## 安装依赖
npm i

## 执行 demo
npm run start

## 最后启动chrome浏览器访问
##  http://127.0.0.1:3000/index
##  http://127.0.0.1:3000/post
##  http://127.0.0.1:3000/list
##  http://127.0.0.1:3000/item

const methods = [
  'GET',
  'PUT',
  'PATCH',
  'POST',
  'DELETE'
];

class Layer {
  constructor(path, methods, middleware, opts) {
    this.path = path;
    this.methods = methods;
    this.middleware = middleware;
    this.opts = opts;
  }
}

class Router {
  constructor(opts = {}) {
    this.stack = [];
  }

  register(path, methods, middleware, opts) {
    let route = new Layer(path, methods, middleware, opts);
    this.stack.push(route);
    return this;
  }

  routes() {

    let stock = this.stack;
    return async function(ctx, next) {
      let currentPath = ctx.path;
      let route;

      for (let i = 0; i < stock.length; i++) {
        let item = stock[i];
        if (currentPath === item.path && item.methods.indexOf(ctx.method) >= 0) {
          route = item.middleware;
          break;
        }
      }

      if (typeof route === 'function') {
        route(ctx, next);
        return;
      }

      await next();
    };
  }
}

methods.forEach(method => {
  Router.prototype[method.toLowerCase()] = Router.prototype[method] = function(path, middleware) {
    this.register(path, [method], middleware);
  };
});

module.exports = Router;

const Koa = require('koa');
const Router = require('./index');
const app = new Koa();

// 初始化路由实例
const router = new Router();

// 注册路由请求信息缓存到实例中
router.get('/index', async ctx => { ctx.body = 'index page'; });
router.get('/post', async ctx => { ctx.body = 'post page'; });
router.get('/list', async ctx => { ctx.body = 'list page'; });
router.get('/item', async ctx => { ctx.body = 'item page'; });

// 路由实例输出父中间件 router.routes()
app.use(router.routes());

app.use(async ctx => {
  ctx.body = '404';
});

app.listen(3000);
console.log('listening on port 3000');