use std::time::Duration;

use bevy::{
    prelude::*,
    winit::cursor::{CursorIcon, CustomCursor, CustomCursorImage},
};

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_systems(
            Startup,
            (setup_cursor_icon, setup_camera, setup_instructions),
        )
        .add_systems(
            Update,
            (
                execute_animation,
                toggle_texture_atlas,
                toggle_flip_x,
                toggle_flip_y,
                cycle_rect,
            ),
        )
        .run();
}

fn setup_cursor_icon(
    mut commands: Commands,
    asset_server: Res<AssetServer>,
    mut texture_atlas_layouts: ResMut<Assets<TextureAtlasLayout>>,
    window: Single<Entity, With<Window>>,
) {
    let layout =
        TextureAtlasLayout::from_grid(UVec2::splat(64), 20, 10, Some(UVec2::splat(5)), None);
    let texture_atlas_layout = texture_atlas_layouts.add(layout);

    let animation_config = AnimationConfig::new(0, 199, 1, 4);

    commands.entity(*window).insert((
        CursorIcon::Custom(CustomCursor::Image(CustomCursorImage {
            // Image to use as the cursor.
            handle: asset_server
                .load("cursors/kenney_crosshairPack/Tilesheet/crosshairs_tilesheet_white.png"),
            // Optional texture atlas allows you to pick a section of the image
            // and animate it.
            texture_atlas: Some(TextureAtlas {
                layout: texture_atlas_layout.clone(),
                index: animation_config.first_sprite_index,
            }),
            flip_x: false,
            flip_y: false,
            // Optional section of the image to use as the cursor.
            rect: None,
            // The hotspot is the point in the cursor image that will be
            // positioned at the mouse cursor's position.
            hotspot: (0, 0),
        })),
        animation_config,
    ));
}

fn setup_camera(mut commands: Commands) {
    commands.spawn(Camera3d::default());
}

fn setup_instructions(mut commands: Commands) {
    commands.spawn((
        Text::new(
            "Press T to toggle the cursor's `texture_atlas`.\n
Press X to toggle the cursor's `flip_x` setting.\n
Press Y to toggle the cursor's `flip_y` setting.\n
Press C to cycle through the sections of the cursor's image using `rect`.",
        ),
        Node {
            position_type: PositionType::Absolute,
            bottom: Val::Px(12.0),
            left: Val::Px(12.0),
            ..default()
        },
    ));
}

#[derive(Component)]
struct AnimationConfig {
    first_sprite_index: usize,
    last_sprite_index: usize,
    increment: usize,
    fps: u8,
    frame_timer: Timer,
}

impl AnimationConfig {
    fn new(first: usize, last: usize, increment: usize, fps: u8) -> Self {
        Self {
            first_sprite_index: first,
            last_sprite_index: last,
            increment,
            fps,
            frame_timer: Self::timer_from_fps(fps),
        }
    }

    fn timer_from_fps(fps: u8) -> Timer {
        Timer::new(Duration::from_secs_f32(1.0 / (fps as f32)), TimerMode::Once)
    }
}

/// This system loops through all the sprites in the [`CursorIcon`]'s
/// [`TextureAtlas`], from [`AnimationConfig`]'s `first_sprite_index` to
/// `last_sprite_index`.
fn execute_animation(time: Res<Time>, mut query: Query<(&mut AnimationConfig, &mut CursorIcon)>) {
    for (mut config, mut cursor_icon) in &mut query {
        if let CursorIcon::Custom(CustomCursor::Image(ref mut image)) = *cursor_icon {
            config.frame_timer.tick(time.delta());

            if config.frame_timer.finished() {
                if let Some(atlas) = image.texture_atlas.as_mut() {
                    atlas.index += config.increment;

                    if atlas.index > config.last_sprite_index {
                        atlas.index = config.first_sprite_index;
                    }

                    config.frame_timer = AnimationConfig::timer_from_fps(config.fps);
                }
            }
        }
    }
}

fn toggle_texture_atlas(
    input: Res<ButtonInput<KeyCode>>,
    mut query: Query<&mut CursorIcon, With<Window>>,
    mut cached_atlas: Local<Option<TextureAtlas>>, // this lets us restore the previous value
) {
    if input.just_pressed(KeyCode::KeyT) {
        for mut cursor_icon in &mut query {
            if let CursorIcon::Custom(CustomCursor::Image(ref mut image)) = *cursor_icon {
                match image.texture_atlas.take() {
                    Some(a) => {
                        // Save the current texture atlas.
                        *cached_atlas = Some(a.clone());
                    }
                    None => {
                        // Restore the cached texture atlas.
                        if let Some(cached_a) = cached_atlas.take() {
                            image.texture_atlas = Some(cached_a);
                        }
                    }
                }
            }
        }
    }
}

fn toggle_flip_x(
    input: Res<ButtonInput<KeyCode>>,
    mut query: Query<&mut CursorIcon, With<Window>>,
) {
    if input.just_pressed(KeyCode::KeyX) {
        for mut cursor_icon in &mut query {
            if let CursorIcon::Custom(CustomCursor::Image(ref mut image)) = *cursor_icon {
                image.flip_x = !image.flip_x;
            }
        }
    }
}

fn toggle_flip_y(
    input: Res<ButtonInput<KeyCode>>,
    mut query: Query<&mut CursorIcon, With<Window>>,
) {
    if input.just_pressed(KeyCode::KeyY) {
        for mut cursor_icon in &mut query {
            if let CursorIcon::Custom(CustomCursor::Image(ref mut image)) = *cursor_icon {
                image.flip_y = !image.flip_y;
            }
        }
    }
}

/// This system alternates the [`CursorIcon`]'s `rect` field between `None` and
/// 4 sections/rectangles of the cursor's image.
fn cycle_rect(input: Res<ButtonInput<KeyCode>>, mut query: Query<&mut CursorIcon, With<Window>>) {
    if !input.just_pressed(KeyCode::KeyC) {
        return;
    }

    const RECT_SIZE: u32 = 32; // half the size of a tile in the texture atlas

    const SECTIONS: [Option<URect>; 5] = [
        Some(URect {
            min: UVec2::ZERO,
            max: UVec2::splat(RECT_SIZE),
        }),
        Some(URect {
            min: UVec2::new(RECT_SIZE, 0),
            max: UVec2::new(2 * RECT_SIZE, RECT_SIZE),
        }),
        Some(URect {
            min: UVec2::new(0, RECT_SIZE),
            max: UVec2::new(RECT_SIZE, 2 * RECT_SIZE),
        }),
        Some(URect {
            min: UVec2::new(RECT_SIZE, RECT_SIZE),
            max: UVec2::splat(2 * RECT_SIZE),
        }),
        None, // reset to None
    ];

    for mut cursor_icon in &mut query {
        if let CursorIcon::Custom(CustomCursor::Image(ref mut image)) = *cursor_icon {
            let next_rect = SECTIONS
                .iter()
                .cycle()
                .skip_while(|&&corner| corner != image.rect)
                .nth(1) // move to the next element
                .unwrap_or(&None);

            image.rect = *next_rect;
        }
    }
}