use bevy::{prelude::*, transform::TransformSystems, window::PrimaryWindow};

use crate::{
    camera::CameraController,
    colonist::{Colonist, MoveOrder, Path, TilePos},
    sim::{SimSpeed, SimTick, format_clock},
    world::{TILE_SIZE, WorldMap},
    worldgen::{WorldGenerated, WorldSeed},
};

pub struct SelectionPlugin;

impl Plugin for SelectionPlugin {
    fn build(&self, app: &mut App) {
        app.init_resource::<Cursor>()
            .init_resource::<Selection>()
            .add_systems(Startup, spawn_tile_info)
            .add_systems(Update, clear_selection.run_if(on_message::<WorldGenerated>))
            .add_systems(
                PostUpdate,
                (
                    update_cursor,
                    update_selection,
                    issue_move_orders,
                    draw_highlights,
                    update_tile_info,
                )
                    .chain()
                    .after(TransformSystems::Propagate),
            );
    }
}

#[derive(Resource, Default, Debug, PartialEq)]
pub struct Cursor {
    pub screen: Option<Vec2>,
    pub world: Option<Vec2>,
    pub tile: Option<UVec2>,
}

#[derive(Resource, Default, Debug, PartialEq, Clone, Copy)]
pub enum Selection {
    #[default]
    None,
    Tile(UVec2),
    Colonist(Entity),
}

#[derive(Component)]
struct TileInfoText;

const HOVER_COLOR: Color = Color::srgba(1.0, 1.0, 1.0, 0.6);
const SELECT_COLOR: Color = Color::srgb(1.0, 0.85, 0.2);
const PATH_COLOR: Color = Color::srgba(1.0, 0.85, 0.2, 0.7);
const PICK_RADIUS: f32 = TILE_SIZE * 0.6;
const CLICK_SLOP_PX: f32 = 4.0;

fn update_cursor(
    map: Res<WorldMap>,
    window: Single<&Window, With<PrimaryWindow>>,
    camera: Single<(&Camera, &GlobalTransform), With<CameraController>>,
    mut cursor: ResMut<Cursor>,
) {
    let (camera, global) = *camera;
    let screen = window.cursor_position();
    let world = screen.and_then(|s| camera.viewport_to_world_2d(global, s).ok());
    let tile = world.and_then(|w| map.tile_at(w));
    cursor.set_if_neq(Cursor {
        screen,
        world,
        tile,
    });
}

fn clear_selection(mut selection: ResMut<Selection>) {
    *selection = Selection::None;
}

fn update_selection(
    buttons: Res<ButtonInput<MouseButton>>,
    keys: Res<ButtonInput<KeyCode>>,
    cursor: Res<Cursor>,
    colonists: Query<(Entity, &Transform), With<Colonist>>,
    mut selection: ResMut<Selection>,
) {
    if keys.just_pressed(KeyCode::Escape) {
        selection.set_if_neq(Selection::None);
    } else if buttons.just_pressed(MouseButton::Left) {
        let picked = cursor.world.and_then(|world| {
            pick_nearest(
                world,
                colonists.iter().map(|(e, t)| (e, t.translation.truncate())),
            )
        });
        let new = match (picked, cursor.tile) {
            (Some(entity), _) => Selection::Colonist(entity),
            (None, Some(tile)) => Selection::Tile(tile),
            (None, None) => Selection::None,
        };
        selection.set_if_neq(new);
    }
}

pub fn pick_nearest(
    point: Vec2,
    candidates: impl Iterator<Item = (Entity, Vec2)>,
) -> Option<Entity> {
    candidates
        .map(|(e, pos)| (e, pos.distance(point)))
        .filter(|&(_, d)| d <= PICK_RADIUS)
        .min_by(|a, b| a.1.total_cmp(&b.1))
        .map(|(e, _)| e)
}

fn issue_move_orders(
    buttons: Res<ButtonInput<MouseButton>>,
    cursor: Res<Cursor>,
    selection: Res<Selection>,
    mut orders: MessageWriter<MoveOrder>,
    mut pressed_at: Local<Option<Vec2>>,
) {
    if buttons.just_pressed(MouseButton::Right) {
        *pressed_at = cursor.screen;
    }
    if !buttons.just_released(MouseButton::Right) {
        return;
    }
    let (Some(press), Some(release)) = (pressed_at.take(), cursor.screen) else {
        return;
    };
    if let (true, Selection::Colonist(colonist), Some(goal)) =
        (is_click(press, release), *selection, cursor.tile)
    {
        orders.write(MoveOrder { colonist, goal });
    }
}

