//! [`MediaPlayer`] over libmpv.
//!
//! The point of difference from `MpvBackend` is [`MpvPlayer::open`]: the start
//! position is applied **at load time**, via mpv's own `start` option, instead
//! of being seeked to afterwards. `loadfile` is asynchronous, so a seek issued
//! after it targets a player that has nothing loaded, fails, and — under the old
//! contract — was discarded. That is DR-241, and it is why resume and transcoded
//! skip both played from zero.
//!
//! A seek arriving during [`Phase::Opening`] is held and applied when the file
//! loads, so no caller has to know where that window begins or ends.
//!
//! TRACES: UR-081, UR-040, UR-005 | DR-244

#![allow(dead_code)] // Wired to PlayerController in DR-245.

use std::sync::{Arc, Mutex};
use std::time::Duration;

use libmpv::Mpv;
use log::{debug, info, warn};

use super::backend::PlayerError;
use super::media_player::{
    duration_from_secs, Capabilities, MediaPlayer, OpenRequest, Phase, PlaybackSnapshot,
};
use crate::utils::lock::MutexSafe;

/// State the event thread writes and the caller reads.
#[derive(Debug)]
struct Shared {
    phase: Phase,
    position: Duration,
    duration: Option<Duration>,
    seekable: bool,
    /// A seek that arrived while opening. Applied on `FileLoaded`.
    deferred_seek: Option<Duration>,
    /// Cleared by `close()`, so an open still in flight cannot come back to life
    /// and start playing after the caller has stopped it.
    open_generation: u64,
}

impl Default for Shared {
    fn default() -> Self {
        Self {
            phase: Phase::Idle,
            position: Duration::ZERO,
            duration: None,
            seekable: false,
            deferred_seek: None,
            open_generation: 0,
        }
    }
}

pub struct MpvPlayer {
    mpv: Arc<Mpv>,
    shared: Arc<Mutex<Shared>>,
    volume: f32,
    muted: bool,
    rate: f64,
    audio_track: Option<i32>,
    subtitle_track: Option<i32>,
}

/// How the engine should talk to the machine.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum Output {
    /// Real audio and video. What the app uses.
    Real,
    /// No audio device, no window. What conformance uses, so the suite can run
    /// on a headless runner without claiming the user's speakers.
    Null,
}

impl MpvPlayer {
    pub fn new(output: Output) -> Result<Self, PlayerError> {
        // mpv refuses to start under a non-C LC_NUMERIC, and anything that has
        // initialised GTK before us will have set one.
        unsafe {
            let c = std::ffi::CString::new("C").unwrap();
            libc::setlocale(libc::LC_NUMERIC, c.as_ptr());
        }

        let mpv = Mpv::new().map_err(|e| PlayerError {
            message: format!("mpv_create failed: {e:?}"),
        })?;

        let set = |k: &str, v: &str| {
            if let Err(e) = mpv.set_property(k, v) {
                warn!("[MpvPlayer] could not set {k}={v}: {e:?}");
            }
        };
        match output {
            Output::Real => {
                set("vo", "libmpv");
            }
            Output::Null => {
                set("ao", "null");
                set("vo", "null");
            }
        }
        set("msg-level", "all=warn");
        // Survive a blip rather than ending the item on it.
        set(
            "stream-lavf-o",
            "reconnect=1,reconnect_streamed=1,reconnect_on_network_error=1,reconnect_delay_max=5",
        );

        let player = Self {
            mpv: Arc::new(mpv),
            shared: Arc::new(Mutex::new(Shared::default())),
            volume: 1.0,
            muted: false,
            rate: 1.0,
            audio_track: None,
            subtitle_track: None,
        };
        player.spawn_events();
        Ok(player)
    }

    fn spawn_events(&self) {
        let mpv = self.mpv.clone();
        let shared = self.shared.clone();

        std::thread::spawn(move || {
            let mut ev = mpv.create_event_context();
            let _ = ev.disable_deprecated_events();
            // Every property matched below must be observed, or libmpv never
            // delivers it and the handler is unreachable (DR-239).
            for prop in ["pause", "eof-reached"] {
                if let Err(e) = ev.observe_property(prop, libmpv::Format::Flag, 0) {
                    warn!("[MpvPlayer] could not observe {prop}: {e:?}");
                }
            }

