importScripts('https://cdn.jsdelivr.net/gh/golang/go@go1.15.7/misc/wasm/wasm_exec.js')

let nextHandlerId = 1
const handlerResolvers = {}
const handlers = []

self.wasmhttp = {
  registerHandler: (handlerId, handler) => {
    handlerResolvers[handlerId](handler)
    delete handlerResolvers[handlerId]
  },
}

function registerWasmHTTPListener(wasm, base, args = []) {
  let path = new URL(registration.scope).pathname
  if (base && base !== '') path = `${trimEnd(path, '/')}/${trimStart(base, '/')}`

  const wasmPromise = fetch(wasm).then(res => res.arrayBuffer())

  addEventListener('fetch', e => {
    const { pathname } = new URL(e.request.url)
    if (!pathname.startsWith(path)) return

    const handlerId = `${nextHandlerId++}`
    const handlerPromise = new Promise(resolve => handlerResolvers[handlerId] = resolve)

    const go = new Go()
    go.env = { WASMHTTP_HANDLER_ID: handlerId, WASMHTTP_PATH: path }
    go.argv = [wasm, ...args]
    // FIXME await ? catch ?
    wasmPromise
      .then(wasm => WebAssembly.instantiate(wasm, go.importObject))
      .then(({ instance }) => go.run(instance))

    e.respondWith(handlerPromise.then(handler => handler(e.request)))
  })
}

function trimStart(s, c) {
  let r = s
  while (r.startsWith(c)) r = r.slice(c.length)
  return r
}

function trimEnd(s, c) {
  let r = s
  while (r.endsWith(c)) r = r.slice(0, -c.length)
  return r
}