//! The `MediaPlayer` contract: one API, interchangeable engines.
//!
//! See docs/specs/media-player-controller.md.
//!
//! This replaces [`PlayerBackend`](super::backend::PlayerBackend), which
//! abstracts a *device* — `load`, then `seek` — rather than an *intent*. That
//! distinction is not academic; it produced four shipped defects in one day:
//!
//! * A start position was not expressible, so every caller sequenced
//!   `load()` + `seek()` itself and each raced the engine's asynchronous load
//!   independently. Resume worked through one caller and silently failed through
//!   another (DR-241).
//! * Whether a stream could be seeked in place was decided *above* the engines,
//!   by a truth table in a command handler, for engines it does not own (DR-238).
//! * Nothing in the contract obliged an engine to report its own state, so a
//!   handler for mpv's `pause` property sat unreachable and the play/pause
//!   control never moved (DR-239).
//!
//! The contract below is written so each of those is a compile-time or
//! conformance-time failure rather than a runtime surprise.
//!
//! TRACES: UR-081 | DR-242

// Scaffolding: nothing consumes this contract until `PlayerController` is
// ported to it (DR-245). Kept out of `cfg(test)` deliberately — it is production
// code being built in shippable steps, not a test fixture. Remove this allow
// when the controller talks to `MediaPlayer`.
#![allow(dead_code)]

use std::time::Duration;

use super::backend::PlayerError;
use super::media::MediaItem;
use crate::repository::stream_selection::StreamSelection;
use crate::settings::AudioSettings;

/// Seconds reported by an engine, as a `Duration`, without trusting the number.
///
/// `Duration::from_secs_f64` **panics** on a negative or non-finite value, and
/// no engine promises otherwise. ExoPlayer reports `C.TIME_UNSET` —
/// `Long::MIN_VALUE`, about -9.2e15 — for a stream whose length it does not
/// know, which is every background-audio handoff: `/Audio/{id}/universal` is a
/// chunked, length-less transcode.
///
/// Held as a float that junk was harmless. Converted to a `Duration` it became
/// a panic that killed the backend mid-handoff and left a black screen with no
/// controls. Every engine crossing into this contract goes through here.
///
/// TRACES: UR-005 | DR-252
pub fn duration_from_secs(seconds: f64) -> Option<Duration> {
    (seconds.is_finite() && seconds > 0.0).then(|| Duration::from_secs_f64(seconds))
}

/// What an engine is doing right now.
///
/// `Opening` is the state the previous design could not express, and is the
/// direct cause of DR-241: a seek that arrived while the engine had nothing
/// loaded had no phase to be queued against, so it was simply discarded and
/// playback began at zero.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum Phase {
    /// Nothing loaded. `close()` must reach this, and must be silent here.
    Idle,
    /// An `open` is in flight. Position is not yet meaningful; a `seek` arriving
    /// now must be honoured once the engine reaches `Ready`, never dropped.
    Opening,
    /// Loaded and able to play, but not advancing.
    Ready,
    Playing,
    Paused,
    /// Reached the end of the item by itself. Distinct from `Idle`, because
    /// autoplay cares which one happened.
    Ended,
    Failed(String),
}

impl Phase {
    /// Whether the engine currently holds an item.
    pub fn has_media(&self) -> bool {
        !matches!(self, Phase::Idle | Phase::Failed(_))
    }

    /// Whether playback is advancing.
    pub fn is_active(&self) -> bool {
        matches!(self, Phase::Playing)
    }
}

/// Everything the UI consumes, read as one coherent value.
///
/// Deliberately a single snapshot rather than a dozen getters: reading position
/// and duration through separate calls is how a paused player reported
/// `<position> / 0.0` when a file unloaded between them.
#[derive(Debug, Clone)]
pub struct PlaybackSnapshot {
    pub phase: Phase,
    pub position: Duration,
    /// `None` while unknown — a live stream, or an item still opening.
    pub duration: Option<Duration>,
    /// Whether `seek` can be expected to land. False for live edges.
    pub seekable: bool,
    /// 0.0 – 1.0.
    pub volume: f32,
    pub muted: bool,
    pub rate: f64,
    pub audio_track: Option<i32>,
    pub subtitle_track: Option<i32>,
}

impl Default for PlaybackSnapshot {
    fn default() -> Self {
        Self {
            phase: Phase::Idle,
            position: Duration::ZERO,
            duration: None,
            seekable: false,
            volume: 1.0,
            muted: false,
            rate: 1.0,
            audio_track: None,
            subtitle_track: None,
        }
    }
}

