katui-present 0.0.3

Presenters: scene diffs translated into terminal bytes on a sink
Documentation 
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//! Backend selection: capabilities in, graphics backend out.

use katui_proto::probe::Capabilities;

/// The graphics backend a presenter strategy drives.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum Backend {
    /// The kitty graphics protocol: images, placements, animation.
    Kitty,
    /// Sixel: paletted bands, one image per changed tile.
    Sixel,
    /// Half and quarter block glyphs over SGR truecolor, the floor every
    /// color terminal understands.
    Blocks,
}

/// Pick the best backend the terminal offers. Kitty wins when present,
/// sixel comes second outside multiplexers, which place sixel images
/// themselves, and blocks carry everything else. Needs-aware choices
/// (alpha, z-order, frame budget) are the presenter strategies' concern.
#[must_use]
pub fn select(caps: &Capabilities) -> Backend {
    if caps.kitty {
        Backend::Kitty
    } else if caps.sixel && !caps.multiplexed() {
        Backend::Sixel
    } else {
        Backend::Blocks
    }
}

impl Backend {
    /// The backend's canonical lowercase name, the one string form every
    /// consumer prints.
    #[must_use]
    pub const fn name(self) -> &'static str {
        match self {
            Self::Kitty => "kitty",
            Self::Sixel => "sixel",
            Self::Blocks => "blocks",
        }
    }
}

#[cfg(test)]
mod tests {
    use super::{Backend, select};
    use katui_proto::probe::{Capabilities, ProbeSource};

    fn caps(kitty: bool, sixel: bool) -> Capabilities {
        Capabilities {
            kitty,
            animation: false,
            sixel,
            truecolor: true,
            identity: None,
            cell: None,
            text_area: None,
            relative_placements: false,
            id_space: katui_proto::kitty::IdSpace::default(),
            trust: ProbeSource::Probed,
        }
    }

    #[test]
    fn kitty_outranks_everything() {
        assert_eq!(select(&caps(true, true)), Backend::Kitty);
        assert_eq!(select(&caps(true, false)), Backend::Kitty);
    }

    #[test]
    fn sixel_comes_second() {
        assert_eq!(select(&caps(false, true)), Backend::Sixel);
    }

    #[test]
    fn blocks_carry_the_rest() {
        assert_eq!(select(&caps(false, false)), Backend::Blocks);
    }
}