//! 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 `get_player_status`
//! (which tells the frontend whether to use a webview `<video>` element).
//!
//! 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

/// The opt-in for native desktop video.
///
/// Off by default while the render path is unproven — the webview path still
/// works and is what ships. This becomes the *default* (and then the only path)
/// when DR-235 lands; the variable is how it is exercised until then.
const ENV_FLAG: &str = "JELLYTAU_NATIVE_VIDEO";

/// Whether mpv should decode and draw video in this process.
///
/// Read fresh rather than cached: it is consulted a handful of times at startup,
/// and a `OnceLock` here would only make it harder to test.
///
/// TRACES: UR-080 | DR-231, DR-235
pub fn enabled() -> bool {
    // Only where a native renderer exists. On Android ExoPlayer already does
    // this and `use_html5_element` is false for entirely separate reasons.
    if !cfg!(all(target_os = "linux", not(target_os = "android"))) {
        return false;
    }
    matches!(
        std::env::var(ENV_FLAG).as_deref(),
        Ok("1") | Ok("true") | Ok("yes")
    )
}

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

    /// Absent, empty, or anything unrecognised means off. A half-set variable
    /// must not half-enable a renderer — the failure mode would be mpv
    /// configured for video with nothing drawing it, i.e. audio playing over a
    /// black rectangle.
    ///
    /// TRACES: UR-080 | DR-231 | UT-216
    #[test]
    fn test_only_explicit_truthy_values_enable_it() {
        let restore = std::env::var(ENV_FLAG).ok();

        for value in ["", "0", "no", "false", "maybe", "2"] {
            std::env::set_var(ENV_FLAG, value);
            assert!(!enabled(), "{value:?} must not enable native video");
        }

        for value in ["1", "true", "yes"] {
            std::env::set_var(ENV_FLAG, value);
            assert_eq!(
                enabled(),
                cfg!(all(target_os = "linux", not(target_os = "android"))),
                "{value:?} enables it exactly where a native renderer exists"
            );
        }

        std::env::remove_var(ENV_FLAG);
        assert!(!enabled(), "absent means off");

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