import Parser from 'rss-parser'
import { Feed } from 'feed'
import Handlebars from 'handlebars/runtime'
import template from './templates/default.precompiled'
import * as striptags from 'striptags'

/**
 * Extra Handlerbars template helpers
 */
Handlebars.registerHelper('isRowElemN', function(index, rowItems, n, options) {
  return index % rowItems == n ? options.fn(this) : options.inverse(this)
})

/**
 * Handle CRON jobs
 * Where information is gathered and HTML and RSS is generated.
 */
addEventListener('scheduled', event => {
  event.waitUntil(handleScheduled())
})

/**
 * Serve the existing generated elements.
 * CACHE is used to speed up the operation.
 */
addEventListener('fetch', event => {
  event.respondWith(handleRequest(event.request))
})

/**
 * Deliver aggregated content according to the formats requested
 * @param {Request} request
 * @returns Response
 */
async function handleRequest(request) {
  const cacheUrl = new URL(request.url)
  const cacheKey = new Request(cacheUrl.toString(), request)
  const cache = caches.default
  const cacheMaxAge = CACHE_MAX_AGE || 3600
  let response = await cache.match(cacheKey)
  if (response) return response

  const path = new URL(request.url).pathname

  if (path === '/') {
    let content = await WORKER_PLANET_STORE.get('html')
    response = new Response(content, {
      headers: {
        'content-type': 'text/html;charset=UTF-8',
        'Cache-Control': `max-age=${cacheMaxAge}`,
      },
    })
  } else if (path === '/rss') {
    let content = await WORKER_PLANET_STORE.get('rss')
    response = new Response(content, {
      headers: {
        'content-type': 'application/rss+xml',
        'Cache-Control': `max-age=${cacheMaxAge}`,
      },
    })
  } else if (path === '/atom') {
    let content = await WORKER_PLANET_STORE.get('atom')
    response = new Response(content, {
      headers: {
        'content-type': 'application/atom+xml',
        'Cache-Control': `max-age=${cacheMaxAge}`,
      },
    })
  } else {
    return new Response('', { status: 404 })
  }
  await cache.put(cacheKey, response.clone())
  return response
}

/**
 * Fetch all source feeds and generate the aggregated content
 */
async function handleScheduled() {
  let feeds = FEEDS.split(',')
  let content = []
  let sources = []

  let promises = []
  for (let url of feeds) {
    promises.push(fetchAndHydrate(url))
  }
  const results = await Promise.allSettled(promises)

  for (let [index, result] of results.entries()) {
    if (result.status == 'fulfilled') {
      let posts = result.value
      let title = posts[0].source_title
      let link = posts[0].source_link
      let name = title != '' ? title : new URL(link).host
      sources.push({ name, link })
      content.push(...posts)
    } else {
      console.log(`Failed to fetch ${feeds[index]}`)
      console.log(result.reason)
    }
  }

  //sort all the elements chronologically (recent first)
  content.sort((a, b) => {
    let aDate = new Date(a.isoDate)
    let bDate = new Date(b.isoDate)
    if (aDate < bDate) {
      return 1
    } else if (aDate === bDate) {
      return 0
    } else {
      return -1
    }
  })

  if (content.length > MAX_SIZE) {
    content = content.slice(0, MAX_SIZE)
  }

  // Generate feed
  let feed = createFeed(content)
  let html = createHTML(content, sources)
  // Store
  await WORKER_PLANET_STORE.put('rss', feed.rss2())
  await WORKER_PLANET_STORE.put('atom', feed.atom1())
  await WORKER_PLANET_STORE.put('html', html)
}

/**
 * Take a feed URL, fetch all items and attach source information
 * @param {String} feed The URL of the feed to be fetched and parsed
 * @returns Array containing all the feed items parsed by rss-parser
 */
async function fetchAndHydrate(feed) {
  console.log(`[fetchAndHydrate] start to fetch feed: ${feed}`)
  let resp = await fetch(feed)
  console.log(`[fetchAndHydrate] response: ${resp.status}`)
  let parser = new Parser()
  let content = await resp.text()
  let contentFeed = await parser.parseString(content)

  for (let item of contentFeed.items) {
    item.source_title = contentFeed.title
    item.source_link = contentFeed.link
    if ('content:encoded' in item) {
      item.content = item['content:encoded']
    }
  }
  console.log(
    `[fetchAndHydrate] Finished fetch feed: ${feed}. ${contentFeed.items.length} items gathered`,
  )
  return contentFeed.items
}

/**
 * Builds a feed object from the provided items
 * @param {Array} items parsed by rss-parser
 * @return Feed object created by feed
 */
function createFeed(items) {
  console.log(`[createFeed] start building the aggregated feed`)
  const feed = new Feed({
    title: TITLE,
    description: DESCRIPTION,
    id: CUSTOM_URL,
    link: CUSTOM_URL,
  })

  for (let item of items) {
    feed.addItem({
      title: item.title,
      id: item.guid,
      link: item.link,
      description: item.contentSnippet,
      content: item.content,
      author: [
        {
          name: item.creator,
          email: '',
          link: item.source_link,
        },
      ],
      contributor: [],
      date: new Date(item.isoDate),
    })
  }
  console.log(`[createFeed] Finished building the aggregated feed`)
  return feed
}
/**
 * Generate the HTML page with the aggregated contents
 * @param {Array} items parsed by rss-parser
 * @returns String with HTML page containing the parsed contents
 */
function createHTML(items, sources) {
  console.log(`[createHTML] building the HTML document`)
  let template = Handlebars.templates['default']
  let dateFormatter = new Intl.DateTimeFormat('pt-PT', { timeZone: 'UTC' })

  for (let item of items) {
    let shortdescription = striptags(item.content).substring(0, 250)
    item.description = shortdescription ? shortdescription + ' [...]' : ''
    item.formattedDate = item.pubDate
      ? dateFormatter.format(new Date(item.pubDate))
      : ''
  }

  return template({
    items: items,
    sources: sources,
    page_title: TITLE,
    page_description: DESCRIPTION,
  })
}