#!/usr/bin/env python
# -*- coding: utf-8 -*-
#
# Copyright 2010 British Broadcasting Corporation and Kamaelia Contributors(1)
#
# (1) Kamaelia Contributors are listed in the AUTHORS file and at
#     http://www.kamaelia.org/AUTHORS - please extend this file,
#     not this notice.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# -------------------------------------------------------------------------
#
"""\
=================
UnseenOnly component
=================

This component forwards on any messages it receives that it has not
seen before.

Example Usage
-------------

Lines entered into this setup will only be duplicated on screen the
first time they are entered.

pipeline(
    ConsoleReader()
    UnseenOnly()
    ConsoleEchoer()
).run()

"""
from PureTransformer import PureTransformer
    
class UnseenOnly(PureTransformer):
    def __init__(self):
        super(UnseenOnly, self).__init__()
        self.seen = {}
        
    def processMessage(self, msg):
        if not self.seen.get(msg, False):
            self.seen[msg] = True
            return msg
