path: root/src/state/models/feed-view.ts

import {makeAutoObservable, runInAction} from 'mobx'
import {
  AppBskyFeedGetTimeline as GetTimeline,
  AppBskyFeedFeedViewPost,
  AppBskyFeedPost,
  AppBskyFeedGetAuthorFeed as GetAuthorFeed,
} from '@atproto/api'
type FeedViewPost = AppBskyFeedFeedViewPost.Main
type ReasonRepost = AppBskyFeedFeedViewPost.ReasonRepost
type PostView = AppBskyFeedPost.View
import {AtUri} from '../../third-party/uri'
import {RootStoreModel} from './root-store'
import * as apilib from '../lib/api'
import {cleanError} from '../../lib/strings'

const PAGE_SIZE = 30

let _idCounter = 0

type FeedViewPostWithThreadMeta = FeedViewPost & {
  _isThreadParent?: boolean
  _isThreadChildElided?: boolean
  _isThreadChild?: boolean
}

export class FeedItemModel {
  // ui state
  _reactKey: string = ''
  _isThreadParent: boolean = false
  _isThreadChildElided: boolean = false
  _isThreadChild: boolean = false
  _hideParent: boolean = true // used to avoid dup post rendering while showing some parents

  // data
  post: PostView
  postRecord?: AppBskyFeedPost.Record
  reply?: FeedViewPost['reply']
  replyParent?: FeedItemModel
  reason?: FeedViewPost['reason']

  constructor(
    public rootStore: RootStoreModel,
    reactKey: string,
    v: FeedViewPostWithThreadMeta,
  ) {
    this._reactKey = reactKey
    this.post = v.post
    if (AppBskyFeedPost.isRecord(this.post.record)) {
      const valid = AppBskyFeedPost.validateRecord(this.post.record)
      if (valid.success) {
        this.postRecord = this.post.record
      } else {
        rootStore.log.warn(
          'Received an invalid app.bsky.feed.post record',
          valid.error,
        )
      }
    } else {
      rootStore.log.warn(
        'app.bsky.feed.getTimeline or app.bsky.feed.getAuthorFeed served an unexpected record type',
        this.post.record,
      )
    }
    this.reply = v.reply
    if (v.reply?.parent) {
      this.replyParent = new FeedItemModel(rootStore, '', {
        post: v.reply.parent,
      })
    }
    this.reason = v.reason
    this._isThreadParent = v._isThreadParent || false
    this._isThreadChild = v._isThreadChild || false
    this._isThreadChildElided = v._isThreadChildElided || false
    makeAutoObservable(this, {rootStore: false})
  }

  copy(v: FeedViewPost) {
    this.post = v.post
    this.reply = v.reply
    if (v.reply?.parent) {
      this.replyParent = new FeedItemModel(this.rootStore, '', {
        post: v.reply.parent,
      })
    } else {
      this.replyParent = undefined
    }
    this.reason = v.reason
  }

  get reasonRepost(): ReasonRepost | undefined {
    if (this.reason?.$type === 'app.bsky.feed.feedViewPost#reasonRepost') {
      return this.reason as ReasonRepost
    }
  }

  async toggleUpvote() {
    const wasUpvoted = !!this.post.viewer.upvote
    const wasDownvoted = !!this.post.viewer.downvote
    const res = await this.rootStore.api.app.bsky.feed.setVote({
      subject: {
        uri: this.post.uri,
        cid: this.post.cid,
      },
      direction: wasUpvoted ? 'none' : 'up',
    })
    runInAction(() => {
      if (wasDownvoted) {
        this.post.downvoteCount--
      }
      if (wasUpvoted) {
        this.post.upvoteCount--
      } else {
        this.post.upvoteCount++
      }
      this.post.viewer.upvote = res.data.upvote
      this.post.viewer.downvote = res.data.downvote
    })
  }

  async toggleDownvote() {
    const wasUpvoted = !!this.post.viewer.upvote
    const wasDownvoted = !!this.post.viewer.downvote
    const res = await this.rootStore.api.app.bsky.feed.setVote({
      subject: {
        uri: this.post.uri,
        cid: this.post.cid,
      },
      direction: wasDownvoted ? 'none' : 'down',
    })
    runInAction(() => {
      if (wasUpvoted) {
        this.post.upvoteCount--
      }
      if (wasDownvoted) {
        this.post.downvoteCount--
      } else {
        this.post.downvoteCount++
      }
      this.post.viewer.upvote = res.data.upvote
      this.post.viewer.downvote = res.data.downvote
    })
  }

