//! Post-download pipeline: tags → MusicBrainz canonicalization → album art
//! → embed → library DB. Also scans the downloads folder on startup so
//! pre-existing files join the library.

use std::collections::HashMap;
use std::path::{Path, PathBuf};
use std::sync::{Arc, Mutex};
use tauri::{Emitter, Manager};

use library::Library;
use metadata::{AlbumMeta, MetadataClient};
use tagger::{TagSummary, TagWrite};

const AUDIO_EXTS: [&str; 8] = ["flac", "mp3", "m4a", "ogg", "opus", "wav", "aac", "wma"];

pub struct LibraryState {
    pub library: Arc<Library>,
    pub(crate) metadata: Arc<MetadataClient>,
    /// Unix seconds of the last user-facing catalog command. The library
    /// identity warmer only works while this has been quiet, so background
    /// warmth never queues ahead of a page the user is actually looking at.
    pub(crate) catalog_activity: std::sync::atomic::AtomicU64,
    art_dir: PathBuf,
    /// (artist, album) lowercase → resolved metadata, deduping MB lookups.
    album_cache: tokio::sync::Mutex<HashMap<(String, String), Option<AlbumMeta>>>,
    /// Serializes art fetch per album key.
    art_locks: Mutex<HashMap<String, Arc<tokio::sync::Mutex<()>>>>,
    /// Download-staging dir (`<root>/<user>/<folder>`) → organized album dir.
    /// Lets late-arriving non-audio extras follow their album, after which the
    /// emptied staging dirs are removed.
    staging_targets: Mutex<HashMap<PathBuf, PathBuf>>,
}

impl LibraryState {
    /// Stamp a user-facing catalog command; the identity warmer defers to this.
    pub(crate) fn touch_catalog_activity(&self) {
        self.catalog_activity
            .store(unix_secs(), std::sync::atomic::Ordering::Relaxed);
    }

    fn catalog_idle_secs(&self) -> u64 {
        let last = self
            .catalog_activity
            .load(std::sync::atomic::Ordering::Relaxed);
        if last == 0 {
            u64::MAX
        } else {
            unix_secs().saturating_sub(last)
        }
    }
}

fn unix_secs() -> u64 {
    std::time::SystemTime::now()
        .duration_since(std::time::UNIX_EPOCH)
        .map(|d| d.as_secs())
        .unwrap_or(0)
}

fn warm_name_key(name: &str) -> String {
    name.to_lowercase()
        .chars()
        .filter(|c| c.is_alphanumeric())
        .collect()
}

/// Background identity warmer: once per app start, walk the library's
/// artists (most recently added first) and touch each one's MusicBrainz
/// identity chain, so the 24h disk cache keeps the artists the user actually
/// visits permanently warm — a cold page's slowest stage (3.7-8.5 s of
/// 1 req/s-gated MusicBrainz) becomes a disk read for library artists.
///
/// Politeness rules, in order of importance:
/// - Never compete with the user: work only after 25 s of catalog quiet.
/// - Never rush MusicBrainz: an 8 s gap after every artist that needed real
///   network work (already-warm artists advance after 1 s).
/// - Bounded: at most 150 artists per app start.
fn spawn_identity_warmer(app: tauri::AppHandle) {
    tauri::async_runtime::spawn(async move {
        // Let startup scans and the user's first page own the providers.
        tokio::time::sleep(std::time::Duration::from_secs(90)).await;
        let state = app.state::<LibraryState>();
        let lib = state.library.clone();
        let Ok(Ok(albums)) = tauri::async_runtime::spawn_blocking(move || lib.list_albums()).await
        else {
            return;
        };
        let mut seen = std::collections::HashSet::new();
        let artists: Vec<String> = albums
            .into_iter()
            .map(|album| album.artist)
            .filter(|artist| !artist.trim().is_empty())
            .filter(|artist| seen.insert(warm_name_key(artist)))
            .take(150)
            .collect();
        if artists.is_empty() {
            return;
        }
        log::info!("identity warmer: {} library artists queued", artists.len());
        let mut warmed = 0usize;
        for artist in artists {
            // Yield to the user for as long as they are browsing.
            loop {
                let idle = state.catalog_idle_secs();
                if idle >= 25 {
                    break;
                }
                tokio::time::sleep(std::time::Duration::from_secs(26 - idle)).await;
            }
            let started = std::time::Instant::now();
            let search = state.metadata.catalog_search(&artist).await;
            let deezer_id = search
                .artists
                .iter()
                .find(|candidate| warm_name_key(&candidate.name) == warm_name_key(&artist))
                .map(|candidate| candidate.id);
            if let Some(deezer_id) = deezer_id {
                let _ = state
                    .metadata
                    .catalog_artist_identity(deezer_id, &artist)
                    .await;
                let _ = state.metadata.catalog_artist_socials(deezer_id).await;
                warmed += 1;
            }
            // Real network work earns MusicBrainz a long gap; a disk-warm
            // artist (sub-second) only needs a token pause.
            let gap = if started.elapsed() < std::time::Duration::from_millis(600) {
                1
            } else {
                8
            };
            tokio::time::sleep(std::time::Duration::from_secs(gap)).await;
        }
        log::info!("identity warmer: warmed {warmed} artists");
    });
}

