use super::backend::{PlayerBackend, PlayerError};
use super::events::{PlayerEventEmitter, PlayerStatusEvent};
use super::media::{MediaItem, MediaSource};
use super::state::PlayerState;
use super::stream_end::ObservedTime;
use crate::playback_reporting::{EventThrottler, PlaybackOperation, PlaybackReporter};
use crate::settings::{AudioSettings, VolumeLevel, EQ_BANDS};
use crate::utils::conversions::{seconds_to_ticks, volume_to_percent};
use crate::utils::lock::MutexSafe;
use libmpv::Mpv;
use log::{debug, error, info, warn};
use std::process::Command;
use std::sync::atomic::{AtomicU64, Ordering};
use std::sync::{Arc, Mutex};
use std::time::{Duration, SystemTime, UNIX_EPOCH};
use tokio::sync::Mutex as TokioMutex;

/// MPV-based player backend for Linux
///
/// Uses libmpv for audio playback with full control over playback state,
/// position tracking, and event handling.
pub struct MpvBackend {
    mpv: Arc<Mpv>,
    state: Arc<Mutex<InternalState>>,
    event_emitter: Option<Arc<dyn PlayerEventEmitter>>,
    audio_settings: AudioSettings,
    playback_reporter: Arc<TokioMutex<Option<PlaybackReporter>>>,
    position_throttler: Arc<EventThrottler>,
    last_seek_time: Arc<AtomicU64>,
    /// Last position/duration seen while a file was loaded.
    ///
    /// `time-pos` and `duration` are live properties of the *loaded* file: at
    /// EOF MPV unloads it and both stop resolving, so reading them straight
    /// through reported 0.0 / unknown exactly when end-of-file handling needed to
    /// know where playback reached. See [`ObservedTime`].
    observed: Arc<Mutex<ObservedTime>>,
    /// A seek that arrived before MPV had a file to seek in.
    ///
    /// `loadfile` is asynchronous: it returns as soon as the command is queued,
    /// so `time-pos` is not yet a resolvable property and setting it fails. A
    /// seek issued in that window used to be dropped on the floor, and the two
    /// callers that do exactly this are the ones a viewer notices — resume, and
    /// a transcoded seek, both of which re-open the stream and then ask for a
    /// position. The stream reloaded and played from zero.
    ///
    /// Held here and applied by the `FileLoaded` arm.
    ///
    /// TRACES: UR-040, UR-005 | DR-241
    pending_seek: Arc<Mutex<Option<f64>>>,
}

struct InternalState {
    current_media: Option<MediaItem>,
    volume: f32,
}

/// Detect which audio system is available on the system
fn detect_audio_system() -> String {
    info!("[MpvBackend] Detecting audio system...");

    // Try PulseAudio/PipeWire first (most common on modern Linux)
    if let Ok(output) = Command::new("pactl").arg("info").output() {
        if output.status.success() {
            let stdout = String::from_utf8_lossy(&output.stdout);
            if stdout.contains("PipeWire") {
                info!("[MpvBackend] Detected PipeWire (with PulseAudio compatibility)");
                return "pulse".to_string();
            } else if stdout.contains("PulseAudio") {
                info!("[MpvBackend] Detected PulseAudio");
                return "pulse".to_string();
            }
        }
    }

    // Try detecting PipeWire directly
    if let Ok(output) = Command::new("pw-cli").arg("info").arg("0").output() {
        if output.status.success() {
            info!("[MpvBackend] Detected PipeWire");
            return "pulse".to_string(); // PipeWire works with pulse driver
        }
    }

    // Check if ALSA is available
    if std::path::Path::new("/proc/asound/cards").exists() {
        info!("[MpvBackend] Falling back to ALSA");
        return "alsa".to_string();
    }

    // Default fallback
    warn!("[MpvBackend] Could not detect audio system, using 'auto'");
    "auto".to_string()
}

/// Helper to get stream URL from MediaItem
fn get_stream_url(media: &MediaItem) -> String {
    match &media.source {
        MediaSource::Remote { stream_url, .. } => stream_url.clone(),
        MediaSource::Local { file_path, .. } => {
            format!("file://{}", file_path.to_string_lossy())
        }
        MediaSource::DirectUrl { url } => url.clone(),
    }
}

/// The mpv handle of the backend this process created, for the video surface.
///
/// A `OnceLock` rather than a field reached through `PlayerBackend`, because the
/// trait is cross-platform and a raw mpv pointer is not something every backend
/// should have to pretend to have. Stored as `usize` because a raw pointer is
/// neither `Send` nor `Sync`; the only consumer is the GTK main thread, which is
/// also where mpv was created.
///
/// Written once at construction and never cleared: the backend outlives the
/// window, so there is no window in which this could dangle while a surface is
/// still using it.
///
/// TRACES: UR-080 | DR-231
static MPV_HANDLE: std::sync::OnceLock<usize> = std::sync::OnceLock::new();

