refactor(hot-cache): extract pure helpers + analysis-prune cluster from hotCachePrefetch.ts (#687)

The prefetch worker / replan orchestration and its shared module state
(pendingQueue, workerRunning, debounceTimer, graceEvictTimer) stay
entirely untouched in hotCachePrefetch.ts. Extracted only what does not
touch that state:

- hotCachePrefetch/helpers.ts       pure helpers — entryKey, byte
                                    estimators, debounceMs, frontend
                                    debug log, PREFETCH_AHEAD, PrefetchJob
- hotCachePrefetch/analysisPrune.ts  self-contained analysis-queue prune
                                    cluster (its own analysisPruneTimer +
                                    lastAnalysisPruneSig state, fully
                                    encapsulated behind a
                                    resetAnalysisPruneState wrapper)

Verbatim moves. The orchestration core diff is import-block + the three
analysis-cleanup lines collapsing to resetAnalysisPruneState() — nothing
else. The MainApp call site imports initHotCachePrefetch unchanged.

src/hotCachePrefetch.ts

@@ -2,7 +2,7 @@ import { buildStreamUrl } from './api/subsonicStreamUrl';
 import type { Track } from './store/playerStoreTypes';
 import { invoke } from '@tauri-apps/api/core';
 import { useAuthStore } from './store/authStore';
-import { HOT_CACHE_PROTECT_AFTER_CURRENT, useHotCacheStore, type HotCacheEntry } from './store/hotCacheStore';
+import { useHotCacheStore } from './store/hotCacheStore';
 import { useOfflineStore } from './store/offlineStore';
 import { usePlayerStore } from './store/playerStore';
 import {
@@ -10,126 +10,25 @@ import {
   clearHotCachePreviousGrace,
   getDeferHotCachePrefetch,
 } from './utils/hotCacheGate';
-
-/** Settings → Logging → Debug (`frontend_debug_log` → Rust stderr), same as normalization / lucky-mix. */
-function hotCacheFrontendDebug(payload: Record<string, unknown>): void {
-  if (useAuthStore.getState().loggingMode !== 'debug') return;
-  void invoke('frontend_debug_log', {
-    scope: 'hot-cache',
-    message: JSON.stringify(payload),
-  }).catch(() => {});
-}
-
-/** How many upcoming queue tracks may be prefetched (only current + next are eviction-protected). */
-const PREFETCH_AHEAD = 5;
-
-function entryKey(serverId: string, trackId: string): string {
-  return `${serverId}:${trackId}`;
-}
-
-/** Sum of on-disk bytes for eviction-protected slots (current + next — same span as `evictToFit`). */
-function sumCachedBytesInProtectedWindow(
-  queue: Track[],
-  queueIndex: number,
-  serverId: string,
-  entries: Record<string, HotCacheEntry>,
-): number {
-  const protectLo = Math.max(0, queueIndex);
-  const protectHi = Math.min(queue.length - 1, queueIndex + HOT_CACHE_PROTECT_AFTER_CURRENT);
-  let sum = 0;
-  for (let i = protectLo; i <= protectHi; i++) {
-    const e = entries[entryKey(serverId, queue[i].id)];
-    if (e) sum += e.sizeBytes || 0;
-  }
-  return sum;
-}
-
-/** Conservative size guess so we do not prefetch when the protected window could exceed the cap. */
-function estimateTrackHotCacheBytes(track: Track): number {
-  const sz = track.size;
-  if (typeof sz === 'number' && Number.isFinite(sz) && sz > 0) {
-    return Math.ceil(sz * 1.06);
-  }
-  const dur =
-    typeof track.duration === 'number' && Number.isFinite(track.duration) && track.duration > 0
-      ? track.duration
-      : 240;
-  const sfx = (track.suffix || '').toLowerCase();
-  const lossless = /^(flac|wav|dsf|dff|alac|ape|wv)$/.test(sfx);
-  let kbps =
-    typeof track.bitRate === 'number' && Number.isFinite(track.bitRate) && track.bitRate > 0
-      ? track.bitRate
-      : 320;
-  if (lossless && kbps < 800) {
-    kbps = Math.max(kbps, 900);
-  }
-  const raw = Math.ceil((dur * kbps * 1000) / 8);
-  return Math.max(256 * 1024, Math.ceil(raw * (lossless ? 1.2 : 1.15)));
-}
-
-type PrefetchJob = { trackId: string; serverId: string; suffix: string };
+import {
+  PREFETCH_AHEAD,
+  type PrefetchJob,
+  entryKey,
+  sumCachedBytesInProtectedWindow,
+  estimateTrackHotCacheBytes,
+  hotCacheFrontendDebug,
+  debounceMs,
+} from './hotCachePrefetch/helpers';
+import {
+  scheduleAnalysisQueuePruneFromPlaybackQueue,
+  resetAnalysisPruneState,
+} from './hotCachePrefetch/analysisPrune';
 