pub fn init(app: &tauri::AppHandle) -> Result<(), String> {
    let data_dir = app.path().app_data_dir().map_err(|e| e.to_string())?;
    std::fs::create_dir_all(&data_dir).map_err(|e| e.to_string())?;
    let art_dir = data_dir.join("art");
    std::fs::create_dir_all(&art_dir).map_err(|e| e.to_string())?;

    let library = Arc::new(Library::open(&data_dir.join("library.db")).map_err(|e| e.to_string())?);
    let repair_library = library.clone();
    let repair_art_dir = art_dir.clone();

    app.manage(LibraryState {
        library,
        // The disk layer only caches slow-moving providers (MusicBrainz,
        // Wikipedia) so a restarted app keeps its supplement/type-hint and
        // description warmth instead of re-serializing MusicBrainz at 1 req/s.
        metadata: Arc::new({
            let client = MetadataClient::new()
                .with_disk_cache(data_dir.join("net-cache-v1"))
                // Its own directory, NOT inside the cache above: that one is
                // pruned by mtime, and these are verdicts rather than cached
                // responses.
                .with_identity_store(data_dir.join("artist-identity-v1"));
            // Hero candidate/scoring diagnostics on demand, so an in-APP hero
            // resolution can be compared against `hero_source_probe` — the two
            // do not always see the same candidate set, and only the app's own
            // trace can explain a selection the user actually saw.
            if std::env::var("SOULSTREAM_HERO_TRACE").is_ok_and(|value| value == "1") {
                client.with_hero_diagnostics()
            } else {
                client
            }
        }),
        catalog_activity: std::sync::atomic::AtomicU64::new(0),
        art_dir,
        album_cache: tokio::sync::Mutex::new(HashMap::new()),
        art_locks: Mutex::new(HashMap::new()),
        staging_targets: Mutex::new(HashMap::new()),
    });

    spawn_identity_warmer(app.clone());

    // Startup: drop rows for deleted files, then index anything new.
    let handle = app.clone();
    tauri::async_runtime::spawn(async move {
        if let Ok(Ok(repaired)) = tauri::async_runtime::spawn_blocking(move || {
            repair_library.repair_art_paths(&repair_art_dir)
        })
        .await
        {
            if repaired > 0 {
                log::info!("library repair: restored {repaired} artwork cache references");
            }
        }
        let state = handle.state::<LibraryState>();
        let lib = state.library.clone();
        let _ = tauri::async_runtime::spawn_blocking(move || lib.prune_missing()).await;
        let lib = state.library.clone();
        if let Ok(Ok(removed)) =
            tauri::async_runtime::spawn_blocking(move || lib.prune_non_audio()).await
        {
            if removed > 0 {
                log::info!("library cleanup: removed {removed} non-audio track rows");
            }
        }
        // Backfill sample-rate / bit-depth / size for tracks indexed before
        // those columns existed, so the Now Playing panel shows full quality
        // info for older library files. Size is the sentinel, so this runs
        // once per file (after prune, every remaining track has a file).
        let lib = state.library.clone();
        let _ = tauri::async_runtime::spawn_blocking(move || {
            let todo = lib.tracks_missing_props().unwrap_or_default();
            if todo.is_empty() {
                return;
            }
            let n = todo.len();
            for (id, path) in todo {
                let p = std::path::Path::new(&path);
                let (sr, bd) = match tagger::read_summary(p) {
                    Ok(s) => (s.sample_rate, s.bit_depth),
                    Err(_) => (None, None),
                };
                let size = std::fs::metadata(p).ok().map(|m| m.len());
                let _ = lib.set_track_props(id, sr, bd, size);
            }
            log::info!("library backfill: audio props for {n} tracks");
        })
        .await;
        // Old staging leftovers: folders emptied by organizing are removed
        // on the fly now, but sweep empties left behind by earlier runs.
        sweep_empty_dirs(&downloads_dir(&handle), 0);
        scan_downloads(&handle).await;
    });
    Ok(())
}

/// Remove empty directory trees below `dir` (post-order; `dir` itself stays).
fn sweep_empty_dirs(dir: &Path, depth: u8) {
    if depth > 6 {
        return;
    }
    let Ok(entries) = std::fs::read_dir(dir) else {
        return;
    };
    for entry in entries.flatten() {
        let path = entry.path();
        if path.is_dir() {
            sweep_empty_dirs(&path, depth + 1);
            // Fails (harmlessly) unless the directory is empty.
            let _ = std::fs::remove_dir(&path);
        }
    }
}

fn downloads_dir(app: &tauri::AppHandle) -> PathBuf {
    let cfg = crate::config::load(app);
    crate::config::download_dir(app, &cfg)
}

