feat(download): 下载 weg.fan 镜像前先制作镜像并展示进度

src-tauri/src/backend.rs

@@ -2457,6 +2457,8 @@ struct ModTaskInfo {
     dependencies: Vec<String>,
     cancel_key: String,
     status: DownloadStatus,
+    /// `data` 里的百分比是「制作镜像」阶段的服务端进度，而不是下载进度。
+    mirror_preparing: bool,
     data: String,
     downloaded_bytes: u64,
     total_bytes: u64,
@@ -2468,6 +2470,8 @@ enum DownloadWorkerMessage {
         index: usize,
         progress: DownloadCallbackInfo,
     },
+    /// 下载前的镜像制作进度（weg.fan 镜像才有）。
+    Preparing { index: usize, progress: f32 },
     Finished {
         index: usize,
         result: Result<(), String>,
@@ -2510,6 +2514,7 @@ fn emit_download_failure(
         dependencies: Vec::new(),
         cancel_key: name.to_string(),
         status: DownloadStatus::Failed,
+        mirror_preparing: false,
         data: error,
         downloaded_bytes: 0,
         total_bytes: 0,
@@ -2593,6 +2598,7 @@ fn expand_dependency_graph(
                     dependencies: Vec::new(),
                     cancel_key: cancel_key.clone(),
                     status: DownloadStatus::Waiting,
+                    mirror_preparing: false,
                     data: "0".to_string(),
                     downloaded_bytes: 0,
                     total_bytes: 0,
@@ -2648,8 +2654,10 @@ fn start_waiting_mod_downloads(
         handles.push(std::thread::spawn(move || {
             let result = std::panic::catch_unwind(std::panic::AssertUnwindSafe(|| {
                 let progress_sender = sender.clone();
+                let download_url =
+                    resolve_download_url(&task_url, index, &progress_sender, &cancel_flag)?;
                 download_mod_file(
-                    &task_url,
+                    &download_url,
                     &task_dest,
                     &mut |progress| {
                         let _ = progress_sender
@@ -2733,14 +2741,24 @@ fn download_mod_queue(
         };
         match message {
             DownloadWorkerMessage::Progress { index, progress } => {
+                tasks[index].mirror_preparing = false;
                 tasks[index].data = format!("{:.2}", progress.progress);
                 tasks[index].downloaded_bytes = progress.downloaded_bytes;
                 tasks[index].total_bytes = progress.total_bytes;
                 tasks[index].speed_bytes_per_sec = progress.speed_bytes_per_sec;
                 emit_download_tasks(tasks, on_event, "pending");
             }
+            DownloadWorkerMessage::Preparing { index, progress } => {
+                tasks[index].mirror_preparing = true;
+                tasks[index].data = format!("{progress:.2}");
+                tasks[index].downloaded_bytes = 0;
+                tasks[index].total_bytes = 0;
+                tasks[index].speed_bytes_per_sec = 0.0;
+                emit_download_tasks(tasks, on_event, "pending");
+            }
             DownloadWorkerMessage::Finished { index, result } => {
                 active -= 1;
+                tasks[index].mirror_preparing = false;
                 match result {
                     Ok(()) => {
                         tasks[index].status = DownloadStatus::Finished;
@@ -2791,6 +2809,79 @@ fn download_mod_queue(
     failed || cancel_flag.load(Ordering::Relaxed)
 }
 