/// The registered handle, or null if no MPV backend was created (initialisation
/// can fail, and the app falls back to a no-op backend rather than dying).
///
/// TRACES: UR-080 | DR-231
pub fn registered_handle() -> *mut libmpv_sys::mpv_handle {
    MPV_HANDLE
        .get()
        .map(|p| *p as *mut libmpv_sys::mpv_handle)
        .unwrap_or(std::ptr::null_mut())
}

impl MpvBackend {
    /// Create a new MPV backend
    pub fn new(
        event_emitter: Option<Arc<dyn PlayerEventEmitter>>,
        playback_reporter: Arc<TokioMutex<Option<PlaybackReporter>>>,
        position_throttler: Arc<EventThrottler>,
    ) -> Result<Self, PlayerError> {
        info!("[MpvBackend] Initializing MPV backend...");

        // MPV requires LC_NUMERIC to be set to "C" locale
        // Set it before initializing MPV, then restore it after
        use std::ffi::CString;
        unsafe {
            let c_locale = CString::new("C").unwrap();
            libc::setlocale(libc::LC_NUMERIC, c_locale.as_ptr());
        }

        let mpv = Mpv::new().map_err(|e| PlayerError {
            message: format!("Failed to initialize MPV: {:?}", e),
        })?;

        // Detect and configure audio output
        let audio_driver = detect_audio_system();
        info!(
            "[MpvBackend] Configuring audio output driver: {}",
            audio_driver
        );

        mpv.set_property("ao", audio_driver.as_str())
            .map_err(|e| PlayerError {
                message: format!(
                    "Failed to set audio output to '{}': {:?}. Make sure audio system is working.",
                    audio_driver, e
                ),
            })?;

        // Enable verbose logging for audio initialization
        mpv.set_property("msg-level", "all=warn,ao=debug")
            .unwrap_or_else(|e| {
                warn!("[MpvBackend] Warning: Could not set MPV log level: {:?}", e);
            });

        // Configure MPV for audio playback
        mpv.set_property("audio-display", "no")
            .map_err(|e| PlayerError {
                message: format!("Failed to configure MPV audio-display: {:?}", e),
            })?;

        // Video is disabled unless this process is drawing it.
        //
        // `video: no` is why mpv has never decoded a frame here: Linux video has
        // always gone through the webview, and decoding it twice would burn a
        // core for a picture nobody sees. With native video on, mpv needs both
        // the decoder *and* `vo=libmpv` — the render API only works through that
        // output, and the default would try to open a window of its own.
        //
        // Set at construction because mpv resolves the video output when it
        // initialises; flipping it later does not re-open one.
        //
        // TRACES: UR-080 | DR-231, DR-235
        if super::native_video::enabled() {
            mpv.set_property("vo", "libmpv").map_err(|e| PlayerError {
                message: format!("Failed to select the libmpv video output: {:?}", e),
            })?;
            info!("[MpvBackend] native video enabled (vo=libmpv)");
        } else {
            mpv.set_property("video", "no").map_err(|e| PlayerError {
                message: format!("Failed to configure MPV video: {:?}", e),
            })?;
        }

        // Set volume to 100% (we'll control via MPV's volume property)
        mpv.set_property("volume", 100i64)
            .map_err(|e| PlayerError {
                message: format!("Failed to set initial volume: {:?}", e),
            })?;

        // Survive a flaky connection instead of dying on it. Without these,
        // ffmpeg's HTTP demuxer gives up the moment a read fails and MPV raises
        // EndFile(ERROR) — a blip on wifi kills the track outright. Reconnecting
        // in the demuxer handles the common case entirely below our level, so
        // most outages never reach the recovery in `player_recover_stream`.
        //
        // Non-fatal: these are ffmpeg-side options whose availability varies with
        // the libmpv/ffmpeg build, and losing resilience is not a reason to
        // refuse to play anything (graceful backend init, CLAUDE.md).
        mpv.set_property(
            "stream-lavf-o",
            "reconnect=1,reconnect_streamed=1,reconnect_on_network_error=1,reconnect_delay_max=5",
        )
        .unwrap_or_else(|e| {
            warn!(
                "[MpvBackend] Could not enable stream reconnection: {:?} — \
                 playback will not survive network interruptions",
                e
            );
        });
        mpv.set_property("network-timeout", 15i64)
            .unwrap_or_else(|e| {
                warn!("[MpvBackend] Could not set network timeout: {:?}", e);
            });

        let state = Arc::new(Mutex::new(InternalState {
            current_media: None,
            volume: 1.0,
        }));