/// Index every audio file under the downloads dir that isn't known yet.
async fn scan_downloads(app: &tauri::AppHandle) {
    let root = downloads_dir(app);
    let mut files = Vec::new();
    collect_audio_files(&root, &mut files, 0);
    if files.is_empty() {
        return;
    }
    log::info!(
        "library scan: {} audio files under {}",
        files.len(),
        root.display()
    );

    let state = app.state::<LibraryState>();
    for path in files {
        let known = {
            let lib = state.library.clone();
            let p = path.to_string_lossy().into_owned();
            tauri::async_runtime::spawn_blocking(move || lib.has_track_path(&p).unwrap_or(false))
                .await
                .unwrap_or(false)
        };
        if !known {
            process_file(app, &path, None).await;
        }
    }
    let _ = app.emit("soulseek:library-changed", ());
}

fn collect_audio_files(dir: &Path, out: &mut Vec<PathBuf>, depth: u8) {
    if depth > 6 {
        return;
    }
    let Ok(entries) = std::fs::read_dir(dir) else {
        return;
    };
    for entry in entries.flatten() {
        let path = entry.path();
        if path.is_dir() {
            collect_audio_files(&path, out, depth + 1);
        } else if path
            .extension()
            .and_then(|e| e.to_str())
            .map(|e| AUDIO_EXTS.contains(&e.to_ascii_lowercase().as_str()))
            .unwrap_or(false)
        {
            out.push(path);
        }
    }
}

/// Run one file through the pipeline. `remote_path` (when this came from a
/// fresh download) improves folder-based metadata parsing.
pub async fn process_file(app: &tauri::AppHandle, local_path: &Path, remote_path: Option<&str>) {
    // Download responses include album artwork and metadata sidecars. Never
    // feed those files to tag parsing or the library database.
    if !is_audio_path(local_path) {
        log::debug!("non-audio download {}", local_path.display());
        // If the rest of this staging folder was already organized, send this
        // extra (cover art, log, cue…) after its album and tidy the folder.
        if remote_path.is_some() {
            if let Some(parent) = local_path.parent() {
                let album_dir = app
                    .state::<LibraryState>()
                    .staging_targets
                    .lock()
                    .unwrap()
                    .get(parent)
                    .cloned();
                if let Some(album_dir) = album_dir {
                    cleanup_staging(app, parent, &album_dir);
                }
            }
        }
        return;
    }
    let state = app.state::<LibraryState>();

    // 1. Existing tags (retry once: freshly-written files can be briefly
    // locked by AV/indexing on Windows).
    let mut summary = TagSummary::default();
    for attempt in 0..2 {
        let p = local_path.to_path_buf();
        match tauri::async_runtime::spawn_blocking(move || tagger::read_summary(&p)).await {
            Ok(Ok(s)) => {
                summary = s;
                break;
            }
            Ok(Err(e)) if attempt == 0 => {
                log::warn!(
                    "tag read failed for {} (retrying): {e}",
                    local_path.display()
                );
                tokio::time::sleep(std::time::Duration::from_millis(750)).await;
            }
            Ok(Err(e)) => log::warn!("tag read failed for {}: {e}", local_path.display()),
            Err(e) => log::warn!("tag read task failed for {}: {e}", local_path.display()),
        }
    }
    let summary: TagSummary = summary;

    // 2. Fill gaps from the path (remote path preferred: original layout).
    let parsed = tagger::parse_from_path(remote_path.unwrap_or(&local_path.to_string_lossy()));
    let artist_guess = summary.artist.clone().or(parsed.artist.clone());
    let album_guess = summary.album.clone().or(parsed.album.clone());
    let title = summary
        .title
        .clone()
        .or(parsed.title.clone())
        .unwrap_or_else(|| {
            local_path
                .file_stem()
                .unwrap_or_default()
                .to_string_lossy()
                .into_owned()
        });

    // 3. Canonicalize via MusicBrainz (cached per album).
    let meta = match (&artist_guess, &album_guess) {
        (Some(artist), Some(album)) => {
            let key = (artist.to_lowercase(), album.to_lowercase());
            let mut cache = state.album_cache.lock().await;
            if let Some(cached) = cache.get(&key) {
                cached.clone()
            } else {
                let looked = state.metadata.lookup_album(artist, album).await;
                cache.insert(key, looked.clone());
                looked
            }
        }
        _ => None,
    };

    let final_artist = meta
        .as_ref()
        .map(|m| m.artist.clone())
        .or(artist_guess)
        .unwrap_or_else(|| "Unknown Artist".into());
    let final_album = meta
        .as_ref()
        .map(|m| m.album.clone())
        .or(album_guess)
        .unwrap_or_else(|| "Unknown Album".into());
    let final_year = summary
        .year
        .or(parsed.year)
        .or(meta.as_ref().and_then(|m| m.year));
    let release_date = meta
        .as_ref()
        .and_then(|m| m.release_date.clone())
        .or_else(|| final_year.map(|year| year.to_string()));
    let mbid = meta.as_ref().and_then(|m| m.release_mbid.clone());

