import sys

import cx_Oracle

from django.db.backends.oracle.introspection import DatabaseIntrospection
from django.utils import six


class OracleIntrospection(DatabaseIntrospection):
    # Associating any OBJECTVAR instances with GeometryField.  Of course,
    # this won't work right on Oracle objects that aren't MDSYS.SDO_GEOMETRY,
    # but it is the only object type supported within Django anyways.
    data_types_reverse = DatabaseIntrospection.data_types_reverse.copy()
    data_types_reverse[cx_Oracle.OBJECT] = 'GeometryField'

    def get_geometry_type(self, table_name, geo_col):
        cursor = self.connection.cursor()
        try:
            # Querying USER_SDO_GEOM_METADATA to get the SRID and dimension information.
            try:
                cursor.execute(
                    'SELECT "DIMINFO", "SRID" FROM "USER_SDO_GEOM_METADATA" '
                    'WHERE "TABLE_NAME"=%s AND "COLUMN_NAME"=%s',
                    (table_name.upper(), geo_col.upper())
                )
                row = cursor.fetchone()
            except Exception as msg:
                new_msg = (
                    'Could not find entry in USER_SDO_GEOM_METADATA '
                    'corresponding to "%s"."%s"\n'
                    'Error message: %s.') % (table_name, geo_col, msg)
                six.reraise(Exception, Exception(new_msg), sys.exc_info()[2])

            # TODO: Research way to find a more specific geometry field type for
            # the column's contents.
            field_type = 'GeometryField'

            # Getting the field parameters.
            field_params = {}
            dim, srid = row
            if srid != 4326:
                field_params['srid'] = srid
            # Length of object array ( SDO_DIM_ARRAY ) is number of dimensions.
            dim = len(dim)
            if dim != 2:
                field_params['dim'] = dim
        finally:
            cursor.close()

        return field_type, field_params
