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hooks/useDownload.ts

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+import * as FileSystem from 'expo-file-system/legacy';
+import AsyncStorage from '@react-native-async-storage/async-storage';
+import { AppState } from 'react-native';
+import { useDownloadStore } from '../store/downloadStore';
+import { getPlayUrlForDownload } from '../services/bilibili';
+
+// 模块级进度节流
+const lastReportedProgress: Record<string, number> = {};
+
+const QUALITY_LABELS: Record<number, string> = {
+  16: '360P',
+  32: '480P',
+  64: '720P',
+  80: '1080P',
+  112: '1080P+',
+  116: '1080P60',
+};
+
+/** 等待 App 回到前台 */
+function waitForActive(): Promise<void> {
+  return new Promise((resolve) => {
+    if (AppState.currentState === 'active') {
+      resolve();
+      return;
+    }
+    const sub = AppState.addEventListener('change', (nextState) => {
+      if (nextState === 'active') {
+        sub.remove();
+        resolve();
+      }
+    });
+  });
+}
+
+/** 读取本地文件实际大小 */
+async function readFileSize(uri: string): Promise<number | undefined> {
+  try {
+    const info = await FileSystem.getInfoAsync(uri, { size: true });
+    if (info.exists) return (info as any).size as number;
+  } catch {}
+  return undefined;
+}
+
+export function useDownload() {
+  const { tasks, addTask, updateTask, removeTask } = useDownloadStore();
+
+  function taskKey(bvid: string, qn: number) {
+    return `${bvid}_${qn}`;
+  }
+
+  function localPath(bvid: string, qn: number) {
+    return `${FileSystem.documentDirectory}${bvid}_${qn}.mp4`;
+  }
+
+  async function startDownload(
+    bvid: string,
+    cid: number,
+    qn: number,
+    qdesc: string,
+    title: string,
+    cover: string,
+  ) {
+    const key = taskKey(bvid, qn);
+    if (tasks[key]?.status === 'downloading') return;
+
+    addTask(key, {
+      bvid, title, cover, qn,
+      qdesc: qdesc || QUALITY_LABELS[qn] || String(qn),
+      status: 'downloading',
+      progress: 0,
+      createdAt: Date.now(),
+    });
+
+    try {
+      const [url, buvid3, sessdata] = await Promise.all([
+        getPlayUrlForDownload(bvid, cid, qn),
+        AsyncStorage.getItem('buvid3'),
+        AsyncStorage.getItem('SESSDATA'),
+      ]);
+      const dest = localPath(bvid, qn);
+
+      const cookies: string[] = [];
+      if (buvid3) cookies.push(`buvid3=${buvid3}`);
+      if (sessdata) cookies.push(`SESSDATA=${sessdata}`);
+
+      const headers = {
+        Referer: 'https://www.bilibili.com',
+        Origin: 'https://www.bilibili.com',
+        'User-Agent':
+          'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36',
+        ...(cookies.length > 0 && { Cookie: cookies.join('; ') }),
+      };
+
+      const progressCallback = (p: FileSystem.DownloadProgressData) => {
+        const { totalBytesWritten, totalBytesExpectedToWrite } = p;
+        const progress = totalBytesExpectedToWrite > 0
+          ? totalBytesWritten / totalBytesExpectedToWrite : 0;
+        const last = lastReportedProgress[key] ?? -1;
+        if (progress - last >= 0.01) {
+          lastReportedProgress[key] = progress;
+          updateTask(key, { progress });
+        }
+      };
+
+      const resumable = FileSystem.createDownloadResumable(url, dest, { headers }, progressCallback);
+
+      // ── 后台暂停 / 前台续传 ──
+      let pausedByBackground = false;
+      const appStateSub = AppState.addEventListener('change', async (nextState) => {
+        if ((nextState === 'background' || nextState === 'inactive') && !pausedByBackground) {
+          pausedByBackground = true;
+          try { await resumable.pauseAsync(); } catch {}
+        }
+      });
+
+      let result = await resumable.downloadAsync();
+
+      // 如果是因为进入后台被暂停（result 为 null 或抛出连接中断），等回前台续传
+      if (!result?.uri && pausedByBackground) {
+        await waitForActive();
+        pausedByBackground = false;
+        try {
+          result = await resumable.resumeAsync();
+        } catch {
+          result = null;
+        }
+      }
+
+      appStateSub.remove();
+      delete lastReportedProgress[key];
+
+      if (result?.uri) {
+        const fileSize = await readFileSize(result.uri);
+        updateTask(key, {
+          status: 'done', progress: 1, localUri: result.uri,
+          ...(fileSize ? { fileSize } : {}),
+        });
+      } else {
+        updateTask(key, { status: 'error', error: '下载失败' });
+      }
+
+    } catch (e: any) {
+      delete lastReportedProgress[key];
+      console.error('[Download] failed:', e);
+
+      // 连接中断 + 已被后台暂停 → 不报错，等回前台后让用户手动重试即可
+      const isConnectionAbort = (e?.message ?? '').includes('connection a');
+      const msg = isConnectionAbort ? '已暂停，返回应用后可重试' : (e?.message ?? '下载失败');
+      updateTask(key, {
+        status: 'error',
+        error: msg.length > 40 ? msg.slice(0, 40) + '...' : msg,
+      });
+    }
+  }
+
+  function getLocalUri(bvid: string, qn: number): string | undefined {
+    return tasks[taskKey(bvid, qn)]?.localUri;
+  }
+
+  function cancelDownload(bvid: string, qn: number) {
+    removeTask(taskKey(bvid, qn));
+  }
+
+  return { tasks, startDownload, getLocalUri, cancelDownload, taskKey };
+}