1 files changed, 101 insertions, 0 deletions
diff --git a/src/state/cache/post-shadow.ts b/src/state/cache/post-shadow.ts
new file mode 100644
index 000000000..e02d4f1ea
--- /dev/null
+++ b/src/state/cache/post-shadow.ts
@@ -0,0 +1,101 @@
+import {useEffect, useState, useMemo} from 'react'
+import EventEmitter from 'eventemitter3'
+import {AppBskyFeedDefs} from '@atproto/api'
+import {batchedUpdates} from '#/lib/batchedUpdates'
+import {Shadow, castAsShadow} from './types'
+import {findAllPostsInQueryData as findAllPostsInNotifsQueryData} from '../queries/notifications/feed'
+import {findAllPostsInQueryData as findAllPostsInFeedQueryData} from '../queries/post-feed'
+import {findAllPostsInQueryData as findAllPostsInThreadQueryData} from '../queries/post-thread'
+import {queryClient} from 'lib/react-query'
+export type {Shadow} from './types'
+
+export interface PostShadow {
+  likeUri: string | undefined
+  likeCount: number | undefined
+  repostUri: string | undefined
+  repostCount: number | undefined
+  isDeleted: boolean
+}
+
+export const POST_TOMBSTONE = Symbol('PostTombstone')
+
+const emitter = new EventEmitter()
+const shadows: WeakMap<
+  AppBskyFeedDefs.PostView,
+  Partial<PostShadow>
+> = new WeakMap()
+
+export function usePostShadow(
+  post: AppBskyFeedDefs.PostView,
+): Shadow<AppBskyFeedDefs.PostView> | typeof POST_TOMBSTONE {
+  const [shadow, setShadow] = useState(() => shadows.get(post))
+  const [prevPost, setPrevPost] = useState(post)
+  if (post !== prevPost) {
+    setPrevPost(post)
+    setShadow(shadows.get(post))
+  }
+
+  useEffect(() => {
+    function onUpdate() {
+      setShadow(shadows.get(post))
+    }
+    emitter.addListener(post.uri, onUpdate)
+    return () => {
+      emitter.removeListener(post.uri, onUpdate)
+    }
+  }, [post, setShadow])
+
+  return useMemo(() => {
+    if (shadow) {
+      return mergeShadow(post, shadow)
+    } else {
+      return castAsShadow(post)
+    }
+  }, [post, shadow])
+}
+
+function mergeShadow(
+  post: AppBskyFeedDefs.PostView,
+  shadow: Partial<PostShadow>,
+): Shadow<AppBskyFeedDefs.PostView> | typeof POST_TOMBSTONE {
+  if (shadow.isDeleted) {
+    return POST_TOMBSTONE
+  }
+  return castAsShadow({
+    ...post,
+    likeCount: 'likeCount' in shadow ? shadow.likeCount : post.likeCount,
+    repostCount:
+      'repostCount' in shadow ? shadow.repostCount : post.repostCount,
+    viewer: {
+      ...(post.viewer || {}),
+      like: 'likeUri' in shadow ? shadow.likeUri : post.viewer?.like,
+      repost: 'repostUri' in shadow ? shadow.repostUri : post.viewer?.repost,
+    },
+  })
+}
+
+export function updatePostShadow(uri: string, value: Partial<PostShadow>) {
+  const cachedPosts = findPostsInCache(uri)
+  for (let post of cachedPosts) {
+    shadows.set(post, {...shadows.get(post), ...value})
+  }
+  batchedUpdates(() => {
+    emitter.emit(uri)
+  })
+}
+
+function* findPostsInCache(
+  uri: string,
+): Generator<AppBskyFeedDefs.PostView, void> {
+  for (let post of findAllPostsInFeedQueryData(queryClient, uri)) {
+    yield post
+  }
+  for (let post of findAllPostsInNotifsQueryData(queryClient, uri)) {
+    yield post
+  }
+  for (let node of findAllPostsInThreadQueryData(queryClient, uri)) {
+    if (node.type === 'post') {
+      yield node.post
+    }
+  }
+}