<?php

class Invoker
{
 private $command = [];

 public function setCommand(Command $command)
 {
 $this->command[] = $command;
 }

 public function exec()
 {
 if(count($this->command) > 0){
 foreach ($this->command as $command) {
 $command->execute();
 }
 }
 }

 public function undo()
 {
 if(count($this->command) > 0){
 foreach ($this->command as $command) {
 $command->undo();
 }
 }
 }
}

abstract class Command
{
 protected $receiver;
 protected $state;
 protected $name;

 public function __construct(Receiver $receiver, $name)
 {
 $this->receiver = $receiver;
 $this->name = $name;
 }

 abstract public function execute();
}

class ConcreteCommand extends Command
{
 public function execute()
 {
 if (!$this->state || $this->state == 2) {
 $this->receiver->action();
 $this->state = 1;
 } else {
 echo $this->name . '命令正在执行,无法再次执行了!', PHP_EOL;
 }

 }

 public function undo()
 {
 if ($this->state == 1) {
 $this->receiver->undo();
 $this->state = 2;
 } else {
 echo $this->name . '命令未执行,无法撤销了!', PHP_EOL;
 }
 }
}

class Receiver
{
 public $name;
 public function __construct($name)
 {
 $this->name = $name;
 }
 public function action()
 {
 echo $this->name . '命令执行了!', PHP_EOL;
 }
 public function undo()
 {
 echo $this->name . '命令撤销了!', PHP_EOL;
 }
}

// 准备执行者
$receiverA = new Receiver('A');
$receiverB = new Receiver('B');
$receiverC = new Receiver('C');

// 准备命令
$commandOne = new ConcreteCommand($receiverA, 'A');
$commandTwo = new ConcreteCommand($receiverB, 'B');
$commandThree = new ConcreteCommand($receiverC, 'C');

// 请求者
$invoker = new Invoker();
$invoker->setCommand($commandOne);
$invoker->setCommand($commandTwo);
$invoker->setCommand($commandThree);
$invoker->exec();
$invoker->undo();

// 新加一个单独的执行者,只执行一个命令
$invokerA = new Invoker();
$invokerA->setCommand($commandOne);
$invokerA->exec();

// 命令A已经执行了,再次执行全部的命令执行者,A命令的state判断无法生效
$invoker->exec();