from django.db.models import Func


def ToChar(expression, output):
    '''
    Custom query to convert timestamp to string.

    Example usage
    queryset.annotate(
        created_date_str=ToChar('created_date', 'DD/MM/YYYY HH25:MI')
        )
    '''

    class ToCharWithoutTZ(Func):
        function = "TO_CHAR"
        template = '%(function)s(%(expressions)s, \'{output}\')'.format(output=output)

    return ToCharWithoutTZ(expression)


def ToCharTZ(expression, timezone, output):
    '''
    Custom query to convert timestamp to string in requested time zone.

    Example usage
    queryset.annotate(
        created_date_str=ToCharTZ('created_date', 'GB', 'DD/MM/YYYY HH25:MI')
        )
    '''

    class ToCharWithTZ(Func):
        function = "TO_CHAR"
        template = '%(function)s(%(expressions)s AT TIME ZONE \'{timezone}\', \'{output}\')'.format(timezone=timezone,
                                                                                                    output=output)

    return ToCharWithTZ(expression)