  async toggleRepost() {
    if (this.post.viewer.repost) {
      await apilib.unrepost(this.rootStore, this.post.viewer.repost)
      runInAction(() => {
        this.post.repostCount--
        this.post.viewer.repost = undefined
      })
    } else {
      const res = await apilib.repost(
        this.rootStore,
        this.post.uri,
        this.post.cid,
      )
      runInAction(() => {
        this.post.repostCount++
        this.post.viewer.repost = res.uri
      })
    }
  }

  async delete() {
    await this.rootStore.api.app.bsky.feed.post.delete({
      did: this.post.author.did,
      rkey: new AtUri(this.post.uri).rkey,
    })
    this.rootStore.emitPostDeleted(this.post.uri)
  }
}

export class FeedModel {
  // state
  isLoading = false
  isRefreshing = false
  hasNewLatest = false
  hasLoaded = false
  error = ''
  params: GetTimeline.QueryParams | GetAuthorFeed.QueryParams
  hasMore = true
  loadMoreCursor: string | undefined
  pollCursor: string | undefined
  _loadPromise: Promise<void> | undefined
  _loadMorePromise: Promise<void> | undefined
  _loadLatestPromise: Promise<void> | undefined
  _updatePromise: Promise<void> | undefined

  // data
  feed: FeedItemModel[] = []

  constructor(
    public rootStore: RootStoreModel,
    public feedType: 'home' | 'author',
    params: GetTimeline.QueryParams | GetAuthorFeed.QueryParams,
  ) {
    makeAutoObservable(
      this,
      {
        rootStore: false,
        params: false,
        loadMoreCursor: false,
        _loadPromise: false,
        _loadMorePromise: false,
        _loadLatestPromise: false,
        _updatePromise: false,
      },
      {autoBind: true},
    )
    this.params = params
  }

  get hasContent() {
    return this.feed.length !== 0
  }

  get hasError() {
    return this.error !== ''
  }

  get isEmpty() {
    return this.hasLoaded && !this.hasContent
  }

  get nonReplyFeed() {
    return this.feed.filter(
      item =>
        !item.reply || // not a reply
        ((item._isThreadParent || // but allow if it's a thread by the user
          item._isThreadChild) &&
          item.reply?.root.author.did === item.post.author.did),
    )
  }

  setHasNewLatest(v: boolean) {
    this.hasNewLatest = v
  }

  // public api
  // =

  /**
   * Load for first render
   */
  async setup(isRefreshing = false) {
    if (isRefreshing) {
      this.isRefreshing = true // set optimistically for UI
    }
    if (this._loadPromise) {
      return this._loadPromise
    }
    await this._pendingWork()
    this.setHasNewLatest(false)
    this._loadPromise = this._initialLoad(isRefreshing)
    await this._loadPromise
    this._loadPromise = undefined
  }

  /**
   * Register any event listeners. Returns a cleanup function.
   */
  registerListeners() {
    const sub = this.rootStore.onPostDeleted(this.onPostDeleted.bind(this))
    return () => sub.remove()
  }

  /**
   * Reset and load
   */
  async refresh() {
    await this.setup(true)
  }

  /**
   * Load more posts to the end of the feed
   */
  async loadMore() {
    if (this._loadMorePromise) {
      return this._loadMorePromise
    }
    await this._pendingWork()
    this._loadMorePromise = this._loadMore()
    await this._loadMorePromise
    this._loadMorePromise = undefined
  }

  /**
   * Load more posts to the start of the feed
   */
  async loadLatest() {
    if (this._loadLatestPromise) {
      return this._loadLatestPromise
    }
    await this._pendingWork()
    this.setHasNewLatest(false)
    this._loadLatestPromise = this._loadLatest()
    await this._loadLatestPromise
    this._loadLatestPromise = undefined
  }

  /**
   * Update content in-place
   */
  async update() {
    if (this._updatePromise) {
      return this._updatePromise
    }
    await this._pendingWork()
    this._updatePromise = this._update()
    await this._updatePromise
    this._updatePromise = undefined
  }

  /**
   * Check if new posts are available
   */
  async checkForLatest() {
    if (this.hasNewLatest) {
      return
    }
    await this._pendingWork()
    const res = await this._getFeed({limit: 1})
    const currentLatestUri = this.pollCursor
    const receivedLatestUri = res.data.feed[0]
      ? res.data.feed[0].post.uri
      : undefined
    const hasNewLatest = Boolean(
      receivedLatestUri &&
        (this.feed.length === 0 || receivedLatestUri !== currentLatestUri),
    )
    this.setHasNewLatest(hasNewLatest)
  }

  /**
   * Removes posts from the feed upon deletion.
   */
  onPostDeleted(uri: string) {
    let i
    do {
      i = this.feed.findIndex(item => item.post.uri === uri)
      if (i !== -1) {
        this.feed.splice(i, 1)
      }
    } while (i !== -1)
  }

