#!/usr/bin/env python

# -*- coding: utf-8 -*-

"""

Command 模式

通过将请求封装为一个对象，解耦请求发送者和接受者，

这种方式可以对请求排队，日志等功能进行支持，同时，

由于请求作为一个独立的对象，支持undo和redo操作

"""

class Document(object):

def __init__(self, filename):

self._contents = []

self._filename = filename

@staticmethod

def open(filename):

print 'Open file {}'.format(filename)

return Document(filename)

def add(self, message):

print 'Add message : {}'.format(message)

self._contents.append(message)

def save(self):

print "Save file '{0}': {1}...".format(self._filename, self._contents[:1])

class CommandMixin(object):

def execute(self):

raise NotImplementedError

class OpenCommand(CommandMixin):

def __init__(self, filename):

self._filename = filename

def execute(self):

return Document.open(self._filename)

class SaveCommand(CommandMixin):

def __init__(self, document):

self._document = document

def execute(self):

self._document.save()

class AddCommand(CommandMixin):

def __init__(self, document, message):

self._document = document

self._message = message

def execute(self):

self._document.add(self._message)

class CommandHandler(object):

def __init__(self):

self._commands = []

def add_command(self, command):

self._commands.append(command)

def flush(self):

# 这里可以加入队列功能

for command in self._commands:

command.execute()

def non_command_use_case():

# 打开文档

document = Document.open('demo.txt')

# 写入文档

document.add('This is the first line')

# 保存文档

document.save()

def command_user_case():

handler = CommandHandler()

# 打开文档

document = OpenCommand('demo.txt').execute()

handler.add_command(AddCommand(document, 'This is the first line'))

handler.add_command(SaveCommand(document))

handler.flush()

if __name__ == '__main__':

non_command_use_case()

command_user_case()