            loop {
                match ev.wait_event(0.25) {
                    Some(Ok(libmpv::events::Event::FileLoaded)) => {
                        let deferred = {
                            let mut s = shared.lock_safe();
                            // Closed while opening: do not start.
                            if s.phase == Phase::Idle {
                                continue;
                            }
                            s.duration = mpv
                                .get_property::<f64>("duration")
                                .ok()
                                .and_then(duration_from_secs);
                            s.seekable = mpv.get_property::<bool>("seekable").unwrap_or(true);
                            s.phase = Phase::Playing;
                            s.deferred_seek.take()
                        };
                        if let Some(to) = deferred {
                            debug!("[MpvPlayer] applying deferred seek to {to:?}");
                            if let Err(e) = mpv.set_property("time-pos", to.as_secs_f64()) {
                                warn!("[MpvPlayer] deferred seek failed: {e:?}");
                            }
                        }
                    }
                    Some(Ok(libmpv::events::Event::PropertyChange { name: "pause", .. })) => {
                        if let Ok(paused) = mpv.get_property::<bool>("pause") {
                            let mut s = shared.lock_safe();
                            if s.phase.has_media() {
                                s.phase = if paused {
                                    Phase::Paused
                                } else {
                                    Phase::Playing
                                };
                            }
                        }
                    }
                    Some(Ok(libmpv::events::Event::EndFile(reason))) => {
                        let mut s = shared.lock_safe();
                        // 0 = EOF. Anything else is a stop, a quit or an error,
                        // and must not read as "the item finished".
                        s.phase = if reason == 0 {
                            Phase::Ended
                        } else {
                            Phase::Idle
                        };
                    }
                    Some(Ok(libmpv::events::Event::Shutdown)) => break,
                    _ => {}
                }

                if let Ok(pos) = mpv.get_property::<f64>("time-pos") {
                    let mut s = shared.lock_safe();
                    if s.phase.has_media() && s.deferred_seek.is_none() {
                        s.position = Duration::from_secs_f64(pos.max(0.0));
                    }
                }
            }
        });
    }
}

impl MediaPlayer for MpvPlayer {
    fn open(&mut self, req: OpenRequest) -> Result<(), PlayerError> {
        {
            let mut s = self.shared.lock_safe();
            *s = Shared {
                phase: Phase::Opening,
                open_generation: s.open_generation + 1,
                ..Shared::default()
            };
            // Report the requested position immediately, so a caller reading
            // back during the open sees where it asked to be rather than zero.
            s.position = req.start;
        }

        // The whole point. `start` is applied by mpv as it opens the file, so
        // there is no window in which the position can be asked for and lost.
        let start = if req.start.is_zero() {
            "none".to_string()
        } else {
            format!("{:.3}", req.start.as_secs_f64())
        };
        self.mpv
            .set_property("start", start.as_str())
            .map_err(|e| PlayerError {
                message: format!("could not set start position: {e:?}"),
            })?;
        self.mpv
            .set_property("pause", !req.autoplay)
            .map_err(|e| PlayerError {
                message: format!("could not set pause: {e:?}"),
            })?;

        info!("[MpvPlayer] open {} at {:?}", req.selection.url, req.start);
        self.mpv
            .command("loadfile", &[&req.selection.url, "replace"])
            .map_err(|e| PlayerError {
                message: format!("loadfile failed: {e:?}"),
            })?;
        Ok(())
    }

    fn play(&mut self) -> Result<(), PlayerError> {
        self.mpv
            .set_property("pause", false)
            .map_err(|e| PlayerError {
                message: format!("play failed: {e:?}"),
            })?;
        let mut s = self.shared.lock_safe();
        if s.phase.has_media() && s.phase != Phase::Opening {
            s.phase = Phase::Playing;
        }
        Ok(())
    }

