from datetime import datetime

LOCK_MODES = (
    'ACCESS SHARE',
    'ROW SHARE',
    'ROW EXCLUSIVE',
    'SHARE UPDATE EXCLUSIVE',
    'SHARE',
    'SHARE ROW EXCLUSIVE',
    'EXCLUSIVE',
    'ACCESS EXCLUSIVE',
)


def require_lock(model, lock):
    """
    Decorator for PostgreSQL's table-level lock functionality

    Example:
        @transaction.commit_on_success
        @require_lock(MyModel, 'ACCESS EXCLUSIVE')
        def myview(request)
            ...

    PostgreSQL's LOCK Documentation:
    http://www.postgresql.org/docs/8.3/interactive/sql-lock.html
    """

    def require_lock_decorator(view_func):
        def wrapper(*args, **kwargs):
            if lock not in LOCK_MODES:
                raise ValueError('%s is not a PostgreSQL supported lock mode.')
            from django.db import connection
            cursor = connection.cursor()
            cursor.execute(
                'LOCK TABLE %s IN %s MODE' % (model._meta.db_table, lock)
            )
            return view_func(*args, **kwargs)

        return wrapper

    return require_lock_decorator


class InvalidResponseError(Exception):
    """Used for all responses other than HTTP 200"""
    pass


def get_key(data, keys: list):
    try:
        val = data[keys.pop(0)]
        while keys:
            val = val[keys.pop(0)]
        return val
    except KeyError:
        return ''


def validate_int(integer):
    return integer if (isinstance(integer, int) and 0 <= integer < 2147483647) else None


def log(text):
    return "{} - {}".format(datetime.now().isoformat(), text)