package demo:gen@1.2.0;

interface types {
    /// Where something is.
    record point {
        x: s32,
        y: s32,
        /// Optional label.
        label: option<string>,
    }

    enum color { red, green, blue }

    flags access { read, write, exec }

    variant shape {
        nothing,
        circle(f32),
        polygon(list<point>),
    }

    type pair = tuple<u8, f64>;
    type names = list<string>;
}

interface host {
    use types.{point, color, shape, access};

    resource canvas {
        constructor(width: u32, height: u32);
        /// Opens a canvas stored on disk.
        open: static func(path: string) -> result<canvas, string>;
        draw: func(shape: shape, at: point, color: color);
        /// Copies `other` on top of this canvas.
        blend: func(other: borrow<canvas>, types: access);
        name: func() -> option<string>;
    }

    /// Shows the canvas and closes it.
    present: func(canvas: canvas) -> u64;
    log: func(message: string);
}

interface guest {
    use types.{point};

    describe: func() -> point;
}

world plugin {
    use host.{canvas};
    use types.{shape, pair};

    import host;

    export guest;
    export start: func(canvas: canvas) -> result<_, string>;
    export measure: func(shape: shape, scale: pair) -> f32;
    export stop: func();
}