        let backend = MpvBackend {
            mpv: {
                let mpv = Arc::new(mpv);
                // Publish the handle for the video surface (DR-231). Ignores a
                // second call: only one MPV backend is ever constructed, and a
                // failed re-init must not replace a live handle.
                let _ = MPV_HANDLE.set(mpv.ctx.as_ptr() as usize);
                mpv
            },
            state,
            event_emitter,
            audio_settings: AudioSettings::default(),
            playback_reporter,
            position_throttler,
            last_seek_time: Arc::new(AtomicU64::new(0)),
            pending_seek: Arc::new(Mutex::new(None)),
            observed: Arc::new(Mutex::new(ObservedTime::default())),
        };

        // Start event loop in background thread
        backend.start_event_loop();

        info!("[MpvBackend] Initialized successfully");
        Ok(backend)
    }

    /// Start the MPV event loop in a background thread
    fn start_event_loop(&self) {
        let mpv = self.mpv.clone();
        let event_emitter = self.event_emitter.clone();
        let state = self.state.clone();
        let reporter = self.playback_reporter.clone();
        let throttler = self.position_throttler.clone();
        let pending_seek_for_events = self.pending_seek.clone();

        std::thread::spawn(move || {
            info!("[MpvBackend] Event loop started");

            let mut ev_ctx = mpv.create_event_context();
            ev_ctx.disable_deprecated_events().unwrap_or_else(|e| {
                error!("[MpvBackend] Failed to disable deprecated events: {:?}", e);
            });

            // libmpv delivers PropertyChange only for properties registered
            // here. Every name matched in the loop below needs a line in this
            // block or its handler is unreachable — an omission that reads as
            // working code, because the handler is sitting right there.
            // UT-218 holds the two lists together.
            //
            // `pause` drives the play/pause control: the UI consumes
            // StateChanged rather than tracking playback itself, per the
            // one-directional state rule. Unobserved, the event never came and
            // the button never moved. Invisible until native video shipped,
            // because the webview <video> element's own DOM events drove that
            // control on Linux.
            //
            // TRACES: UR-005 | DR-239
            ev_ctx
                .observe_property("pause", libmpv::Format::Flag, 0)
                .unwrap_or_else(|e| {
                    error!(
                        "[MpvBackend] Failed to observe 'pause': {:?} — the play/pause \
                         control will not follow the player",
                        e
                    );
                });

            loop {
                match ev_ctx.wait_event(1.0) {
                    Some(Ok(event)) => match event {
                        libmpv::events::Event::StartFile => {
                            debug!("[MpvBackend] Starting file");
                        }
                        libmpv::events::Event::FileLoaded => {
                            info!("[MpvBackend] File loaded");

                            // Apply a seek that arrived while there was nothing
                            // to seek in. TRACES: UR-040, UR-005 | DR-241
                            {
                                let target = pending_seek_for_events.lock_safe().take();
                                if let Some(position) = target {
                                    match mpv.set_property("time-pos", position) {
                                        Ok(()) => info!(
                                            "[MpvBackend] applied deferred seek to {position}"
                                        ),
                                        Err(e) => warn!(
                                            "[MpvBackend] deferred seek to {position} failed: {:?}",
                                            e
                                        ),
                                    }
                                }
                            }

                            // Geometry, so "the picture does not fill the screen"
                            // can be attributed rather than guessed at. `width`/
                            // `height` are the decoded frame; `dwidth`/`dheight`
                            // are what mpv will *display* after aspect
                            // correction. A file that carries its letterbox
                            // baked into the picture reports a 16:9 dwidth and
                            // is then pillarboxed on a wider panel — which looks
                            // identical to a rendering bug from outside.
                            {
                                let n = |k: &str| mpv.get_property::<i64>(k).unwrap_or(-1);
                                info!(
                                    "[MpvBackend] video geometry: {}x{} decoded, {}x{} display, aspect {:?}",
                                    n("width"),
                                    n("height"),
                                    n("dwidth"),
                                    n("dheight"),
                                    mpv.get_property::<f64>("video-params/aspect").ok(),
                                );
                            }

                            // Get duration
                            if let Ok(duration) = mpv.get_property::<f64>("duration") {
                                if let Some(emitter) = &event_emitter {
                                    emitter.emit(PlayerStatusEvent::MediaLoaded { duration });
                                }
                            }
                        }
                        libmpv::events::Event::PlaybackRestart => {
                            debug!("[MpvBackend] Playback started/resumed");

                            let media_id = state
                                .lock_safe()
                                .current_media
                                .as_ref()
                                .map(|m| m.id.clone());

