import sqlparse
from collections import namedtuple



"""
contextManager
"""


def split(s: str):
    """
    it is used to split SQL string to tuple.
    :param s: sql String
    :return: tuple
    """
    res = list(filter(lambda x: x != "" and x != ";", s.replace("\n", "").split(" ")))
    if len(res) == 0:
        return tuple()
    else:
        res[-1] = res[-1].rstrip(";")
        return tuple(map(lambda x: x.lower(), res))

def sqltuple2json(t: tuple):
    from_tag = "from"
    table_name = t[t.index(from_tag)+1] if from_tag in t else ""

    print(table_name)


SqlType = {
    "select": "select",
    "create": "create",
    "drop": "drop",
    "alter": "alter",
    "insert": "insert",
    "explain": "explain",
    "update": "update",
    "delete": "delete"
}


def get_sql_type(t: tuple):
    return SqlType[t[0]]


def get_collection(t: tuple):
    sql_type = get_sql_type(t)
    if sql_type is "select":
        from_tag = "from"
        return t[t.index(from_tag) + 1] if from_tag in t else ""





class Parse:

    __slots__ = ()

    @staticmethod
    def parse(t: tuple):
        sql_type = get_sql_type(t)
        if sql_type is "select":
            table_name = t[t.index("from") + 1] if "from" in t else ""
            if not table_name:
                raise SQLMongoException("collection is empty")
            condition = t[t.index("where") + 1:] if "where" in t else ""
            columns = Parse._get_columns(t[t.index("select") + 1:t.index("from")])
            if not condition:
                if columns == ("*",):
                    return {}
                else:
                    res = list(map(lambda x: (x, 1), columns))
                    if "id" in columns:
                        res.append(("_id", 0))
                    return dict(res)

    @staticmethod
    def _get_columns(t: tuple)->tuple:
        return tuple(map(lambda x: x.strip(","), filter(lambda x: x != ",", t)))


class SQLMongoException(Exception):
    pass


if __name__ == '__main__':
    r = split(b)
    s = sqlparse.format(b)
    print("---",s)
    parsed = Parse.parse(r)
    print(parsed)