from django.db.backends import BaseDatabaseIntrospection
from MySQLdb import ProgrammingError, OperationalError
from MySQLdb.constants import FIELD_TYPE
import re

foreign_key_re = re.compile(r"\sCONSTRAINT `[^`]*` FOREIGN KEY \(`([^`]*)`\) REFERENCES `([^`]*)` \(`([^`]*)`\)")

class DatabaseIntrospection(BaseDatabaseIntrospection):
    data_types_reverse = {
        FIELD_TYPE.BLOB: 'TextField',
        FIELD_TYPE.CHAR: 'CharField',
        FIELD_TYPE.DECIMAL: 'DecimalField',
        FIELD_TYPE.NEWDECIMAL: 'DecimalField',
        FIELD_TYPE.DATE: 'DateField',
        FIELD_TYPE.DATETIME: 'DateTimeField',
        FIELD_TYPE.DOUBLE: 'FloatField',
        FIELD_TYPE.FLOAT: 'FloatField',
        FIELD_TYPE.INT24: 'IntegerField',
        FIELD_TYPE.LONG: 'IntegerField',
        FIELD_TYPE.LONGLONG: 'IntegerField',
        FIELD_TYPE.SHORT: 'IntegerField',
        FIELD_TYPE.STRING: 'CharField',
        FIELD_TYPE.TIMESTAMP: 'DateTimeField',
        FIELD_TYPE.TINY: 'IntegerField',
        FIELD_TYPE.TINY_BLOB: 'TextField',
        FIELD_TYPE.MEDIUM_BLOB: 'TextField',
        FIELD_TYPE.LONG_BLOB: 'TextField',
        FIELD_TYPE.VAR_STRING: 'CharField',
    }

    def get_table_list(self, cursor):
        "Returns a list of table names in the current database."
        cursor.execute("SHOW TABLES")
        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."
        cursor.execute("SELECT * FROM %s LIMIT 1" % self.connection.ops.quote_name(table_name))
        return cursor.description

    def _name_to_index(self, cursor, table_name):
        """
        Returns a dictionary of {field_name: field_index} for the given table.
        Indexes are 0-based.
        """
        return dict([(d[0], i) for i, d in enumerate(self.get_table_description(cursor, table_name))])

    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.
        """
        my_field_dict = self._name_to_index(cursor, table_name)
        constraints = []
        relations = {}
        try:
            # This should work for MySQL 5.0.
            cursor.execute("""
                SELECT column_name, referenced_table_name, referenced_column_name
                FROM information_schema.key_column_usage
                WHERE table_name = %s
                    AND table_schema = DATABASE()
                    AND referenced_table_name IS NOT NULL
                    AND referenced_column_name IS NOT NULL""", [table_name])
            constraints.extend(cursor.fetchall())
        except (ProgrammingError, OperationalError):
            # Fall back to "SHOW CREATE TABLE", for previous MySQL versions.
            # Go through all constraints and save the equal matches.
            cursor.execute("SHOW CREATE TABLE %s" % self.connection.ops.quote_name(table_name))
            for row in cursor.fetchall():
                pos = 0
                while True:
                    match = foreign_key_re.search(row[1], pos)
                    if match == None:
                        break
                    pos = match.end()
                    constraints.append(match.groups())

        for my_fieldname, other_table, other_field in constraints:
            other_field_index = self._name_to_index(cursor, other_table)[other_field]
            my_field_index = my_field_dict[my_fieldname]
            relations[my_field_index] = (other_field_index, other_table)

        return relations

    def get_indexes(self, cursor, table_name):
        """
        Returns a dictionary of fieldname -> infodict for the given table,
        where each infodict is in the format:
            {'primary_key': boolean representing whether it's the primary key,
             'unique': boolean representing whether it's a unique index}
        """
        cursor.execute("SHOW INDEX FROM %s" % self.connection.ops.quote_name(table_name))
        indexes = {}
        for row in cursor.fetchall():
            indexes[row[4]] = {'primary_key': (row[2] == 'PRIMARY'), 'unique': not bool(row[1])}
        return indexes