优化动漫数据源图片降级策略

src/lib/utils.ts

@@ -159,6 +159,24 @@ type AnimeImageSource =
 const BANGUMI_IMAGE_FALLBACK_UNTIL_KEY = 'bangumiImageFallbackUntil';
 const BANGUMI_IMAGE_FALLBACK_SIGNATURE_KEY = 'bangumiImageFallbackSignature';
 const BANGUMI_IMAGE_FALLBACK_DURATION = 60 * 60 * 1000;
+/** 探测主源图片域主页超时（404 也算通） */
+const BANGUMI_IMAGE_PROBE_TIMEOUT_MS = 5000;
+/** 探测成功后的内存缓存，避免列表刷屏时重复探测 */
+const BANGUMI_IMAGE_PROBE_OK_TTL_MS = 15 * 60 * 1000;
+
+type BangumiImageProbeCache = {
+  signature: string;
+  reachable: boolean | null;
+  okUntil: number;
+  inflight: Promise<boolean> | null;
+};
+
+let bangumiImageProbeCache: BangumiImageProbeCache = {
+  signature: '',
+  reachable: null,
+  okUntil: 0,
+  inflight: null,
+};
 
 function normalizeBaseUrl(baseUrl: string): string {
   return baseUrl.trim().replace(/\/+$/, '');
@@ -239,10 +257,50 @@ function getBangumiImageFallbackSignature(): string {
   });
 }
 
+function getBangumiImageProbeSignature(): string {
+  return JSON.stringify({
+    primary: getPrimaryBangumiImageSource(),
+    imageBaseUrl: getBangumiImageBaseUrl(),
+  });
+}
+
+/** 当前主源图片域 origin；server-proxy 无需探测返回 null */
+function getBangumiImageProbeOrigin(): string | null {
+  const primary = getPrimaryBangumiImageSource();
+  switch (primary) {
+    case 'server-proxy':
+      return null;
+    case 'sakura':
+      return 'https://lain.bangumi.lol';
+    case 'custom-baseurl': {
+      const base = getBangumiImageBaseUrl();
+      if (!base) return 'https://lain.bgm.tv';
+      try {
+        return new URL(base).origin;
+      } catch {
+        return null;
+      }
+    }
+    case 'direct':
+    default:
+      return 'https://lain.bgm.tv';
+  }
+}
+
+export function clearBangumiImageProbeCache(): void {
+  bangumiImageProbeCache = {
+    signature: '',
+    reachable: null,
+    okUntil: 0,
+    inflight: null,
+  };
+}
+
 export function clearBangumiImageFallbackCache(): void {
   if (typeof window === 'undefined') return;
   localStorage.removeItem(BANGUMI_IMAGE_FALLBACK_UNTIL_KEY);
   localStorage.removeItem(BANGUMI_IMAGE_FALLBACK_SIGNATURE_KEY);
+  clearBangumiImageProbeCache();
 }
 
 export function markBangumiImageFallbackActive(): void {
@@ -257,6 +315,92 @@ export function markBangumiImageFallbackActive(): void {
   );
 }
 
+/**
+ * 探测主源图片域是否可达：请求 origin 主页（常见 404），5s 超时 + 防缓存。
+ * no-cors 下任意完成（含 404）视为可达；超时/DNS/断网视为不可达。
+ * 失败时写入 sticky 降级（若有备源）。全局单飞 + 成功缓存 15 分钟。
+ * @returns true=主源可用，false=应走备源
+ */
+export async function ensureBangumiImagePrimaryProbed(): Promise<boolean> {
+  if (typeof window === 'undefined') return true;
+
+  if (isBangumiImageFallbackActive()) {
+    return false;
+  }
+
+  const origin = getBangumiImageProbeOrigin();
+  if (!origin) {
+    return true;
+  }
+
+  const signature = getBangumiImageProbeSignature();
+  const now = Date.now();
+
+  if (
+    bangumiImageProbeCache.signature === signature &&
+    bangumiImageProbeCache.reachable === true &&
+    bangumiImageProbeCache.okUntil > now
+  ) {
+    return true;
+  }
+
+  if (
+    bangumiImageProbeCache.signature === signature &&
+    bangumiImageProbeCache.inflight
+  ) {
+    return bangumiImageProbeCache.inflight;
+  }
+
+  const probePromise = (async (): Promise<boolean> => {
+    const url = `${origin}/?_cb=${Date.now()}_${Math.random()
+      .toString(36)
+      .slice(2, 10)}`;
+    try {
+      await fetch(url, {
+        method: 'GET',
+        mode: 'no-cors',
+        cache: 'no-store',
+        credentials: 'omit',
+        signal: AbortSignal.timeout(BANGUMI_IMAGE_PROBE_TIMEOUT_MS),
+      });
+      bangumiImageProbeCache = {
+        signature,
+        reachable: true,
+        okUntil: Date.now() + BANGUMI_IMAGE_PROBE_OK_TTL_MS,
+        inflight: null,
+      };
+      return true;
+    } catch {
+      bangumiImageProbeCache = {
+        signature,
+        reachable: false,
+        okUntil: 0,
+        inflight: null,
+      };
+      const primary = getPrimaryBangumiImageSource();
+      if (getBackupBangumiImageSource(primary)) {
+        markBangumiImageFallbackActive();
+      }
+      return false;
+    }
+  })();
+
+  bangumiImageProbeCache = {
+    signature,
+    reachable: bangumiImageProbeCache.reachable,
+    okUntil: bangumiImageProbeCache.okUntil,
+    inflight: probePromise,
+  };
+
+  return probePromise;
+}
+
+/** 非阻塞触发主源图片域探测（processImageUrl / 首屏侧调用） */
+export function scheduleBangumiImagePrimaryProbe(): void {
+  if (typeof window === 'undefined') return;
+  void ensureBangumiImagePrimaryProbed();
+}
+
 function normalizeComparableUrl(url: string): string {
   if (typeof window === 'undefined') return url;
 
@@ -441,12 +585,16 @@ export function processImageUrl(originalUrl: string): string {
 
   // 处理 Bangumi 图片代理。直连模式尊重用户选择，不代理图片；
   // 仅在服务器代理 / 自定义 Base URL 模式下使用本站图片代理。
+  // sticky 降级中走备源；否则用主源，并非阻塞探测主源图片域主页（5s，404 算通）。
   if (isBangumiImageUrl(originalUrl)) {
     const primary = getPrimaryBangumiImageSource();
     const backup = getBackupBangumiImageSource(primary);
     if (backup && isBangumiImageFallbackActive()) {
       return buildBangumiImageUrl(originalUrl, backup);
     }
+    if (primary !== 'server-proxy' && backup) {
+      scheduleBangumiImagePrimaryProbe();
+    }
     return buildBangumiImageUrl(originalUrl, primary);
   }