feat: add background download manager with progress reporting

Co-authored-by: Cursor <cursoragent@cursor.com>

src-tauri/src/commands/video.rs

@@ -1,5 +1,8 @@
 use crate::models::{CookieSource, VideoMetadata};
-use crate::services::video_resolver;
+use crate::services::{download_manager, video_resolver};
+use serde::Serialize;
+use std::io::{BufRead, BufReader};
+use tauri::ipc::Channel;
 
 #[tauri::command]
 pub async fn resolve_url(
@@ -10,3 +13,76 @@ pub async fn resolve_url(
         .await
         .map_err(|e| format!("Task failed: {e}"))?
 }
+
+#[derive(Clone, Serialize)]
+#[serde(rename_all = "camelCase", tag = "event", content = "data")]
+pub enum DownloadEvent {
+    Progress { percent: f64 },
+    FilePath { path: String },
+    Finished { success: bool, path: String },
+    Error { message: String },
+}
+
+#[tauri::command]
+pub async fn start_download(
+    url: String,
+    cookie_source: CookieSource,
+    on_event: Channel<DownloadEvent>,
+) -> Result<(), String> {
+    tokio::task::spawn_blocking(move || {
+        let temp_dir = std::env::temp_dir()
+            .join("video-clipper")
+            .to_string_lossy()
+            .to_string();
+        std::fs::create_dir_all(&temp_dir)
+            .map_err(|e| format!("Failed to create temp dir: {e}"))?;
+
+        let (mut child, _template) =
+            download_manager::start_download(&url, &cookie_source, &temp_dir)?;
+
+        let Some(stderr) = child.stderr.take() else {
+            let status = child
+                .wait()
+                .map_err(|e| format!("Download failed: {e}"))?;
+            let _ = on_event.send(DownloadEvent::Finished {
+                success: status.success(),
+                path: String::new(),
+            });
+            return Ok(());
+        };
+
+        let reader = BufReader::new(stderr);
+        let mut last_file_path: Option<String> = None;
+
+        for line in reader.lines().map_while(Result::ok) {
+            if let Some(pct) = download_manager::parse_progress_line(&line) {
+                let _ = on_event.send(DownloadEvent::Progress { percent: pct });
+            }
+
+            if line.contains("[download] Destination:")
+                || line.contains("[Merger] Merging formats into")
+            {
+                if let Some(path) = line.split(": ").nth(1) {
+                    let trimmed = path.trim().trim_matches('"').to_string();
+                    let _ = on_event.send(DownloadEvent::FilePath {
+                        path: trimmed.clone(),
+                    });
+                    last_file_path = Some(trimmed);
+                }
+            }
+        }
+
+        let status = child
+            .wait()
+            .map_err(|e| format!("Download failed: {e}"))?;
+        let path = last_file_path.unwrap_or_default();
+        let _ = on_event.send(DownloadEvent::Finished {
+            success: status.success(),
+            path,
+        });
+
+        Ok(())
+    })
+    .await
+    .map_err(|e| format!("Task failed: {e}"))?
+}