import re
import sqlparse
from sqlparse.sql import IdentifierList, Identifier, Function
from sqlparse.tokens import Keyword, DML, Punctuation

cleanup_regex = {
        # This matches only alphanumerics and underscores.
        'alphanum_underscore': re.compile(r'(\w+)$'),
        # This matches everything except spaces, parens and comma.
        'most_punctuations': re.compile(r'([^\.(),\s]+)$'),
        # This matches everything except a space.
        'all_punctuations': re.compile('([^\s]+)$'),
        }

def last_word(text, include='alphanum_underscore'):
    """
    Find the last word in a sentence.

    >>> last_word('abc')
    'abc'
    >>> last_word(' abc')
    'abc'
    >>> last_word('')
    ''
    >>> last_word(' ')
    ''
    >>> last_word('abc ')
    ''
    >>> last_word('abc def')
    'def'
    >>> last_word('abc def ')
    ''
    >>> last_word('abc def;')
    ''
    >>> last_word('bac $def')
    'def'
    >>> last_word('bac $def', True)
    '$def'
    >>> last_word('bac \def', True)
    '\\\\def'
    >>> last_word('bac \def;', True)
    '\\\\def;'
    """

    if not text:   # Empty string
        return ''

    if text[-1].isspace():
        return ''
    else:
        regex = cleanup_regex[include]
        matches = regex.search(text)
        if matches:
            return matches.group(0)
        else:
            return ''


# This code is borrowed from sqlparse example script.
# <url>
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() in ('SELECT', 'INSERT',
                'UPDATE', 'CREATE', 'DELETE'):
            return True
    return False

def extract_from_part(parsed, stop_at_punctuation=True):
    tbl_prefix_seen = False
    for item in parsed.tokens:
        if tbl_prefix_seen:
            if is_subselect(item):
                for x in extract_from_part(item, stop_at_punctuation):
                    yield x
            elif stop_at_punctuation and item.ttype is Punctuation:
                raise StopIteration
            # An incomplete nested select won't be recognized correctly as a
            # sub-select. eg: 'SELECT * FROM (SELECT id FROM user'. This causes
            # the second FROM to trigger this elif condition resulting in a
            # StopIteration. So we need to ignore the keyword if the keyword
            # FROM.
            # Also 'SELECT * FROM abc JOIN def' will trigger this elif
            # condition. So we need to ignore the keyword JOIN.
            elif item.ttype is Keyword and item.value.upper() not in ('FROM', 'JOIN'):
                raise StopIteration
            else:
                yield item
        elif ((item.ttype is Keyword or item.ttype is Keyword.DML) and
                item.value.upper() in ('FROM', 'INTO', 'UPDATE', 'TABLE', 'JOIN',)):
            tbl_prefix_seen = True
        # 'SELECT a, FROM abc' will detect FROM as part of the column list.
        # So this check here is necessary.
        elif isinstance(item, IdentifierList):
            for identifier in item.get_identifiers():
                if (identifier.ttype is Keyword and
                        identifier.value.upper() == 'FROM'):
                    tbl_prefix_seen = True
                    break

def extract_table_identifiers(token_stream):
    for item in token_stream:
        if isinstance(item, IdentifierList):
            for identifier in item.get_identifiers():
                # Sometimes Keywords (such as FROM ) are classified as
                # identifiers which don't have the get_real_name() method.
                try:
                    real_name = identifier.get_real_name()
                except AttributeError:
                    continue
                if real_name:
                    yield (real_name, identifier.get_alias() or real_name)
        elif isinstance(item, Identifier):
            real_name = item.get_real_name()
            if real_name:
                yield (real_name, item.get_alias() or real_name)
        elif isinstance(item, Function):
            yield (item.get_name(), item.get_name())

# extract_tables is inspired from examples in the sqlparse lib.
def extract_tables(sql, include_alias=False):
    """Extract the table names from an SQL statment.

    Returns a list of table names if include_alias=False (default).
    If include_alias=True, then a dictionary is returned where the keys are
    aliases and values are real table names.

    """
    parsed = sqlparse.parse(sql)
    if not parsed:
        return []
    # INSERT statements must stop looking for tables at the sign of first
    # Punctuation. eg: INSERT INTO abc (col1, col2) VALUES (1, 2)
    # abc is the table name, but if we don't stop at the first lparen, then
    # we'll identify abc, col1 and col2 as table names.
    insert_stmt = parsed[0].token_first().value.lower() == 'insert'
    stream = extract_from_part(parsed[0], stop_at_punctuation=insert_stmt)
    if include_alias:
        return dict((alias, t) for t, alias in extract_table_identifiers(stream))
    else:
        return [x[0] for x in extract_table_identifiers(stream)]

def find_prev_keyword(sql):
    if not sql.strip():
        return None

    for t in reversed(list(sqlparse.parse(sql)[0].flatten())):
        if t.is_keyword or t.value == '(':
            return t.value

if __name__ == '__main__':
    sql = 'select * from (select t. from tabl t'
    print extract_tables(sql, True)