                            if let Some(emitter) = &event_emitter {
                                emitter.emit(PlayerStatusEvent::StateChanged {
                                    state: "playing".to_string(),
                                    media_id,
                                });
                            }
                        }
                        libmpv::events::Event::PropertyChange { name: "pause", .. } => {
                            // Handle pause state changes
                            if let Ok(is_paused) = mpv.get_property::<bool>("pause") {
                                let media_id = state
                                    .lock_safe()
                                    .current_media
                                    .as_ref()
                                    .map(|m| m.id.clone());

                                if let Some(emitter) = &event_emitter {
                                    emitter.emit(PlayerStatusEvent::StateChanged {
                                        state: if is_paused { "paused" } else { "playing" }
                                            .to_string(),
                                        media_id,
                                    });
                                }
                            }
                        }
                        libmpv::events::Event::EndFile(reason) => {
                            debug!("[MpvBackend] End file with reason: {}", reason);

                            // Only emit PlaybackEnded for natural track completion (EOF = 0)
                            // Don't emit for Stop (2), Quit (3), Error (4), or other reasons
                            // Constants from MPV_END_FILE_REASON enum: EOF=0, STOP=2, QUIT=3, ERROR=4
                            const MPV_END_FILE_REASON_EOF: u32 = 0;
                            const MPV_END_FILE_REASON_STOP: u32 = 2;
                            const MPV_END_FILE_REASON_QUIT: u32 = 3;
                            const MPV_END_FILE_REASON_ERROR: u32 = 4;

                            if reason == MPV_END_FILE_REASON_EOF {
                                debug!("[MpvBackend] Track finished naturally (EOF), emitting PlaybackEnded");
                                if let Some(emitter) = &event_emitter {
                                    emitter.emit(PlayerStatusEvent::PlaybackEnded);
                                }
                            } else if reason == MPV_END_FILE_REASON_STOP {
                                debug!("[MpvBackend] Track stopped (loading new track), NOT emitting PlaybackEnded");
                                // Don't emit - user is loading a new track
                            } else if reason == MPV_END_FILE_REASON_QUIT {
                                debug!("[MpvBackend] Player quitting, NOT emitting PlaybackEnded");
                                // Don't emit - player is shutting down
                            } else if reason == MPV_END_FILE_REASON_ERROR {
                                // NOT PlaybackEnded — the track did not finish, so
                                // autoplay must not advance. It is an error, and it
                                // has to be *said*: emitting nothing here left
                                // playback halted with the UI still showing
                                // "playing" and no way back. Marked recoverable so
                                // the frontend echoes it into player_recover_stream,
                                // which re-opens the stream where it stopped —
                                // MPV's own reconnect handles shorter blips before
                                // they ever get this far.
                                warn!("[MpvBackend] Track ended with an error — reporting as recoverable");
                                if let Some(emitter) = &event_emitter {
                                    emitter.emit(PlayerStatusEvent::Error {
                                        message: "Playback stream failed".to_string(),
                                        recoverable: true,
                                    });
                                }
                            } else {
                                debug!("[MpvBackend] Unknown end file reason {}, NOT emitting PlaybackEnded", reason);
                            }
                        }
                        libmpv::events::Event::Shutdown => {
                            info!("[MpvBackend] Shutdown event received");
                            break;
                        }
                        _ => {}
                    },
                    Some(Err(e)) => {
                        error!("[MpvBackend] Event error: {:?}", e);
                    }
                    None => {
                        // Timeout, continue
                    }
                }

                std::thread::sleep(Duration::from_millis(10));
            }

            info!("[MpvBackend] Event loop ended");
        });

        // Start position update thread
        let mpv_for_position = self.mpv.clone();
        let emitter_for_position = self.event_emitter.clone();
        let state_for_position = self.state.clone();
        let reporter_for_position = reporter.clone();
        let throttler_for_position = throttler.clone();
        let last_seek_time_for_position = self.last_seek_time.clone();
        let observed_for_position = self.observed.clone();

        std::thread::spawn(move || {
            loop {
                std::thread::sleep(Duration::from_millis(250));

                // Get current position and duration
                // Note: We emit position updates even when paused so scrubbing works
                if let (Ok(pos), Ok(dur)) = (
                    mpv_for_position.get_property::<f64>("time-pos"),
                    mpv_for_position.get_property::<f64>("duration"),
                ) {
                    // Remember it: both properties belong to the *loaded* file and
                    // stop resolving the instant MPV unloads it at EOF, which is
                    // exactly when end-of-file handling asks where playback got to.
                    // Recorded before the post-seek skip below so a track that ends
                    // right after a seek still reports the seek target, not zero.
                    observed_for_position.lock_safe().record(pos, dur);

