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

# This matches only alphanumerics and underscores.
_LAST_WORD_RE = re.compile(r'(\w+)$')
# This matches everything except a space.
_LAST_WORD_SPL_RE = re.compile(r'([^\s]+)$')

def last_word(text, include_special_chars=False):
    """
    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 = _LAST_WORD_SPL_RE if include_special_chars else _LAST_WORD_RE
        result = regex.findall(text)
        if result:
            return result[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):
    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() in ('FROM', 'INTO',
                'UPDATE', 'TABLE', ):
            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

def extract_tables(sql):
    stream = extract_from_part(sqlparse.parse(sql)[0])
    return list(extract_table_identifiers(stream))