use bevy::prelude::*;

struct SnakeHead;
struct Materials {
    head_material: Handle<ColorMaterial>,
}

fn setup(commands: &mut Commands, mut materials: ResMut<Assets<ColorMaterial>>) {
    commands.spawn(Camera2dBundle::default());
    commands.insert_resource(Materials {
        head_material: materials.add(Color::rgb(0.7, 0.7, 0.7).into()),
    });
}

fn spawn_snake(commands: &mut Commands, materials: Res<Materials>) {
    commands
        .spawn(SpriteBundle {
            material: materials.head_material.clone(),
            sprite: Sprite::new(Vec2::new(10.0, 10.0)),
            ..Default::default()
        })
        .with(SnakeHead);
}

fn snake_movement(
    keyboard_input: Res<Input<KeyCode>>,
    mut head_positions: Query<&mut Transform, With<SnakeHead>>,
) {
    for mut transform in head_positions.iter_mut() {
        if keyboard_input.pressed(KeyCode::Left) {
            transform.translation.x -= 2.;
        }
        if keyboard_input.pressed(KeyCode::Right) {
            transform.translation.x += 2.;
        }
        if keyboard_input.pressed(KeyCode::Down) {
            transform.translation.y -= 2.;
        }
        if keyboard_input.pressed(KeyCode::Up) {
            transform.translation.y += 2.;
        }
    }
}

fn main() {
    App::build()
        .add_startup_system(setup.system())
        .add_startup_stage("game_setup", SystemStage::single(spawn_snake.system()))
        .add_system(snake_movement.system())
        .add_plugins(DefaultPlugins)
        .run();
}