pub fn is_click(press: Vec2, release: Vec2) -> bool {
    press.distance(release) <= CLICK_SLOP_PX
}

fn draw_highlights(
    mut gizmos: Gizmos,
    cursor: Res<Cursor>,
    selection: Res<Selection>,
    colonists: Query<(&Transform, &Path), With<Colonist>>,
) {
    if let Some(tile) = cursor.tile {
        gizmos.rect_2d(
            WorldMap::tile_center(tile),
            Vec2::splat(TILE_SIZE),
            HOVER_COLOR,
        );
    }
    match *selection {
        Selection::None => {}
        Selection::Tile(tile) => {
            gizmos.rect_2d(
                WorldMap::tile_center(tile),
                Vec2::splat(TILE_SIZE),
                SELECT_COLOR,
            );
        }
        Selection::Colonist(entity) => {
            let Ok((transform, path)) = colonists.get(entity) else {
                return;
            };
            let pos = transform.translation.truncate();
            gizmos.circle_2d(pos, TILE_SIZE * 0.5, SELECT_COLOR);
            let points = path.0.iter().map(|&t| WorldMap::tile_center(t));
            gizmos.linestrip_2d(std::iter::once(pos).chain(points), PATH_COLOR);
        }
    }
}

fn spawn_tile_info(mut commands: Commands) {
    commands.spawn((
        TileInfoText,
        Text::default(),
        TextFont::from_font_size(14.0),
        Node {
            position_type: PositionType::Absolute,
            top: px(8),
            left: px(8),
            padding: UiRect::all(px(6)),
            ..default()
        },
        BackgroundColor(Color::srgba(0.0, 0.0, 0.0, 0.5)),
    ));
}

fn update_tile_info(
    map: Res<WorldMap>,
    cursor: Res<Cursor>,
    selection: Res<Selection>,
    colonists: Query<(&Colonist, &TilePos, &Path)>,
    time: Res<Time<Virtual>>,
    tick: Res<SimTick>,
    speed: Res<SimSpeed>,
    seed: Res<WorldSeed>,
    mut text: Single<&mut Text, With<TileInfoText>>,
) {
    let selected = match *selection {
        Selection::None => "-".to_string(),
        Selection::Tile(tile) => describe_tile(&map, Some(tile)),
        Selection::Colonist(entity) => colonists
            .get(entity)
            .map(|(colonist, tile, path)| describe_colonist(colonist, tile.0, path.0.len()))
            .unwrap_or_else(|_| "-".into()),
    };
    let clock = format_clock(*tick);
    let speed = describe_speed(*speed, time.is_paused());
    let info = format!(
        "{clock}  {speed}\nSeed: {} (R: new world)\nHover: {}\nSelected: {selected}",
        seed.0,
        describe_tile(&map, cursor.tile)
    );
    if text.0 != info {
        text.0 = info;
    }
}

pub fn describe_tile(map: &WorldMap, tile: Option<UVec2>) -> String {
    match tile.and_then(|t| map.get(t.as_ivec2()).map(|terrain| (t, terrain))) {
        Some((t, terrain)) => format!("({}, {}) {terrain:?}", t.x, t.y),
        None => "-".into(),
    }
}

pub fn describe_speed(speed: SimSpeed, paused: bool) -> String {
    if paused {
        "PAUSED".into()
    } else {
        format!("{}x", speed.multiplier())
    }
}

pub fn describe_colonist(colonist: &Colonist, tile: UVec2, steps_left: usize) -> String {
    let activity = match steps_left {
        0 => "idle".to_string(),
        n => format!("moving, {n} steps left"),
    };
    format!("{} at ({}, {}), {activity}", colonist.name, tile.x, tile.y)
}

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

    fn selection_app(cursor: Cursor, selection: Selection) -> App {
        let mut app = App::new();
        app.init_resource::<ButtonInput<MouseButton>>()
            .init_resource::<ButtonInput<KeyCode>>()
            .insert_resource(cursor)
            .insert_resource(selection)
            .add_message::<MoveOrder>()
            .add_systems(Update, (update_selection, issue_move_orders));
        app
    }

    fn cursor_on_tile(tile: UVec2) -> Cursor {
        Cursor {
            screen: Some(Vec2::new(50.0, 50.0)),
            world: Some(WorldMap::tile_center(tile)),
            tile: Some(tile),
        }
    }

    fn press(app: &mut App, button: MouseButton) {
        app.world_mut()
            .resource_mut::<ButtonInput<MouseButton>>()
            .press(button);
        app.update();
    }

    fn release(app: &mut App, button: MouseButton) {
        let mut input = app.world_mut().resource_mut::<ButtonInput<MouseButton>>();
        input.clear();
        input.release(button);
        app.update();
    }

    fn selection(app: &App) -> Selection {
        *app.world().resource::<Selection>()
    }

    fn sent_orders(app: &mut App) -> Vec<(Entity, UVec2)> {
        app.world_mut()
            .resource_mut::<Messages<MoveOrder>>()
            .drain()
            .map(|o| (o.colonist, o.goal))
            .collect()
    }