 let debounceTimer: ReturnType<typeof setTimeout> | null = null;
 /** Fires `replanNow` once grace for the ex-current track ends so eviction can drop it. */
 let graceEvictTimer: ReturnType<typeof setTimeout> | null = null;
 const pendingQueue: PrefetchJob[] = [];
 let workerRunning = false;
-let analysisPruneTimer: ReturnType<typeof setTimeout> | null = null;
-let lastAnalysisPruneSig = '';
-const ANALYSIS_PRUNE_DEBOUNCE_MS = 1200;
-
-type AnalysisPrunePendingResult = {
-  keepCount: number;
-  httpRemoved: number;
-  cpuRemovedJobs: number;
-  cpuRemovedWaiters: number;
-};
-
-function scheduleAnalysisQueuePruneFromPlaybackQueue(): void {
-  const { queue, currentTrack } = usePlayerStore.getState();
-  const keepTrackIds: string[] = [];
-  const seen = new Set<string>();
-  const pushId = (id: string | undefined | null) => {
-    if (!id) return;
-    const tid = id.trim();
-    if (!tid || seen.has(tid)) return;
-    seen.add(tid);
-    keepTrackIds.push(tid);
-  };
-  pushId(currentTrack?.id);
-  for (const track of queue) {
-    pushId(track.id);
-    if (keepTrackIds.length >= 1000) break;
-  }
-  const sig = JSON.stringify(keepTrackIds);
-  if (sig === lastAnalysisPruneSig) return;
-  lastAnalysisPruneSig = sig;
-  if (analysisPruneTimer) {
-    clearTimeout(analysisPruneTimer);
-    analysisPruneTimer = null;
-  }
-  analysisPruneTimer = setTimeout(() => {
-    analysisPruneTimer = null;
-    void invoke<AnalysisPrunePendingResult>('analysis_prune_pending_to_track_ids', { trackIds: keepTrackIds })
-      .then(result => {
-        if (!result) return;
-        hotCacheFrontendDebug({
-          event: 'analysis-prune',
-          keepCount: result.keepCount,
-          removedHttp: result.httpRemoved,
-          removedCpuJobs: result.cpuRemovedJobs,
-          removedCpuWaiters: result.cpuRemovedWaiters,
-        });
-      })
-      .catch(() => {});
-  }, ANALYSIS_PRUNE_DEBOUNCE_MS);
-}
-
-function debounceMs(): number {
-  const s = useAuthStore.getState().hotCacheDebounceSec;
-  if (!Number.isFinite(s) || s < 0) return 0;
-  return Math.min(600, s) * 1000;
-}
 
 function scheduleEvictAfterPreviousGrace(): void {
   if (graceEvictTimer) {
@@ -454,9 +353,7 @@ export function initHotCachePrefetch(): () => void {
     debounceTimer = null;
     if (graceEvictTimer) clearTimeout(graceEvictTimer);
     graceEvictTimer = null;
-    if (analysisPruneTimer) clearTimeout(analysisPruneTimer);
-    analysisPruneTimer = null;
-    lastAnalysisPruneSig = '';
+    resetAnalysisPruneState();
     pendingQueue.length = 0;
     clearHotCachePreviousGrace();
   };

