from django import forms

from django.contrib.gis.db.backend import SpatialBackend

from django.utils.translation import ugettext_lazy as _

class GeometryField(forms.Field):

    """

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

    accepted by SpatialBackend.Geometry is accepted by this form.  By default, 

    this is GEOSGeometry, which accepts WKT, HEXEWKB, WKB, 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.'),

    }

    def __init__(self, **kwargs):

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

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

        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:

                # The geometry column allows NULL, return None.

                return None

            else:

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

        try:

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

            geom = SpatialBackend.Geometry(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'])

        return geom