/**
 * helpers.js
 *
 * Additional state-less helper methods.
 */

/**
 * Makes a AJAX request, streaming each line as it arrives. Type should be text/plain,
 * each line will be interpreted as JSON separately.
 *
 * @param path The path to connect to.
 * @param callback A callback with a JSON payload. Called for every line as it comes.
 * @param successCallback A callback with a raw text payload.
 * @param failCallback A fail callback. Optional.
 * @param data POST data. Optional.
 */
export function stream_ajax (path, callback, successCallback, failCallback, data) {
  const req = new XMLHttpRequest()

  console.log('Making streaming HTTP request to ' + path)

  req.addEventListener('load', function () {
    // The server can sometimes return a string error. Make sure we handle this.
    if (this.status === 200) {
      successCallback(this.responseText)
    } else {
      failCallback(this.responseText)
    }
  })

  let buffer = ''
  let seenBytes = 0

  req.onreadystatechange = function () {
    if (req.readyState > 2) {
      buffer += req.responseText.substr(seenBytes)

      let pointer
      while ((pointer = buffer.indexOf('\n')) >= 0) {
        const line = buffer.substring(0, pointer).trim()
        buffer = buffer.substring(pointer + 1)

        if (line.length === 0) {
          continue
        }

        const contents = JSON.parse(line)
        callback(contents)
      }

      seenBytes = req.responseText.length
    }
  }

  req.addEventListener('error', failCallback)

  req.open(data == null ? 'GET' : 'POST', path + '?nocache=' + Date.now(), true)
  // Rocket only currently supports URL encoded forms.
  req.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded')

  if (data != null) {
    let form = ''

    for (const key in data) {
      if (!data[key]) {
        continue
      }

      if (form !== '') {
        form += '&'
      }

      form += encodeURIComponent(key) + '=' + encodeURIComponent(data[key])
    }

    req.send(form)
  } else {
    req.send()
  }
}