    // A repeated save downloads (or copies from the stream cache) into a
    // staging folder first.  Do this check before organization: otherwise the
    // collision-safe filename suffix (" (2)") makes it a new path and creates
    // a duplicate track row for the same song.
    if remote_path.is_some() {
        let lib = state.library.clone();
        let artist = final_artist.clone();
        let album = final_album.clone();
        let track = title.clone();
        match tauri::async_runtime::spawn_blocking(move || lib.has_track(&artist, &album, &track))
            .await
        {
            Ok(Ok(true)) => {
                log::info!(
                    "skipping duplicate library track: {} — {} — {}",
                    final_artist,
                    final_album,
                    title
                );
                if let Err(e) = std::fs::remove_file(local_path) {
                    log::warn!(
                        "could not discard duplicate staging file {}: {e}",
                        local_path.display()
                    );
                }
                return;
            }
            Ok(Err(e)) => log::warn!("could not check for duplicate library track: {e}"),
            Err(e) => log::warn!("duplicate library check task failed: {e}"),
            Ok(Ok(false)) => {}
        }
    }

    // 4. Album art (once per album; serialized against concurrent tracks).
    let rg_mbid = meta.as_ref().and_then(|m| m.release_group_mbid.clone());
    let art_path = fetch_art_cached(
        &state,
        &final_artist,
        &final_album,
        mbid.as_deref(),
        rg_mbid.as_deref(),
        false,
    )
    .await;

    let artist_art_path = fetch_artist_art_cached(&state, &final_artist).await;

    // 5. Write tags. Fresh downloads carry the canonical cover, replacing
    // whatever picture the uploader embedded (config-gated) so the file, the
    // library, and the catalog all show the same artwork. Startup-scanned
    // files are never stripped: they only gain art when they have none.
    let cfg = crate::config::load(app);
    let replace_embedded = remote_path.is_some() && crate::config::replace_embedded_art(&cfg);
    let embed_max_edge = crate::config::embed_art_max_edge(&cfg);
    let art_bytes = match (&art_path, replace_embedded || !summary.has_art) {
        (Some(p), true) => std::fs::read(p).ok(),
        _ => None,
    };
    let write = TagWrite {
        artist: summary.artist.is_none().then_some(final_artist.clone()),
        album_artist: summary
            .album_artist
            .is_none()
            .then_some(final_artist.clone()),
        album: summary.album.is_none().then_some(final_album.clone()),
        title: summary.title.is_none().then_some(title.clone()),
        track_no: summary.track_no.or(parsed.track_no),
        year: summary.year.is_none().then(|| final_year).flatten(),
    };
    {
        let p = local_path.to_path_buf();
        let res = tauri::async_runtime::spawn_blocking(move || {
            let embed = art_bytes.map(|b| prepare_embed_art(b, embed_max_edge));
            tagger::write_tags(&p, &write, embed.as_deref(), replace_embedded)
        })
        .await;
        if let Ok(Err(e)) = res {
            log::warn!("tagging {} failed: {e}", local_path.display());
        }
    }

    // 6. Fresh downloads become part of the managed library/share folder.
    // Keep an existing library exactly where it is; reorganizing old files is
    // a deliberate future action, not a surprise side effect of startup scan.
    let library_path = if remote_path.is_some() {
        organize_download(
            app,
            local_path,
            &final_artist,
            &final_album,
            release_date.as_deref(),
            final_year,
        )
    } else {
        local_path.to_path_buf()
    };

    // 6b. The canonical cover also becomes the album folder's cover.jpg /
    // folder.jpg, so Explorer and any other player show the artwork the app
    // does — stale uploader art under those names is replaced.
    if remote_path.is_some() && crate::config::write_folder_cover(&cfg) {
        if let (Some(album_dir), Some(art)) = (library_path.parent(), &art_path) {
            let (dir, art) = (album_dir.to_path_buf(), art.clone());
            let _ =
                tauri::async_runtime::spawn_blocking(move || write_album_folder_cover(&dir, &art))
                    .await;
        }
    }

    // 7. Library rows.
    {
        let lib = state.library.clone();
        let p = library_path.to_string_lossy().into_owned();
        let art = art_path.as_ref().map(|a| a.to_string_lossy().into_owned());
        let track_no = summary.track_no.or(parsed.track_no);
        let (duration, bitrate) = (summary.duration_secs, summary.bitrate_kbps);
        let (sample_rate, bit_depth) = (summary.sample_rate, summary.bit_depth);
        let size = std::fs::metadata(&library_path).ok().map(|m| m.len());
        let (artist, album, title2) = (final_artist.clone(), final_album.clone(), title.clone());
        let now = std::time::SystemTime::now()
            .duration_since(std::time::UNIX_EPOCH)
            .map(|d| d.as_secs() as i64)
            .unwrap_or(0);
        let res = tauri::async_runtime::spawn_blocking(move || -> library::Result<()> {
            let album_id = lib.upsert_album(
                &artist,
                &album,
                final_year,
                art.as_deref(),
                artist_art_path.as_deref(),
                mbid.as_deref(),
                now,
            )?;
            if let Some(a) = &art {
                lib.set_album_art(album_id, a)?;
            }
            lib.upsert_track(
                album_id,
                track_no,
                &title2,
                &artist,
                duration,
                bitrate,
                sample_rate,
                bit_depth,
                size,
                &p,
                now,
            )?;
            Ok(())
        })
        .await;
        if let Ok(Err(e)) = res {
            log::warn!("library insert for {} failed: {e}", local_path.display());
        }
    }

