from django import forms

from django.utils.translation import ugettext_lazy as _

# While this couples the geographic forms to the GEOS library,

# it decouples from database (by not importing SpatialBackend).

from django.contrib.gis.geos import GEOSGeometry

class GeometryField(forms.Field):

    """

    This is the basic form field for a Geometry.  Any textual input that is

    accepted by GEOSGeometry is accepted by this form.  By default,

    this includes WKT, HEXEWKB, WKB (in a buffer), and GeoJSON.

    """

    widget = forms.Textarea

    default_error_messages = {

        'no_geom' : _(u'No geometry value provided.'),

        'invalid_geom' : _(u'Invalid geometry value.'),

        'invalid_geom_type' : _(u'Invalid geometry type.'),

        'transform_error' : _(u'An error occurred when transforming the geometry '

                              'to the SRID of the geometry form field.'),

        }

    def __init__(self, **kwargs):

        # Pop out attributes from the database field, or use sensible

        # defaults (e.g., allow None).

        self.srid = kwargs.pop('srid', None)

        self.geom_type = kwargs.pop('geom_type', 'GEOMETRY')

        self.null = kwargs.pop('null', True)

        super(GeometryField, self).__init__(**kwargs)

    def clean(self, value):

        """

        Validates that the input value can be converted to a Geometry

        object (which is returned).  A ValidationError is raised if

        the value cannot be instantiated as a Geometry.

        """

        if not value:

            if self.null and not self.required:

                # The geometry column allows NULL and is not required.

                return None

            else:

                raise forms.ValidationError(self.error_messages['no_geom'])

        # Trying to create a Geometry object from the form value.

        try:

            geom = GEOSGeometry(value)

        except:

            raise forms.ValidationError(self.error_messages['invalid_geom'])

        # Ensuring that the geometry is of the correct type (indicated

        # using the OGC string label).

        if str(geom.geom_type).upper() != self.geom_type and not self.geom_type == 'GEOMETRY':

            raise forms.ValidationError(self.error_messages['invalid_geom_type'])

        # Transforming the geometry if the SRID was set.

        if self.srid:

            if not geom.srid:

                # Should match that of the field if not given.

                geom.srid = self.srid

            elif self.srid != -1 and self.srid != geom.srid:

                try:

                    geom.transform(self.srid)

                except:

                    raise forms.ValidationError(self.error_messages['transform_error'])

        return geom