import {
  AppBskyActorDefs,
  AppBskyEmbedRecord,
  AppBskyEmbedRecordWithMedia,
  AppBskyFeedDefs,
  AppBskyFeedPost,
} from '@atproto/api'

import {isPostInLanguage} from '../../locale/helpers'
import {FALLBACK_MARKER_POST} from './feed/home'
import {ReasonFeedSource} from './feed/types'

type FeedViewPost = AppBskyFeedDefs.FeedViewPost

export type FeedTunerFn = (
  tuner: FeedTuner,
  slices: FeedViewPostsSlice[],
  dryRun: boolean,
) => FeedViewPostsSlice[]

type FeedSliceItem = {
  post: AppBskyFeedDefs.PostView
  record: AppBskyFeedPost.Record
  parentAuthor: AppBskyActorDefs.ProfileViewBasic | undefined
  isParentBlocked: boolean
  isParentNotFound: boolean
}

type AuthorContext = {
  author: AppBskyActorDefs.ProfileViewBasic
  parentAuthor: AppBskyActorDefs.ProfileViewBasic | undefined
  grandparentAuthor: AppBskyActorDefs.ProfileViewBasic | undefined
  rootAuthor: AppBskyActorDefs.ProfileViewBasic | undefined
}

export class FeedViewPostsSlice {
  _reactKey: string
  _feedPost: FeedViewPost
  items: FeedSliceItem[]
  isIncompleteThread: boolean
  isFallbackMarker: boolean
  isOrphan: boolean
  rootUri: string

  constructor(feedPost: FeedViewPost) {
    const {post, reply, reason} = feedPost
    this.items = []
    this.isIncompleteThread = false
    this.isFallbackMarker = false
    this.isOrphan = false
    if (AppBskyFeedDefs.isPostView(reply?.root)) {
      this.rootUri = reply.root.uri
    } else {
      this.rootUri = post.uri
    }
    this._feedPost = feedPost
    this._reactKey = `slice-${post.uri}-${
      feedPost.reason?.indexedAt || post.indexedAt
    }`
    if (feedPost.post.uri === FALLBACK_MARKER_POST.post.uri) {
      this.isFallbackMarker = true
      return
    }
    if (
      !AppBskyFeedPost.isRecord(post.record) ||
      !AppBskyFeedPost.validateRecord(post.record).success
    ) {
      return
    }
    const parent = reply?.parent
    const isParentBlocked = AppBskyFeedDefs.isBlockedPost(parent)
    const isParentNotFound = AppBskyFeedDefs.isNotFoundPost(parent)
    let parentAuthor: AppBskyActorDefs.ProfileViewBasic | undefined
    if (AppBskyFeedDefs.isPostView(parent)) {
      parentAuthor = parent.author
    }
    this.items.push({
      post,
      record: post.record,
      parentAuthor,
      isParentBlocked,
      isParentNotFound,
    })
    if (!reply || reason) {
      return
    }
    if (
      !AppBskyFeedDefs.isPostView(parent) ||
      !AppBskyFeedPost.isRecord(parent.record) ||
      !AppBskyFeedPost.validateRecord(parent.record).success
    ) {
      this.isOrphan = true
      return
    }
    const root = reply.root
    const rootIsView =
      AppBskyFeedDefs.isPostView(root) ||
      AppBskyFeedDefs.isBlockedPost(root) ||
      AppBskyFeedDefs.isNotFoundPost(root)
    /*
     * If the parent is also the root, we just so happen to have the data we
     * need to compute if the parent's parent (grandparent) is blocked. This
     * doesn't always happen, of course, but we can take advantage of it when
     * it does.
     */
    const grandparent =
      rootIsView && parent.record.reply?.parent.uri === root.uri
        ? root
        : undefined
    const grandparentAuthor = reply.grandparentAuthor
    const isGrandparentBlocked = Boolean(
      grandparent && AppBskyFeedDefs.isBlockedPost(grandparent),
    )
    const isGrandparentNotFound = Boolean(
      grandparent && AppBskyFeedDefs.isNotFoundPost(grandparent),
    )
    this.items.unshift({
      post: parent,
      record: parent.record,
      parentAuthor: grandparentAuthor,
      isParentBlocked: isGrandparentBlocked,
      isParentNotFound: isGrandparentNotFound,
    })
    if (isGrandparentBlocked) {
      this.isOrphan = true
      // Keep going, it might still have a root, and we need this for thread
      // de-deduping
    }
    if (
      !AppBskyFeedDefs.isPostView(root) ||
      !AppBskyFeedPost.isRecord(root.record) ||
      !AppBskyFeedPost.validateRecord(root.record).success
    ) {
      this.isOrphan = true
      return
    }
    if (root.uri === parent.uri) {
      return
    }
    this.items.unshift({
      post: root,
      record: root.record,
      isParentBlocked: false,
      isParentNotFound: false,
      parentAuthor: undefined,
    })
    if (parent.record.reply?.parent.uri !== root.uri) {
      this.isIncompleteThread = true
    }
  }