+/// 下载前的镜像制作（只有 weg.fan 镜像的下载地址会走到里面）：
+/// 先让镜像开始制作文件、轮询服务端进度并把进度发给下载管理，最后返回可以下载
+/// 的地址。不是镜像地址时原样返回 URL。
+fn prepare_mirror_before_download(
+    url: &str,
+    index: usize,
+    sender: &std::sync::mpsc::Sender<DownloadWorkerMessage>,
+    cancel_flag: &Arc<AtomicBool>,
+) -> anyhow::Result<String> {
+    let prepared = wegfan::prepare_mirror(url, cancel_flag, &mut |current, total| {
+        let progress = if total == 0 {
+            0.0
+        } else {
+            100.0 * current as f32 / total as f32
+        };
+        let _ = sender.send(DownloadWorkerMessage::Preparing { index, progress });
+    })?;
+    Ok(prepared.unwrap_or_else(|| url.to_string()))
+}
+
+/// 制作镜像失败时显示在下载管理里的原因。后面的原始错误来自 wegfan 模块：
+/// `/start` 请求失败、`/status` 查不到（接口不可用）、文件未收录、轮询超时等。
+fn mirror_prepare_failure(error: &anyhow::Error) -> String {
+    format!("制作镜像失败：{error:#}")
+}
+
+/// 决定这次任务用哪个 URL 下载。不是 weg.fan 镜像地址（其它镜像、直连）时原样
+/// 返回；镜像制作失败时返回失败原因，由调用方把任务置为失败——不再悄悄退回直连。
+fn resolve_download_url(
+    url: &str,
+    index: usize,
+    sender: &std::sync::mpsc::Sender<DownloadWorkerMessage>,
+    cancel_flag: &Arc<AtomicBool>,
+) -> Result<String, String> {
+    match prepare_mirror_before_download(url, index, sender, cancel_flag) {
+        Ok(url) => Ok(url),
+        // 取消依旧保持现有的取消语义（任务进入已取消，而不是失败）。
+        Err(error) if cancel_flag.load(Ordering::Relaxed) => Err(error.to_string()),
+        Err(error) => Err(mirror_prepare_failure(&error)),
+    }
+}
+
+#[cfg(test)]
+mod download_mirror_tests {
+    use super::*;
+
+    /// 其它镜像、直连地址不经过镜像制作，按原样下载。
+    #[test]
+    fn non_mirror_urls_are_downloaded_directly() {
+        let (sender, _receiver) = std::sync::mpsc::channel();
+        let cancel_flag = Arc::new(AtomicBool::new(false));
+        for url in [
+            "https://gamebanana.com/dl/844056",
+            "https://celestemodupdater.0x0a.de/banana-mirror/844056.zip",
+        ] {
+            assert_eq!(
+                resolve_download_url(url, 0, &sender, &cancel_flag),
+                Ok(url.to_string())
+            );
+        }
+    }
+
+    /// 制作镜像失败时把原因交给下载任务（界面显示「制作镜像失败：…」），
+    /// 不再回退到直连下载。
+    #[test]
+    fn mirror_failure_reports_the_reason() {
+        let error = anyhow::anyhow!("Failed to query mirror status of 123: connection refused");
+        let message = mirror_prepare_failure(&error);
+        assert!(message.starts_with("制作镜像失败："), "{message}");
+        assert!(message.contains("connection refused"), "{message}");
+    }
+}
+
 fn make_path_compatible_name(name: &str) -> String {
     name.replace([' ', ':', '/', '\\', '?', '*', '\"', '<', '>', '|'], "_")
 }
@@ -3765,6 +3856,7 @@ mod local_package_tests {
                 dependencies: Vec::new(),
                 cancel_key: "A".to_string(),
                 status: DownloadStatus::Waiting,
+                mirror_preparing: false,
                 data: "0".to_string(),
                 downloaded_bytes: 0,
                 total_bytes: 0,
@@ -3778,6 +3870,7 @@ mod local_package_tests {
                 dependencies: Vec::new(),
                 cancel_key: "A".to_string(),
                 status: DownloadStatus::Waiting,
+                mirror_preparing: false,
                 data: "0".to_string(),
                 downloaded_bytes: 0,
                 total_bytes: 0,
@@ -5900,6 +5993,7 @@ fn download_mod_with_roots(
                 dependencies: Vec::new(),
                 cancel_key: name.clone(),
                 status: DownloadStatus::Waiting,
+                mirror_preparing: false,
                 data: String::new(),
                 downloaded_bytes: 0,
                 total_bytes: 0,