# -*- coding: utf8 -*-

from sys import stdout as console

# Handling 'exit' command

class SessionClosed(Exception):

def __init__(self, value):

self.value = value

# Interface

class Command:

def execute(self):

raise NotImplementedError()

def cancel(self):

raise NotImplementedError()

def name():

raise NotImplementedError()

# rm command

class RmCommand(Command):

def execute(self):

console.write("You are executed \"rm\" command\n")

def cancel(self):

console.write("You are canceled \"rm\" command\n")

def name(self):

return "rm"

# uptime command

class UptimeCommand(Command):

def execute(self):

console.write("You are executed \"uptime\" command\n")

def cancel(self):

console.write("You are canceled \"uptime\" command\n")

def name(self):

return "uptime"

# undo command

class UndoCommand(Command):

def execute(self):

try:

cmd = HISTORY.pop()

TRASH.append(cmd)

console.write("Undo command \"{0}\"\n".format(cmd.name()))

cmd.cancel()

except IndexError:

console.write("ERROR: HISTORY is empty\n")

def name(self):

return "undo"

# redo command

class RedoCommand(Command):

def execute(self):

try:

cmd = TRASH.pop()

HISTORY.append(cmd)

console.write("Redo command \"{0}\"\n".format(cmd.name()))

cmd.execute()

except IndexError:

console.write("ERROR: TRASH is empty\n")

def name(self):

return "redo"

# history command

class HistoryCommand(Command):

def execute(self):

i = 0

for cmd in HISTORY:

console.write("{0}: {1}\n".format(i, cmd.name()))

i = i + 1

def name(self):

print "history"

# exit command

class ExitCommand(Command):

def execute(self):

raise SessionClosed("Good bay!")

def name(self):

return "exit"

# available commands

COMMANDS = {'rm': RmCommand(), 'uptime': UptimeCommand(), 'undo':

UndoCommand(), 'redo': RedoCommand(), 'history': HistoryCommand(),

'exit': ExitCommand()}

HISTORY = list()

TRASH = list()

# Shell

def main():

try:

while True:

console.flush()

console.write("pysh >> ")

cmd = raw_input()

try:

command = COMMANDS[cmd]

command.execute()

if (not isinstance(command, UndoCommand) and not

isinstance(command, RedoCommand) and not

isinstance(command, HistoryCommand)):

TRASH = list()

HISTORY.append(command)

except KeyError:

console.write("ERROR: Command \"%s\" not found\n" % cmd)

except SessionClosed as e:

console.write(e.value)

if __name__ == "__main__":

main()