                    // Check if we recently seeked - skip position updates briefly after seeks
                    // to avoid "jumping to zero" visual glitches while MPV is seeking
                    let now = SystemTime::now()
                        .duration_since(UNIX_EPOCH)
                        .unwrap()
                        .as_millis() as u64;
                    let last_seek = last_seek_time_for_position.load(Ordering::Relaxed);
                    let time_since_seek = now.saturating_sub(last_seek);

                    // Skip position updates for 150ms after a seek to let MPV stabilize
                    if time_since_seek < 150 {
                        continue;
                    }

                    // Emit position update event (even when paused, for scrubbing)
                    if let Some(emitter) = &emitter_for_position {
                        emitter.emit(PlayerStatusEvent::PositionUpdate {
                            position: pos,
                            duration: dur,
                        });
                    }

                    // Check if we're playing for progress reporting
                    let is_paused = mpv_for_position
                        .get_property::<bool>("pause")
                        .unwrap_or(true);

                    // Only report progress to server when playing (not paused)
                    if !is_paused {
                        // Throttled progress reporting (every 30s)
                        let jellyfin_id = {
                            let state = state_for_position.lock_safe();
                            state
                                .current_media
                                .as_ref()
                                .and_then(|m| m.jellyfin_id().map(|s| s.to_string()))
                        };

                        if let Some(item_id) = jellyfin_id {
                            if throttler_for_position.should_report(&item_id) {
                                let position_ticks = seconds_to_ticks(pos);
                                let reporter_clone = reporter_for_position.clone();
                                let item_id_clone = item_id.clone();

                                // Spawn async task to report progress
                                // Check if we're in a Tokio runtime, otherwise spawn a new thread with its own runtime
                                if let Ok(handle) = tokio::runtime::Handle::try_current() {
                                    handle.spawn(async move {
                                        let reporter_guard = reporter_clone.lock().await;
                                        if let Some(reporter_instance) = reporter_guard.as_ref() {
                                            let operation = PlaybackOperation::Progress {
                                                item_id: item_id_clone.clone(),
                                                position_ticks,
                                                is_paused: false,
                                            };

                                            match reporter_instance.report(operation, true).await {
                                                Ok(_) => debug!(
                                                    "[MpvBackend] Reported progress for {}",
                                                    item_id_clone
                                                ),
                                                Err(e) => warn!(
                                                    "[MpvBackend] Failed to report progress: {}",
                                                    e
                                                ),
                                            }
                                        }
                                    });
                                } else {
                                    // Fallback: spawn in a new thread with its own runtime
                                    std::thread::spawn(move || {
                                        let rt = tokio::runtime::Runtime::new().unwrap();
                                        rt.block_on(async move {
                                            let reporter_guard = reporter_clone.lock().await;
                                            if let Some(reporter_instance) = reporter_guard.as_ref() {
                                                let operation = PlaybackOperation::Progress {
                                                    item_id: item_id_clone.clone(),
                                                    position_ticks,
                                                    is_paused: false,
                                                };

                                                match reporter_instance.report(operation, true).await {
                                                    Ok(_) => debug!("[MpvBackend] Reported progress for {}", item_id_clone),
                                                    Err(e) => warn!("[MpvBackend] Failed to report progress: {}", e),
                                                }
                                            }
                                        });
                                    });
                                }

                                throttler_for_position.mark_reported(&item_id);
                            }
                        }
                    }
                }
            }
        });
    }
}

impl PlayerBackend for MpvBackend {
    fn load(&mut self, media: &MediaItem) -> Result<(), PlayerError> {
        let stream_url = get_stream_url(media);
        info!("[MpvBackend] Loading: {} - {}", media.title, stream_url);

        // Update state
        {
            let mut state = self.state.lock_safe();
            state.current_media = Some(media.clone());
        }
        // A different file: the previous one's timestamp must not survive as this
        // one's "last observed" position.
        self.observed.lock_safe().reset();

        // Load the media file
        self.mpv
            .command("loadfile", &[&stream_url])
            .map_err(|e| PlayerError {
                message: format!("Failed to load file: {:?}", e),
            })?;

        debug!("[MpvBackend] Load command sent successfully");
        Ok(())
    }

    fn play(&mut self) -> Result<(), PlayerError> {
        debug!("[MpvBackend] Play command");

        self.mpv
            .set_property("pause", false)
            .map_err(|e| PlayerError {
                message: format!("Failed to play: {:?}", e),
            })?;

        Ok(())
    }

    fn pause(&mut self) -> Result<(), PlayerError> {
        debug!("[MpvBackend] Pause command");

        self.mpv
            .set_property("pause", true)
            .map_err(|e| PlayerError {
                message: format!("Failed to pause: {:?}", e),
            })?;

