import re

from django.db.backends.base.introspection import (
    BaseDatabaseIntrospection, FieldInfo, TableInfo,
)
from django.db.models.indexes import Index

field_size_re = re.compile(r'^\s*(?:var)?char\s*\(\s*(\d+)\s*\)\s*$')


def get_field_size(name):
    """ Extract the size number from a "varchar(11)" type name """
    m = field_size_re.search(name)
    return int(m.group(1)) if m else None


# 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',
        'bigint': 'BigIntegerField',
        'integer unsigned': 'PositiveIntegerField',
        'decimal': 'DecimalField',
        'real': 'FloatField',
        'text': 'TextField',
        'char': 'CharField',
        'blob': 'BinaryField',
        'date': 'DateField',
        'datetime': 'DateTimeField',
        'time': 'TimeField',
    }

    def __getitem__(self, key):
        key = key.lower()
        try:
            return self.base_data_types_reverse[key]
        except KeyError:
            size = get_field_size(key)
            if size is not None:
                return ('CharField', {'max_length': size})
            raise KeyError


class DatabaseIntrospection(BaseDatabaseIntrospection):
    data_types_reverse = FlexibleFieldLookupDict()

    def get_table_list(self, cursor):
        """Return a list of table and view names in the current database."""
        # Skip the sqlite_sequence system table used for autoincrement key
        # generation.
        cursor.execute("""
            SELECT name, type FROM sqlite_master
            WHERE type in ('table', 'view') AND NOT name='sqlite_sequence'
            ORDER BY name""")
        return [TableInfo(row[0], row[1][0]) for row in cursor.fetchall()]

    def get_table_description(self, cursor, table_name):
        """
        Return a description of the table with the DB-API cursor.description
        interface.
        """
        return [
            FieldInfo(
                info['name'],
                info['type'],
                None,
                info['size'],
                None,
                None,
                info['null_ok'],
                info['default'],
            ) for info in self._table_info(cursor, table_name)
        ]

    def get_sequences(self, cursor, table_name, table_fields=()):
        pk_col = self.get_primary_key_column(cursor, table_name)
        return [{'table': table_name, 'column': pk_col}]

    def get_relations(self, cursor, table_name):
        """
        Return a dictionary of {field_name: (field_name_other_table, other_table)}
        representing all relationships to the given table.
        """
        # Dictionary of relations to return
        relations = {}

        # Schema for this table
        cursor.execute("SELECT sql FROM sqlite_master WHERE tbl_name = %s AND type = %s", [table_name, "table"])
        try:
            results = cursor.fetchone()[0].strip()
        except TypeError:
            # It might be a view, then no results will be returned
            return relations
        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_desc in results.split(','):
            field_desc = field_desc.strip()
            if field_desc.startswith("UNIQUE"):
                continue

            m = re.search(r'references (\S*) ?\(["|]?(.*)["|]?\)', field_desc, re.I)
            if not m:
                continue
            table, column = [s.strip('"') for s in m.groups()]

            if field_desc.startswith("FOREIGN KEY"):
                # Find name of the target FK field
                m = re.match(r'FOREIGN KEY\s*\(([^\)]*)\).*', field_desc, re.I)
                field_name = m.groups()[0].strip('"')
            else:
                field_name = field_desc.split()[0].strip('"')

            cursor.execute("SELECT sql FROM sqlite_master WHERE tbl_name = %s", [table])
            result = cursor.fetchall()[0]
            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_desc in other_table_results.split(','):
                other_desc = other_desc.strip()
                if other_desc.startswith('UNIQUE'):
                    continue

                other_name = other_desc.split(' ', 1)[0].strip('"')
                if other_name == column:
                    relations[field_name] = (other_name, table)
                    break

        return relations

    def get_key_columns(self, cursor, table_name):
        """
        Return a list of (column_name, referenced_table_name, referenced_column_name)
        for all key columns in given table.
        """
        key_columns = []

        # Schema for this table
        cursor.execute("SELECT sql FROM sqlite_master WHERE tbl_name = %s AND type = %s", [table_name, "table"])
        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(r'"(.*)".*references (.*) \(["|](.*)["|]\)', field_desc, re.I)
            if not m:
                continue

