#!/usr/bin/env python
# -*- coding: utf-8 -*-
#
# Copyright (C) 2016 Andi Albrecht, albrecht.andi@gmail.com
#
# This example is part of python-sqlparse and is released under
# the BSD License: http://www.opensource.org/licenses/bsd-license.php
#
# This example illustrates how to extract table names from nested
# SELECT statements.
#
# See:
# http://groups.google.com/group/sqlparse/browse_thread/thread/b0bd9a022e9d4895

import sqlparse
from sqlparse.sql import IdentifierList, Identifier
from sqlparse.tokens import Keyword, DML


def is_subselect(parsed):
    if not parsed.is_group():
        return False
    for item in parsed.tokens:
        if item.ttype is DML and item.value.upper() == 'SELECT':
            return True
    return False


def extract_from_part(parsed):
    from_seen = False
    for item in parsed.tokens:
        if from_seen:
            if is_subselect(item):
                for x in extract_from_part(item):
                    yield x
            elif item.ttype is Keyword:
                raise StopIteration
            else:
                yield item
        elif item.ttype is Keyword and item.value.upper() == 'FROM':
            from_seen = True


def extract_table_identifiers(token_stream):
    for item in token_stream:
        if isinstance(item, IdentifierList):
            for identifier in item.get_identifiers():
                yield identifier.get_name()
        elif isinstance(item, Identifier):
            yield item.get_name()
        # It's a bug to check for Keyword here, but in the example
        # above some tables names are identified as keywords...
        elif item.ttype is Keyword:
            yield item.value


# TODO(bkyryliuk): add logic to support joins and unions.
def extract_tables(sql):
    stream = extract_from_part(sqlparse.parse(sql)[0])
    return list(extract_table_identifiers(stream))