track change qol

src/stores/nowPlayingTrackTransitionStore.ts

@@ -0,0 +1,59 @@
+import { create } from 'zustand';
+import type { PlaybackTarget } from '@/stores/playbackTargetStore';
+
+export type NowPlayingTrackTransitionDirection = 'next' | 'previous';
+
+interface NowPlayingTrackTransitionHint {
+  direction: NowPlayingTrackTransitionDirection;
+  target: PlaybackTarget;
+  issuedAt: number;
+}
+
+interface NowPlayingTrackTransitionStore {
+  hint: NowPlayingTrackTransitionHint | null;
+  markDirection: (
+    direction: NowPlayingTrackTransitionDirection,
+    target: PlaybackTarget,
+  ) => void;
+}
+
+const DIRECTION_HINT_LIFETIME_MS = 5_000;
+
+/**
+ * Short-lived transport intent shared by the independently animated Now
+ * Playing surfaces. It is session-only and never persisted.
+ */
+export const useNowPlayingTrackTransitionStore =
+  create<NowPlayingTrackTransitionStore>((set) => ({
+    hint: null,
+    markDirection: (direction, target) =>
+      set({
+        hint: {
+          direction,
+          target,
+          issuedAt: Date.now(),
+        },
+      }),
+  }));
+
+export function markNowPlayingTrackTransitionDirection(
+  direction: NowPlayingTrackTransitionDirection,
+  target: PlaybackTarget,
+): void {
+  useNowPlayingTrackTransitionStore.getState().markDirection(direction, target);
+}
+
+export function resolveNowPlayingTrackTransitionDirection(
+  hint: NowPlayingTrackTransitionHint | null,
+  target: PlaybackTarget,
+  now = Date.now(),
+): NowPlayingTrackTransitionDirection {
+  if (
+    hint?.target === target &&
+    now - hint.issuedAt >= 0 &&
+    now - hint.issuedAt <= DIRECTION_HINT_LIFETIME_MS
+  ) {
+    return hint.direction;
+  }
+  return 'next';
+}