/**
* Constants
*/

const proxy = HttpProxy.createProxyServer()

let eventRegistered = false

/**
* Koa Http Proxy Middleware
*/
export const httpProxy = (urlPattern, options?) => (ctx, next) => {

if (!mathPath(urlPattern, ctx.req.url)) return next()
let opts = Object.assign({}, options)
if (typeof options === 'function') {
const { params, path } = mathPath(urlPattern, ctx.req.url)
opts = options.call(options, params)
}
// object-rest-spread is still in stage-3
// https://github.com/tc39/proposal-object-rest-spread
const { logs, rewrite, events } = opts

const httpProxyOpts = Object.keys(opts)
.filter(n => ['logs', 'rewrite', 'events'].indexOf(n) < 0)
.reduce((prev, cur) => {
prev[cur] = opts[cur]
return prev
}, {})

return new Promise((resolve, reject) => {
ctx.req.oldPath = ctx.req.url

if (typeof rewrite === 'function') {
ctx.req.url = rewrite(ctx.req.url)
}

if (logs) logger(ctx, opts.target)

if (events && typeof events === 'object' && !eventRegistered) {
Object.entries(events).forEach(([event, handler]) => {
proxy.on(event, handler)
})
eventRegistered = true
}

proxy.web(ctx.req, ctx.res, httpProxyOpts, e => {
const status = {
ECONNREFUSED: 503,
ETIMEOUT: 504
}[e.code]
if (status) ctx.status = status
resolve()
})
})
}

function logger(ctx, target) {
console.log('%s - %s %s proxy to -> %s', new Date().toISOString(), ctx.req.method, ctx.req.oldPath, url.resolve(target, ctx.req.url))
}