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# Source code for safe.storage.vector

    """**Vector Module**

    .. tip:: Provides functionality for manipulation of vector data. The data can
       be in-memory or file based.

    Resources for understanding vector data formats and the OGR library:
    Treatise on vector data model: http://www.esri.com/news/arcuser/0401/topo.html
    OGR C++ reference: http://www.gdal.org/ogr

    """

    __author__ = 'Ole Nielsen <ole.moller.nielsen@gmail.com>'
    __revision__ = '$Format:%H$'
    __date__ = '01/11/2010'
    __license__ = "GPL"
    __copyright__ = 'Copyright 2012, Australia Indonesia Facility for '
    __copyright__ += 'Disaster Reduction'

    import os
    import sys
    import numpy
    import logging

    import copy as copy_module
    from osgeo import ogr, gdal
    from safe.common.utilities import (verify,
                                       ugettext as safe_tr)
    from safe.common.exceptions import ReadLayerError, WriteLayerError
    from safe.common.exceptions import GetDataError, InaSAFEError

    from layer import Layer
    from projection import Projection
    from geometry import Polygon
    from utilities import DRIVER_MAP, TYPE_MAP
    from utilities import read_keywords
    from utilities import write_keywords
    from utilities import get_geometry_type
    from utilities import is_sequence
    from utilities import array2line
    from utilities import calculate_polygon_centroid
    from utilities import points_along_line
    from utilities import geometrytype2string
    from utilities import get_ringdata, get_polygondata
    from utilities import rings_equal

    LOGGER = logging.getLogger('InaSAFE')
    _pseudo_inf = float(99999999)

    class Vector(Layer):
        """Class for abstraction of vector data.
        """

        def __init__(self, data=None, projection=None, geometry=None,
                     geometry_type=None, name=None, keywords=None,
                     style_info=None, sublayer=None):
            """Initialise object with either geometry or filename

            Args:
                * data: Can be either
                    * A filename of a vector file format known to GDAL.
                    * List of dictionaries of field names and attribute values
                      associated with each point coordinate.
                    * None
                * projection: Geospatial reference in WKT format.
                    Only used if geometry is provided as a numeric array,
                    if None, WGS84 geographic is assumed.
                * geometry: A list of either point coordinates or polygons/lines
                    (see note below).
                * geometry_type: Desired interpretation of geometry.
                    Valid options are 'point', 'line', 'polygon' or
                    the ogr types: 1, 2, 3.
                    If None, a geometry_type will be inferred from the data.
                * name: Optional name for layer. If None, basename is used.
                * keywords: Optional dictionary with keywords that describe the
                    layer. When the layer is stored, these keywords will
                    be written into an associated file with extension
                    '.keywords'.

                    Keywords can for example be used to display text about the
                    layer in an application.
                * style_info: Dictionary with information about how this layer
                    should be styled. See impact_functions/styles.py
                    for examples.
                * sublayer: str Optional sublayer (band name in the case of raster,
                      table name in case of sqlite etc.) to load. Only applicable
                      to those dataformats supporting more than one layer in the
                      data file.

            Returns:
                * An instance of class Vector.

            Raises:
                * Propogates any exceptions encountered.

            Notes:

                If data is a filename, all other arguments are ignored
                as they will be inferred from the file.

                The geometry type will be inferred from the dimensions of geometry.
                If each entry is one set of coordinates the type will be
                ogr.wkbPoint,
                if it is an array of coordinates the type will be ogr.wkbPolygon.

                To cast array entries as lines set geometry_type explicitly to
                'line' in the call to Vector. Otherwise, they will default to
                polygons.

                Each polygon or line feature take the form of an Nx2 array
                representing vertices where line segments are joined.

