siftlode/frontend/src/components/PlaylistsProvider.tsx

import { createContext, useCallback, useContext, useMemo, useState, type ReactNode } from "react";
import { getAccountRaw, LS, setAccountRaw } from "../lib/storage";
import { useAccountRehydrate } from "../lib/useAccountRehydrate";
import { useUrlMirror } from "../lib/useUrlMirror";
import { useNavigation } from "./NavigationProvider";

// Owns the Playlists module's shared local state — the rail's name filter and the selected playlist
// — lifted out of the App god component so the header search box, the PlaylistsRail, and the
// Playlists detail pane read it via hooks instead of prop-drilling through App. Mirrors
// FeedFiltersProvider / NavigationProvider (split State + Actions contexts, one-line hooks; composed
// in main.tsx around <App/>).
//
// The `search` term is ephemeral (resets on reload, like the other list filters); the selected
// playlist is per-account persisted (LS.playlist) so a reload returns you to it. Neither is
// server-synced, and an account switch does a full reload, so init-from-storage is all the
// hydration these need — no per-account load effect (unlike the server-backed feed filters).

type PlaylistsState = {
  search: string;
  selectedId: number | null;
};

interface PlaylistsActions {
  setSearch: (q: string) => void;
  setSelectedId: (id: number | null) => void;
}

const StateContext = createContext<PlaylistsState>({ search: "", selectedId: null });
const ActionsContext = createContext<PlaylistsActions>({
  setSearch: () => {},
  setSelectedId: () => {},
});

export function usePlaylists(): PlaylistsState {
  return useContext(StateContext);
}
export function usePlaylistsActions(): PlaylistsActions {
  return useContext(ActionsContext);
}

function readSelectedId(): number | null {
  // A ?pl bookmark wins over the stored selection so a pasted link opens that playlist. Accept only a
  // positive integer id — a bare "?pl=" gives Number("")===0 (finite!) and "?pl=1.5" a fractional id,
  // both of which would select a non-existent playlist.
  const fromUrl = new URLSearchParams(window.location.search).get("pl");
  const n = fromUrl ? Number(fromUrl) : NaN;
  if (Number.isInteger(n) && n > 0) return n;
  const s = getAccountRaw(LS.playlist);
  return s ? Number(s) : null;
}

export function PlaylistsProvider({ children }: { children: ReactNode }) {
  const [search, setSearchState] = useState("");
  const [selectedId, setSelectedIdState] = useState<number | null>(readSelectedId);

  // Re-read the selected playlist once the account is pinned after mount (first load on a fresh tab):
  // this provider mounts above <App>, which pins the account only after /api/me.
  const markDirty = useAccountRehydrate(() => setSelectedIdState(readSelectedId()));

  const setSearch = useCallback((q: string) => setSearchState(q), []);
  const setSelectedId = useCallback(
    (id: number | null) => {
      markDirty();
      setSelectedIdState(id);
      if (id != null) setAccountRaw(LS.playlist, String(id));
    },
    [markDirty],
  );

  // Mirror the selected playlist to ?pl on the Playlists page so it's bookmarkable; clear it elsewhere
  // (the localStorage copy still restores it on return). useUrlMirror keeps ?page and the other nav
  // params intact.
  const { page } = useNavigation();
  useUrlMirror({ pl: page === "playlists" && selectedId != null ? String(selectedId) : null });

  const state = useMemo<PlaylistsState>(() => ({ search, selectedId }), [search, selectedId]);
  const actions = useMemo<PlaylistsActions>(
    () => ({ setSearch, setSelectedId }),
    [setSearch, setSelectedId],
  );

  return (
    <ActionsContext.Provider value={actions}>
      <StateContext.Provider value={state}>{children}</StateContext.Provider>
    </ActionsContext.Provider>
  );
}