//! Whether this process renders video natively, answered once.
//!
//! Three things need this and must agree: the mpv backend (which has to be
//! configured for video *at construction*, before anything plays), the video
//! surface (which has nothing to draw otherwise), and the device profile.
//!
//! It is a function rather than three `env::var` checks for the reason this
//! codebase keeps rediscovering: a capability answered in several places is a
//! capability whose answers drift. Four separate bugs this cycle came from
//! exactly that shape — a webview's decode limits applied to ExoPlayer, a
//! transcode target contradicting a direct-play claim, a codec list hardcoded in
//! a URL builder. One source, read by everyone.
//!
//! TRACES: UR-080 | DR-231, DR-235

/// Whether mpv should decode and draw video in this process.
///
/// True wherever mpv is the desktop video renderer: Linux since DR-235 phase 1,
/// Windows since DR-237. There is no opt-out and no webview fallback — the
/// webview `<video>` path is gone, so "off" would leave nothing drawing the
/// picture. It was the `JELLYTAU_NATIVE_VIDEO` opt-in while the render path was
/// being proven; the variable is ignored.
///
/// TRACES: UR-080 | DR-231, DR-235
pub fn enabled() -> bool {
    // On Android ExoPlayer draws video and `use_html5_element` is false for
    // entirely separate reasons.
    cfg!(any(target_os = "linux", target_os = "windows"))
}

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

    /// mpv draws video on Linux and Windows with nothing to opt into, and the retired
    /// variable cannot opt back out: with the webview path gone, "off"
    /// would configure mpv for audio only with nothing else to draw the picture.
    ///
    /// TRACES: UR-080 | DR-235, DR-237 | UT-271
    #[test]
    fn desktop_always_renders_video_natively() {
        let restore = std::env::var("JELLYTAU_NATIVE_VIDEO").ok();

        for value in [None, Some("0"), Some("false"), Some("1")] {
            match value {
                Some(v) => std::env::set_var("JELLYTAU_NATIVE_VIDEO", v),
                None => std::env::remove_var("JELLYTAU_NATIVE_VIDEO"),
            }
            assert_eq!(
                enabled(),
                cfg!(any(target_os = "linux", target_os = "windows")),
                "JELLYTAU_NATIVE_VIDEO={value:?} must not decide the renderer"
            );
        }

        match restore {
            Some(v) => std::env::set_var("JELLYTAU_NATIVE_VIDEO", v),
            None => std::env::remove_var("JELLYTAU_NATIVE_VIDEO"),
        }
    }
}