    let _ = app.emit("soulseek:library-changed", ());
}

async fn fetch_artist_art_cached(
    state: &tauri::State<'_, LibraryState>,
    artist: &str,
) -> Option<String> {
    let key: String = artist
        .to_lowercase()
        .chars()
        .map(|c| if c.is_ascii_alphanumeric() { c } else { '_' })
        .collect();
    let target = state.art_dir.join(format!("artist-{key}.jpg"));
    let original = state.art_dir.join(format!("artist-{key}-original"));
    // Older portraits were stored without a source/thumbnail split. Re-fetch
    // those once so the new high-quality thumbnail path takes effect.
    if target.exists() && original.exists() {
        return Some(target.to_string_lossy().into_owned());
    }
    let bytes = state.metadata.fetch_artist_art(artist).await?;
    std::fs::write(&original, &bytes).ok()?;
    write_artist_thumbnail(&bytes, &target)?;
    Some(target.to_string_lossy().into_owned())
}

/// Preserve the original portrait, but hand the webview a clean 512px
/// thumbnail generated with Lanczos3. This is large enough for a 2x card and
/// avoids browser scaling a huge compressed source directly into the tile.
fn write_artist_thumbnail(bytes: &[u8], target: &Path) -> Option<()> {
    let decoded = image::load_from_memory(bytes).ok()?;
    let thumb = decoded.resize(512, 512, image::imageops::FilterType::Lanczos3);
    let mut out = std::io::Cursor::new(Vec::new());
    let encoder = image::codecs::jpeg::JpegEncoder::new_with_quality(&mut out, 92);
    thumb.write_with_encoder(encoder).ok()?;
    std::fs::write(target, out.into_inner()).ok()
}

/// Refresh portraits for every distinct artist already represented in the
/// library. Existing cache files are replaced so Settings can recover from a
/// failed lookup or a poor match.
pub async fn refresh_all_artist_art(app: &tauri::AppHandle) -> Result<usize, String> {
    let state = app.state::<LibraryState>();
    let albums = {
        let lib = state.library.clone();
        tauri::async_runtime::spawn_blocking(move || lib.list_albums())
            .await
            .map_err(|e| e.to_string())?
            .map_err(|e| e.to_string())?
    };
    let mut artists = std::collections::BTreeSet::new();
    for album in albums {
        artists.insert(album.artist);
    }
    let mut refreshed = 0;
    for artist in artists {
        let key: String = artist
            .to_lowercase()
            .chars()
            .map(|c| if c.is_ascii_alphanumeric() { c } else { '_' })
            .collect();
        let target = state.art_dir.join(format!("artist-{key}.jpg"));
        let original = state.art_dir.join(format!("artist-{key}-original"));
        let _ = std::fs::remove_file(&target);
        let _ = std::fs::remove_file(&original);
        if let Some(bytes) = state.metadata.fetch_artist_art(&artist).await {
            if std::fs::write(&original, &bytes).is_ok()
                && write_artist_thumbnail(&bytes, &target).is_some()
            {
                let path = target.to_string_lossy().into_owned();
                let lib = state.library.clone();
                let artist2 = artist.clone();
                tauri::async_runtime::spawn_blocking(move || lib.set_artist_art(&artist2, &path))
                    .await
                    .map_err(|e| e.to_string())?
                    .map_err(|e| e.to_string())?;
                refreshed += 1;
            }
        }
    }
    let _ = app.emit("soulseek:library-changed", ());
    Ok(refreshed)
}

pub fn is_audio_path(path: &Path) -> bool {
    path.extension()
        .and_then(|e| e.to_str())
        .map(|e| AUDIO_EXTS.contains(&e.to_ascii_lowercase().as_str()))
        .unwrap_or(false)
}

