use bevy::{
    input::mouse::{AccumulatedMouseScroll, MouseScrollPixelsPerLine},
    prelude::*,
    window::PrimaryWindow,
};

use crate::world::WorldMap;

pub struct CameraPlugin;

const DRAG_BUTTONS: [MouseButton; 2] = [MouseButton::Middle, MouseButton::Right];

impl Plugin for CameraPlugin {
    fn build(&self, app: &mut App) {
        app.add_systems(Startup, spawn_camera).add_systems(
            Update,
            (keyboard_pan, drag_pan, scroll_zoom, clamp_to_world).chain(),
        );
    }
}

#[derive(Component, Clone, Debug)]
pub struct CameraController {
    pub pan_speed: f32,
    pub fast_multiplier: f32,
    pub zoom_per_line: f32,
    pub min_scale: f32,
    pub max_scale: f32,
}

impl Default for CameraController {
    fn default() -> Self {
        Self {
            pan_speed: 600.0,
            fast_multiplier: 3.0,
            zoom_per_line: 0.15,
            min_scale: 0.2,
            max_scale: 4.0,
        }
    }
}

fn spawn_camera(mut commands: Commands, map: Res<WorldMap>) {
    commands.spawn((
        Camera2d,
        CameraController::default(),
        Transform::from_translation((map.world_size() / 2.0).extend(0.0)),
    ));
}

fn ortho(projection: &mut Projection) -> &mut OrthographicProjection {
    match projection {
        Projection::Orthographic(o) => o,
        _ => panic!("camera must use an orthographic projection"),
    }
}

fn keyboard_pan(
    keys: Res<ButtonInput<KeyCode>>,
    time: Res<Time>,
    camera: Single<(&mut Transform, &mut Projection, &CameraController)>,
) {
    let (mut transform, mut projection, controller) = camera.into_inner();
    let mut dir = Vec2::ZERO;
    for (key, d) in [
        (KeyCode::KeyW, Vec2::Y),
        (KeyCode::ArrowUp, Vec2::Y),
        (KeyCode::KeyS, Vec2::NEG_Y),
        (KeyCode::ArrowDown, Vec2::NEG_Y),
        (KeyCode::KeyA, Vec2::NEG_X),
        (KeyCode::ArrowLeft, Vec2::NEG_X),
        (KeyCode::KeyD, Vec2::X),
        (KeyCode::ArrowRight, Vec2::X),
    ] {
        if keys.pressed(key) {
            dir += d;
        }
    }
    if dir == Vec2::ZERO {
        return;
    }
    let fast = keys.any_pressed([KeyCode::ShiftLeft, KeyCode::ShiftRight]);
    let speed = controller.pan_speed * if fast { controller.fast_multiplier } else { 1.0 };
    let scale = ortho(&mut projection).scale;
    transform.translation += (dir.normalize() * speed * scale * time.delta_secs()).extend(0.0);
}

fn drag_pan(
    buttons: Res<ButtonInput<MouseButton>>,
    window: Single<&Window, With<PrimaryWindow>>,
    camera: Single<(&mut Transform, &mut Projection), With<CameraController>>,
    mut last_cursor: Local<Option<Vec2>>,
) {
    let cursor = window.cursor_position();
    let previous = std::mem::replace(&mut *last_cursor, cursor);
    if !buttons.any_pressed(DRAG_BUTTONS) {
        return;
    }
    let (Some(cursor), Some(previous)) = (cursor, previous) else {
        return;
    };
    let (mut transform, mut projection) = camera.into_inner();
    let scale = ortho(&mut projection).scale;
    transform.translation += (screen_to_world_delta(cursor - previous) * -scale).extend(0.0);
}

fn scroll_zoom(
    scroll: Res<AccumulatedMouseScroll>,
    pixels_per_line: Res<MouseScrollPixelsPerLine>,
    window: Single<&Window, With<PrimaryWindow>>,
    camera: Single<(
        &Camera,
        &GlobalTransform,
        &mut Transform,
        &mut Projection,
        &CameraController,
    )>,
) {
    let lines = scroll.to_lines(&pixels_per_line).delta.y;
    if lines == 0.0 {
        return;
    }
    let (camera, global, mut transform, mut projection, controller) = camera.into_inner();
    let projection = ortho(&mut projection);
    let old_scale = projection.scale;
    let new_scale = (old_scale * (1.0 - lines * controller.zoom_per_line))
        .clamp(controller.min_scale, controller.max_scale);
    projection.scale = new_scale;

    let focus = window
        .cursor_position()
        .and_then(|cursor| camera.viewport_to_world_2d(global, cursor).ok());
    if let Some(focus) = focus {
        let pos = zoom_towards(transform.translation.truncate(), focus, old_scale, new_scale);
        transform.translation = pos.extend(transform.translation.z);
    }
}

fn clamp_to_world(map: Res<WorldMap>, mut camera: Single<&mut Transform, With<CameraController>>) {
    let clamped = clamp_to_rect(camera.translation.truncate(), Vec2::ZERO, map.world_size());
    camera.translation = clamped.extend(camera.translation.z);
}

pub fn screen_to_world_delta(screen: Vec2) -> Vec2 {
    Vec2::new(screen.x, -screen.y)
}

pub fn zoom_towards(camera: Vec2, focus: Vec2, old_scale: f32, new_scale: f32) -> Vec2 {
    focus + (camera - focus) * (new_scale / old_scale)
}

pub fn clamp_to_rect(pos: Vec2, min: Vec2, max: Vec2) -> Vec2 {
    pos.clamp(min, max)
}

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

    fn world_point_at_offset(camera: Vec2, scale: f32, screen_offset: Vec2) -> Vec2 {
        camera + screen_offset * scale
    }

    #[test]
    fn zooming_keeps_the_point_under_the_cursor_fixed() {
        let camera = Vec2::new(100.0, 50.0);
        let cursor_offset = Vec2::new(200.0, -120.0);
        let focus = world_point_at_offset(camera, 1.0, cursor_offset);

        let new_camera = zoom_towards(camera, focus, 1.0, 0.5);

        assert!(world_point_at_offset(new_camera, 0.5, cursor_offset).abs_diff_eq(focus, 1e-4));
    }

    #[test]
    fn zooming_on_camera_center_does_not_move_camera() {
        let camera = Vec2::new(10.0, 20.0);
        assert_eq!(zoom_towards(camera, camera, 1.0, 3.0), camera);
    }

    #[test]
    fn dragging_moves_world_opposite_to_screen_y_because_screen_y_points_down() {
        assert_eq!(screen_to_world_delta(Vec2::new(3.0, 4.0)), Vec2::new(3.0, -4.0));
    }

    #[test]
    fn camera_center_cannot_leave_the_world_so_the_map_stays_on_screen() {
        let max = Vec2::new(100.0, 50.0);
        assert_eq!(clamp_to_rect(Vec2::new(-5.0, 60.0), Vec2::ZERO, max), Vec2::new(0.0, 50.0));
        assert_eq!(clamp_to_rect(Vec2::new(5.0, 6.0), Vec2::ZERO, max), Vec2::new(5.0, 6.0));
    }
}