jellytau/src-tauri/src/player/legacy_player.rs

//! A [`MediaPlayer`] over the old [`PlayerBackend`] trait.
//!
//! Two purposes.
//!
//! **Migration.** Engines not yet ported — ExoPlayer, the webview element, the
//! null backend — keep working while `PlayerController` moves onto the new
//! contract (DR-245). Without this the port would have to land all four engines
//! at once.
//!
//! **Evidence.** It reproduces exactly what every caller used to do: `load`,
//! then `play`, then `seek` for a start position. Running the conformance suite
//! against it therefore shows the old path failing the cases the new one passes,
//! on the same engine and the same media — which is the difference between
//! asserting that a design was wrong and demonstrating it.
//!
//! It is deliberately a faithful reproduction, not a fixed-up one. Making it
//! pass would defeat the point.
//!
//! TRACES: UR-081 | DR-245

use std::time::Duration;

use super::backend::{PlayerBackend, PlayerError};
use super::media_player::{
    duration_from_secs, Capabilities, MediaPlayer, OpenRequest, Phase, PlaybackSnapshot,
};
use super::state::PlayerState;

pub struct LegacyPlayer<B: PlayerBackend> {
    inner: B,
    /// Declared at construction: this wrapper is generic over engines with very
    /// different abilities, and only the composition root knows which one it
    /// just built. Guessing here would reintroduce exactly the inference DR-238
    /// removed.
    capabilities: Capabilities,
    /// The old trait has no notion of "opening", so this is the best the wrapper
    /// can do: it knows an item was handed over, not whether the engine is ready
    /// for one. That gap is the whole problem.
    has_item: bool,
}

impl<B: PlayerBackend> LegacyPlayer<B> {
    pub fn new(inner: B, capabilities: Capabilities) -> Self {
        Self {
            inner,
            capabilities,
            has_item: false,
        }
    }
}

impl<B: PlayerBackend + Send> MediaPlayer for LegacyPlayer<B> {
    /// Load, play, then seek — the sequence every caller used to write.
    ///
    /// The seek is issued immediately, because a caller has no way to know when
    /// the engine becomes ready. On an engine whose load is asynchronous it
    /// fails and is discarded, and playback begins at zero: DR-241, reproduced.
    fn open(&mut self, req: OpenRequest) -> Result<(), PlayerError> {
        self.inner.load(&req.media)?;
        self.has_item = true;
        if req.autoplay {
            self.inner.play()?;
        }
        if !req.start.is_zero() {
            // Faithfully ignoring the failure, exactly as the old callers did.
            let _ = self.inner.seek(req.start.as_secs_f64());
        }
        Ok(())
    }

    fn play(&mut self) -> Result<(), PlayerError> {
        self.inner.play()
    }

    fn pause(&mut self) -> Result<(), PlayerError> {
        self.inner.pause()
    }

    fn close(&mut self) -> Result<(), PlayerError> {
        self.has_item = false;
        self.inner.stop()
    }

    fn seek(&mut self, to: Duration) -> Result<(), PlayerError> {
        self.inner.seek(to.as_secs_f64())
    }

    fn set_volume(&mut self, volume: f32) -> Result<(), PlayerError> {
        self.inner.set_volume(volume)
    }

    /// The old trait has no mute. Folding it into volume would lose the user's
    /// level, so this reports unsupported rather than pretending.
    fn set_muted(&mut self, _muted: bool) -> Result<(), PlayerError> {
        Err(PlayerError {
            message: "mute is not supported by this backend".to_string(),
        })
    }

    fn set_rate(&mut self, _rate: f64) -> Result<(), PlayerError> {
        Err(PlayerError {
            message: "playback rate is not supported by this backend".to_string(),
        })
    }

    fn select_audio_track(&mut self, index: Option<i32>) -> Result<(), PlayerError> {
        self.inner.set_audio_track(index.unwrap_or(-1))
    }

    fn select_subtitle_track(&mut self, index: Option<i32>) -> Result<(), PlayerError> {
        self.inner.set_subtitle_track(index)
    }