                If polygons have holes, their geometry must be passed in as a
                list of polygon geometry objects
                (as defined in module geometry.py)
            """

            # Invoke common layer constructor
            Layer.__init__(self,
                           name=name,
                           projection=projection,
                           keywords=keywords,
                           style_info=style_info,
                           sublayer=sublayer)

            # Input checks
            if data is None and geometry is None:
                # Instantiate empty object
                self.geometry_type = None
                self.extent = [0, 0, 0, 0]
                return

            if isinstance(data, basestring):
                self.read_from_file(data)
            else:
                # Assume that data is provided as sequences provided as
                # arguments to the Vector constructor
                # with extra keyword arguments supplying metadata

                msg = 'Geometry must be specified'
                verify(geometry is not None, msg)

                msg = 'Geometry must be a sequence'
                verify(is_sequence(geometry), msg)

                if len(geometry) > 0 and isinstance(geometry[0], Polygon):
                    self.geometry_type = ogr.wkbPolygon
                    self.geometry = geometry
                else:
                    self.geometry_type = get_geometry_type(geometry, geometry_type)

                    if self.is_polygon_data:
                        # Convert to objects if input is a list of simple arrays
                        self.geometry = [Polygon(outer_ring=x) for x in geometry]
                    else:
                        # Convert to list if input is an array
                        if isinstance(geometry, numpy.ndarray):
                            self.geometry = geometry.tolist()
                        else:
                            self.geometry = geometry

                if data is None:
                    # Generate default attribute as OGR will do that anyway
                    # when writing
                    data = []
                    for i in range(len(geometry)):
                        data.append({'ID': i})

                # Check data
                self.data = data
                if data is not None:
                    msg = 'Data must be a sequence'
                    verify(is_sequence(data), msg)

                    msg = ('The number of entries in geometry and data '
                           'must be the same')
                    verify(len(geometry) == len(data), msg)

                # Establish extent
                if len(geometry) == 0:
                    # Degenerate layer
                    self.extent = [0, 0, 0, 0]
                    return

                # Compute bounding box for each geometry type
                minx = miny = sys.maxint
                maxx = maxy = -minx
                if self.is_point_data:
                    A = numpy.array(self.get_geometry())
                    minx = min(A[:, 0])
                    maxx = max(A[:, 0])
                    miny = min(A[:, 1])
                    maxy = max(A[:, 1])
                elif self.is_line_data:
                    for g in self.get_geometry():
                        A = numpy.array(g)
                        minx = min(minx, min(A[:, 0]))
                        maxx = max(maxx, max(A[:, 0]))
                        miny = min(miny, min(A[:, 1]))
                        maxy = max(maxy, max(A[:, 1]))
                elif self.is_polygon_data:
                    # Do outer ring only
                    for g in self.get_geometry(as_geometry_objects=False):
                        A = numpy.array(g)
                        minx = min(minx, min(A[:, 0]))
                        maxx = max(maxx, max(A[:, 0]))
                        miny = min(miny, min(A[:, 1]))
                        maxy = max(maxy, max(A[:, 1]))

                self.extent = [minx, maxx, miny, maxy]

        def __str__(self):
            """Render as name, number of features, geometry type
            """

            g_type_str = geometrytype2string(self.geometry_type)
            return ('Vector data set: %s, %i features, geometry type '
                    '%s (%s)' % (self.name,
                                 len(self),
                                 str(self.geometry_type),
                                 g_type_str))

        def __len__(self):
            """Size of vector layer defined as number of features
            """

            if hasattr(self, 'geometry') and self.geometry is not None:
                return len(self.geometry)
            else:
                return 0

        def __eq__(self, other, rtol=1.0e-5, atol=1.0e-8):
            """Override '==' to allow comparison with other vector objecs

            Args:
               * other: Vector instance to compare to
               * rtol, atol: Relative and absolute tolerance.
                           See numpy.allclose for details

            Note:
                The algorithm will try to falsify every aspect of equality for the
                two layers such as data, geometry, projection, keywords etc.
                Only if none of them can be falsified will it return True.
            """

            # Check type
            if not isinstance(other, Vector):
                msg = ('Vector instance cannot be compared to %s'
                       ' as its type is %s ' % (str(other), type(other)))
                raise TypeError(msg)