/// What an engine can do, so callers adapt without naming engines.
///
/// If a caller ever branches on *which* engine it holds, this struct is missing
/// something — add it here rather than sniffing. Engine identity leaking into
/// callers is the coupling DR-238 came from.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct Capabilities {
    /// The engine renders pictures, not only sound.
    pub video: bool,
    /// Audio settings (EQ, normalisation, gapless) are honoured.
    pub audio_settings: bool,
    /// Subtitle tracks can be selected without re-opening.
    pub subtitle_switching: bool,
    /// Audio tracks can be selected without re-opening.
    pub audio_track_switching: bool,
    /// A *server-side transcode* can be seeked without re-opening the stream.
    ///
    /// True for hls.js, which seeks within the VOD playlist it is handed and
    /// lets the server catch up. False for mpv, whose HLS demuxer cannot make
    /// the server transcode from a new offset.
    ///
    /// Declared by the engine rather than inferred by the caller. The previous
    /// design decided this from `is_hls` and `use_html5` in a command handler —
    /// on behalf of engines it did not own — which is how "who renders" came to
    /// mean "how do I seek" and why a transcoded seek silently did nothing the
    /// moment native video changed the renderer (DR-238).
    ///
    /// Re-negotiating a stream needs the repository, which sits above the
    /// engine, so the engine states the capability and the caller acts on it.
    pub seeks_transcoded_in_place: bool,
}

impl Capabilities {
    /// mpv.
    ///
    /// Cannot seek a server-side transcode in place: its HLS demuxer will not
    /// make the server produce segments from a new offset, so the stream has to
    /// be re-opened.
    pub fn mpv() -> Self {
        Self {
            video: true,
            audio_settings: true,
            subtitle_switching: true,
            audio_track_switching: true,
            seeks_transcoded_in_place: false,
        }
    }

    /// ExoPlayer.
    ///
    /// **Can** seek a transcode in place. It is a full HLS client, so like
    /// hls.js it seeks within the VOD playlist it was handed and lets the
    /// server catch up. Grouping it with mpv as "a native engine" gets this
    /// exactly backwards — being native is not the property that matters here,
    /// speaking HLS is, and that is the whole reason this is declared per
    /// engine rather than inferred from a category.
    pub fn exoplayer() -> Self {
        Self {
            video: true,
            audio_settings: true,
            subtitle_switching: true,
            audio_track_switching: true,
            seeks_transcoded_in_place: true,
        }
    }

    /// An engine that renders through the webview element, where hls.js seeks
    /// within the playlist it was handed.
    pub fn webview() -> Self {
        Self {
            video: true,
            audio_settings: false,
            subtitle_switching: true,
            audio_track_switching: false,
            seeks_transcoded_in_place: true,
        }
    }
}

/// A request to present an item.
///
/// `start` is the reason this type exists. Carrying it here — rather than
/// leaving callers to `seek` after `open` — is what closes the load/seek race,
/// because the engine is the only layer that knows when its pipeline can accept
/// a position.
#[derive(Debug, Clone)]
pub struct OpenRequest {
    pub media: MediaItem,
    pub selection: StreamSelection,
    /// Where to begin. `Duration::ZERO` means the start of the item.
    pub start: Duration,
    pub audio_track: Option<i32>,
    pub subtitle_track: Option<i32>,
    /// Begin playing as soon as the engine is able.
    pub autoplay: bool,
}

impl OpenRequest {
    /// Open at the beginning, playing.
    pub fn new(media: MediaItem, selection: StreamSelection) -> Self {
        Self {
            media,
            selection,
            start: Duration::ZERO,
            audio_track: None,
            subtitle_track: None,
            autoplay: true,
        }
    }

    pub fn starting_at(mut self, start: Duration) -> Self {
        self.start = start;
        self
    }
}

