import re

from django.db.backends import BaseDatabaseIntrospection

# This light wrapper "fakes" a dictionary interface, because some SQLite data

# types include variables in them -- e.g. "varchar(30)" -- and can't be matched

# as a simple dictionary lookup.

class FlexibleFieldLookupDict:

    # Maps SQL types to Django Field types. Some of the SQL types have multiple

    # entries here because SQLite allows for anything and doesn't normalize the

    # field type; it uses whatever was given.

    base_data_types_reverse = {

        'bool': 'BooleanField',

        'boolean': 'BooleanField',

        'smallint': 'SmallIntegerField',

        'smallint unsigned': 'PositiveSmallIntegerField',

        'smallinteger': 'SmallIntegerField',

        'int': 'IntegerField',

        'integer': 'IntegerField',

        'integer unsigned': 'PositiveIntegerField',

        'decimal': 'DecimalField',

        'real': 'FloatField',

        'text': 'TextField',

        'char': 'CharField',

        'date': 'DateField',

        'datetime': 'DateTimeField',

        'time': 'TimeField',

    }

    def __getitem__(self, key):

        key = key.lower()

        try:

            return self.base_data_types_reverse[key]

        except KeyError:

            import re

            m = re.search(r'^\s*(?:var)?char\s*\(\s*(\d+)\s*\)\s*$', key)

            if m:

                return ('CharField', {'max_length': int(m.group(1))})

            raise KeyError

class DatabaseIntrospection(BaseDatabaseIntrospection):

    data_types_reverse = FlexibleFieldLookupDict()

    def get_table_list(self, cursor):

        "Returns a list of table names in the current database."

        # Skip the sqlite_sequence system table used for autoincrement key

        # generation.

        cursor.execute("""

            SELECT name FROM sqlite_master

            WHERE type='table' AND NOT name='sqlite_sequence'

            ORDER BY name""")

        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."

        return [(info['name'], info['type'], None, None, None, None,

                 info['null_ok']) for info in self._table_info(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.

        """

        # Dictionary of relations to return

        relations = {}

        # Schema for this table

        cursor.execute("SELECT sql FROM sqlite_master WHERE tbl_name = %s", [table_name])

        results = cursor.fetchone()[0].strip()

        results = results[results.index('(')+1:results.rindex(')')]

        # Walk through and look for references to other tables. SQLite doesn't

        # really have enforced references, but since it echoes out the SQL used

        # to create the table we can look for REFERENCES statements used there.

        for field_index, field_desc in enumerate(results.split(',')):

            field_desc = field_desc.strip()

            if field_desc.startswith("UNIQUE"):

                continue

            m = re.search('references (.*) \(["|](.*)["|]\)', field_desc, re.I)

            if not m:

                continue

            table, column = [s.strip('"') for s in m.groups()]

            cursor.execute("SELECT sql FROM sqlite_master WHERE tbl_name = %s", [table])

            result = cursor.fetchone()

            if not result:

                continue

            other_table_results = result[0].strip()

            li, ri = other_table_results.index('('), other_table_results.rindex(')')

            other_table_results = other_table_results[li+1:ri]

            for other_index, other_desc in enumerate(other_table_results.split(',')):

                other_desc = other_desc.strip()

                if other_desc.startswith('UNIQUE'):

                    continue

                name = other_desc.split(' ', 1)[0].strip('"')

                if name == column:

                    relations[field_index] = (other_index, table)

                    break

        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}

        """

        indexes = {}

        for info in self._table_info(cursor, table_name):

            indexes[info['name']] = {'primary_key': info['pk'] != 0,

                                     'unique': False}

        cursor.execute('PRAGMA index_list(%s)' % self.connection.ops.quote_name(table_name))

        # seq, name, unique

        for index, unique in [(field[1], field[2]) for field in cursor.fetchall()]:

            if not unique:

                continue

            cursor.execute('PRAGMA index_info(%s)' % self.connection.ops.quote_name(index))

            info = cursor.fetchall()

            # Skip indexes across multiple fields

            if len(info) != 1:

                continue

            name = info[0][2] # seqno, cid, name

            indexes[name]['unique'] = True

        return indexes

    def _table_info(self, cursor, name):

        cursor.execute('PRAGMA table_info(%s)' % self.connection.ops.quote_name(name))

        # cid, name, type, notnull, dflt_value, pk

        return [{'name': field[1],

                 'type': field[2],

                 'null_ok': not field[3],

                 'pk': field[5]     # undocumented

                 } for field in cursor.fetchall()]