src/hotCachePrefetch/analysisPrune.ts

@@ -0,0 +1,61 @@
+import { invoke } from '@tauri-apps/api/core';
+import { usePlayerStore } from '../store/playerStore';
+import { hotCacheFrontendDebug } from './helpers';
+
+let analysisPruneTimer: ReturnType<typeof setTimeout> | null = null;
+let lastAnalysisPruneSig = '';
+const ANALYSIS_PRUNE_DEBOUNCE_MS = 1200;
+
+type AnalysisPrunePendingResult = {
+  keepCount: number;
+  httpRemoved: number;
+  cpuRemovedJobs: number;
+  cpuRemovedWaiters: number;
+};
+
+export function scheduleAnalysisQueuePruneFromPlaybackQueue(): void {
+  const { queue, currentTrack } = usePlayerStore.getState();
+  const keepTrackIds: string[] = [];
+  const seen = new Set<string>();
+  const pushId = (id: string | undefined | null) => {
+    if (!id) return;
+    const tid = id.trim();
+    if (!tid || seen.has(tid)) return;
+    seen.add(tid);
+    keepTrackIds.push(tid);
+  };
+  pushId(currentTrack?.id);
+  for (const track of queue) {
+    pushId(track.id);
+    if (keepTrackIds.length >= 1000) break;
+  }
+  const sig = JSON.stringify(keepTrackIds);
+  if (sig === lastAnalysisPruneSig) return;
+  lastAnalysisPruneSig = sig;
+  if (analysisPruneTimer) {
+    clearTimeout(analysisPruneTimer);
+    analysisPruneTimer = null;
+  }
+  analysisPruneTimer = setTimeout(() => {
+    analysisPruneTimer = null;
+    void invoke<AnalysisPrunePendingResult>('analysis_prune_pending_to_track_ids', { trackIds: keepTrackIds })
+      .then(result => {
+        if (!result) return;
+        hotCacheFrontendDebug({
+          event: 'analysis-prune',
+          keepCount: result.keepCount,
+          removedHttp: result.httpRemoved,
+          removedCpuJobs: result.cpuRemovedJobs,
+          removedCpuWaiters: result.cpuRemovedWaiters,
+        });
+      })
+      .catch(() => {});
+  }, ANALYSIS_PRUNE_DEBOUNCE_MS);
+}
+
+/** Tear-down for the analysis-prune state — used by initHotCachePrefetch's cleanup. */
+export function resetAnalysisPruneState(): void {
+  if (analysisPruneTimer) clearTimeout(analysisPruneTimer);
+  analysisPruneTimer = null;
+  lastAnalysisPruneSig = '';
+}

src/hotCachePrefetch/helpers.ts

@@ -0,0 +1,68 @@
+import { invoke } from '@tauri-apps/api/core';
+import type { Track } from '../store/playerStoreTypes';
+import { useAuthStore } from '../store/authStore';
+import { HOT_CACHE_PROTECT_AFTER_CURRENT, type HotCacheEntry } from '../store/hotCacheStore';
+
+/** Settings → Logging → Debug (`frontend_debug_log` → Rust stderr), same as normalization / lucky-mix. */
+export function hotCacheFrontendDebug(payload: Record<string, unknown>): void {
+  if (useAuthStore.getState().loggingMode !== 'debug') return;
+  void invoke('frontend_debug_log', {
+    scope: 'hot-cache',
+    message: JSON.stringify(payload),
+  }).catch(() => {});
+}
+
+/** How many upcoming queue tracks may be prefetched (only current + next are eviction-protected). */
+export const PREFETCH_AHEAD = 5;
+
+export type PrefetchJob = { trackId: string; serverId: string; suffix: string };
+
+export function entryKey(serverId: string, trackId: string): string {
+  return `${serverId}:${trackId}`;
+}
+
+/** Sum of on-disk bytes for eviction-protected slots (current + next — same span as `evictToFit`). */
+export function sumCachedBytesInProtectedWindow(
+  queue: Track[],
+  queueIndex: number,
+  serverId: string,
+  entries: Record<string, HotCacheEntry>,
+): number {
+  const protectLo = Math.max(0, queueIndex);
+  const protectHi = Math.min(queue.length - 1, queueIndex + HOT_CACHE_PROTECT_AFTER_CURRENT);
+  let sum = 0;
+  for (let i = protectLo; i <= protectHi; i++) {
+    const e = entries[entryKey(serverId, queue[i].id)];
+    if (e) sum += e.sizeBytes || 0;
+  }
+  return sum;
+}
+
+/** Conservative size guess so we do not prefetch when the protected window could exceed the cap. */
+export function estimateTrackHotCacheBytes(track: Track): number {
+  const sz = track.size;
+  if (typeof sz === 'number' && Number.isFinite(sz) && sz > 0) {
+    return Math.ceil(sz * 1.06);
+  }
+  const dur =
+    typeof track.duration === 'number' && Number.isFinite(track.duration) && track.duration > 0
+      ? track.duration
+      : 240;
+  const sfx = (track.suffix || '').toLowerCase();
+  const lossless = /^(flac|wav|dsf|dff|alac|ape|wv)$/.test(sfx);
+  let kbps =
+    typeof track.bitRate === 'number' && Number.isFinite(track.bitRate) && track.bitRate > 0
+      ? track.bitRate
+      : 320;
+  if (lossless && kbps < 800) {
+    kbps = Math.max(kbps, 900);
+  }
+  const raw = Math.ceil((dur * kbps * 1000) / 8);
+  return Math.max(256 * 1024, Math.ceil(raw * (lossless ? 1.2 : 1.15)));
+}
+
+export function debounceMs(): number {
+  const s = useAuthStore.getState().hotCacheDebounceSec;
+  if (!Number.isFinite(s) || s < 0) return 0;
+  return Math.min(600, s) * 1000;
+}