use eframe::egui;

pub trait MapProjection: Send + Sync {
    fn project(&self, lon: f64, lat: f64, rect: egui::Rect) -> egui::Pos2;
    fn unproject(&self, pos: egui::Pos2, rect: egui::Rect) -> (f64, f64);
    fn name(&self) -> &'static str;
}

pub struct Equirectangular;

impl MapProjection for Equirectangular {
    fn project(&self, lon: f64, lat: f64, rect: egui::Rect) -> egui::Pos2 {
        egui::pos2(
            rect.left() + ((lon + 180.0) / 360.0) as f32 * rect.width(),
            rect.top() + ((90.0 - lat) / 180.0) as f32 * rect.height(),
        )
    }

    fn unproject(&self, pos: egui::Pos2, rect: egui::Rect) -> (f64, f64) {
        let lon = (pos.x - rect.left()) as f64 / rect.width() as f64 * 360.0 - 180.0;
        let lat = 90.0 - (pos.y - rect.top()) as f64 / rect.height() as f64 * 180.0;
        (lon, lat)
    }

    fn name(&self) -> &'static str {
        "Equirectangular"
    }
}

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

    fn unit_rect() -> egui::Rect {
        egui::Rect::from_min_size(egui::Pos2::ZERO, egui::vec2(360.0, 180.0))
    }

    #[test]
    fn roundtrip_center() {
        let proj = Equirectangular;
        let r = unit_rect();
        let pos = proj.project(0.0, 0.0, r);
        let (lon, lat) = proj.unproject(pos, r);
        assert!((lon).abs() < 1e-4);
        assert!((lat).abs() < 1e-4);
    }

    #[test]
    fn roundtrip_corners() {
        let proj = Equirectangular;
        let r = unit_rect();
        for (lon, lat) in [(-180.0_f64, 90.0_f64), (180.0, -90.0), (-180.0, -90.0), (180.0, 90.0)] {
            let pos = proj.project(lon, lat, r);
            let (lon2, lat2) = proj.unproject(pos, r);
            assert!((lon - lon2).abs() < 1e-4, "lon {lon} → {lon2}");
            assert!((lat - lat2).abs() < 1e-4, "lat {lat} → {lat2}");
        }
    }

    #[test]
    fn project_prime_meridian_equator() {
        let proj = Equirectangular;
        let r = unit_rect();
        let pos = proj.project(0.0, 0.0, r);
        assert!((pos.x - 180.0).abs() < 1e-3, "x={}", pos.x);
        assert!((pos.y - 90.0).abs() < 1e-3, "y={}", pos.y);
    }

    #[test]
    fn rect_scaling() {
        let proj = Equirectangular;
        let r = egui::Rect::from_min_size(egui::pos2(10.0, 20.0), egui::vec2(720.0, 360.0));
        let pos = proj.project(0.0, 0.0, r);
        assert!((pos.x - 370.0).abs() < 1e-3, "x={}", pos.x);
        assert!((pos.y - 200.0).abs() < 1e-3, "y={}", pos.y);
    }
}