            # Check keywords
            if self.keywords != other.keywords:
                return False

            # Check number of features match
            if len(self) != len(other):
                return False

            # Check projection
            if self.projection != other.projection:
                return False

            # Check geometry type
            if self.geometry_type != other.geometry_type:
                return False

            # Check geometry
            if self.is_polygon_data:
                geom0 = self.get_geometry(as_geometry_objects=True)
                geom1 = other.get_geometry(as_geometry_objects=True)
            else:
                geom0 = self.get_geometry()
                geom1 = other.get_geometry()

            if len(geom0) != len(geom1):
                return False

            if self.is_point_data:
                if not numpy.allclose(geom0, geom1,
                                      rtol=rtol, atol=atol):
                    return False
            elif self.is_line_data:
                # Check vertices of each line
                for i in range(len(geom0)):

                    if not rings_equal(geom0[i], geom1[i], rtol=rtol, atol=atol):
                        return False

            elif self.is_polygon_data:
                # Check vertices of outer and inner rings
                for i in range(len(geom0)):

                    x = geom0[i].outer_ring
                    y = geom1[i].outer_ring
                    if not rings_equal(x, y, rtol=rtol, atol=atol):
                        return False

                    for j, ring0 in enumerate(geom0[i].inner_rings):
                        ring1 = geom1[i].inner_rings[j]
                        if not rings_equal(ring0, ring1, rtol=rtol, atol=atol):
                            return False

            else:
                msg = ('== not implemented for geometry type: %s'
                       % self.geometry_type)
                raise InaSAFEError(msg)

            # Check keys for attribute values
            x = self.get_data()
            y = other.get_data()

            if x is None:
                if y is not None:
                    return False
            else:
                for key in x[0]:
                    for i in range(len(y)):
                        if key not in y[i]:
                            return False

                for key in y[0]:
                    for i in range(len(x)):
                        if key not in x[i]:
                            return False

                # Check attribute values
                for i, a in enumerate(x):
                    for key in a:
                        X = a[key]
                        Y = y[i][key]

                        if X != Y:
                            # Not obviously equal, try some special cases

                            try:
                                # Try numerical comparison with tolerances
                                res = numpy.allclose(X, Y,
                                                     rtol=rtol, atol=atol)
                            except (NotImplementedError, TypeError):
                                # E.g. '' (Not implemented)
                                # or   None or {} (Type error)
                                pass
                            else:
                                if not res:
                                    return False

                            # Finally cast as booleans.
                            # This will e.g. match False with None or ''
                            if not (bool(X) is bool(Y)):
                                return False

            # Vector layers are identical up to the specified tolerance
            return True

        def read_from_file(self, filename):
            """Read and unpack vector data.

            It is assumed that the file contains only one layer with the
            pertinent features. Further it is assumed for the moment that
            all geometries are points.

            * A feature is a geometry and a set of attributes.
            * A geometry refers to location and can be point, line, polygon or
              combinations thereof.
            * The attributes or obtained through GetField()

            The full OGR architecture is documented at
            * http://www.gdal.org/ogr/ogr_arch.html
            * http://www.gdal.org/ogr/ogr_apitut.html

            Examples are at
            * danieljlewis.org/files/2010/09/basicpythonmap.pdf
            * http://invisibleroads.com/tutorials/gdal-shapefile-points-save.html
            * http://www.packtpub.com/article/geospatial-data-python-geometry

            Limitation of the Shapefile are documented in
            http://resources.esri.com/help/9.3/ArcGISDesktop/com/Gp_ToolRef/
            geoprocessing_tool_reference/
            geoprocessing_considerations_for_shapefile_output.htm
            """

            basename = os.path.splitext(filename)[0]

            # Look for any keywords
            self.keywords = read_keywords(basename + '.keywords')

            # FIXME (Ole): Should also look for style file to populate style_info

            # Determine name
            if 'title' in self.keywords:
                title = self.keywords['title']

                # Lookup internationalised title if available
                title = safe_tr(title)

                vectorname = title
            else:
                # Use basename without leading directories as name
                vectorname = os.path.split(basename)[-1]

            if self.name is None:
                self.name = vectorname
            self.filename = filename
            self.geometry_type = None  # In case there are no features

            fid = ogr.Open(filename)
            if fid is None:
                msg = 'Could not open %s' % filename
                raise ReadLayerError(msg)

            # Assume that file contains all data in one layer
            msg = 'Only one vector layer currently allowed'
            if fid.GetLayerCount() > 1 and self.sublayer is None:
                msg = ('WARNING: Number of layers in %s are %i. '
                       'Only the first layer will currently be '
                       'used. Specify sublayer when creating '
                       'the Vector if you wish to use a different layer.'
                       % (filename, fid.GetLayerCount()))
                LOGGER.warn(msg)
                # Why do we raise an exception if it is only a warning? TS
                raise ReadLayerError(msg)

            if self.sublayer is not None:
                layer = fid.GetLayerByName(self.sublayer)
            else:
                layer = fid.GetLayerByIndex(0)