    fn snapshot(&self) -> PlaybackSnapshot {
        let phase = match self.inner.state() {
            _ if !self.has_item => Phase::Idle,
            PlayerState::Playing { .. } => Phase::Playing,
            PlayerState::Paused { .. } => Phase::Paused,
            PlayerState::Idle => Phase::Idle,
            PlayerState::Error { error, .. } => Phase::Failed(error),
            // `Loading` is the closest the old trait comes to an opening state,
            // but it is set once the engine has accepted the item rather than
            // while it is still accepting it — which is precisely the window it
            // cannot describe.
            PlayerState::Loading { .. } | PlayerState::Seeking { .. } => Phase::Ready,
        };
        PlaybackSnapshot {
            phase,
            position: duration_from_secs(self.inner.position()).unwrap_or(Duration::ZERO),
            duration: self.inner.duration().and_then(duration_from_secs),
            seekable: true,
            volume: self.inner.volume(),
            muted: false,
            rate: 1.0,
            audio_track: None,
            subtitle_track: None,
        }
    }

    fn set_audio_settings(
        &mut self,
        settings: &crate::settings::AudioSettings,
    ) -> Result<(), PlayerError> {
        self.inner.set_audio_settings(settings)
    }

    fn audio_settings(&self) -> crate::settings::AudioSettings {
        self.inner.audio_settings()
    }

    fn capabilities(&self) -> Capabilities {
        self.capabilities
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::player::media::MediaItem;
    use crate::settings::AudioSettings;

    /// A backend that answers badly, on purpose.
    ///
    /// Every engine the conformance suite drives reports sane numbers, which is
    /// why it passed while a real one did not: ExoPlayer returns
    /// `C.TIME_UNSET` — `Long::MIN_VALUE`, about -9.2e15 seconds — for any
    /// stream whose length it does not know, and the adapter converted that
    /// straight into a `Duration` and panicked the whole backend.
    ///
    /// The old `PlayerBackend` contract is a plain `f64`. It never promised
    /// finite, never promised positive, and nothing enforced it. So this is the
    /// engine the suites were missing.
    struct HostileBackend {
        duration: f64,
        position: f64,
    }

    impl PlayerBackend for HostileBackend {
        fn load(&mut self, _media: &MediaItem) -> Result<(), PlayerError> {
            Ok(())
        }
        fn play(&mut self) -> Result<(), PlayerError> {
            Ok(())
        }
        fn pause(&mut self) -> Result<(), PlayerError> {
            Ok(())
        }
        fn stop(&mut self) -> Result<(), PlayerError> {
            Ok(())
        }
        fn seek(&mut self, _position: f64) -> Result<(), PlayerError> {
            Ok(())
        }
        fn set_volume(&mut self, _volume: f32) -> Result<(), PlayerError> {
            Ok(())
        }
        fn position(&self) -> f64 {
            self.position
        }
        fn duration(&self) -> Option<f64> {
            Some(self.duration)
        }
        fn state(&self) -> PlayerState {
            PlayerState::Idle
        }
        fn volume(&self) -> f32 {
            1.0
        }
        fn set_audio_settings(&mut self, _s: &AudioSettings) -> Result<(), PlayerError> {
            Ok(())
        }
        fn audio_settings(&self) -> AudioSettings {
            AudioSettings::default()
        }
        fn set_audio_track(&mut self, _i: i32) -> Result<(), PlayerError> {
            Ok(())
        }
        fn set_subtitle_track(&mut self, _i: Option<i32>) -> Result<(), PlayerError> {
            Ok(())
        }
    }

    fn hostile(duration: f64, position: f64) -> LegacyPlayer<HostileBackend> {
        LegacyPlayer::new(
            HostileBackend { duration, position },
            crate::player::media_player::Capabilities::mpv(),
        )
    }

    /// Reading an engine that answers badly must not take the process down.
    ///
    /// This is DR-252 as a test. It fails — by panicking — against the adapter
    /// as originally written, which is the property the conformance suite could
    /// not have: it only ever drove engines that behave.
    ///
    /// TRACES: UR-005 | DR-252 | UT-223
    #[test]
    fn test_snapshot_survives_an_engine_that_answers_badly() {
        // The exact value ExoPlayer reports for an unknown length.
        let s = hostile(-9_223_372_036_854_776.0, 0.0).snapshot();
        assert_eq!(s.duration, None, "a negative duration is not a duration");

        for bad in [f64::NAN, f64::NEG_INFINITY, f64::INFINITY, -1.0, 0.0] {
            let s = hostile(bad, bad).snapshot();
            assert_eq!(s.duration, None, "{bad} should not become a duration");
            assert_eq!(
                s.position,
                Duration::ZERO,
                "{bad} should not become a position"
            );
        }

        // And a well-behaved engine still works.
        let s = hostile(6997.024, 540.0).snapshot();
        assert_eq!(s.duration, Some(Duration::from_secs_f64(6997.024)));
        assert_eq!(s.position, Duration::from_secs_f64(540.0));
    }
}