returns the ReportTaskContext in submitted jobs based on the
        QgsTask id.
        """
        ctxs = [ctx for ctx, tid in self._submitted_tasks.items() if tid == task_id]
        if len(ctxs) == 0:
            return None

        return ctxs[0]

    def _drain_queue(self):
        """
        Launch pending tasks from the queue until the concurrency limit is
        reached again or the queue is empty.
        """
        while (
            self._pending_queue
            and len(self._submitted_tasks) < self.MAX_CONCURRENT_TASKS
        ):
            next_ctx = self._pending_queue.popleft()
            # Skip contexts that have been overrun while waiting in the queue
            if self.is_task_overrun(next_ctx):
                continue
            self._launch_task(next_ctx)

    def on_task_status_changed(self, task_id: int, status: QgsTask.TaskStatus):
        # Slot raised when the status of a task has changed.
        ctx = self.task_context_by_id(task_id)

        if ctx is None:
            return

        if status == QgsTask.Running:
            self.task_running.emit(ctx.id())

        # Remove context file if task has been successfully completed.
        elif status == QgsTask.Complete:
            if ctx in self._ctx_file_paths:
                ctx_file_path = self._ctx_file_paths[ctx]
                ctx_file = QFile(ctx_file_path)
                status = ctx_file.remove()
                if not status:
                    log(f"Unable to remove report context file: {ctx_file_path}")

            # Remove from list of submitted tasks
            self.remove_task_context(ctx)

            # Emit task_completed signal
            self.task_completed.emit(ctx.id())

            # Launch next queued task(s) if any
            self._drain_queue()

        elif status == QgsTask.Terminated:
            # Also free up the slot when a task fails / is cancelled
            self.remove_task_context(ctx)
            self._drain_queue()


report_generator_manager = ReportGeneratorManager()