  // state transitions
  // =

  private _xLoading(isRefreshing = false) {
    this.isLoading = true
    this.isRefreshing = isRefreshing
    this.error = ''
  }

  private _xIdle(err?: any) {
    this.isLoading = false
    this.isRefreshing = false
    this.hasLoaded = true
    this.error = err ? cleanError(err.toString()) : ''
    if (err) {
      this.rootStore.log.error('Posts feed request failed', err)
    }
  }

  // loader functions
  // =

  private async _pendingWork() {
    if (this._loadPromise) {
      await this._loadPromise
    }
    if (this._loadMorePromise) {
      await this._loadMorePromise
    }
    if (this._loadLatestPromise) {
      await this._loadLatestPromise
    }
    if (this._updatePromise) {
      await this._updatePromise
    }
  }

  private async _initialLoad(isRefreshing = false) {
    this._xLoading(isRefreshing)
    try {
      const res = await this._getFeed({limit: PAGE_SIZE})
      await this._replaceAll(res)
      this._xIdle()
    } catch (e: any) {
      this._xIdle(e)
    }
  }

  private async _loadLatest() {
    this._xLoading()
    try {
      const res = await this._getFeed({limit: PAGE_SIZE})
      await this._prependAll(res)
      this._xIdle()
    } catch (e: any) {
      this._xIdle(e)
    }
  }

  private async _loadMore() {
    if (!this.hasMore || this.hasError) {
      return
    }
    this._xLoading()
    try {
      const res = await this._getFeed({
        before: this.loadMoreCursor,
        limit: PAGE_SIZE,
      })
      await this._appendAll(res)
      this._xIdle()
    } catch (e: any) {
      this._xIdle(e)
    }
  }

  private async _update() {
    if (!this.feed.length) {
      return
    }
    this._xLoading()
    let numToFetch = this.feed.length
    let cursor
    try {
      do {
        const res: GetTimeline.Response = await this._getFeed({
          before: cursor,
          limit: Math.min(numToFetch, 100),
        })
        if (res.data.feed.length === 0) {
          break // sanity check
        }
        this._updateAll(res)
        numToFetch -= res.data.feed.length
        cursor = res.data.cursor
      } while (cursor && numToFetch > 0)
      this._xIdle()
    } catch (e: any) {
      this._xIdle(e)
    }
  }

  private async _replaceAll(
    res: GetTimeline.Response | GetAuthorFeed.Response,
  ) {
    this.pollCursor = res.data.feed[0]?.post.uri
    return this._appendAll(res, true)
  }

  private async _appendAll(
    res: GetTimeline.Response | GetAuthorFeed.Response,
    replace = false,
  ) {
    this.loadMoreCursor = res.data.cursor
    this.hasMore = !!this.loadMoreCursor
    const orgLen = this.feed.length

    const reorgedFeed = preprocessFeed(res.data.feed)

    const toAppend: FeedItemModel[] = []
    for (const item of reorgedFeed) {
      const itemModel = new FeedItemModel(
        this.rootStore,
        `item-${_idCounter++}`,
        item,
      )
      toAppend.push(itemModel)
    }
    runInAction(() => {
      if (replace) {
        this.feed = toAppend
      } else {
        this.feed = this.feed.concat(toAppend)
      }
      dedupReposts(this.feed)
      dedupParents(this.feed.slice(orgLen)) // we slice to avoid modifying rendering of already-shown posts
    })
  }

  private async _prependAll(
    res: GetTimeline.Response | GetAuthorFeed.Response,
  ) {
    this.pollCursor = res.data.feed[0]?.post.uri

    const toPrepend: FeedItemModel[] = []
    for (const item of res.data.feed) {
      if (this.feed.find(item2 => item2.post.uri === item.post.uri)) {
        break // stop here - we've hit a post we already have
      }

      const itemModel = new FeedItemModel(
        this.rootStore,
        `item-${_idCounter++}`,
        item,
      )
      toPrepend.push(itemModel)
    }
    runInAction(() => {
      this.feed = toPrepend.concat(this.feed)
    })
  }

  private _updateAll(res: GetTimeline.Response | GetAuthorFeed.Response) {
    for (const item of res.data.feed) {
      const existingItem = this.feed.find(
        // HACK: need to find the reposts' item, so we have to check for that -prf
        item2 =>
          item.post.uri === item2.post.uri &&
          // @ts-ignore todo
          item.reason?.by?.did === item2.reason?.by?.did,
      )
      if (existingItem) {
        existingItem.copy(item)
      }
    }
  }

