Detached QPs and hidden replies (#4878)

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

src/state/threadgate-hidden-replies.tsx

@@ -0,0 +1,69 @@
+import React from 'react'
+
+type StateContext = {
+  uris: Set<string>
+  recentlyUnhiddenUris: Set<string>
+}
+type ApiContext = {
+  addHiddenReplyUri: (uri: string) => void
+  removeHiddenReplyUri: (uri: string) => void
+}
+
+const StateContext = React.createContext<StateContext>({
+  uris: new Set(),
+  recentlyUnhiddenUris: new Set(),
+})
+
+const ApiContext = React.createContext<ApiContext>({
+  addHiddenReplyUri: () => {},
+  removeHiddenReplyUri: () => {},
+})
+
+export function Provider({children}: {children: React.ReactNode}) {
+  const [uris, setHiddenReplyUris] = React.useState<Set<string>>(new Set())
+  const [recentlyUnhiddenUris, setRecentlyUnhiddenUris] = React.useState<
+    Set<string>
+  >(new Set())
+
+  const stateCtx = React.useMemo(
+    () => ({
+      uris,
+      recentlyUnhiddenUris,
+    }),
+    [uris, recentlyUnhiddenUris],
+  )
+
+  const apiCtx = React.useMemo(
+    () => ({
+      addHiddenReplyUri(uri: string) {
+        setHiddenReplyUris(prev => new Set(prev.add(uri)))
+        setRecentlyUnhiddenUris(prev => {
+          prev.delete(uri)
+          return new Set(prev)
+        })
+      },
+      removeHiddenReplyUri(uri: string) {
+        setHiddenReplyUris(prev => {
+          prev.delete(uri)
+          return new Set(prev)
+        })
+        setRecentlyUnhiddenUris(prev => new Set(prev.add(uri)))
+      },
+    }),
+    [setHiddenReplyUris],
+  )
+
+  return (
+    <ApiContext.Provider value={apiCtx}>
+      <StateContext.Provider value={stateCtx}>{children}</StateContext.Provider>
+    </ApiContext.Provider>
+  )
+}
+
+export function useThreadgateHiddenReplyUris() {
+  return React.useContext(StateContext)
+}
+
+export function useThreadgateHiddenReplyUrisAPI() {
+  return React.useContext(ApiContext)
+}