        Ok(())
    }

    fn stop(&mut self) -> Result<(), PlayerError> {
        debug!("[MpvBackend] Stop command");

        self.mpv.command("stop", &[]).map_err(|e| PlayerError {
            message: format!("Failed to stop: {:?}", e),
        })?;

        let mut state = self.state.lock_safe();
        state.current_media = None;

        Ok(())
    }

    fn seek(&mut self, position: f64) -> Result<(), PlayerError> {
        debug!("[MpvBackend] Seek to {} seconds", position);

        // Record the seek time to suppress position updates briefly
        let now = SystemTime::now()
            .duration_since(UNIX_EPOCH)
            .unwrap()
            .as_millis() as u64;
        self.last_seek_time.store(now, Ordering::Relaxed);

        // `time-pos` only resolves while a file is loaded. `loadfile` is
        // asynchronous, so a seek issued straight after a reload — resume, or a
        // transcoded seek — lands in a window where this fails, and dropping it
        // there is what makes the stream play from zero instead of the position
        // that was asked for. Hold it and let `FileLoaded` apply it.
        // TRACES: UR-040, UR-005 | DR-241
        if let Err(e) = self.mpv.set_property("time-pos", position) {
            debug!(
                "[MpvBackend] seek to {position} deferred until the file loads ({:?})",
                e
            );
            *self.pending_seek.lock_safe() = Some(position);
            self.observed.lock_safe().record_position(position);
            return Ok(());
        }

        // A seek that lands clears any earlier deferred one: the newer intent wins.
        *self.pending_seek.lock_safe() = None;

        // The poll thread suppresses updates for 150ms after a seek, so without
        // this a file ending inside that window would report the pre-seek time.
        self.observed.lock_safe().record_position(position);

        Ok(())
    }

    fn set_volume(&mut self, volume: f32) -> Result<(), PlayerError> {
        let clamped = volume.clamp(0.0, 1.0);
        debug!("[MpvBackend] Set volume to {}", clamped);

        // MPV expects volume as percentage (0-100)
        let mpv_volume = volume_to_percent(clamped as f64) as i64;

        self.mpv
            .set_property("volume", mpv_volume)
            .map_err(|e| PlayerError {
                message: format!("Failed to set volume: {:?}", e),
            })?;

        let mut state = self.state.lock_safe();
        state.volume = clamped;

        Ok(())
    }

    /// Current position — the live `time-pos`, or the last one observed while a
    /// file was loaded.
    ///
    /// The fallback is the point: `time-pos` is a property of the *loaded* file,
    /// so at EOF it stops resolving and a bare `unwrap_or(0.0)` reported 0:00 at
    /// exactly the moment end-of-file handling asks where playback reached.
    ///
    /// TRACES: UR-005 | DR-130 | UT-121
    fn position(&self) -> f64 {
        let live = self.mpv.get_property::<f64>("time-pos").ok();
        self.observed.lock_safe().position_or_last(live)
    }

    /// Total duration — live, or the last one observed. Unloaded at EOF for the
    /// same reason as `position`.
    ///
    /// TRACES: UR-005 | DR-130 | UT-121
    fn duration(&self) -> Option<f64> {
        let live = self.mpv.get_property::<f64>("duration").ok();
        self.observed.lock_safe().duration_or_last(live)
    }

    fn state(&self) -> PlayerState {
        let state = self.state.lock_safe();

        if let Some(ref media) = state.current_media {
            let is_paused = self.mpv.get_property::<bool>("pause").unwrap_or(true);
            let position = self.position();
            let duration = self.duration().unwrap_or(0.0);

            if is_paused {
                PlayerState::Paused {
                    media: media.clone(),
                    position,
                    duration,
                }
            } else {
                PlayerState::Playing {
                    media: media.clone(),
                    position,
                    duration,
                }
            }
        } else {
            PlayerState::Idle
        }
    }

    fn volume(&self) -> f32 {
        let state = self.state.lock_safe();
        state.volume
    }

    fn set_audio_settings(&mut self, settings: &AudioSettings) -> Result<(), PlayerError> {
        info!("[MpvBackend] Applying audio settings");
        self.audio_settings = settings.clone();

        // Apply gapless playback
        if settings.gapless_playback {
            self.mpv
                .set_property("gapless-audio", "yes")
                .map_err(|e| PlayerError {
                    message: format!("Failed to enable gapless: {:?}", e),
                })?;
        } else {
            self.mpv
                .set_property("gapless-audio", "no")
                .map_err(|e| PlayerError {
                    message: format!("Failed to disable gapless: {:?}", e),
                })?;
        }

