import renderContent from './render-content/index.js'
import getLinkData from './get-link-data.js'
import getApplicableVersions from './get-applicable-versions.js'
import { getDataByLanguage } from './get-data.js'
import { executeWithFallback } from './render-with-fallback.js'

const renderOpts = { textOnly: true }

// This module returns an object that contains a single featured learning track
// and an array of all the other learning tracks for the current version.
export default async function processLearningTracks(rawLearningTracks, context) {
  const learningTracks = []

  let featuredTrack

  if (!context.currentProduct) {
    throw new Error(`Missing context.currentProduct value.`)
  }

  for (const rawTrackName of rawLearningTracks) {
    let isFeaturedTrack = false

    // Track names in frontmatter may include Liquid conditionals.
    const renderedTrackName = await renderContent(rawTrackName, context, renderOpts)
    if (!renderedTrackName) continue

    // Find the data for the current product and track name.

    if (context.currentProduct.includes('.')) {
      throw new Error(`currentProduct can not contain a . (${context.currentProduct})`)
    }
    if (renderedTrackName.includes('.')) {
      throw new Error(`renderedTrackName can not contain a . (${renderedTrackName})`)
    }

    // Note: this will use the translated learning tracks and automatically
    // fall back to English if they don't exist on disk in the translation.
    const track = getDataByLanguage(
      `learning-tracks.${context.currentProduct}.${renderedTrackName}`,
      context.currentLanguage
    )
    if (!track) {
      throw new Error(`No learning track called '${renderedTrackName}'.`)
    }

    // If the current language isn't 'en' we need to prepare and have the
    // English quivalent ready.
    // We do this for two reasons:
    //
    //   1. For each learning-track .yml file (in data) always want the
    //      English values for `guides`, `versions`, `featured_track`.
    //       Meaning, for the translated learning tracks we only keep the
    //      `title` and `description`.
    //
    //   2. When we attempt to render the translated learning tracks'
    //      `title` and `description`, if they are failing to render,
    //      we need to have the English `title` and `description` to
    //      fall back to.
    //
    let enTrack
    if (context.currentLanguage !== 'en') {
      enTrack = getDataByLanguage(
        `learning-tracks.${context.currentProduct}.${renderedTrackName}`,
        'en'
      )
      // Sometimes the translations have more than just translated the
      // `title` and `description`, but also things that don't make sense
      // to translate like `guides` and `versions`. Always draw that
      // from the English equivalent.
      track.guides = enTrack.guides
      track.versions = enTrack.versions
      track.featured_track = enTrack.featured_track
    }

    // If there is no `versions` prop in the learning track frontmatter, assume the track should display in all versions.
    if (track.versions) {
      const trackVersions = getApplicableVersions(track.versions)

      // If the current version is not included, do not display the track.
      if (!trackVersions.includes(context.currentVersion)) {
        continue
      }
    }

    const title = await executeWithFallback(
      context,
      () => renderContent(track.title, context, renderOpts),
      (enContext) => renderContent(enTrack.title, enContext, renderOpts)
    )
    const description = await executeWithFallback(
      context,
      () => renderContent(track.description, context, renderOpts),
      (enContext) => renderContent(enTrack.description, enContext, renderOpts)
    )

    const learningTrack = {
      trackName: renderedTrackName,
      trackProduct: context.currentProduct || null,
      title,
      description,
      // getLinkData respects versioning and only returns guides available in the current version;
      // if no guides are available, the learningTrack.guides property will be an empty array.
      guides: await getLinkData(track.guides, context),
    }

    // Determine if this is the featured track.
    if (track.featured_track) {
      // Featured track properties may be booleans or string that include Liquid conditionals with versioning.
      // We need to parse any strings to determine if the featured track is relevant for this version.
      isFeaturedTrack =
        track.featured_track === true ||
        (await renderContent(track.featured_track, context, renderOpts)) === 'true'

      if (isFeaturedTrack) {
        featuredTrack = learningTrack
      }
    }

    // Only add the track to the array of tracks if there are guides in this version and it's not the featured track.
    if (learningTrack.guides.length && !isFeaturedTrack) {
      learningTracks.push(learningTrack)
    }
  }

  return { featuredTrack, learningTracks }
}