    fn pause(&mut self) -> Result<(), PlayerError> {
        self.mpv
            .set_property("pause", true)
            .map_err(|e| PlayerError {
                message: format!("pause failed: {e:?}"),
            })?;
        let mut s = self.shared.lock_safe();
        if s.phase.has_media() && s.phase != Phase::Opening {
            s.phase = Phase::Paused;
        }
        Ok(())
    }

    fn close(&mut self) -> Result<(), PlayerError> {
        // State first: an open still in flight checks this on FileLoaded and
        // must not proceed to play after the caller has stopped it.
        {
            let mut s = self.shared.lock_safe();
            *s = Shared {
                open_generation: s.open_generation,
                ..Shared::default()
            };
        }
        // Idempotent: stopping an already-stopped mpv is not an error worth
        // propagating, and callers legitimately close twice on teardown.
        if let Err(e) = self.mpv.command("stop", &[]) {
            debug!("[MpvPlayer] stop on an idle player: {e:?}");
        }
        Ok(())
    }

    fn seek(&mut self, to: Duration) -> Result<(), PlayerError> {
        {
            let mut s = self.shared.lock_safe();
            match s.phase {
                // Held, not dropped. The caller cannot see this window.
                Phase::Opening => {
                    s.deferred_seek = Some(to);
                    s.position = to;
                    return Ok(());
                }
                Phase::Idle | Phase::Failed(_) => {
                    return Err(PlayerError {
                        message: "seek with nothing open".to_string(),
                    })
                }
                _ => s.position = to,
            }
        }
        self.mpv
            .set_property("time-pos", to.as_secs_f64())
            .map_err(|e| PlayerError {
                message: format!("seek failed: {e:?}"),
            })
    }

    fn set_volume(&mut self, volume: f32) -> Result<(), PlayerError> {
        let clamped = volume.clamp(0.0, 1.0);
        self.volume = clamped;
        self.mpv
            .set_property("volume", (clamped as f64) * 100.0)
            .map_err(|e| PlayerError {
                message: format!("set_volume failed: {e:?}"),
            })
    }

    fn set_muted(&mut self, muted: bool) -> Result<(), PlayerError> {
        self.muted = muted;
        self.mpv
            .set_property("mute", muted)
            .map_err(|e| PlayerError {
                message: format!("set_muted failed: {e:?}"),
            })
    }

    fn set_rate(&mut self, rate: f64) -> Result<(), PlayerError> {
        self.rate = rate;
        self.mpv
            .set_property("speed", rate)
            .map_err(|e| PlayerError {
                message: format!("set_rate failed: {e:?}"),
            })
    }

    fn select_audio_track(&mut self, index: Option<i32>) -> Result<(), PlayerError> {
        self.audio_track = index;
        let value = index.map(|i| i.to_string()).unwrap_or_else(|| "no".into());
        self.mpv
            .set_property("aid", value.as_str())
            .map_err(|e| PlayerError {
                message: format!("select_audio_track failed: {e:?}"),
            })
    }

    fn select_subtitle_track(&mut self, index: Option<i32>) -> Result<(), PlayerError> {
        self.subtitle_track = index;
        let value = index.map(|i| i.to_string()).unwrap_or_else(|| "no".into());
        self.mpv
            .set_property("sid", value.as_str())
            .map_err(|e| PlayerError {
                message: format!("select_subtitle_track failed: {e:?}"),
            })
    }

    fn snapshot(&self) -> PlaybackSnapshot {
        let s = self.shared.lock_safe();
        PlaybackSnapshot {
            phase: s.phase.clone(),
            position: s.position,
            duration: s.duration,
            seekable: s.seekable,
            volume: self.volume,
            muted: self.muted,
            rate: self.rate,
            audio_track: self.audio_track,
            subtitle_track: self.subtitle_track,
        }
    }

    fn capabilities(&self) -> Capabilities {
        Capabilities {
            video: true,
            audio_settings: true,
            subtitle_switching: true,
            audio_track_switching: true,
            // mpv's HLS demuxer cannot make the server transcode from a new
            // offset, so a transcoded seek must re-open the stream.
            seeks_transcoded_in_place: false,
        }
    }
}