## 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/app1
##  http://127.0.0.1:3000/app1

const path = require('path');
const compose = require('./compose');

function mount(prefix, app) {
  let middleware = app.middleware;
  let middlewareStream = compose(middleware || []);
  if( prefix === '/' ) {
    return middlewareStream;
  }

  return async function( ctx, next ) {
    let mountPath = matchPath(ctx.path); 
    if( !mountPath ) {
      return await next();
    }

    let originPath = ctx.path;
    ctx.path = mountPath;

    await middlewareStream(ctx, async () => {
      ctx.path = originPath;
      await next();
      ctx.path = mountPath
    });

    ctx.path =  originPath;
  }

  function matchPath( originPath ) {
    if( originPath.indexOf(prefix) < 0 ) {
      return false;
    }
    const mountPath = originPath.replace(prefix, '') || '/';
    if( mountPath[0] !== '/' ) {
      return false;
    }
    return mountPath;
  }

}

module.exports = mount;

const mount = require('./index');
const Koa = require('koa');

const app1 = new Koa();
const app2 = new Koa();

app1.use(async (ctx, next) => {
  await next()
  ctx.body = 'app 1'
})


app2.use(async (ctx, next) => {
  await next()
  ctx.body = 'app 2'
})

const app = new Koa()

app.use(mount('/app1', app1))
app.use(mount('/app2', app2))

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