(function () {
  const Tracker = function () {
    let sessionId = null
    let sentOnLeave = false

    this.getSrc = function () {
      const checker = document.getElementById('acChecker')
      if (checker) {
        // Cleanup pixel tag, some sites rewrite it causing broken display
        checker.style.display = 'none'
        checker.src = ''
        return checker.getAttribute('data-src')
      }

      // Fallback to get src from noscript pixel tag
      const noscriptElems = document.getElementsByTagName('noscript')
      for (const elem of noscriptElems) {
        // <noscript> content is not available via DOM, access as text
        const html = elem.textContent || elem.innerHTML
        if (!html) {
          console.error('There is no noscript (pixel) on the page')
        }
        if (html.trim().startsWith('<img')) {
          return html.split('"')[1]
        }
      }
    }

    this.getUrlParams = function () {
      // parse pixel data in order to check a correct pixel
      const params = this.src.split('?')[1]
      const pixelData = params ? params.split('&')
        .reduce((acc, elem) => {
          const parsed = elem.split('=');
          return Object.assign(acc, { [parsed[0]]: parsed[1] })
        }, {}) : []
      const elems = this.src.split('/')
      return {
        scheme: elems[0].concat('//'),
        host: elems[2],
        queryParams: pixelData,
        id: elems[4],
      }
    }

    // async XHR for regular requests
    this.sendReq = function (method, url, data, cb) {
      const request = new XMLHttpRequest()
      if (cb) request.addEventListener('load', cb)
      request.open(method, url, true) // async
      request.setRequestHeader('Content-Type', 'application/json')
      request.send(JSON.stringify(data))
      return request
    }

    this.handlePixelResp = function () {
      if (this.status === 200) {
        try {
          sessionId = JSON.parse(this.responseText).session_id
        } catch (e) {
          console.error('Bad JSON in pixel response', e)
        }
      } else {
        console.error('Cannot handle request response', this.status)
      }
    }

    this.handlePixel = function () {
      this.src = this.getSrc()
      if (!this.src) return

      const urlData = this.getUrlParams()
      const url = [urlData.scheme, urlData.host, '/api/pixels/calculate_pixel/'].join('')

      // request body
      let location
      try {
        // if we get any browser's restriction exception just get the current window loc href
        location = window.parent.location.href
      } catch (e) {
        location = window.location.href
      }

      const data = {
        source_url: location,
        referrer_url: document.referrer,
        id: urlData.id,
      }

      this.sendReq('POST', url, data, this.handlePixelResp)
    }

    // last gasp
    this.sendOnLeave = function (url, data) {
      const body = JSON.stringify(data)

      // sendBeacon
      if (navigator.sendBeacon) {
        const blob = new Blob([body], { type: 'text/plain;charset=UTF-8' })
        return navigator.sendBeacon(url, blob)
      }

      // Fallback
      if (window.fetch) {
        fetch(url, {
          method: 'POST',
          body,
          keepalive: true,
          credentials: 'omit',
          headers: { 'Content-Type': 'text/plain;charset=UTF-8' },
        }).catch(() => {})
        return true
      }

      return false
    }

    this.checkTimeOnPage = function () {
      if (!sessionId) return
      if (!this.src) return

      if (sentOnLeave) return
      sentOnLeave = true

      const urlData = this.getUrlParams()
      const url = [urlData.scheme, urlData.host, '/api/change_session_data/'].join('')

      const payload = { session_id: sessionId }

      this.sendOnLeave(url, payload)
    }

    this.run = function () {
      window.addEventListener('load', () => this.handlePixel())

      // Main leaving handler
      window.addEventListener('pagehide', () => {
        this.checkTimeOnPage()
      })

      // Additional check
      document.addEventListener('visibilitychange', () => {
        if (document.visibilityState === 'hidden') {
          this.checkTimeOnPage()
        }
      })

      // If the user get back/forward (bfcache), drop sentOnLeave
      window.addEventListener('pageshow', () => {
        sentOnLeave = false
      })
    }
  }

  const tracker = new Tracker()
  tracker.run()
})()