Detached QPs and hidden replies (#4878)

Co-authored-by: Hailey <me@haileyok.com>

src/state/queries/threadgate/util.ts

@@ -0,0 +1,141 @@
+import {AppBskyFeedDefs, AppBskyFeedThreadgate} from '@atproto/api'
+
+import {ThreadgateAllowUISetting} from '#/state/queries/threadgate/types'
+
+export function threadgateViewToAllowUISetting(
+  threadgateView: AppBskyFeedDefs.ThreadgateView | undefined,
+): ThreadgateAllowUISetting[] {
+  const threadgate =
+    threadgateView &&
+    AppBskyFeedThreadgate.isRecord(threadgateView.record) &&
+    AppBskyFeedThreadgate.validateRecord(threadgateView.record).success
+      ? threadgateView.record
+      : undefined
+  return threadgateRecordToAllowUISetting(threadgate)
+}
+
+/**
+ * Converts a full {@link AppBskyFeedThreadgate.Record} to a list of
+ * {@link ThreadgateAllowUISetting}, for use by app UI.
+ */
+export function threadgateRecordToAllowUISetting(
+  threadgate: AppBskyFeedThreadgate.Record | undefined,
+): ThreadgateAllowUISetting[] {
+  /*
+   * If `threadgate` doesn't exist (default), or if `threadgate.allow === undefined`, it means
+   * anyone can reply.
+   *
+   * If `threadgate.allow === []` it means no one can reply, and we translate to UI code
+   * here. This was a historical choice, and we have no lexicon representation
+   * for 'replies disabled' other than an empty array.
+   */
+  if (!threadgate || threadgate.allow === undefined) {
+    return [{type: 'everybody'}]
+  }
+  if (threadgate.allow.length === 0) {
+    return [{type: 'nobody'}]
+  }
+
+  const settings: ThreadgateAllowUISetting[] = threadgate.allow
+    .map(allow => {
+      let setting: ThreadgateAllowUISetting | undefined
+      if (allow.$type === 'app.bsky.feed.threadgate#mentionRule') {
+        setting = {type: 'mention'}
+      } else if (allow.$type === 'app.bsky.feed.threadgate#followingRule') {
+        setting = {type: 'following'}
+      } else if (allow.$type === 'app.bsky.feed.threadgate#listRule') {
+        setting = {type: 'list', list: allow.list}
+      }
+      return setting
+    })
+    .filter(n => !!n)
+  return settings
+}
+
+/**
+ * Converts an array of {@link ThreadgateAllowUISetting} to the `allow` prop on
+ * {@link AppBskyFeedThreadgate.Record}.
+ *
+ * If the `allow` property on the record is undefined, we infer that to mean
+ * that everyone can reply. If it's an empty array, we infer that to mean that
+ * no one can reply.
+ */
+export function threadgateAllowUISettingToAllowRecordValue(
+  threadgate: ThreadgateAllowUISetting[],
+): AppBskyFeedThreadgate.Record['allow'] {
+  if (threadgate.find(v => v.type === 'everybody')) {
+    return undefined
+  }
+
+  let allow: (
+    | AppBskyFeedThreadgate.MentionRule
+    | AppBskyFeedThreadgate.FollowingRule
+    | AppBskyFeedThreadgate.ListRule
+  )[] = []
+
+  if (!threadgate.find(v => v.type === 'nobody')) {
+    for (const rule of threadgate) {
+      if (rule.type === 'mention') {
+        allow.push({$type: 'app.bsky.feed.threadgate#mentionRule'})
+      } else if (rule.type === 'following') {
+        allow.push({$type: 'app.bsky.feed.threadgate#followingRule'})
+      } else if (rule.type === 'list') {
+        allow.push({
+          $type: 'app.bsky.feed.threadgate#listRule',
+          list: rule.list,
+        })
+      }
+    }
+  }
+
+  return allow
+}
+
+/**
+ * Merges two {@link AppBskyFeedThreadgate.Record} objects, combining their
+ * `allow` and `hiddenReplies` arrays and de-deduplicating them.
+ *
+ * Note: `allow` can be undefined here, be sure you don't accidentally set it
+ * to an empty array. See other comments in this file.
+ */
+export function mergeThreadgateRecords(
+  prev: AppBskyFeedThreadgate.Record,
+  next: Partial<AppBskyFeedThreadgate.Record>,
+): AppBskyFeedThreadgate.Record {
+  // can be undefined if everyone can reply!
+  const allow: AppBskyFeedThreadgate.Record['allow'] | undefined =
+    prev.allow || next.allow
+      ? [...(prev.allow || []), ...(next.allow || [])].filter(
+          (v, i, a) => a.findIndex(t => t.$type === v.$type) === i,
+        )
+      : undefined
+  const hiddenReplies = Array.from(
+    new Set([...(prev.hiddenReplies || []), ...(next.hiddenReplies || [])]),
+  )
+
+  return createThreadgateRecord({
+    post: prev.post,
+    allow, // can be undefined!
+    hiddenReplies,
+  })
+}
+
+/**
+ * Create a new {@link AppBskyFeedThreadgate.Record} object with the given
+ * properties.
+ */
+export function createThreadgateRecord(
+  threadgate: Partial<AppBskyFeedThreadgate.Record>,
+): AppBskyFeedThreadgate.Record {
+  if (!threadgate.post) {
+    throw new Error('Cannot create a threadgate record without a post URI')
+  }
+
+  return {
+    $type: 'app.bsky.feed.threadgate',
+    post: threadgate.post,
+    createdAt: new Date().toISOString(),
+    allow: threadgate.allow, // can be undefined!
+    hiddenReplies: threadgate.hiddenReplies || [],
+  }
+}