from logging import getLogger

from sqlalchemy import types, Column, Table

from geoalchemy import Geometry, GeometryColumn, GeometryDDL, GeometryExtensionColumn
from geoalchemy.postgis import PGComparator


from ckan.lib.base import config
from ckan import model
from ckan.model import Session
from ckan.model import meta
from ckan.model.domain_object import DomainObject

log = getLogger(__name__)

package_extent_table = None

DEFAULT_SRID = 4326 #(WGS 84)

def setup(srid=None):

    if package_extent_table is None:
        define_spatial_tables(srid)
        log.debug('Spatial tables defined in memory')

    if model.package_table.exists():
        if not Table('geometry_columns',meta.metadata).exists() or \
            not Table('spatial_ref_sys',meta.metadata).exists():
            raise Exception('The spatial extension is enabled, but PostGIS ' + \
                    'has not been set up in the database. ' + \
                    'Please refer to the "Setting up PostGIS" section in the README.')


        if not package_extent_table.exists():
            try:
                package_extent_table.create()
            except Exception,e:
                # Make sure the table does not remain incorrectly created
                # (eg without geom column or constraints)
                if package_extent_table.exists():
                    Session.execute('DROP TABLE package_extent')
                    Session.commit()

                raise e

            log.debug('Spatial tables created')
        else:
            log.debug('Spatial tables already exist')
            # Future migrations go here

    else:
        log.debug('Spatial tables creation deferred')


class PackageExtent(DomainObject):
    def __init__(self, package_id=None, the_geom=None):
        self.package_id = package_id
        self.the_geom = the_geom

def define_spatial_tables(db_srid=None):

    global package_extent_table

    if not db_srid:
        db_srid = int(config.get('ckan.spatial.srid', DEFAULT_SRID))
    else:
        db_srid = int(db_srid)

    package_extent_table = Table('package_extent', meta.metadata,
                    Column('package_id', types.UnicodeText, primary_key=True),
                    GeometryExtensionColumn('the_geom', Geometry(2,srid=db_srid)))


    meta.mapper(PackageExtent, package_extent_table, properties={
            'the_geom': GeometryColumn(package_extent_table.c.the_geom,
                                            comparator=PGComparator)})

    # enable the DDL extension
    GeometryDDL(package_extent_table)