/// Move a newly completed download into one album directory under the managed
/// root. The filename remains intact, preserving track numbering supplied by
/// the source. If a matching file exists, retain both files with a suffix.
fn organize_download(
    app: &tauri::AppHandle,
    source: &Path,
    artist: &str,
    album: &str,
    release_date: Option<&str>,
    year: Option<u32>,
) -> PathBuf {
    let cfg = crate::config::load(app);
    let date = display_date(release_date).unwrap_or_else(|| {
        year.map(|y| y.to_string())
            .unwrap_or_else(|| "Unknown date".into())
    });
    let rendered = render_layout(
        crate::config::library_layout(&cfg),
        artist,
        album,
        &date,
        year,
    );
    // Separators written in the layout create subfolders. Separators inside
    // tag values were flattened by render_layout, so metadata can neither
    // split folders nor escape the library root ("..", trailing dots and
    // empty segments are dropped by safe_segment).
    let mut target_dir = crate::config::download_dir(app, &cfg);
    let mut depth = 0;
    for seg in rendered.split(['/', '\\']) {
        let seg = safe_segment(seg);
        if seg.is_empty() {
            continue;
        }
        target_dir = target_dir.join(seg);
        depth += 1;
    }
    if depth == 0 {
        target_dir = target_dir.join("Unknown Album");
    }
    if std::fs::create_dir_all(&target_dir).is_err() {
        return source.to_path_buf();
    }
    let name = source.file_name().unwrap_or_default().to_string_lossy();
    let mut target = target_dir.join(safe_component(&name));
    if source == target {
        return source.to_path_buf();
    }
    if target.exists() {
        let stem = target
            .file_stem()
            .unwrap_or_default()
            .to_string_lossy()
            .into_owned();
        let ext = target
            .extension()
            .map(|e| format!(".{}", e.to_string_lossy()))
            .unwrap_or_default();
        for n in 2..10_000 {
            let candidate = target_dir.join(format!("{stem} ({n}){ext}"));
            if !candidate.exists() {
                target = candidate;
                break;
            }
        }
    }
    match std::fs::rename(source, &target) {
        Ok(()) => {
            // Remember where this staging folder's album lives, then tidy it:
            // once the last track leaves, remaining extras follow and the
            // empty staging dirs are removed.
            if let Some(parent) = source.parent() {
                app.state::<LibraryState>()
                    .staging_targets
                    .lock()
                    .unwrap()
                    .insert(parent.to_path_buf(), target_dir.clone());
                cleanup_staging(app, parent, &target_dir);
            }
            target
        }
        Err(e) => {
            log::warn!("could not organize {}: {e}", source.display());
            source.to_path_buf()
        }
    }
}

/// Non-audio files worth keeping next to the organized album.
const EXTRA_EXTS: &[&str] = &[
    "jpg", "jpeg", "png", "gif", "webp", "bmp", "nfo", "txt", "log", "cue", "m3u", "m3u8", "pdf",
    "sfv", "md5", "accurip",
];

/// If `staging` holds no more audio or in-flight downloads, move its album
/// extras into `album_dir` and delete the emptied staging directories up to
/// (but excluding) the download root. Backs off untouched at the first sign
/// of anything unexpected: pending `.partial` files, subfolders, or file
/// types outside the extras allowlist.
fn cleanup_staging(app: &tauri::AppHandle, staging: &Path, album_dir: &Path) {
    let root = downloads_dir(app);
    if !staging.starts_with(&root) || staging == root || album_dir.starts_with(staging) {
        return;
    }
    let Ok(entries) = std::fs::read_dir(staging) else {
        return;
    };
    let mut extras = Vec::new();
    for entry in entries.flatten() {
        let path = entry.path();
        if path.is_dir() || is_audio_path(&path) {
            return;
        }
        let ext = path
            .extension()
            .and_then(|e| e.to_str())
            .map(|e| e.to_ascii_lowercase())
            .unwrap_or_default();
        if ext == "partial" || !EXTRA_EXTS.contains(&ext.as_str()) {
            return;
        }
        extras.push(path);
    }
    for src in extras {
        let name = src
            .file_name()
            .unwrap_or_default()
            .to_string_lossy()
            .into_owned();
        let dst = album_dir.join(safe_component(&name));
        if dst.exists() {
            // The album already has this extra; the copy adds nothing.
            let _ = std::fs::remove_file(&src);
        } else if std::fs::rename(&src, &dst).is_err() {
            return; // locked or cross-volume oddity: keep the folder
        }
    }
    let mut dir = staging.to_path_buf();
    while dir != root && dir.starts_with(&root) && std::fs::remove_dir(&dir).is_ok() {
        app.state::<LibraryState>()
            .staging_targets
            .lock()
            .unwrap()
            .remove(&dir);
        match dir.parent() {
            Some(p) => dir = p.to_path_buf(),
            None => break,
        }
    }
}

fn render_layout(layout: &str, artist: &str, album: &str, date: &str, year: Option<u32>) -> String {
    layout
        .replace("{artist}", &clean_chars(artist))
        .replace("{album}", &clean_chars(album))
        .replace("{date}", &clean_chars(date))
        .replace(
            "{year}",
            &year
                .map(|v| v.to_string())
                .unwrap_or_else(|| "Unknown year".into()),
        )
}

/// MusicBrainz uses ISO dates. Display the fully-known dates in the requested
/// day-month-year ordering while preserving partial dates such as "1997".
fn display_date(raw: Option<&str>) -> Option<String> {
    let raw = raw?.trim();
    let parts: Vec<_> = raw.split('-').collect();
    match parts.as_slice() {
        [year, month, day] if year.len() == 4 && month.len() == 2 && day.len() == 2 => {
            Some(format!("{day}-{month}-{year}"))
        }
        _ if !raw.is_empty() => Some(raw.to_string()),
        _ => None,
    }
}

