中介者模式

• 定义：用一个中介对象来封装一系列的对象交互。中介者使各对象不需要显示地互相引用，从而使其耦合松散，而且可以独立地改变它们之间的交互

// 定义中介者
interface Mediator {
    notify(sender: object, event: string): void;
}
// 具体实现中介者
class ConcreteMediator implements Mediator {
    private component1: Component1;

    private component2: Component2;

    constructor(c1: Component1, c2: Component2) {
        this.component1 = c1;
        this.component1.setMediator(this);
        this.component2 = c2;
        this.component2.setMediator(this);
    }

    public notify(sender: object, event: string): void {
        if (event === 'A') {
            console.log('Mediator reacts on A and triggers following operations:');
            this.component2.doC();
        }

        if (event === 'D') {
            console.log('Mediator reacts on D and triggers following operations:');
            this.component1.doB();
            this.component2.doC();
        }
    }
}
// 定义基础组件类
class BaseComponent {
    protected mediator: Mediator;

    constructor(mediator?: Mediator) {
        this.mediator = mediator!;
    }

    public setMediator(mediator: Mediator): void {
        this.mediator = mediator;
    }
}
// 实现具体组件
class Component1 extends BaseComponent {
    public doA(): void {
        console.log('Component 1 does A.');
        this.mediator.notify(this, 'A');
    }

    public doB(): void {
        console.log('Component 1 does B.');
        this.mediator.notify(this, 'B');
    }
}

class Component2 extends BaseComponent {
    public doC(): void {
        console.log('Component 2 does C.');
        this.mediator.notify(this, 'C');
    }

    public doD(): void {
        console.log('Component 2 does D.');
        this.mediator.notify(this, 'D');
    }
}

// 使用
const c1 = new Component1();
const c2 = new Component2();
// 绑定组件中的中介者
const mediator = new ConcreteMediator(c1, c2);
// 组件分别触发中介者
console.log('Client triggers operation A.');
c1.doA();

console.log('');
console.log('Client triggers operation D.');
c2.doD();

• 缺点：中介者可能会演化为上帝对象