from django.forms.widgets import Textarea
from django.template import loader, Context
from django.templatetags.static import static
from django.utils import six
from django.utils import translation

from django.contrib.gis.gdal import OGRException
from django.contrib.gis.geos import GEOSGeometry, GEOSException, fromstr

# Creating a template context that contains Django settings
# values needed by admin map templates.
geo_context = Context({'LANGUAGE_BIDI' : translation.get_language_bidi()})

class OpenLayersWidget(Textarea):
    """
    Renders an OpenLayers map using the WKT of the geometry.
    """
    def render(self, name, value, attrs=None):
        # Update the template parameters with any attributes passed in.
        if attrs: self.params.update(attrs)

        # Defaulting the WKT value to a blank string -- this
        # will be tested in the JavaScript and the appropriate
        # interface will be constructed.
        self.params['wkt'] = ''

        # If a string reaches here (via a validation error on another
        # field) then just reconstruct the Geometry.
        if isinstance(value, six.string_types):
            try:
                value = GEOSGeometry(value)
            except (GEOSException, ValueError):
                value = None

        if value and value.geom_type.upper() != self.geom_type:
            value = None

        # Constructing the dictionary of the map options.
        self.params['map_options'] = self.map_options()

        # Constructing the JavaScript module name using the name of
        # the GeometryField (passed in via the `attrs` keyword).
        # Use the 'name' attr for the field name (rather than 'field')
        self.params['name'] = name
        # note: we must switch out dashes for underscores since js
        # functions are created using the module variable
        js_safe_name = self.params['name'].replace('-','_')
        self.params['module'] = 'geodjango_%s' % js_safe_name

        if value:
            # Transforming the geometry to the projection used on the
            # OpenLayers map.
            srid = self.params['srid']
            if value.srid != srid:
                try:
                    ogr = value.ogr
                    ogr.transform(srid)
                    wkt = ogr.wkt
                except OGRException:
                    wkt = ''
            else:
                wkt = value.wkt

            # Setting the parameter WKT with that of the transformed
            # geometry.
            self.params['wkt'] = wkt

        return loader.render_to_string(self.template, self.params,
                                       context_instance=geo_context)

    def map_options(self):
        "Builds the map options hash for the OpenLayers template."

        # JavaScript construction utilities for the Bounds and Projection.
        def ol_bounds(extent):
            return 'new OpenLayers.Bounds(%s)' % str(extent)
        def ol_projection(srid):
            return 'new OpenLayers.Projection("EPSG:%s")' % srid

        # An array of the parameter name, the name of their OpenLayers
        # counterpart, and the type of variable they are.
        map_types = [('srid', 'projection', 'srid'),
                     ('display_srid', 'displayProjection', 'srid'),
                     ('units', 'units', str),
                     ('max_resolution', 'maxResolution', float),
                     ('max_extent', 'maxExtent', 'bounds'),
                     ('num_zoom', 'numZoomLevels', int),
                     ('max_zoom', 'maxZoomLevels', int),
                     ('min_zoom', 'minZoomLevel', int),
                     ]

        # Building the map options hash.
        map_options = {}
        for param_name, js_name, option_type in map_types:
            if self.params.get(param_name, False):
                if option_type == 'srid':
                    value = ol_projection(self.params[param_name])
                elif option_type == 'bounds':
                    value = ol_bounds(self.params[param_name])
                elif option_type in (float, int):
                    value = self.params[param_name]
                elif option_type in (str,):
                    value = '"%s"' % self.params[param_name]
                else:
                    raise TypeError
                map_options[js_name] = value
        return map_options

    def _has_changed(self, initial, data):
        """ Compare geographic value of data with its initial value. """

        # Ensure we are dealing with a geographic object
        if isinstance(initial, six.string_types):
            try:
                initial = GEOSGeometry(initial)
            except (GEOSException, ValueError):
                initial = None

        # Only do a geographic comparison if both values are available
        if initial and data:
            data = fromstr(data)
            data.transform(initial.srid)
            # If the initial value was not added by the browser, the geometry
            # provided may be slightly different, the first time it is saved.
            # The comparison is done with a very low tolerance.
            return not initial.equals_exact(data, tolerance=0.000001)
        else:
            # Check for change of state of existence
            return bool(initial) != bool(data)