            # Get spatial extent
            self.extent = layer.GetExtent()

            # Get projection
            p = layer.GetSpatialRef()
            self.projection = Projection(p)

            layer.ResetReading()

            # Extract coordinates and attributes for all features
            geometry = []
            data = []
            # Use feature iterator
            for feature in layer:
                # Record coordinates ordered as Longitude, Latitude
                G = feature.GetGeometryRef()
                if G is None:
                    msg = ('Geometry was None in filename %s ' % filename)
                    raise ReadLayerError(msg)
                else:
                    self.geometry_type = G.GetGeometryType()
                    if self.is_point_data:
                        geometry.append((G.GetX(), G.GetY()))
                    elif self.is_line_data:
                        ring = get_ringdata(G)
                        geometry.append(ring)
                    elif self.is_polygon_data:
                        polygon = get_polygondata(G)
                        geometry.append(polygon)
                    elif self.is_multi_polygon_data:
                        try:
                            G = ogr.ForceToPolygon(G)
                        except:
                            msg = ('Got geometry type Multipolygon (%s) for '
                                   'filename %s and could not convert it to '
                                   'singlepart. However, you can use QGIS '
                                   'functionality to convert multipart vector '
                                   'data to singlepart (Vector -> Geometry Tools '
                                   '-> Multipart to Singleparts and use the '
                                   'resulting dataset.'
                                   % (ogr.wkbMultiPolygon, filename))
                            raise ReadLayerError(msg)
                        else:
                            # Read polygon data as single part
                            self.geometry_type = ogr.wkbPolygon
                            polygon = get_polygondata(G)
                            geometry.append(polygon)
                    else:
                        msg = ('Only point, line and polygon geometries are '
                               'supported. '
                               'Geometry type in filename %s '
                               'was %s.' % (filename,
                                            self.geometry_type))
                        raise ReadLayerError(msg)

                # Record attributes by name
                number_of_fields = feature.GetFieldCount()
                fields = {}
                for j in range(number_of_fields):
                    name = feature.GetFieldDefnRef(j).GetName()

                    # FIXME (Ole): Ascertain the type of each field?
                    #              We need to cast each appropriately?
                    #              This is issue #66
                    #              (https://github.com/AIFDR/riab/issues/66)
                    #feature_type = feature.GetFieldDefnRef(j).GetType()
                    fields[name] = feature.GetField(j)

                        # We do this because there is NaN problem on windows
                        # NaN value must be converted to _pseudo_in to solve the
                        # problem. But, when InaSAFE read the file, it'll be
                        # converted back to NaN value, so that NaN in InaSAFE is a
                        # numpy.nan
                        # please check https://github.com/AIFDR/inasafe/issues/269
                        # for more information
                    if fields[name] == _pseudo_inf:
                        fields[name] = float('nan')
                    #print 'Field', name, feature_type, j, fields[name]

                data.append(fields)
            # Store geometry coordinates as a compact numeric array
            self.geometry = geometry
            self.data = data

        def write_to_file(self, filename, sublayer=None):
            """Save vector data to file

            Args:
                * filename: filename with extension .shp or .gml
                * sublayer: Optional string for writing a sublayer. Ignored
                      unless we are writing to an sqlite file.

            Note:
                Shp limitation, if attribute names are longer than 10
                characters they will be truncated. This is due to limitations in
                the shp file driver and has to be done here since gdal v1.7 onwards
                has changed its handling of this issue:
                http://www.gdal.org/ogr/drv_shapefile.html

                **For this reason we recommend writing to spatialite.**

            """

            # Check file format
            basename, extension = os.path.splitext(filename)

            msg = ('Invalid file type for file %s. Only extensions '
                   'sqlite, shp or gml allowed.' % filename)
            verify(extension in ['.sqlite', '.shp', '.gml'], msg)
            driver = DRIVER_MAP[extension]

            # FIXME (Ole): Tempory flagging of GML issue (ticket #18)
            if extension == '.gml':
                msg = ('OGR GML driver does not store geospatial reference.'
                       'This format is disabled for the time being. See '
                       'https://github.com/AIFDR/riab/issues/18')
                raise WriteLayerError(msg)

