# -*- coding: utf-8 -*-
# pylint: disable=C,R,W
from __future__ import absolute_import
from __future__ import division
from __future__ import print_function
from __future__ import unicode_literals

import logging

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

RESULT_OPERATIONS = {'UNION', 'INTERSECT', 'EXCEPT', 'SELECT'}
ON_KEYWORD = 'ON'
PRECEDES_TABLE_NAME = {'FROM', 'JOIN', 'DESC', 'DESCRIBE', 'WITH'}


class SupersetQuery(object):
    def __init__(self, sql_statement):
        self.sql = sql_statement
        self._table_names = set()
        self._alias_names = set()
        self._limit = None
        # TODO: multistatement support

        logging.info('Parsing with sqlparse statement {}'.format(self.sql))
        self._parsed = sqlparse.parse(self.sql)
        for statement in self._parsed:
            self.__extract_from_token(statement)
            self._limit = self._extract_limit_from_query(statement)
        self._table_names = self._table_names - self._alias_names

    @property
    def tables(self):
        return self._table_names

    @property
    def limit(self):
        return self._limit

    def is_select(self):
        return self._parsed[0].get_type() == 'SELECT'

    def is_explain(self):
        return self.sql.strip().upper().startswith('EXPLAIN')

    def is_readonly(self):
        """Pessimistic readonly, 100% sure statement won't mutate anything"""
        return self.is_select() or self.is_explain()

    def stripped(self):
        return self.sql.strip(' \t\n;')

    @staticmethod
    def __precedes_table_name(token_value):
        for keyword in PRECEDES_TABLE_NAME:
            if keyword in token_value:
                return True
        return False

    @staticmethod
    def __get_full_name(identifier):
        if len(identifier.tokens) > 1 and identifier.tokens[1].value == '.':
            return '{}.{}'.format(identifier.tokens[0].value,
                                  identifier.tokens[2].value)
        return identifier.get_real_name()

    @staticmethod
    def __is_result_operation(keyword):
        for operation in RESULT_OPERATIONS:
            if operation in keyword.upper():
                return True
        return False

    @staticmethod
    def __is_identifier(token):
        return isinstance(token, (IdentifierList, Identifier))

    def __process_identifier(self, identifier):
        # exclude subselects
        if '(' not in '{}'.format(identifier):
            self._table_names.add(self.__get_full_name(identifier))
            return

        # store aliases
        if hasattr(identifier, 'get_alias'):
            self._alias_names.add(identifier.get_alias())
        if hasattr(identifier, 'tokens'):
            # some aliases are not parsed properly
            if identifier.tokens[0].ttype == Name:
                self._alias_names.add(identifier.tokens[0].value)
        self.__extract_from_token(identifier)

    def as_create_table(self, table_name, overwrite=False):
        """Reformats the query into the create table as query.

        Works only for the single select SQL statements, in all other cases
        the sql query is not modified.
        :param superset_query: string, sql query that will be executed
        :param table_name: string, will contain the results of the
            query execution
        :param overwrite, boolean, table table_name will be dropped if true
        :return: string, create table as query
        """
        exec_sql = ''
        sql = self.stripped()
        if overwrite:
            exec_sql = 'DROP TABLE IF EXISTS {table_name};\n'
        exec_sql += 'CREATE TABLE {table_name} AS \n{sql}'
        return exec_sql.format(**locals())

    def __extract_from_token(self, token):
        if not hasattr(token, 'tokens'):
            return

        table_name_preceding_token = False

        for item in token.tokens:
            if item.is_group and not self.__is_identifier(item):
                self.__extract_from_token(item)

            if item.ttype in Keyword:
                if self.__precedes_table_name(item.value.upper()):
                    table_name_preceding_token = True
                    continue

            if not table_name_preceding_token:
                continue

            if item.ttype in Keyword or item.value == ',':
                if (self.__is_result_operation(item.value) or
                        item.value.upper() == ON_KEYWORD):
                    table_name_preceding_token = False
                    continue
                # FROM clause is over
                break

            if isinstance(item, Identifier):
                self.__process_identifier(item)

            if isinstance(item, IdentifierList):
                for token in item.tokens:
                    if self.__is_identifier(token):
                        self.__process_identifier(token)

    def _get_limit_from_token(self, token):
        if token.ttype == sqlparse.tokens.Literal.Number.Integer:
            return int(token.value)
        elif token.is_group:
            return int(token.get_token_at_offset(1).value)

    def _extract_limit_from_query(self, statement):
        limit_token = None
        for pos, item in enumerate(statement.tokens):
            if item.ttype in Keyword and item.value.lower() == 'limit':
                limit_token = statement.tokens[pos + 2]
                return self._get_limit_from_token(limit_token)

    def get_query_with_new_limit(self, new_limit):
        """returns the query with the specified limit"""
        """does not change the underlying query"""
        if not self._limit:
            return self.sql + ' LIMIT ' + str(new_limit)
        limit_pos = None
        tokens = self._parsed[0].tokens
        # Add all items to before_str until there is a limit
        for pos, item in enumerate(tokens):
            if item.ttype in Keyword and item.value.lower() == 'limit':
                limit_pos = pos
                break
        limit = tokens[limit_pos + 2]
        if limit.ttype == sqlparse.tokens.Literal.Number.Integer:
            tokens[limit_pos + 2].value = new_limit
        elif limit.is_group:
            tokens[limit_pos + 2].value = (
                '{}, {}'.format(next(limit.get_identifiers()), new_limit)
            )

        str_res = ''
        for i in tokens:
            str_res += str(i.value)
        return str_res