from __future__ import unicode_literals

from django.db.backends import BaseDatabaseIntrospection, FieldInfo


class DatabaseIntrospection(BaseDatabaseIntrospection):
    # Maps type codes to Django Field types.
    data_types_reverse = {
        16: 'BooleanField',
        17: 'BinaryField',
        20: 'BigIntegerField',
        21: 'SmallIntegerField',
        23: 'IntegerField',
        25: 'TextField',
        700: 'FloatField',
        701: 'FloatField',
        869: 'GenericIPAddressField',
        1042: 'CharField', # blank-padded
        1043: 'CharField',
        1082: 'DateField',
        1083: 'TimeField',
        1114: 'DateTimeField',
        1184: 'DateTimeField',
        1266: 'TimeField',
        1700: 'DecimalField',
    }
        
    def get_table_list(self, cursor):
        "Returns a list of table names in the current database."
        cursor.execute("""
            SELECT c.relname
            FROM pg_catalog.pg_class c
            LEFT JOIN pg_catalog.pg_namespace n ON n.oid = c.relnamespace
            WHERE c.relkind IN ('r', 'v', '')
                AND n.nspname NOT IN ('pg_catalog', 'pg_toast')
                AND pg_catalog.pg_table_is_visible(c.oid)""")
        return [row[0] for row in cursor.fetchall()]

    def get_table_description(self, cursor, table_name):
        "Returns a description of the table, with the DB-API cursor.description interface."
        # As cursor.description does not return reliably the nullable property,
        # we have to query the information_schema (#7783)
        cursor.execute("""
            SELECT column_name, is_nullable
            FROM information_schema.columns
            WHERE table_name = %s""", [table_name])
        null_map = dict(cursor.fetchall())
        cursor.execute("SELECT * FROM %s LIMIT 1" % self.connection.ops.quote_name(table_name))
        return [FieldInfo(*(line[:6] + (null_map[line[0]]=='YES',)))
                for line in cursor.description]

    def get_relations(self, cursor, table_name):
        """
        Returns a dictionary of {field_index: (field_index_other_table, other_table)}
        representing all relationships to the given table. Indexes are 0-based.
        """
        cursor.execute("""
            SELECT con.conkey, con.confkey, c2.relname
            FROM pg_constraint con, pg_class c1, pg_class c2
            WHERE c1.oid = con.conrelid
                AND c2.oid = con.confrelid
                AND c1.relname = %s
                AND con.contype = 'f'""", [table_name])
        relations = {}
        for row in cursor.fetchall():
            # row[0] and row[1] are single-item lists, so grab the single item.
            relations[row[0][0] - 1] = (row[1][0] - 1, row[2])
        return relations

    def get_key_columns(self, cursor, table_name):
        key_columns = []
        cursor.execute("""
            SELECT kcu.column_name, ccu.table_name AS referenced_table, ccu.column_name AS referenced_column
            FROM information_schema.constraint_column_usage ccu
            LEFT JOIN information_schema.key_column_usage kcu
                ON ccu.constraint_catalog = kcu.constraint_catalog
                    AND ccu.constraint_schema = kcu.constraint_schema
                    AND ccu.constraint_name = kcu.constraint_name
            LEFT JOIN information_schema.table_constraints tc
                ON ccu.constraint_catalog = tc.constraint_catalog
                    AND ccu.constraint_schema = tc.constraint_schema
                    AND ccu.constraint_name = tc.constraint_name
            WHERE kcu.table_name = %s AND tc.constraint_type = 'FOREIGN KEY'""" , [table_name])
        key_columns.extend(cursor.fetchall())
        return key_columns

    def get_indexes(self, cursor, table_name):
        # This query retrieves each index on the given table, including the
        # first associated field name
        cursor.execute("""
            SELECT attr.attname, idx.indkey, idx.indisunique, idx.indisprimary
            FROM pg_catalog.pg_class c, pg_catalog.pg_class c2,
                pg_catalog.pg_index idx, pg_catalog.pg_attribute attr
            WHERE c.oid = idx.indrelid
                AND idx.indexrelid = c2.oid
                AND attr.attrelid = c.oid
                AND attr.attnum = idx.indkey[0]
                AND c.relname = %s""", [table_name])
        indexes = {}
        for row in cursor.fetchall():
            # row[1] (idx.indkey) is stored in the DB as an array. It comes out as
            # a string of space-separated integers. This designates the field
            # indexes (1-based) of the fields that have indexes on the table.
            # Here, we skip any indexes across multiple fields.
            if ' ' in row[1]:
                continue
            indexes[row[0]] = {'primary_key': row[3], 'unique': row[2]}
        return indexes