  get isQuotePost() {
    const embed = this._feedPost.post.embed
    return (
      AppBskyEmbedRecord.isView(embed) ||
      AppBskyEmbedRecordWithMedia.isView(embed)
    )
  }

  get isReply() {
    return (
      AppBskyFeedPost.isRecord(this._feedPost.post.record) &&
      !!this._feedPost.post.record.reply
    )
  }

  get reason() {
    return '__source' in this._feedPost
      ? (this._feedPost.__source as ReasonFeedSource)
      : this._feedPost.reason
  }

  get feedContext() {
    return this._feedPost.feedContext
  }

  get isRepost() {
    const reason = this._feedPost.reason
    return AppBskyFeedDefs.isReasonRepost(reason)
  }

  get likeCount() {
    return this._feedPost.post.likeCount ?? 0
  }

  containsUri(uri: string) {
    return !!this.items.find(item => item.post.uri === uri)
  }

  getAuthors(): AuthorContext {
    const feedPost = this._feedPost
    let author: AppBskyActorDefs.ProfileViewBasic = feedPost.post.author
    let parentAuthor: AppBskyActorDefs.ProfileViewBasic | undefined
    let grandparentAuthor: AppBskyActorDefs.ProfileViewBasic | undefined
    let rootAuthor: AppBskyActorDefs.ProfileViewBasic | undefined
    if (feedPost.reply) {
      if (AppBskyFeedDefs.isPostView(feedPost.reply.parent)) {
        parentAuthor = feedPost.reply.parent.author
      }
      if (feedPost.reply.grandparentAuthor) {
        grandparentAuthor = feedPost.reply.grandparentAuthor
      }
      if (AppBskyFeedDefs.isPostView(feedPost.reply.root)) {
        rootAuthor = feedPost.reply.root.author
      }
    }
    return {
      author,
      parentAuthor,
      grandparentAuthor,
      rootAuthor,
    }
  }
}

export class FeedTuner {
  seenKeys: Set<string> = new Set()
  seenUris: Set<string> = new Set()
  seenRootUris: Set<string> = new Set()

  constructor(public tunerFns: FeedTunerFn[]) {}

  tune(
    feed: FeedViewPost[],
    {dryRun}: {dryRun: boolean} = {
      dryRun: false,
    },
  ): FeedViewPostsSlice[] {
    let slices: FeedViewPostsSlice[] = feed
      .map(item => new FeedViewPostsSlice(item))
      .filter(s => s.items.length > 0 || s.isFallbackMarker)

    // run the custom tuners
    for (const tunerFn of this.tunerFns) {
      slices = tunerFn(this, slices.slice(), dryRun)
    }

    slices = slices.filter(slice => {
      if (this.seenKeys.has(slice._reactKey)) {
        return false
      }
      // Some feeds, like Following, dedupe by thread, so you only see the most recent reply.
      // However, we don't want per-thread dedupe for author feeds (where we need to show every post)
      // or for feedgens (where we want to let the feed serve multiple replies if it chooses to).
      // To avoid showing the same context (root and/or parent) more than once, we do last resort
      // per-post deduplication. It hides already seen posts as long as this doesn't break the thread.
      for (let i = 0; i < slice.items.length; i++) {
        const item = slice.items[i]
        if (this.seenUris.has(item.post.uri)) {
          if (i === 0) {
            // Omit contiguous seen leading items.
            // For example, [A -> B -> C], [A -> D -> E], [A -> D -> F]
            // would turn into [A -> B -> C], [D -> E], [F].
            slice.items.splice(0, 1)
            i--
          }
          if (i === slice.items.length - 1) {
            // If the last item in the slice was already seen, omit the whole slice.
            // This means we'd miss its parents, but the user can "show more" to see them.
            // For example, [A ... E -> F], [A ... D -> E], [A ... C -> D], [A -> B -> C]
            // would get collapsed into [A ... E -> F], with B/C/D considered seen.
            return false
          }
        } else {
          if (!dryRun) {
            this.seenUris.add(item.post.uri)
          }
        }
      }
      if (!dryRun) {
        this.seenKeys.add(slice._reactKey)
      }
      return true
    })

    return slices
  }

  static removeReplies(
    tuner: FeedTuner,
    slices: FeedViewPostsSlice[],
    _dryRun: boolean,
  ) {
    for (let i = 0; i < slices.length; i++) {
      const slice = slices[i]
      if (
        slice.isReply &&
        !slice.isRepost &&
        // This is not perfect but it's close as we can get to
        // detecting threads without having to peek ahead.
        !areSameAuthor(slice.getAuthors())
      ) {
        slices.splice(i, 1)
        i--
      }
    }
    return slices
  }

  static removeReposts(
    tuner: FeedTuner,
    slices: FeedViewPostsSlice[],
    _dryRun: boolean,
  ) {
    for (let i = 0; i < slices.length; i++) {
      if (slices[i].isRepost) {
        slices.splice(i, 1)
        i--
      }
    }
    return slices
  }

