Perceptual-hash dedup: desktop UI + shared pipeline (3.7, part 3)

Extracts the dedup pipeline (mtime-gate -> parallel fingerprint -> prune
-> group) into `fingerprint::rebuild_and_group`, returning groups of file
paths. Both front-ends now call it and map paths to their own review
rows — web's run_dedup is refactored onto it (no behaviour change; the
integration test still passes).

Desktop: the 🩺 Maintenance screen gains a "Similar content (perceptual)"
section — a Scan button that runs the fingerprint job on a background
thread (live "N / total" progress via shared atomics + an mpsc result
channel), grouped results with a recommended-keep marker, and a per-group
"Remove non-recommended copies" that deletes via the existing
remove_files path and re-scans. Closes the desktop/web parity gap for
content-aware dedup.

118 tests pass.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app.rs

@@ -43,6 +43,23 @@ enum Screen {
     Maintenance,
 }
 
+/// One video in a perceptual-similarity group (desktop dedup review).
+#[derive(Clone)]
+struct SimVideo {
+    video_id: String,
+    title: String,
+    channel: String,
+    file_size: Option<u64>,
+    files: Vec<PathBuf>,
+    recommended_keep: bool,
+}
+
+/// A cluster of videos that share visual content across different IDs.
+#[derive(Clone)]
+struct SimGroup {
+    videos: Vec<SimVideo>,
+}
+
 #[derive(Clone, PartialEq)]
 enum SortMode {
     Title,
@@ -168,6 +185,13 @@ pub struct App {
     transcript_video: Option<String>,
     transcript_cues: Vec<crate::vtt::Cue>,
     transcript_query: String,
+    // Perceptual dedup (background fingerprint job + results)
+    dedup_running: bool,
+    dedup_started: bool,
+    dedup_progress: std::sync::Arc<(std::sync::atomic::AtomicUsize, std::sync::atomic::AtomicUsize)>,
+    dedup_rx: Option<Receiver<Result<Vec<SimGroup>, String>>>,
+    dedup_groups: Vec<SimGroup>,
+    dedup_error: Option<String>,
     // Scheduler
     last_scheduled_check: Option<Instant>,
     // Cards cache — recomputed only when inputs change
@@ -496,6 +520,15 @@ impl App {
             transcript_video: None,
             transcript_cues: Vec::new(),
             transcript_query: String::new(),
+            dedup_running: false,
+            dedup_started: false,
+            dedup_progress: std::sync::Arc::new((
+                std::sync::atomic::AtomicUsize::new(0),
+                std::sync::atomic::AtomicUsize::new(0),
+            )),
+            dedup_rx: None,
+            dedup_groups: Vec::new(),
+            dedup_error: None,
             last_scheduled_check: None,
             cards_cache: Vec::new(),
             cards_cache_key: None,
@@ -871,6 +904,69 @@ impl App {
         }
     }
 
+    /// Kick off the background perceptual-dedup job: fingerprint new/changed
+    /// videos (cached by mtime), group by visual similarity, deliver the
+    /// result over a channel. No-op if a job is already running.
+    fn start_dedup(&mut self) {
+        if self.dedup_running { return; }
+        let mut inputs = Vec::new();
+        let mut by_path: HashMap<String, SimVideo> = HashMap::new();
+        let mut valid_paths: HashSet<String> = HashSet::new();
+        for ch in &self.library {
+            let channel = ch.name.clone();
+            for v in ch.videos.iter().chain(ch.playlists.iter().flat_map(|p| p.videos.iter())) {
+                let Some(vp) = &v.video_path else { continue };
+                let path_str = vp.display().to_string();
+                valid_paths.insert(path_str.clone());
+                inputs.push(crate::fingerprint::FpInput {
+                    path: vp.clone(),
+                    mtime_unix: v.mtime_unix.map(|m| m as i64).unwrap_or(0),
+                    video_id: v.id.clone(),
+                    duration_secs: v.duration_secs.unwrap_or(0.0),
+                });
+                let mut files = vec![vp.clone()];
+                for p in [v.thumb_path.as_ref(), v.info_path.as_ref(), v.description_path.as_ref()]
+                    .into_iter().flatten() { files.push(p.clone()); }
+                for s in &v.subtitles { files.push(s.path.clone()); }
+                by_path.insert(path_str, SimVideo {
+                    video_id: v.id.clone(), title: v.title.clone(), channel: channel.clone(),
+                    file_size: v.file_size, files, recommended_keep: false,
+                });
+            }
+        }
+        use std::sync::atomic::Ordering;
+        self.dedup_progress.0.store(0, Ordering::Relaxed);
+        self.dedup_progress.1.store(0, Ordering::Relaxed);
+        self.dedup_running = true;
+        self.dedup_started = true;
+        self.dedup_error = None;
+        self.dedup_groups.clear();
+
+        let db = self.db.clone();
+        let progress = self.dedup_progress.clone();
+        let (tx, rx) = std::sync::mpsc::channel();
+        self.dedup_rx = Some(rx);
+        let workers = std::thread::available_parallelism().map(|n| n.get()).unwrap_or(4);
+        std::thread::spawn(move || {
+            let res = crate::fingerprint::rebuild_and_group(
+                &db, inputs, &valid_paths, workers, &progress.0, &progress.1,
+            ).map(|path_groups| {
+                let mut groups = Vec::new();
+                for paths in path_groups {
+                    let mut vids: Vec<SimVideo> =
+                        paths.iter().filter_map(|p| by_path.get(p).cloned()).collect();
+                    if vids.len() < 2 { continue; }
+                    let keep = vids.iter().enumerate()
+                        .max_by_key(|(_, v)| v.file_size.unwrap_or(0)).map(|(i, _)| i);
+                    for (i, v) in vids.iter_mut().enumerate() { v.recommended_keep = Some(i) == keep; }
+                    groups.push(SimGroup { videos: vids });
+                }
+                groups
+            });
+            let _ = tx.send(res);
+        });
+    }
+
     /// Find a video by id anywhere in the library and play it. Used by the
     /// full-text search results, where we only have the id.
     fn play_by_id(&mut self, id: &str) {
@@ -1942,11 +2038,35 @@ impl App {
     fn maintenance_screen(&mut self, ctx: &egui::Context) {
         let report = self.health_report.clone().unwrap_or_default();
 