    #[test]
    fn clicking_selects_the_hovered_tile() {
        let mut app = selection_app(cursor_on_tile(UVec2::new(3, 4)), Selection::None);
        press(&mut app, MouseButton::Left);
        assert_eq!(selection(&app), Selection::Tile(UVec2::new(3, 4)));
    }

    #[test]
    fn clicking_a_colonist_selects_it_instead_of_its_tile() {
        let tile = UVec2::new(3, 4);
        let mut app = selection_app(cursor_on_tile(tile), Selection::None);
        let colonist = app
            .world_mut()
            .spawn((
                Colonist { name: "Ada".into() },
                Transform::from_translation(WorldMap::tile_center(tile).extend(1.0)),
            ))
            .id();
        press(&mut app, MouseButton::Left);
        assert_eq!(selection(&app), Selection::Colonist(colonist));
    }

    #[test]
    fn clicking_outside_the_world_clears_the_selection() {
        let mut app = selection_app(Cursor::default(), Selection::Tile(UVec2::new(3, 4)));
        press(&mut app, MouseButton::Left);
        assert_eq!(selection(&app), Selection::None);
    }

    #[test]
    fn escape_clears_the_selection() {
        let mut app = selection_app(
            cursor_on_tile(UVec2::ONE),
            Selection::Tile(UVec2::new(3, 4)),
        );
        app.world_mut()
            .resource_mut::<ButtonInput<KeyCode>>()
            .press(KeyCode::Escape);
        app.update();
        assert_eq!(selection(&app), Selection::None);
    }

    #[test]
    fn right_click_orders_selected_colonist_to_hovered_tile() {
        let colonist = Entity::from_raw_u32(7).unwrap();
        let mut app = selection_app(
            cursor_on_tile(UVec2::new(5, 6)),
            Selection::Colonist(colonist),
        );
        press(&mut app, MouseButton::Right);
        release(&mut app, MouseButton::Right);
        assert_eq!(sent_orders(&mut app), vec![(colonist, UVec2::new(5, 6))]);
    }

    #[test]
    fn right_drag_does_not_order_because_it_pans_the_camera() {
        let colonist = Entity::from_raw_u32(7).unwrap();
        let mut app = selection_app(
            cursor_on_tile(UVec2::new(5, 6)),
            Selection::Colonist(colonist),
        );
        press(&mut app, MouseButton::Right);
        app.world_mut().resource_mut::<Cursor>().screen = Some(Vec2::new(200.0, 50.0));
        release(&mut app, MouseButton::Right);
        assert!(sent_orders(&mut app).is_empty());
    }

    #[test]
    fn pick_nearest_ignores_far_candidates() {
        let a = Entity::from_raw_u32(1).unwrap();
        let b = Entity::from_raw_u32(2).unwrap();
        let candidates = [(a, Vec2::new(5.0, 0.0)), (b, Vec2::new(2.0, 0.0))];
        assert_eq!(pick_nearest(Vec2::ZERO, candidates.into_iter()), Some(b));
        assert_eq!(
            pick_nearest(Vec2::new(100.0, 0.0), candidates.into_iter()),
            None
        );
    }

    #[test]
    fn describe_tile_shows_coordinates_and_terrain() {
        let map = WorldMap::filled(UVec2::new(4, 4), Terrain::Sand);
        assert_eq!(describe_tile(&map, Some(UVec2::new(1, 2))), "(1, 2) Sand");
        assert_eq!(describe_tile(&map, None), "-");
    }

    #[test]
    fn describe_speed_shows_multiplier_or_paused() {
        assert_eq!(describe_speed(SimSpeed::Fastest, false), "6x");
        assert_eq!(describe_speed(SimSpeed::Fast, true), "PAUSED");
    }

    #[test]
    fn describe_colonist_shows_activity() {
        let ada = Colonist { name: "Ada".into() };
        assert_eq!(
            describe_colonist(&ada, UVec2::new(1, 2), 0),
            "Ada at (1, 2), idle"
        );
        assert_eq!(
            describe_colonist(&ada, UVec2::new(1, 2), 3),
            "Ada at (1, 2), moving, 3 steps left"
        );
    }
}