/// Anything that can present media.
///
/// Implementations: `MpvPlayer` (Linux/Windows), `ExoPlayerPlayer` (Android),
/// `WebviewPlayer` (HTML5 element), and `FakePlayer` for tests. Every one of
/// them must pass [`super::conformance`].
pub trait MediaPlayer: Send {
    /// Present `req.selection`, beginning at `req.start`.
    ///
    /// One operation, deliberately. An engine that cannot start at an offset
    /// natively absorbs that internally — by deferring until loaded, or by
    /// re-opening — because it is the only layer that knows when it can.
    /// Callers must never follow `open` with a `seek` to achieve a start
    /// position; that is the bug this signature exists to prevent.
    fn open(&mut self, req: OpenRequest) -> Result<(), PlayerError>;

    fn play(&mut self) -> Result<(), PlayerError>;
    fn pause(&mut self) -> Result<(), PlayerError>;

    /// Stop and release the current item.
    ///
    /// Must be **idempotent** and must leave the engine **silent**. "Stopped"
    /// and "producing no audio" were not the same thing in the previous design,
    /// and the gap between them is audible.
    fn close(&mut self) -> Result<(), PlayerError>;

    /// Seek to an absolute position on the item's own timeline.
    ///
    /// Whether that is an in-place seek or a re-open of the stream is the
    /// engine's business: hls.js seeks within a VOD playlist, mpv's HLS demuxer
    /// cannot make a server transcode from a new offset. Callers state the
    /// destination and nothing else.
    fn seek(&mut self, to: Duration) -> Result<(), PlayerError>;

    fn set_volume(&mut self, volume: f32) -> Result<(), PlayerError>;
    fn set_muted(&mut self, muted: bool) -> Result<(), PlayerError>;
    fn set_rate(&mut self, rate: f64) -> Result<(), PlayerError>;

    fn select_audio_track(&mut self, index: Option<i32>) -> Result<(), PlayerError>;
    fn select_subtitle_track(&mut self, index: Option<i32>) -> Result<(), PlayerError>;

    /// One coherent read of the engine's state.
    fn snapshot(&self) -> PlaybackSnapshot;

    fn capabilities(&self) -> Capabilities;

    /// Apply EQ, normalisation and gapless settings.
    ///
    /// Provided rather than required: engines that cannot honour them say so
    /// through [`Capabilities::audio_settings`] and inherit this no-op, instead
    /// of every implementation carrying an `Ok(())` it does not mean.
    fn set_audio_settings(&mut self, _settings: &AudioSettings) -> Result<(), PlayerError> {
        Ok(())
    }

    fn audio_settings(&self) -> AudioSettings {
        AudioSettings::default()
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    /// The value that killed the backend: `C.TIME_UNSET` as seconds.
    ///
    /// ExoPlayer reports it for any stream whose length it does not know, and
    /// `Duration::from_secs_f64` panics on it. A player must not be the place
    /// anyone discovers a float was strange.
    ///
    /// TRACES: UR-005 | DR-252 | UT-222
    #[test]
    fn test_junk_durations_do_not_panic() {
        // Long::MIN_VALUE milliseconds, as ExoPlayer hands it over.
        assert_eq!(duration_from_secs(-9_223_372_036_854_776.0), None);
        assert_eq!(duration_from_secs(-1.0), None);
        assert_eq!(duration_from_secs(0.0), None, "zero is not a duration");
        assert_eq!(duration_from_secs(f64::NAN), None);
        assert_eq!(duration_from_secs(f64::INFINITY), None);
        assert_eq!(duration_from_secs(f64::NEG_INFINITY), None);

        // A real one still survives.
        assert_eq!(
            duration_from_secs(6997.024),
            Some(Duration::from_secs_f64(6997.024))
        );
    }
}