  static removeQuotePosts(
    tuner: FeedTuner,
    slices: FeedViewPostsSlice[],
    _dryRun: boolean,
  ) {
    for (let i = 0; i < slices.length; i++) {
      if (slices[i].isQuotePost) {
        slices.splice(i, 1)
        i--
      }
    }
    return slices
  }

  static removeOrphans(
    tuner: FeedTuner,
    slices: FeedViewPostsSlice[],
    _dryRun: boolean,
  ) {
    for (let i = 0; i < slices.length; i++) {
      if (slices[i].isOrphan) {
        slices.splice(i, 1)
        i--
      }
    }
    return slices
  }

  static dedupThreads(
    tuner: FeedTuner,
    slices: FeedViewPostsSlice[],
    dryRun: boolean,
  ): FeedViewPostsSlice[] {
    for (let i = 0; i < slices.length; i++) {
      const rootUri = slices[i].rootUri
      if (!slices[i].isRepost && tuner.seenRootUris.has(rootUri)) {
        slices.splice(i, 1)
        i--
      } else {
        if (!dryRun) {
          tuner.seenRootUris.add(rootUri)
        }
      }
    }
    return slices
  }

  static followedRepliesOnly({userDid}: {userDid: string}) {
    return (
      tuner: FeedTuner,
      slices: FeedViewPostsSlice[],
      _dryRun: boolean,
    ): FeedViewPostsSlice[] => {
      for (let i = 0; i < slices.length; i++) {
        const slice = slices[i]
        if (slice.isReply && !shouldDisplayReplyInFollowing(slice, userDid)) {
          slices.splice(i, 1)
          i--
        }
      }
      return slices
    }
  }

  /**
   * This function filters a list of FeedViewPostsSlice items based on whether they contain text in a
   * preferred language.
   * @param {string[]} preferredLangsCode2 - An array of preferred language codes in ISO 639-1 or ISO 639-2 format.
   * @returns A function that takes in a `FeedTuner` and an array of `FeedViewPostsSlice` objects and
   * returns an array of `FeedViewPostsSlice` objects.
   */
  static preferredLangOnly(preferredLangsCode2: string[]) {
    return (
      tuner: FeedTuner,
      slices: FeedViewPostsSlice[],
      _dryRun: boolean,
    ): FeedViewPostsSlice[] => {
      // early return if no languages have been specified
      if (!preferredLangsCode2.length || preferredLangsCode2.length === 0) {
        return slices
      }

      const candidateSlices = slices.filter(slice => {
        for (const item of slice.items) {
          if (isPostInLanguage(item.post, preferredLangsCode2)) {
            return true
          }
        }
        // if item does not fit preferred language, remove it
        return false
      })

      // if the language filter cleared out the entire page, return the original set
      // so that something always shows
      if (candidateSlices.length === 0) {
        return slices
      }

      return candidateSlices
    }
  }
}

function areSameAuthor(authors: AuthorContext): boolean {
  const {author, parentAuthor, grandparentAuthor, rootAuthor} = authors
  const authorDid = author.did
  if (parentAuthor && parentAuthor.did !== authorDid) {
    return false
  }
  if (grandparentAuthor && grandparentAuthor.did !== authorDid) {
    return false
  }
  if (rootAuthor && rootAuthor.did !== authorDid) {
    return false
  }
  return true
}

function shouldDisplayReplyInFollowing(
  slice: FeedViewPostsSlice,
  userDid: string,
): boolean {
  if (slice.isRepost) {
    return true
  }
  const authors = slice.getAuthors()
  const {author, parentAuthor, grandparentAuthor, rootAuthor} = authors
  if (!isSelfOrFollowing(author, userDid)) {
    // Only show replies from self or people you follow.
    return false
  }
  if (
    (!parentAuthor || parentAuthor.did === author.did) &&
    (!rootAuthor || rootAuthor.did === author.did) &&
    (!grandparentAuthor || grandparentAuthor.did === author.did)
  ) {
    // Always show self-threads.
    return true
  }
  if (
    parentAuthor &&
    parentAuthor.did !== author.did &&
    rootAuthor &&
    rootAuthor.did === author.did &&
    slice.items.length > 2
  ) {
    // If you follow A, show A -> someone[>0 likes] -> A chains too.
    // This is different from cases below because you only know one person.
    const parentPost = slice.items[1].post
    const parentLikeCount = parentPost.likeCount ?? 0
    if (parentLikeCount > 0) {
      return true
    }
  }
  // From this point on we need at least one more reason to show it.
  if (
    parentAuthor &&
    parentAuthor.did !== author.did &&
    isSelfOrFollowing(parentAuthor, userDid)
  ) {
    return true
  }
  if (
    grandparentAuthor &&
    grandparentAuthor.did !== author.did &&
    isSelfOrFollowing(grandparentAuthor, userDid)
  ) {
    return true
  }
  if (
    rootAuthor &&
    rootAuthor.did !== author.did &&
    isSelfOrFollowing(rootAuthor, userDid)
  ) {
    return true
  }
  return false
}

function isSelfOrFollowing(
  profile: AppBskyActorDefs.ProfileViewBasic,
  userDid: string,
) {
  return Boolean(profile.did === userDid || profile.viewer?.following)
}