        // Audio filter chain: build a single lavfi graph combining the EQ
        // peaking bands and (optionally) a dynamic loudness normalizer, and
        // set the `af` property. An empty string clears all filters. Both
        // features share one `af` graph because MPV exposes a single filter
        // property. See docs/architecture/05-platform-backends.md and IR-020.
        let af = build_af_filter(settings);
        self.mpv
            .set_property("af", af.as_str())
            .map_err(|e| PlayerError {
                message: format!("Failed to set audio filters: {:?}", e),
            })?;

        // TODO: Implement crossfade via MPV audio filters if needed

        Ok(())
    }

    fn audio_settings(&self) -> AudioSettings {
        self.audio_settings.clone()
    }
}

/// Build the full MPV `af` (audio filter) value from the audio settings.
///
/// Combines the equalizer peaking bands and the loudness-normalization filter
/// into a single `lavfi` graph, because MPV exposes one `af` property. The
/// normalizer runs *after* the EQ so it levels the post-EQ signal. Returns an
/// empty string when neither feature contributes a filter, which clears `af`.
///
/// TRACES: UR-027, UR-033 | IR-020, DR-036
fn build_af_filter(settings: &AudioSettings) -> String {
    let mut entries = eq_filter_entries(settings.equalizer_enabled, &settings.equalizer_bands);
    if let Some(norm) = normalize_filter_entry(settings.normalize_volume, settings.volume_level) {
        entries.push(norm);
    }

    if entries.is_empty() {
        return String::new();
    }
    format!("lavfi=[{}]", entries.join(","))
}

/// Peaking-EQ filter entries (unwrapped), one ffmpeg `equalizer` (two-pole
/// peaking) per band with a non-zero gain, e.g.
/// `equalizer=f=31:width_type=o:width=1:g=5`. Returns an empty vec when the EQ
/// is disabled or every gain is ~0. Gains are assumed already normalised by
/// [`AudioSettings::with_equalizer_normalised`]; bands beyond [`EQ_BANDS`] are
/// ignored.
///
/// TRACES: UR-027 | IR-020
fn eq_filter_entries(enabled: bool, bands: &[f32]) -> Vec<String> {
    if !enabled {
        return Vec::new();
    }
    bands
        .iter()
        .zip(EQ_BANDS.iter())
        .filter(|(gain, _)| gain.abs() >= 0.05) // skip ~0 dB bands
        .map(|(gain, freq)| {
            // width_type=o → octave bandwidth; width=1 → one octave per band.
            format!("equalizer=f={}:width_type=o:width=1:g={}", freq, gain)
        })
        .collect()
}

/// Reference peak (`dynaudnorm` `p`, linear amplitude) for the default
/// [`VolumeLevel::Normal`] (−14 LUFS) target, leaving −1.2 dB of headroom.
const NORMALIZE_REF_PEAK: f32 = 0.87;
/// Reference loudness the peak table is anchored at (Normal preset, −14 LUFS).
const NORMALIZE_REF_LUFS: f32 = -14.0;

/// The loudness-normalization filter entry (unwrapped), or `None` when
/// normalization is disabled. Uses ffmpeg's `dynaudnorm`, a gentle real-time
/// dynamic normalizer that avoids the gain "pumping" `loudnorm`'s single-pass
/// mode can produce on very dynamic material.
///
/// `dynaudnorm` targets a peak amplitude (`p`, linear 0–1), not a LUFS value,
/// so the Loud/Normal/Quiet presets become *approximate*: each preset's LUFS
/// offset from the Normal reference is applied as a dB offset to the reference
/// peak, preserving the Loud > Normal > Quiet ordering. `g=15` (gaussian window
/// size) further smooths gain changes; the peak is clamped to a safe (0, 0.99]
/// so loud presets never request full-scale.
///
/// TRACES: UR-033 | DR-036
fn normalize_filter_entry(enabled: bool, level: VolumeLevel) -> Option<String> {
    if !enabled {
        return None;
    }
    // LUFS above the reference → louder → higher peak; each +1 LUFS ≈ +1 dB.
    let db_offset = level.target_lufs() - NORMALIZE_REF_LUFS;
    let peak = (NORMALIZE_REF_PEAK * 10f32.powf(db_offset / 20.0)).clamp(0.10, 0.99);
    // 3 decimals is plenty for a peak target and keeps the filter string stable.
    Some(format!("dynaudnorm=p={:.3}:g=15", peak))
}

impl Drop for MpvBackend {
    fn drop(&mut self) {
        info!("[MpvBackend] Shutting down");
        // MPV will be automatically cleaned up
    }
}

#[cfg(test)]
mod af_filter_tests {
    use super::{build_af_filter, eq_filter_entries, normalize_filter_entry};
    use crate::settings::{AudioSettings, VolumeLevel};

    fn settings() -> AudioSettings {
        AudioSettings {
            equalizer_enabled: false,
            equalizer_bands: vec![0.0; 10],
            normalize_volume: false,
            ..AudioSettings::default()
        }
    }