  protected _getFeed(
    params: GetTimeline.QueryParams | GetAuthorFeed.QueryParams = {},
  ): Promise<GetTimeline.Response | GetAuthorFeed.Response> {
    params = Object.assign({}, this.params, params)
    if (this.feedType === 'home') {
      return this.rootStore.api.app.bsky.feed.getTimeline(
        params as GetTimeline.QueryParams,
      )
    } else {
      return this.rootStore.api.app.bsky.feed.getAuthorFeed(
        params as GetAuthorFeed.QueryParams,
      )
    }
  }
}

interface Slice {
  index: number
  length: number
}
function preprocessFeed(feed: FeedViewPost[]): FeedViewPostWithThreadMeta[] {
  const reorg: FeedViewPostWithThreadMeta[] = []

  // phase one: identify threads and reorganize them into the feed so
  // that they are in order and marked as part of a thread
  for (let i = feed.length - 1; i >= 0; i--) {
    const item = feed[i] as FeedViewPostWithThreadMeta

    const selfReplyUri = getSelfReplyUri(item)
    if (selfReplyUri) {
      const parentIndex = reorg.findIndex(
        item2 => item2.post.uri === selfReplyUri,
      )
      if (parentIndex !== -1 && !reorg[parentIndex]._isThreadParent) {
        reorg[parentIndex]._isThreadParent = true
        item._isThreadChild = true
        reorg.splice(parentIndex + 1, 0, item)
        continue
      }
    }
    reorg.unshift(item)
  }

  // phase two: identify the positions of the threads
  let activeSlice = -1
  let threadSlices: Slice[] = []
  for (let i = 0; i < reorg.length; i++) {
    const item = reorg[i] as FeedViewPostWithThreadMeta
    if (activeSlice === -1) {
      if (item._isThreadParent) {
        activeSlice = i
      }
    } else {
      if (!item._isThreadChild) {
        threadSlices.push({index: activeSlice, length: i - activeSlice})
        if (item._isThreadParent) {
          activeSlice = i
        } else {
          activeSlice = -1
        }
      }
    }
  }
  if (activeSlice !== -1) {
    threadSlices.push({index: activeSlice, length: reorg.length - activeSlice})
  }

  // phase three: reorder the feed so that the timestamp of the
  // last post in a thread establishes its ordering
  for (const slice of threadSlices) {
    const removed: FeedViewPostWithThreadMeta[] = reorg.splice(
      slice.index,
      slice.length,
    )
    const targetDate = new Date(ts(removed[removed.length - 1]))
    let newIndex = reorg.findIndex(item => new Date(ts(item)) < targetDate)
    if (newIndex === -1) {
      newIndex = reorg.length
    }
    reorg.splice(newIndex, 0, ...removed)
    slice.index = newIndex
  }

  // phase four: compress any threads that are longer than 3 posts
  let removedCount = 0
  for (const slice of threadSlices) {
    if (slice.length > 3) {
      reorg.splice(slice.index - removedCount + 1, slice.length - 3)
      reorg[slice.index - removedCount]._isThreadChildElided = true
      removedCount += slice.length - 3
    }
  }

  return reorg
}

// WARNING: mutates `feed`
function dedupReposts(feed: FeedItemModel[]) {
  // remove duplicates caused by reposts
  for (let i = 0; i < feed.length; i++) {
    const item1 = feed[i]
    for (let j = i + 1; j < feed.length; j++) {
      const item2 = feed[j]
      if (item1.post.uri === item2.post.uri) {
        feed.splice(j, 1)
        j--
      }
    }
  }
}

// WARNING: mutates `feed`
function dedupParents(feed: FeedItemModel[]) {
  // only show parents that aren't already in the feed
  for (let i = 0; i < feed.length; i++) {
    const item1 = feed[i]
    if (!item1.replyParent || item1._isThreadChild) {
      continue
    }
    let hideParent = false
    for (let j = 0; j < feed.length; j++) {
      const item2 = feed[j]
      if (
        item1.replyParent.post.uri === item2.post.uri || // the post itself is there
        (j < i && item1.replyParent.post.uri === item2.replyParent?.post.uri) // another reply already showed it
      ) {
        hideParent = true
        break
      }
    }
    item1._hideParent = hideParent
  }
}

function getSelfReplyUri(item: FeedViewPost): string | undefined {
  return item.reply?.parent.author.did === item.post.author.did
    ? item.reply?.parent.uri
    : undefined
}

function ts(item: FeedViewPost | FeedItemModel): string {
  if (item.reason?.indexedAt) {
    // @ts-ignore need better type checks
    return item.reason.indexedAt
  }
  return item.post.indexedAt
}