/// Replace characters Windows forbids in file names.
fn clean_chars(value: &str) -> String {
    value
        .chars()
        .map(|c| match c {
            '<' | '>' | ':' | '"' | '/' | '\\' | '|' | '?' | '*' => '_',
            c if (c as u32) < 0x20 => '_',
            c => c,
        })
        .collect()
}

/// One path segment: cleaned and trimmed; Windows rejects trailing dots and
/// spaces. May return an empty string (caller decides the fallback).
fn safe_segment(value: &str) -> String {
    clean_chars(value)
        .trim()
        .trim_end_matches([' ', '.'])
        .to_string()
}

fn safe_component(value: &str) -> String {
    let trimmed = safe_segment(value);
    if trimmed.is_empty() {
        "Unknown Album".into()
    } else {
        trimmed
    }
}

/// `<art_dir>/<artist - album>.jpg`, fetched at most once per album.
/// `force` refetches even when a cached file exists.
pub async fn fetch_art_cached(
    state: &tauri::State<'_, LibraryState>,
    artist: &str,
    album: &str,
    mbid: Option<&str>,
    rg_mbid: Option<&str>,
    force: bool,
) -> Option<PathBuf> {
    let key: String = format!("{artist} - {album}")
        .to_lowercase()
        .chars()
        .map(|c| match c {
            '<' | '>' | ':' | '"' | '/' | '\\' | '|' | '?' | '*' => '_',
            c if (c as u32) < 0x20 => '_',
            c => c,
        })
        .collect();
    let target = state.art_dir.join(format!("{key}.jpg"));

    let lock = {
        let mut locks = state.art_locks.lock().unwrap();
        locks
            .entry(key.clone())
            .or_insert_with(|| Arc::new(tokio::sync::Mutex::new(())))
            .clone()
    };
    let _guard = lock.lock().await;

    if target.exists() && !force {
        return Some(target);
    }
    let bytes = state
        .metadata
        .fetch_art(mbid, rg_mbid, artist, album)
        .await?;
    std::fs::write(&target, &bytes).ok()?;
    log::info!(
        "album art saved: {} ({} KB)",
        target.display(),
        bytes.len() / 1024
    );
    Some(target)
}

/// Downscale the canonical cover for embedding into audio files. `max_edge`
/// 0 embeds the original untouched; anything already at or under the cap
/// passes through byte-for-byte. Oversized covers are Lanczos3-resized and
/// re-encoded as JPEG 92 so a 3000px original doesn't add megabytes to every
/// track — the full-resolution file stays in the art cache and album folder.
fn prepare_embed_art(bytes: Vec<u8>, max_edge: u32) -> Vec<u8> {
    if max_edge == 0 {
        return bytes;
    }
    let Ok(img) = image::load_from_memory(&bytes) else {
        return bytes;
    };
    if img.width().max(img.height()) <= max_edge {
        return bytes;
    }
    let resized = img.resize(max_edge, max_edge, image::imageops::FilterType::Lanczos3);
    let mut output = std::io::Cursor::new(Vec::new());
    let encoder = image::codecs::jpeg::JpegEncoder::new_with_quality(&mut output, 92);
    match resized.into_rgb8().write_with_encoder(encoder) {
        Ok(()) => output.into_inner(),
        Err(_) => bytes,
    }
}

/// Write the canonical cover into the album folder as `cover.jpg` and
/// `folder.jpg` — the two names Explorer and virtually every player read.
/// Rare PNG originals are re-encoded as JPEG 95 so the extension never lies.
/// A same-length file is assumed already ours and skipped.
fn write_album_folder_cover(album_dir: &Path, art_file: &Path) {
    let Ok(bytes) = std::fs::read(art_file) else {
        return;
    };
    let jpeg = if bytes.starts_with(b"\x89PNG") {
        let Ok(img) = image::load_from_memory(&bytes) else {
            return;
        };
        let mut output = std::io::Cursor::new(Vec::new());
        let encoder = image::codecs::jpeg::JpegEncoder::new_with_quality(&mut output, 95);
        if img.into_rgb8().write_with_encoder(encoder).is_err() {
            return;
        }
        output.into_inner()
    } else {
        bytes
    };
    // Always write the two canonical names, and additionally overwrite any
    // *existing* generic art-slot file an uploader left behind (albumart.jpg,
    // front.jpg, …) — players that prefer those names must not show stale art.
    // Only .jpg/.jpeg names are replaced in place; scans/booklets keep their
    // distinctive filenames and are never touched.
    const GENERIC_ART_NAMES: [&str; 6] = [
        "albumart.jpg",
        "albumart.jpeg",
        "album.jpg",
        "front.jpg",
        "front.jpeg",
        "thumb.jpg",
    ];
    let existing_generic: Vec<String> = std::fs::read_dir(album_dir)
        .map(|entries| {
            entries
                .flatten()
                .filter_map(|e| e.file_name().into_string().ok())
                .filter(|n| GENERIC_ART_NAMES.contains(&n.to_ascii_lowercase().as_str()))
                .collect()
        })
        .unwrap_or_default();
    for name in ["cover.jpg", "folder.jpg"]
        .into_iter()
        .chain(existing_generic.iter().map(String::as_str))
    {
        let target = album_dir.join(name);
        let already_ours = std::fs::metadata(&target)
            .map(|m| m.len() == jpeg.len() as u64)
            .unwrap_or(false);
        if already_ours {
            continue;
        }
        if let Err(e) = std::fs::write(&target, &jpeg) {
            log::warn!("could not write album cover {}: {e}", target.display());
        }
    }
}

