// Fetch all my playlists
let playlists = []
// Fetch the max of 50 playlists at a time
let url = `https://api.spotify.com/v1/me/playlists?limit=50`

do {
  const { items, next } = await require("@pipedreamhq/platform").axios(this, {
    method: "GET",
    url,
    params: {
      fields: "items(owner,external_urls,id,images,name,snapshot_id)"
    },
    headers: {
      // Use the OAuth access token from the Spotify OAuth grant.
      // See https://docs.pipedream.com/workflows/steps/code/auth/#the-auths-object
      Authorization: `Bearer ${auths.spotify.oauth_access_token}`,
    },
  })

  playlists = playlists.concat(items)
  url = next
} while (url)

// Return only playlists owned by others
this.playlists = playlists.filter(playlist => {
  return playlist.owner.id !== auths.spotify.oauth_uid
})

const axios = require("axios")
const _ = require("lodash")

// Keep track of changes by playlist ID
const changes = {}

// Retrieve the old state of the playlists from workflow state
// https://docs.pipedream.com/workflows/steps/code/#managing-state
const oldPlaylistState = this.$checkpoint || {}

// Fetch the newest state and save for the next run
newPlaylistState = await getCurrentPlaylistState(steps.get_saved_playlists.playlists)

if (_.isEmpty(oldPlaylistState)) {
  this.$checkpoint = newPlaylistState
  $end("Saved initial playlist data. Will check for changes on next run.")
}

// The snapshot_id changes with playlist changes. Compare the saved
// snapshot_id with the current to see what playlists changed
// https://developer.spotify.com/documentation/general/guides/working-with-playlists/#version-control-and-snapshots
if (!_.isEmpty(oldPlaylistState)) {
  const playlistsThatChanged = steps.get_saved_playlists.playlists.filter(playlist => {
    // If we have a new playlist (no old state stored for the playlist), move on
    if (!oldPlaylistState[playlist.id]) {
      return false
    }
    return oldPlaylistState[playlist.id].snapshot_id !== playlist.snapshot_id
  })

  if (!playlistsThatChanged.length) {
    this.$checkpoint = newPlaylistState
    $end("No playlists changed")
  }

  // For playlists that changed, find the diff.
  // We only care about songs that are in the new state and not in the old.
  for (const playlist of playlistsThatChanged) {
    const { id, images, name, external_urls } = playlist
    const oldTracks = _.sortBy(oldPlaylistState[id].tracks, 'track.id')
    const newTracks = _.sortBy(newPlaylistState[id].tracks, 'track.id')
    const trackDiff = _.differenceBy(newTracks, oldTracks, 'track.id')
    if (!trackDiff.length) {
      continue
    }
    changes[id] = {
      images,
      link: external_urls.spotify,
      name,
      trackDiff,
    }
  }

  if (_.isEmpty(changes)) {
    this.$checkpoint = newPlaylistState
    $end("No new tracks")
  }

  // Format and send email
  formatAndSendEmail(changes)
}

this.$checkpoint = newPlaylistState

async function getCurrentPlaylistState(playlists) {
  const currentPlaylistState = {}
  for (const playlist of playlists) {
    const { id, external_urls, images, name, snapshot_id } = playlist
    let tracks = []
    // Fetch the max of 100 tracks at a time
    let url = `https://api.spotify.com/v1/playlists/${id}/tracks?limit=100`

    do {
      const { items, next } = (await axios({
        method: "GET",
        url,
        params: {
          fields: "items(track(id,name,artists))"
        },
        headers: {
          Authorization: `Bearer ${auths.spotify.oauth_access_token}`,
        },
      })).data

      tracks = tracks.concat(items)
      url = next
    } while (url)

    currentPlaylistState[id] = {
      link: external_urls.spotify,
      images,
      name,
      snapshot_id,
      tracks,
    }
  }

  return currentPlaylistState
}

function formatAndSendEmail(changes) {
  let html = ''
  for (let [id, playlist] of Object.entries(changes)) {
    const { link, images, name, trackDiff } = playlist
    html += `<strong>New tracks on <a href="${link}">${name}</a></strong><br><br>
    <img width="200px" alt="${name}" src="${images[0].url}"><br><br>
    
    ${trackDiff.map(t => {
      const { name, artists } = t.track
      const artistString = artists.map(a => a.name).join(', ')
      return `${name} by ${artistString}`
    }).join('<br>')}
    <br><br>`
  }

  // Send yourself an email
  // https://docs.pipedream.com/destinations/email/#adding-an-email-destination
  $send.email({
    subject: "Updates to Spotify playlists you follow",
    html,
  })
}