    /// Disabled EQ, or an all-zero curve, produces no EQ entries.
    ///
    /// TRACES: UR-027 | IR-020 | UT-083
    #[test]
    fn test_eq_entries_empty_when_disabled_or_flat() {
        assert!(eq_filter_entries(false, &[5.0, -3.0, 2.0]).is_empty());
        assert!(eq_filter_entries(true, &[0.0; 10]).is_empty());
        // Sub-threshold gains count as flat.
        assert!(eq_filter_entries(true, &[0.01, -0.02]).is_empty());
    }

    /// Enabled EQ builds one peaking `equalizer` per non-zero band at the right
    /// centre frequency and gain, chained inside a single `lavfi` filter.
    ///
    /// TRACES: UR-027 | IR-020 | UT-084
    #[test]
    fn test_eq_filter_builds_lavfi_chain() {
        // First band (31 Hz) +5 dB, third band (125 Hz) -2 dB, rest flat.
        let mut s = settings();
        s.equalizer_enabled = true;
        s.equalizer_bands = vec![5.0, 0.0, -2.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0];
        let af = build_af_filter(&s);
        assert!(af.starts_with("lavfi=["), "wrapped in lavfi: {af}");
        assert!(af.ends_with("]"));
        assert!(af.contains("equalizer=f=31:width_type=o:width=1:g=5"));
        assert!(af.contains("equalizer=f=125:width_type=o:width=1:g=-2"));
        // Only two bands are non-zero → exactly two peaking filters.
        assert_eq!(af.matches("equalizer=").count(), 2);
    }

    /// Disabled normalization yields no filter entry; the combined `af` for a
    /// fully default (all-off) settings is empty, which clears `af`.
    ///
    /// TRACES: UR-033 | DR-036 | UT-085
    #[test]
    fn test_normalize_disabled_produces_no_filter() {
        assert!(normalize_filter_entry(false, VolumeLevel::Normal).is_none());
        assert_eq!(build_af_filter(&settings()), "");
    }

    /// Enabled normalization emits a `dynaudnorm` filter with a peak target, and
    /// the peak preserves the Loud > Normal > Quiet ordering.
    ///
    /// TRACES: UR-033 | DR-036 | UT-086
    #[test]
    fn test_normalize_peak_preserves_preset_ordering() {
        fn peak_of(entry: &str) -> f32 {
            // "dynaudnorm=p=0.870:g=15" → 0.870
            entry
                .split("p=")
                .nth(1)
                .and_then(|s| s.split(':').next())
                .and_then(|s| s.parse().ok())
                .expect("parseable peak")
        }

        let loud = normalize_filter_entry(true, VolumeLevel::Loud).unwrap();
        let normal = normalize_filter_entry(true, VolumeLevel::Normal).unwrap();
        let quiet = normalize_filter_entry(true, VolumeLevel::Quiet).unwrap();
        for entry in [&loud, &normal, &quiet] {
            assert!(
                entry.starts_with("dynaudnorm="),
                "dynaudnorm filter: {entry}"
            );
        }
        assert!(
            peak_of(&loud) > peak_of(&normal) && peak_of(&normal) > peak_of(&quiet),
            "Loud {} > Normal {} > Quiet {}",
            peak_of(&loud),
            peak_of(&normal),
            peak_of(&quiet),
        );
        // Every preset stays within the safe (0, 0.99] clamp.
        for p in [peak_of(&loud), peak_of(&normal), peak_of(&quiet)] {
            assert!(p > 0.0 && p <= 0.99, "peak in range: {p}");
        }

        let mut s = settings();
        s.normalize_volume = true;
        s.volume_level = VolumeLevel::Quiet;
        let af = build_af_filter(&s);
        assert!(af.starts_with("lavfi=["));
        assert!(af.contains("dynaudnorm=p="));
    }

    /// EQ and normalization coexist in one `lavfi` graph, with the normalizer
    /// placed after the EQ bands so it levels the post-EQ signal.
    ///
    /// TRACES: UR-027, UR-033 | IR-020, DR-036 | UT-087
    #[test]
    fn test_eq_and_normalize_combine_in_order() {
        let mut s = settings();
        s.equalizer_enabled = true;
        s.equalizer_bands = vec![5.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0];
        s.normalize_volume = true;
        s.volume_level = VolumeLevel::Normal;
        let af = build_af_filter(&s);

        let eq_pos = af.find("equalizer=").expect("has EQ");
        let norm_pos = af.find("dynaudnorm=").expect("has normalizer");
        assert!(eq_pos < norm_pos, "normalizer runs after EQ: {af}");
    }
}