            # Derive layername from filename (excluding preceding dirs)
            if sublayer is None or extension == '.shp':
                layername = os.path.split(basename)[-1]
            else:
                layername = sublayer

            # Get vector data
            if self.is_polygon_data:
                geometry = self.get_geometry(as_geometry_objects=True)
            else:
                geometry = self.get_geometry()
            data = self.get_data()

            N = len(geometry)

            # Clear any previous file of this name (ogr does not overwrite)
            try:
                os.remove(filename)
            except OSError:
                pass

            # Create new file with one layer
            drv = ogr.GetDriverByName(driver)
            if drv is None:
                msg = 'OGR driver %s not available' % driver
                raise WriteLayerError(msg)

            ds = drv.CreateDataSource(filename)
            if ds is None:
                msg = 'Creation of output file %s failed' % filename
                raise WriteLayerError(msg)

            lyr = ds.CreateLayer(layername,
                                 self.projection.spatial_reference,
                                 self.geometry_type)
            if lyr is None:
                msg = 'Could not create layer %s as %s' % (layername, filename)
                raise WriteLayerError(msg)

            # Define attributes if any
            store_attributes = False
            fields = []
            if data is not None:
                if len(data) > 0:
                    try:
                        fields = data[0].keys()
                    except:
                        msg = ('Input parameter "attributes" was specified '
                               'but it does not contain list of dictionaries '
                               'with field information as expected. The first '
                               'element is %s' % data[0])
                        raise WriteLayerError(msg)
                    else:
                        # Establish OGR types for each element
                        ogrtypes = {}
                        for name in fields:
                            att = data[0][name]
                            py_type = type(att)
                            msg = ('Unknown type for storing vector '
                                   'data: %s, %s' % (name, str(py_type)[1:-1]))
                            verify(py_type in TYPE_MAP, msg)
                            ogrtypes[name] = TYPE_MAP[py_type]

                else:
                    #msg = ('Input parameter "data" was specified '
                    #       'but appears to be empty')
                    #raise InaSAFEError(msg)
                    pass

                # Create attribute fields in layer
                store_attributes = True
                for name in fields:
                    fd = ogr.FieldDefn(name, ogrtypes[name])
                    # FIXME (Ole): Trying to address issue #16
                    #              But it doesn't work and
                    #              somehow changes the values of MMI in test
                    #width = max(128, len(name))
                    #print name, width
                    #fd.SetWidth(width)

                    # Silent handling of warnings like
                    # Warning 6: Normalized/laundered field name:
                    #'CONTENTS_LOSS_AUD' to 'CONTENTS_L'
                    gdal.PushErrorHandler('CPLQuietErrorHandler')
                    if lyr.CreateField(fd) != 0:
                        msg = 'Could not create field %s' % name
                        raise WriteLayerError(msg)

                    # Restore error handler
                    gdal.PopErrorHandler()

            # Store geometry
            geom = ogr.Geometry(self.geometry_type)
            layer_def = lyr.GetLayerDefn()
            for i in range(N):
                # Create new feature instance
                feature = ogr.Feature(layer_def)

                # Store geometry and check
                if self.is_point_data:
                    x = float(geometry[i][0])
                    y = float(geometry[i][1])
                    geom.SetPoint_2D(0, x, y)
                elif self.is_line_data:
                    geom = array2line(geometry[i],
                                      geometry_type=ogr.wkbLineString)
                elif self.is_polygon_data:
                    # Create polygon geometry
                    geom = ogr.Geometry(ogr.wkbPolygon)

                    # Add outer ring
                    linear_ring = array2line(geometry[i].outer_ring,
                                             geometry_type=ogr.wkbLinearRing)
                    geom.AddGeometry(linear_ring)

                    # Add inner rings if any
                    for A in geometry[i].inner_rings:
                        geom.AddGeometry(array2line(A,
                                         geometry_type=ogr.wkbLinearRing))
                else:
                    msg = 'Geometry type %s not implemented' % self.geometry_type
                    raise WriteLayerError(msg)

                feature.SetGeometry(geom)

                G = feature.GetGeometryRef()
                if G is None:
                    msg = 'Could not create GeometryRef for file %s' % filename
                    raise WriteLayerError(msg)

