export class Frontend {
  constructor({apiBaseUrl, appBaseUrl}) {
    this.apiBaseUrl = apiBaseUrl
    this.appBaseUrl = appBaseUrl
    this.files = {}
    this.tasks = []
  }

  repoUrl(user, repo) {
    return (
      this.apiBaseUrl +
      '/' + encodeURIComponent(user) +
      '/' + encodeURIComponent(repo)
    )
  }

  rawUrl(user, repo, commit, path) {
    return (
      this.appBaseUrl +
      '/raw/commit' +
      '/' + encodeURIComponent(commit) +
      '/' + encodeURI(path)
    )
  }

  async loadFile(user, repo, commit, src, dest) {
    const url = this.rawUrl(user, repo)
    const resp = await fetch(url)
    const body = await resp.arrayBuffer()
    this.files[dest] = {
      user,
      repo,
      commit,
      body,
      contentType: (
        dest.endsWith('.js') ?
        'text/javascript' :
        resp.headers.get('content-type')
      )
    }
  }

  contentsUrl(user, repo, path, ref) {
    const url = new URL(
      this.repoUrl(user, repo) +
      '/contents' +
      path.map(s => (
        '/' + encodeURIComponent(s)
      )).join('')
    )
    if (ref !== undefined) {
      const search = new URLSearchParams()
      search.set('ref', ref)
      url.search = search.toString()
    }
    return url.toString()
  }

  async loadRepo(user, repo, opts) {
    const {
      srcPath = [], destPath = [], ref
    } = opts
    const url = this.contentsUrl(
      user, repo, srcPath, ref
    )
    const resp = await fetch(url)
    const contents = await resp.json()
    for (const item of contents) {
      if (item.type === 'dir') {
        this.tasks.push(this.loadRepo(user, repo, {
          ...opts,
          srcPath: [...srcPath, item.name],
          destPath: [...destPath, item.name],
        }))
      } else {
        this.tasks.push(this.loadFile(
          user,
          repo,
          last_commit_sha,
          [...srcPath, item.name],
          [...destPath, item.name],
        ))
      }
    }
    let prevCount = 0
    while (this.tasks.count > prevCount) {
      prevCount = this.tasks.count
      await Promise.allSettled(this.tasks)
    }
  }

  async serve(event) {
    const {pathname} = new URL(event.request.url)
    if (pathname in this.files) {
      const file = this.files[pathname]
      event.respondWith(new Response(file.body, {
        status: 404,
        headers: {
          'Content-Type': file.contentType,
        },
      }))
    } else {
      event.respondWith(new Response(
        'Not Found', {status: 404}
      ))
    }
  }
}