            # This will append (column_name, referenced_table_name, referenced_column_name) to key_columns
            key_columns.append(tuple(s.strip('"') for s in m.groups()))

        return key_columns

    def get_primary_key_column(self, cursor, table_name):
        """Return the column name of the primary key for the given table."""
        # Don't use PRAGMA because that causes issues with some transactions
        cursor.execute("SELECT sql FROM sqlite_master WHERE tbl_name = %s AND type = %s", [table_name, "table"])
        row = cursor.fetchone()
        if row is None:
            raise ValueError("Table %s does not exist" % table_name)
        results = row[0].strip()
        results = results[results.index('(') + 1:results.rindex(')')]
        for field_desc in results.split(','):
            field_desc = field_desc.strip()
            m = re.search('"(.*)".*PRIMARY KEY( AUTOINCREMENT)?', field_desc)
            if m:
                return m.groups()[0]
        return None

    def _table_info(self, cursor, name):
        cursor.execute('PRAGMA table_info(%s)' % self.connection.ops.quote_name(name))
        # cid, name, type, notnull, default_value, pk
        return [{
            'name': field[1],
            'type': field[2],
            'size': get_field_size(field[2]),
            'null_ok': not field[3],
            'default': field[4],
            'pk': field[5],  # undocumented
        } for field in cursor.fetchall()]

    def get_constraints(self, cursor, table_name):
        """
        Retrieve any constraints or keys (unique, pk, fk, check, index) across
        one or more columns.
        """
        constraints = {}
        # Get the index info
        cursor.execute("PRAGMA index_list(%s)" % self.connection.ops.quote_name(table_name))
        for row in cursor.fetchall():
            # Sqlite3 3.8.9+ has 5 columns, however older versions only give 3
            # columns. Discard last 2 columns if there.
            number, index, unique = row[:3]
            # Get the index info for that index
            cursor.execute('PRAGMA index_info(%s)' % self.connection.ops.quote_name(index))
            for index_rank, column_rank, column in cursor.fetchall():
                if index not in constraints:
                    constraints[index] = {
                        "columns": [],
                        "primary_key": False,
                        "unique": bool(unique),
                        "foreign_key": False,
                        "check": False,
                        "index": True,
                    }
                constraints[index]['columns'].append(column)
            # Add type and column orders for indexes
            if constraints[index]['index'] and not constraints[index]['unique']:
                # SQLite doesn't support any index type other than b-tree
                constraints[index]['type'] = Index.suffix
                cursor.execute(
                    "SELECT sql FROM sqlite_master "
                    "WHERE type='index' AND name=%s" % self.connection.ops.quote_name(index)
                )
                orders = []
                # There would be only 1 row to loop over
                for sql, in cursor.fetchall():
                    order_info = sql.split('(')[-1].split(')')[0].split(',')
                    orders = ['DESC' if info.endswith('DESC') else 'ASC' for info in order_info]
                constraints[index]['orders'] = orders
        # Get the PK
        pk_column = self.get_primary_key_column(cursor, table_name)
        if pk_column:
            # SQLite doesn't actually give a name to the PK constraint,
            # so we invent one. This is fine, as the SQLite backend never
            # deletes PK constraints by name, as you can't delete constraints
            # in SQLite; we remake the table with a new PK instead.
            constraints["__primary__"] = {
                "columns": [pk_column],
                "primary_key": True,
                "unique": False,  # It's not actually a unique constraint.
                "foreign_key": False,
                "check": False,
                "index": False,
            }
        # Get foreign keys
        cursor.execute('PRAGMA foreign_key_list(%s)' % self.connection.ops.quote_name(table_name))
        for row in cursor.fetchall():
            # Remaining on_update/on_delete/match values are of no interest here
            id_, seq, table, from_, to = row[:5]
            constraints['fk_%d' % id_] = {
                'columns': [from_],
                'primary_key': False,
                'unique': False,
                'foreign_key': (table, to),
                'check': False,
                'index': False,
            }
        return constraints