                # Store attributes
                if store_attributes:
                    for j, name in enumerate(fields):
                        actual_field_name = layer_def.GetFieldDefn(j).GetNameRef()

                        val = data[i][name]

                        if type(val) == numpy.ndarray:
                            # A singleton of type <type 'numpy.ndarray'> works
                            # for gdal version 1.6 but fails for version 1.8
                            # in SetField with error: NotImplementedError:
                            # Wrong number of arguments for overloaded function
                            val = float(val)
                        elif val is None:
                            val = ''

                        # We do this because there is NaN problem on windows
                        # NaN value must be converted to _pseudo_in to solve the
                        # problem. But, when InaSAFE read the file, it'll be
                        # converted back to NaN value, so that NaN in InaSAFE is a
                        # numpy.nan
                        # please check https://github.com/AIFDR/inasafe/issues/269
                        # for more information
                        if val != val:
                            val = _pseudo_inf

                        feature.SetField(actual_field_name, val)

                # Save this feature
                if lyr.CreateFeature(feature) != 0:
                    msg = 'Failed to create feature %i in file %s' % (i, filename)
                    raise WriteLayerError(msg)

                feature.Destroy()

            # Write keywords if any
            write_keywords(self.keywords, basename + '.keywords')

            # FIXME (Ole): Maybe store style_info

        def copy(self):
            """Return copy of vector layer

            This copy will be equal to self in the sense defined by __eq__
            """

            if self.is_polygon_data:
                geometry = self.get_geometry(copy=True, as_geometry_objects=True)
            else:
                geometry = self.get_geometry(copy=True)

            return Vector(data=self.get_data(copy=True),
                          geometry=geometry,
                          projection=self.get_projection(),
                          keywords=self.get_keywords())

        def get_attribute_names(self):
            """Get available attribute names

            These are the ones that can be used with get_data
            """

            return self.data[0].keys()

        def get_data(self, attribute=None, index=None, copy=False):
            """Get vector attributes

            Note:
                Data is returned as a list where each entry is a dictionary of
                attributes for one feature. Entries in get_geometry() and
                get_data() are related as 1-to-1

                If optional argument attribute is specified and a valid name,
                then the list of values for that attribute is returned.

                If optional argument index is specified on the that value will
                be returned. Any value of index is ignored if attribute is None.

                If optional argument copy is True and all attributes are requested,
                a copy will be returned. Otherwise a pointer to the data is
                returned.
            """

            if hasattr(self, 'data'):
                if attribute is None:
                    if copy:
                        return copy_module.deepcopy(self.data)
                    else:
                        return self.data
                else:
                    msg = ('Specified attribute %s does not exist in '
                           'vector layer %s. Valid names are %s'
                           '' % (attribute, self, self.data[0].keys()))
                    verify(attribute in self.data[0], msg)

                    if index is None:
                        # Return all values for specified attribute
                        return [x[attribute] for x in self.data]
                    else:
                        # Return value for specified attribute and index
                        msg = ('Specified index must be either None or '
                               'an integer. I got %s' % index)
                        verify(isinstance(index, int), msg)

                        msg = ('Specified index must lie within the bounds '
                               'of vector layer %s which is [%i, %i]'
                               '' % (self, 0, len(self) - 1))
                        verify(0 <= index < len(self), msg)

                        return self.data[index][attribute]
            else:
                msg = 'Vector data instance does not have any attributes'
                raise GetDataError(msg)

        def get_geometry_type(self):
            """Return geometry type for vector layer
            """
            return self.geometry_type

        def get_geometry_name(self):
            """Return geometry name for vector layer
            """
            return geometrytype2string(self.geometry_type)

        def get_geometry(self, copy=False, as_geometry_objects=False):
            """Return geometry for vector layer.

            Depending on the feature type, geometry is

            geometry type     output type
            -----------------------------
            point             list of 2x1 array of longitudes and latitudes)
            line              list of arrays of coordinates
            polygon           list of arrays of coordinates

            Optional boolean argument as_geometry_objects will change the return
            value to a list of geometry objects rather than a list of arrays.
            This currently only applies to polygon geometries
            """

            if copy:
                geometry = copy_module.deepcopy(self.geometry)
            else:
                geometry = self.geometry

            if self.is_polygon_data:
                if not as_geometry_objects:
                    geometry = [p.outer_ring for p in geometry]
            else:
                if as_geometry_objects:
                    msg = ('Argument as_geometry_objects can currently '
                           'be True only for polygon data')
                    raise InaSAFEError(msg)

            return geometry

        def get_bounding_box(self):
            """Get bounding box coordinates for vector layer.

