Refactor feed manipulation and rendering to be more robust (#297)

src/lib/api/feed-manip.ts

@@ -0,0 +1,186 @@
+import {AppBskyFeedFeedViewPost} from '@atproto/api'
+type FeedViewPost = AppBskyFeedFeedViewPost.Main
+
+export type FeedTunerFn = (
+  tuner: FeedTuner,
+  slices: FeedViewPostsSlice[],
+) => void
+
+export class FeedViewPostsSlice {
+  constructor(public items: FeedViewPost[] = []) {}
+
+  get uri() {
+    if (this.isReply) {
+      return this.items[1].post.uri
+    }
+    return this.items[0].post.uri
+  }
+
+  get ts() {
+    if (this.items[0].reason?.indexedAt) {
+      return this.items[0].reason.indexedAt as string
+    }
+    return this.items[0].post.indexedAt
+  }
+
+  get isThread() {
+    return (
+      this.items.length > 1 &&
+      this.items.every(
+        item => item.post.author.did === this.items[0].post.author.did,
+      )
+    )
+  }
+
+  get isReply() {
+    return this.items.length === 2 && !this.isThread
+  }
+
+  get rootItem() {
+    if (this.isReply) {
+      return this.items[1]
+    }
+    return this.items[0]
+  }
+
+  containsUri(uri: string) {
+    return !!this.items.find(item => item.post.uri === uri)
+  }
+
+  insert(item: FeedViewPost) {
+    const selfReplyUri = getSelfReplyUri(item)
+    const i = this.items.findIndex(item2 => item2.post.uri === selfReplyUri)
+    if (i !== -1) {
+      this.items.splice(i + 1, 0, item)
+    } else {
+      this.items.push(item)
+    }
+  }
+
+  flattenReplyParent() {
+    if (this.items[0].reply?.parent) {
+      this.items.splice(0, 0, {post: this.items[0].reply?.parent})
+    }
+  }
+
+  logSelf() {
+    console.log(
+      `- Slice ${this.items.length}${this.isThread ? ' (thread)' : ''} -`,
+    )
+    for (const item of this.items) {
+      console.log(
+        `  ${item.reason ? `RP by ${item.reason.by.handle}: ` : ''}${
+          item.post.author.handle
+        }: ${item.reply ? `(Reply ${item.reply.parent.author.handle}) ` : ''}${
+          item.post.record.text
+        }`,
+      )
+    }
+  }
+}
+
+export class FeedTuner {
+  seenUris: Set<string> = new Set()
+
+  constructor() {}
+
+  reset() {
+    this.seenUris.clear()
+  }
+
+  tune(
+    feed: FeedViewPost[],
+    tunerFns: FeedTunerFn[] = [],
+  ): FeedViewPostsSlice[] {
+    const slices: FeedViewPostsSlice[] = []
+
+    // arrange the posts into thread slices
+    for (let i = feed.length - 1; i >= 0; i--) {
+      const item = feed[i]
+
+      const selfReplyUri = getSelfReplyUri(item)
+      if (selfReplyUri) {
+        const parent = slices.find(item2 => item2.containsUri(selfReplyUri))
+        if (parent) {
+          parent.insert(item)
+          continue
+        }
+      }
+      slices.unshift(new FeedViewPostsSlice([item]))
+    }
+
+    // remove any items already "seen"
+    for (let i = slices.length - 1; i >= 0; i--) {
+      if (this.seenUris.has(slices[i].uri)) {
+        slices.splice(i, 1)
+      }
+    }
+
+    // turn non-threads with reply parents into threads
+    for (const slice of slices) {
+      if (
+        !slice.isThread &&
+        !slice.items[0].reason &&
+        slice.items[0].reply?.parent &&
+        !this.seenUris.has(slice.items[0].reply?.parent.uri)
+      ) {
+        slice.flattenReplyParent()
+      }
+    }
+
+    // sort by slice roots' timestamps
+    slices.sort((a, b) => b.ts.localeCompare(a.ts))
+
+    // run the custom tuners
+    for (const tunerFn of tunerFns) {
+      tunerFn(this, slices)
+    }
+
+    for (const slice of slices) {
+      for (const item of slice.items) {
+        this.seenUris.add(item.post.uri)
+      }
+      slice.logSelf()
+    }
+
+    return slices
+  }
+
+  static dedupReposts(tuner: FeedTuner, slices: FeedViewPostsSlice[]) {
+    // remove duplicates caused by reposts
+    for (let i = 0; i < slices.length; i++) {
+      const item1 = slices[i]
+      for (let j = i + 1; j < slices.length; j++) {
+        const item2 = slices[j]
+        if (item2.isThread) {
+          // dont dedup items that are rendering in a thread as this can cause rendering errors
+          continue
+        }
+        if (item1.containsUri(item2.items[0].post.uri)) {
+          slices.splice(j, 1)
+          j--
+        }
+      }
+    }
+  }
+
+  static likedRepliesOnly(tuner: FeedTuner, slices: FeedViewPostsSlice[]) {
+    // remove any replies without any likes
+    for (let i = slices.length - 1; i >= 0; i--) {
+      if (slices[i].isThread) {
+        continue
+      }
+      const item = slices[i].rootItem
+      const isRepost = Boolean(item.reason)
+      if (item.reply && !isRepost && item.post.upvoteCount === 0) {
+        slices.splice(i, 1)
+      }
+    }
+  }
+}
+
+function getSelfReplyUri(item: FeedViewPost): string | undefined {
+  return item.reply?.parent.author.did === item.post.author.did
+    ? item.reply?.parent.uri
+    : undefined
+}