/// Force-refetch an album's art with fresh MusicBrainz data and re-embed
/// it into every track (replacing whatever is there).
pub async fn refresh_album_art(app: &tauri::AppHandle, album_id: i64) -> Result<String, String> {
    let state = app.state::<LibraryState>();

    let lib = state.library.clone();
    let row = tauri::async_runtime::spawn_blocking(move || lib.get_album(album_id))
        .await
        .map_err(|e| e.to_string())?
        .map_err(|e| e.to_string())?
        .ok_or("album not found")?;
    let (album, _stored_mbid) = row;

    // Fresh lookup for both MBIDs (the DB only stores the release MBID).
    let meta = state
        .metadata
        .lookup_album(&album.artist, &album.title)
        .await;
    let mbid = meta.as_ref().and_then(|m| m.release_mbid.clone());
    let rg_mbid = meta.as_ref().and_then(|m| m.release_group_mbid.clone());

    let art_path = fetch_art_cached(
        &state,
        &album.artist,
        &album.title,
        mbid.as_deref(),
        rg_mbid.as_deref(),
        true,
    )
    .await
    .ok_or("no art found for this album")?;

    let art_str = art_path.to_string_lossy().into_owned();
    {
        let lib = state.library.clone();
        let a = art_str.clone();
        tauri::async_runtime::spawn_blocking(move || lib.set_album_art(album_id, &a))
            .await
            .map_err(|e| e.to_string())?
            .map_err(|e| e.to_string())?;
    }

    // Re-embed into every track, replacing the old picture, and refresh the
    // album folder's cover.jpg/folder.jpg so every surface agrees again.
    let cfg = crate::config::load(app);
    let embed_max_edge = crate::config::embed_art_max_edge(&cfg);
    let lib = state.library.clone();
    let tracks = tauri::async_runtime::spawn_blocking(move || lib.album_tracks(album_id))
        .await
        .map_err(|e| e.to_string())?
        .map_err(|e| e.to_string())?;
    let bytes = std::fs::read(&art_path).map_err(|e| e.to_string())?;
    let embed = {
        let b = bytes.clone();
        tauri::async_runtime::spawn_blocking(move || prepare_embed_art(b, embed_max_edge))
            .await
            .map_err(|e| e.to_string())?
    };
    let mut album_dirs = std::collections::BTreeSet::new();
    for t in &tracks {
        if let Some(dir) = Path::new(&t.path).parent() {
            album_dirs.insert(dir.to_path_buf());
        }
    }
    for t in tracks {
        let b = embed.clone();
        let p = PathBuf::from(&t.path);
        let res = tauri::async_runtime::spawn_blocking(move || tagger::replace_art(&p, &b)).await;
        if let Ok(Err(e)) = res {
            log::warn!("re-embed art failed for {}: {e}", t.path);
        }
    }
    if crate::config::write_folder_cover(&cfg) {
        let art = art_path.clone();
        let _ = tauri::async_runtime::spawn_blocking(move || {
            for dir in album_dirs {
                write_album_folder_cover(&dir, &art);
            }
        })
        .await;
    }

    let _ = app.emit("soulseek:library-changed", ());
    Ok(art_str)
}

/// Upgrade every library album to the canonical high-resolution cover:
/// refetch, re-embed, and rewrite folder covers. Returns how many albums
/// succeeded. MusicBrainz throttling makes this roughly one album per
/// second; progress lands in the log.
pub async fn refresh_all_album_art(app: &tauri::AppHandle) -> Result<usize, String> {
    let state = app.state::<LibraryState>();
    let albums = {
        let lib = state.library.clone();
        tauri::async_runtime::spawn_blocking(move || lib.list_albums())
            .await
            .map_err(|e| e.to_string())?
            .map_err(|e| e.to_string())?
    };
    let total = albums.len();
    let mut refreshed = 0;
    for (i, album) in albums.into_iter().enumerate() {
        match refresh_album_art(app, album.id).await {
            Ok(_) => refreshed += 1,
            Err(e) => log::warn!(
                "art refresh failed for {} - {}: {e}",
                album.artist,
                album.title
            ),
        }
        log::info!("album art refresh: {}/{total}", i + 1);
    }
    Ok(refreshed)
}