+        // Drain the background dedup result if it's ready.
+        let mut dedup_done = None;
+        if let Some(rx) = &self.dedup_rx {
+            if let Ok(res) = rx.try_recv() { dedup_done = Some(res); }
+        }
+        if let Some(res) = dedup_done {
+            match res {
+                Ok(groups) => self.dedup_groups = groups,
+                Err(e) => self.dedup_error = Some(e),
+            }
+            self.dedup_running = false;
+            self.dedup_rx = None;
+        }
+
         // Actions are collected during rendering and applied after the closure
         // to avoid borrowing `self` while the report is borrowed immutably.
         let mut to_remove: Vec<PathBuf> = Vec::new();
         let mut to_repair: Vec<String> = Vec::new();
         let mut rescan_health = false;
+        let mut start_dedup = false;
+        let mut dedup_remove: Vec<PathBuf> = Vec::new();
+        let dedup_groups = self.dedup_groups.clone();
+        let dedup_running = self.dedup_running;
+        let dedup_started = self.dedup_started;
+        let dedup_error = self.dedup_error.clone();
+        let (dedup_done_n, dedup_total_n) = {
+            use std::sync::atomic::Ordering;
+            (self.dedup_progress.0.load(Ordering::Relaxed), self.dedup_progress.1.load(Ordering::Relaxed))
+        };
 
         egui::CentralPanel::default().show(ctx, |ui| {
             ui.horizontal(|ui| {
@@ -2026,6 +2146,55 @@ impl App {
                             }
                         });
                     }
+
+                    // ── Similar content (perceptual dedup) ──────────────────
+                    ui.add_space(12.0);
+                    ui.heading("Similar content (perceptual)");
+                    ui.label(egui::RichText::new(
+                        "Finds the same video re-uploaded under a different ID — mirrors, \
+                         re-encodes, resolution changes — by comparing sampled frames. The \
+                         first scan fingerprints your library (a few minutes); it's cached \
+                         after, so re-scans are quick.").weak().small());
+                    if dedup_running {
+                        ui.horizontal(|ui| {
+                            ui.spinner();
+                            let t = if dedup_total_n > 0 { dedup_total_n.to_string() } else { "…".into() };
+                            ui.label(format!("Fingerprinting {dedup_done_n} / {t} new videos…"));
+                        });
+                        ctx.request_repaint(); // keep progress live
+                    } else {
+                        if ui.button("🔍 Scan for similar content").clicked() {
+                            start_dedup = true;
+                        }
+                        if let Some(err) = &dedup_error {
+                            ui.colored_label(egui::Color32::from_rgb(0xf8, 0x71, 0x71),
+                                format!("Last scan error: {err}"));
+                        }
+                        if dedup_started {
+                            ui.label(egui::RichText::new(format!(
+                                "{} similar group(s)", dedup_groups.len())).weak());
+                        }
+                        for (gi, g) in dedup_groups.iter().enumerate() {
+                            ui.group(|ui| {
+                                ui.label(egui::RichText::new(
+                                    format!("Group {} — {} copies", gi + 1, g.videos.len())).strong());
+                                for v in &g.videos {
+                                    let size = v.file_size.map(format_size)
+                                        .unwrap_or_else(|| "no video".to_string());
+                                    let tag = if v.recommended_keep { "✓ keep" } else { "✗ remove" };
+                                    ui.label(format!("  {} · {} · {} — {}",
+                                        v.title, v.channel, size, tag));
+                                }
+                                if ui.button("🗑 Remove non-recommended copies").clicked() {
+                                    for v in &g.videos {
+                                        if !v.recommended_keep {
+                                            dedup_remove.extend(v.files.iter().cloned());
+                                        }
+                                    }
+                                }
+                            });
+                        }
+                    }
             });
         });
 
@@ -2050,11 +2219,25 @@ impl App {
             self.status = format!("Queued {} repair(s) — see Downloads", to_repair.len());
             self.show_downloads = true;
         }
+        if !dedup_remove.is_empty() {
+            let (removed, errors) =
+                crate::maintenance::remove_files(&self.library_root, &dedup_remove);
+            self.status = if errors.is_empty() {
+                format!("Removed {removed} file(s)")
+            } else {
+                format!("Removed {removed} file(s), {} error(s)", errors.len())
+            };
+            changed = true;
+            start_dedup = true; // re-scan so the deleted copies drop out
+        }
         if changed || rescan_health {
             self.rescan();
             self.health_report =
                 Some(crate::maintenance::scan(&self.library_root, &self.library));
         }
+        if start_dedup {
+            self.start_dedup();
+        }
     }
 
     fn stats_screen(&mut self, ctx: &egui::Context) {