//! Demonstrates how to have the camera follow a target object

use bevy::prelude::*;
use bevy_panorbit_camera::{PanOrbitCamera, PanOrbitCameraPlugin};
use std::f32::consts::TAU;

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_plugins(PanOrbitCameraPlugin)
        .add_systems(Startup, setup)
        .add_systems(Update, (animate_cube, cam_follow).chain())
        .run();
}

#[derive(Component)]
struct Cube;

fn setup(
    mut commands: Commands,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<StandardMaterial>>,
) {
    // Ground
    commands.spawn((
        Mesh3d(meshes.add(Plane3d::default().mesh().size(5.0, 5.0))),
        MeshMaterial3d(materials.add(Color::srgb(0.3, 0.5, 0.3))),
    ));
    // Cube
    commands
        .spawn((
            Mesh3d(meshes.add(Cuboid::new(1.0, 1.0, 1.0))),
            MeshMaterial3d(materials.add(Color::srgb(0.8, 0.7, 0.6))),
            Transform::from_xyz(0.0, 0.5, 0.0),
        ))
        .insert(Cube);
    // Light
    commands.spawn((
        PointLight {
            shadows_enabled: true,
            ..default()
        },
        Transform::from_xyz(4.0, 8.0, 4.0),
    ));
    // Camera
    commands.spawn((
        Transform::from_translation(Vec3::new(0.0, 1.5, 5.0)),
        PanOrbitCamera {
            // Panning the camera changes the focus, and so you most likely want to disable
            // panning when setting the focus manually
            pan_sensitivity: 0.0,
            // If you want to fully control the camera's focus, set smoothness to 0 so it
            // immediately snaps to that location. If you want the 'follow' to be smoothed,
            // leave this at default or set it to something between 0 and 1.
            pan_smoothness: 0.0,
            ..default()
        },
    ));
}

/// Move the cube in a circle around the Y axis
fn animate_cube(
    time: Res<Time>,
    mut cube_q: Query<&mut Transform, With<Cube>>,
    mut angle: Local<f32>,
) {
    if let Ok(mut cube_tfm) = cube_q.get_single_mut() {
        // Rotate 20 degrees a second, wrapping around to 0 after a full rotation
        *angle += 20f32.to_radians() * time.delta_secs() % TAU;
        // Convert angle to position
        let pos = Vec3::new(angle.sin() * 1.5, 0.5, angle.cos() * 1.5);
        cube_tfm.translation = pos;
    }
}

/// Set the camera's focus to the cube's position
fn cam_follow(mut pan_orbit_q: Query<&mut PanOrbitCamera>, cube_q: Query<&Transform, With<Cube>>) {
    if let Ok(mut pan_orbit) = pan_orbit_q.get_single_mut() {
        if let Ok(cube_tfm) = cube_q.get_single() {
            pan_orbit.target_focus = cube_tfm.translation;
            // Whenever changing properties manually like this, it's necessary to force
            // PanOrbitCamera to update this frame (by default it only updates when there are
            // input events).
            pan_orbit.force_update = true;
        }
    }
}