PHP 中介者模式

用一个中介对象封装一系列的对象交互，中介者使各对象不需要显示地相互作用，从而使其耦合松散，并且可以独立地改变它们指间的交互。

• 中介者模式的组成

  1. Mediator抽象中介者角色：抽象中介者角色定义统一的接口，用于各同事角色之间的通信。
  2. Concrete Mediator具体中介者角色：具体中介者角色通过协调各同事角色实现协作行为，因此它必须依赖于各个同事角色。
  3. Colleague同事角色：每一个同事角色都知道中介者角色，而且与其他的同事角色通信的时候，一定要通过中介者角色协作。每个同事类的行为分为两种：一种是同事本身的行为，比如改变对象本身的状态，处理自己的行为等，这种方法叫做自发行为（Self-Method），与其他的同事类或中介者

• 中介者模式的优点：

减少类间的依赖，把原有的一对多的依赖变成了一对一的依赖，同事类只依赖中介者，减少了依赖，同时降低了类间的耦合。

• 中介者模式的缺点：

中介者会膨胀得很大，而且逻辑复杂，原本N个对象直接的相互依赖关系转换为中介者和同事类的依赖关系，同事类越多，中介者的逻辑就越复杂。

• 使用场景：

中介者模式适用于多个对象之间紧密耦合的情况，紧密耦合的标准是：在类图中出现了蜘蛛网状结构。在这种情况下一定要考虑使用中介者模式，这有利于把蜘蛛网梳理为星型结构，使原本复杂混乱的关系变得清晰简单。

<?php
namespace pattern\mediator;
/**
 * 中介者模式
 * Mediator（抽象中介者）、Concrete Mediator（具体中介者）、Colleague（同事）
 */
abstract class AbstractMediator {
    public abstract function inviteRegistor(AbstractColleague $introductor, $username);
}
final class ConcreteMediator extends AbstractMediator {
    public function inviteRegistor(AbstractColleague $introductor, $username) {
        $parent = $introductor->getParentColleague();
        if ($this->ifColleagueHasParent($introductor)) {
            $this->inviteRegistor($parent, $username);
        }
        return $parent->getId();
    }
    private function ifColleagueHasParent(AbstractColleague $colleague) {
        if ($colleague instanceof  Admin) {
            return false;
        } else {
            return true;
        }
    }
}

abstract class AbstractColleague {
    protected $_mediator = null;
    protected $_id;
    public function __construct(AbstractMediator $mediator) {
        $this->_mediator = $mediator;
    }
    public abstract function publishNews();
    public abstract function userRegistor($username);
    public abstract function getParentColleague();
    public abstract function getId();
}
final class Admin extends AbstractColleague {
    public function __construct(AbstractMediator $mediator) {
        parent::__construct($mediator);
        $this->_id = 1000;
    }
    public function publishNews() {
        echo $this->_id . ' published a news' . PHP_EOL;
    }
    public function userRegistor($username) {
        echo $username . ' registor after get ' . $this->_id . '\'s news' . PHP_EOL;
        $adminId = $this->_mediator->inviteRegistor($this, $username);
        echo 'Admin::admin ' . $adminId . ' received ' . $username . ' registration from member ' . $this->_id . PHP_EOL;
    }
    public function getParentColleague() {
        return $this;
    }
    public function getId() {
        return $this->_id;
    }
}
final class Member extends AbstractColleague {
    public function __construct(AbstractMediator $mediator) {
        parent::__construct($mediator);
        $this->_id = rand(1001, 9999);
    }
    public function userRegistor($username) {
        echo $username . ' registor after get ' . $this->_id . '\'s news' . PHP_EOL;
        $adminId = $this->_mediator->inviteRegistor($this, $username);
        echo 'Member::admin ' . $adminId . ' received ' . $username . ' registration from member ' . $this->_id . PHP_EOL;
    }
    public function publishNews() {
        echo $this->_id . ' published a news' . PHP_EOL;
    }
    public function getParentColleague() {
        return new Admin($this->_mediator);
    }
    public function getId() {
        return $this->_id;
    }
}
final class SubMember extends AbstractColleague {
    public function __construct(AbstractMediator $mediator) {
        parent::__construct($mediator);
        $this->_id = rand(10001, 99999);
    }
    public function userRegistor($username) {
        echo $username . ' registor after get ' . $this->_id . '\'s news' . PHP_EOL;
        $adminId = $this->_mediator->inviteRegistor($this, $username);
        echo 'SubMember::admin ' . $adminId . ' received ' . $username . ' registration from member ' . $this->_id . PHP_EOL;
    }
    public function publishNews() {
        echo $this->_id . ' published a news' . PHP_EOL;
    }
    public function getParentColleague() {
        return new Admin($this->_mediator);
    }
    public function getId() {
        return $this->_id;
    }
}

$mediator = new ConcreteMediator();
$admin = new Admin($mediator);
$member = new Member($mediator);
$submember = new SubMember($mediator);

$admin->publishNews();
$admin->userRegistor('lili');

$member->publishNews();
$member->userRegistor('john');

$submember->publishNews();
$submember->userRegistor('rotina');