            Format is [West, South, East, North]
            """
            e = self.extent
            return [e[0],  # West
                    e[2],  # South
                    e[1],  # East
                    e[3]]  # North

        def get_extrema(self, attribute=None):
            """Get min and max values from specified attribute

            Return min, max
            """
            if attribute is None:
                msg = ('Valid attribute name must be specified in get_extrema '
                       'for vector layers. I got None.')
                raise InaSAFEError(msg)

            x = self.get_data(attribute)
            return min(x), max(x)

        def get_topN(self, attribute, N=10):
            """Get top N features

            Args:
                * attribute: The name of attribute where values are sought
                * N: How many

            Returns:
                * layer: New vector layer with selected features
            """

            # Input checks
            msg = ('Specfied attribute must be a string. '
                   'I got %s' % (type(attribute)))
            verify(isinstance(attribute, basestring), msg)

            msg = 'Specified attribute was empty'
            verify(attribute != '', msg)

            msg = 'N must be a positive number. I got %i' % N
            verify(N > 0, msg)

            # Create list of values for specified attribute
            values = self.get_data(attribute)

            # Sort and select using Schwarzian transform
            A = zip(values, self.data, self.geometry)
            A.sort()

            # Pick top N and unpack
            data, geometry = zip(*A[-N:])[1:]

            # Create new Vector instance and return
            return Vector(data=data,
                          projection=self.get_projection(),
                          geometry=geometry,
                          keywords=self.get_keywords())

        @property
        def is_point_data(self):
            return self.is_vector and (self.geometry_type == ogr.wkbPoint or
                self.geometry_type == ogr.wkbPoint25D)

        @property
        def is_line_data(self):
            return self.is_vector and (self.geometry_type == ogr.wkbLineString or
                self.geometry_type == ogr.wkbLineString25D)

        @property
        def is_polygon_data(self):
            return self.is_vector and (self.geometry_type == ogr.wkbPolygon or
                self.geometry_type == ogr.wkbPolygon25D)

        @property
        def is_multi_polygon_data(self):
            return self.is_vector and self.geometry_type == ogr.wkbMultiPolygon

    #----------------------------------
    # Helper functions for class Vector
    #----------------------------------
    def convert_line_to_points(V, delta):
        """Convert line vector data to point vector data

        Args:
            * V: Vector layer with line data
            * delta: Incremental step to find the points
        Returns:
            * Vector layer with point data and the same attributes as V
        """

        msg = 'Input data %s must be line vector data' % V
        verify(V.is_line_data, msg)

        geometry = V.get_geometry()
        data = V.get_data()
        N = len(V)

        # Calculate centroids for each polygon
        points = []
        new_data = []
        for i in range(N):
            c = points_along_line(geometry[i], delta)
            # We need to create a data entry for each point.
            # FIXME (Ole): What on earth is this?
            # pylint: disable=W0621
            new_data.extend([data[i] for _ in c])
            # pylint: enable=W0621
            points.extend(c)

        # Create new point vector layer with same attributes and return
        V = Vector(data=new_data,
                   projection=V.get_projection(),
                   geometry=points,
                   name='%s_point_data' % V.get_name(),
                   keywords=V.get_keywords())
        return V

    def convert_polygons_to_centroids(V):
        """Convert polygon vector data to point vector data

        Args:
            * V: Vector layer with polygon data

        Returns:
            * Vector layer with point data and the same attributes as V
        """

        msg = 'Input data %s must be polygon vector data' % V
        verify(V.is_polygon_data, msg)

        geometry = V.get_geometry()
        N = len(V)

        # Calculate points for each polygon
        centroids = []
        for i in range(N):
            c = calculate_polygon_centroid(geometry[i])
            centroids.append(c)

        # Create new point vector layer with same attributes and return
        V = Vector(data=V.get_data(),
                   projection=V.get_projection(),
                   geometry=centroids,
                   name='%s_centroid_data' % V.get_name(),
                   keywords=V.get_keywords())
        return V

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