rss-viewer-browser-extension/src/main.ts

import browser from 'webextension-polyfill';

const parseItemImage = (item: Element) => {
  const images =
    Array.from(item.getElementsByTagName('media:content'))
      .filter((content) =>
        (content.getAttribute('type') || '').startsWith('image/') ||
         content.getAttribute('medium') === 'image'
       )

  if (!images.length)
    return

  const { url } = images.reduce((maxImage, content) => {
      const width = parseFloat(content.getAttribute('width') || '0')
      if (width > maxImage.width) {
        maxImage.url = content.getAttribute('url') || ''
        maxImage.width = width
      }

      return maxImage
    }, {
      width: parseFloat(images[0].getAttribute('width') || '0'),
      url: images[0].getAttribute('url'),
    })

    return {
      url: url
    }
}

const pubDateToInterval = (item: Element) => {
  const dateStr = getNodeContent(item, 'pubDate')
  if (!dateStr?.length)
    return

  // @ts-ignore
  let interval = ((new Date()) - (new Date(dateStr))) / 1000
  let unit = 'seconds'

  if (interval >= 60) {
    interval /= 60
    unit = 'minutes'
  }

  if (unit == 'minutes' && interval >= 60) {
    interval /= 60
    unit = 'hours'
  }

  if (unit == 'hours' && interval >= 24) {
    interval /= 24
    unit = 'days'
  }

  if (unit == 'days' && interval >= 30) {
    interval /= 30
    unit = 'months'
  }

  return `${interval.toFixed(0)} ${unit}`
}

const getNodeContent = (parent: Element, tagName: string) =>
  // @ts-ignore
  parent.getElementsByTagName(tagName)[0]?.firstChild?.wholeText

const parseFeed = (channel: Element) => {
  const imageElement = channel.getElementsByTagName('image')[0]
  const itemTime = (item: {pubDate: string}) => {
    const dateStr = item.pubDate
    if (!dateStr?.length)
      return 0
    return (new Date(dateStr)).getTime()
  }

  return {
    feedData: {
      title: getNodeContent(channel, 'title'),
      description: getNodeContent(channel, 'description'),
      feedUrl: window.location.href,
      homeUrl: getNodeContent(channel, 'link'),
      image: imageElement ? {
        title: getNodeContent(imageElement, 'title'),
        imageUrl: getNodeContent(imageElement, 'url'),
        targetUrl: getNodeContent(imageElement, 'link'),
      } : null,

      items: Array.from(channel.getElementsByTagName('item')).map((item) => {
        return {
          title: getNodeContent(item, 'title'),
          description: getNodeContent(item, 'description'),
          url: getNodeContent(item, 'link'),
          image: parseItemImage(item),
          pubDate: getNodeContent(item, 'pubDate'),
          age: pubDateToInterval(item),
          categories: Array.from(item.getElementsByTagName('category')).map((cat) =>
            cat.firstChild?.textContent
          ),
        }
      }).sort((a, b) => itemTime(b) - itemTime(a))
    }
  }
}

const getFeedRoot = () => {
  const xmlDoc = document.documentElement
  if (xmlDoc.tagName === 'rss')
    return xmlDoc

  // Chrome-based browsers may wrap the XML into an HTML view
  const webkitSource = document.getElementById('webkit-xml-viewer-source-xml')
  if (webkitSource)
    return webkitSource

  // For some ugly reasons, some RSS feeds are rendered inside of a <pre> in a normal HTML DOM
  const preElements = document.getElementsByTagName('pre')
  if (preElements.length !== 1)
    return

  const text = preElements[0].innerText
  const parser = new DOMParser()
  let innerXmlDoc = null

  try {
    // @ts-ignore
    innerXmlDoc = parser.parseFromString(text, 'text/xml')
  } catch (e) { }

  if (!innerXmlDoc)
    return

  // @ts-ignore
  const root = innerXmlDoc.documentElement
  if (root.tagName === 'rss')
    return root
}

browser.runtime.onMessage.addListener(async (message: {type: Object}) => {
  if (message.type !== 'renderFeed')
    return

  const xmlDoc = getFeedRoot()
  if (!xmlDoc)
    // Not an RSS feed
    return

  const channel = xmlDoc.getElementsByTagName('channel')[0]
  if (!channel)
    return

  browser.storage.local.set(parseFeed(channel))
  window.location.href = browser.runtime.getURL('viewer/index.html')
})