//! Demonstrates how shadow biases affect shadows in a 3d scene.

use std::f32::consts::PI;

use bevy::{input::mouse::MouseMotion, prelude::*};

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_systems(Startup, setup)
        .add_systems(
            Update,
            (
                adjust_point_light_biases,
                toggle_light,
                adjust_directional_light_biases,
                camera_controller,
            ),
        )
        .run();
}

/// set up a 3D scene to test shadow biases and perspective projections
fn setup(
    mut commands: Commands,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<StandardMaterial>>,
) {
    let spawn_plane_depth = 500.0f32;
    let spawn_height = 2.0;
    let sphere_radius = 0.25;

    let white_handle = materials.add(StandardMaterial {
        base_color: Color::WHITE,
        perceptual_roughness: 1.0,
        ..default()
    });
    let sphere_handle = meshes.add(
        Mesh::try_from(shape::Icosphere {
            radius: sphere_radius,
            ..default()
        })
        .unwrap(),
    );

    commands.spawn(PointLightBundle {
        transform: Transform::from_xyz(5.0, 5.0, 0.0),
        point_light: PointLight {
            intensity: 0.0,
            range: spawn_plane_depth,
            color: Color::WHITE,
            shadow_depth_bias: 0.0,
            shadow_normal_bias: 0.0,
            shadows_enabled: true,
            ..default()
        },
        ..default()
    });

    commands.spawn(DirectionalLightBundle {
        directional_light: DirectionalLight {
            illuminance: 100000.0,
            shadow_depth_bias: 0.0,
            shadow_normal_bias: 0.0,
            shadows_enabled: true,
            ..default()
        },
        transform: Transform::from_rotation(Quat::from_euler(
            EulerRot::ZYX,
            0.0,
            PI / 2.,
            -PI / 4.,
        )),
        ..default()
    });

    // camera
    commands.spawn((
        Camera3dBundle {
            transform: Transform::from_xyz(-1.0, 1.0, 1.0)
                .looking_at(Vec3::new(-1.0, 1.0, 0.0), Vec3::Y),
            ..default()
        },
        CameraController::default(),
    ));

    for z_i32 in -spawn_plane_depth as i32..=0 {
        commands.spawn(PbrBundle {
            mesh: sphere_handle.clone(),
            material: white_handle.clone(),
            transform: Transform::from_xyz(0.0, spawn_height, z_i32 as f32),
            ..default()
        });
    }

    // ground plane
    commands.spawn(PbrBundle {
        mesh: meshes.add(shape::Plane::from_size(2.0 * spawn_plane_depth).into()),
        material: white_handle,
        ..default()
    });

    let style = TextStyle {
        font_size: 20.,
        ..default()
    };
    commands.spawn(
        TextBundle::from_sections([
            TextSection::new("Controls:\n", style.clone()),
            TextSection::new("WSAD  - forward/back/strafe left/right\n", style.clone()),
            TextSection::new("E / Q - up / down\n", style.clone()),
            TextSection::new(
                "L     - switch between directional and point lights [",
                style.clone(),
            ),
            TextSection::new("DirectionalLight", style.clone()),
            TextSection::new("]\n", style.clone()),
            TextSection::new("1/2   - change point light depth bias [", style.clone()),
            TextSection::new("0.00", style.clone()),
            TextSection::new("]\n", style.clone()),
            TextSection::new("3/4   - change point light normal bias [", style.clone()),
            TextSection::new("0.0", style.clone()),
            TextSection::new("]\n", style.clone()),
            TextSection::new("5/6   - change direction light depth bias [", style.clone()),
            TextSection::new("0.00", style.clone()),
            TextSection::new("]\n", style.clone()),
            TextSection::new(
                "7/8   - change direction light normal bias [",
                style.clone(),
            ),
            TextSection::new("0.0", style.clone()),
            TextSection::new("]", style),
        ])
        .with_style(Style {
            position_type: PositionType::Absolute,
            top: Val::Px(12.0),
            left: Val::Px(12.0),
            ..default()
        }),
    );
}

fn toggle_light(
    input: Res<Input<KeyCode>>,
    mut point_lights: Query<&mut PointLight>,
    mut directional_lights: Query<&mut DirectionalLight>,
    mut example_text: Query<&mut Text>,
) {
    if input.just_pressed(KeyCode::L) {
        for mut light in &mut point_lights {
            light.intensity = if light.intensity == 0.0 {
                example_text.single_mut().sections[4].value = "PointLight".to_string();
                100000000.0
            } else {
                0.0
            };
        }
        for mut light in &mut directional_lights {
            light.illuminance = if light.illuminance == 0.0 {
                example_text.single_mut().sections[4].value = "DirectionalLight".to_string();
                100000.0
            } else {
                0.0
            };
        }
    }
}

fn adjust_point_light_biases(
    input: Res<Input<KeyCode>>,
    mut query: Query<&mut PointLight>,
    mut example_text: Query<&mut Text>,
) {
    let depth_bias_step_size = 0.01;
    let normal_bias_step_size = 0.1;
    for mut light in &mut query {
        if input.just_pressed(KeyCode::Key1) {
            light.shadow_depth_bias -= depth_bias_step_size;
            example_text.single_mut().sections[7].value = format!("{:.2}", light.shadow_depth_bias);
        }
        if input.just_pressed(KeyCode::Key2) {
            light.shadow_depth_bias += depth_bias_step_size;
            example_text.single_mut().sections[7].value = format!("{:.2}", light.shadow_depth_bias);
        }
        if input.just_pressed(KeyCode::Key3) {
            light.shadow_normal_bias -= normal_bias_step_size;
            example_text.single_mut().sections[10].value =
                format!("{:.1}", light.shadow_normal_bias);
        }
        if input.just_pressed(KeyCode::Key4) {
            light.shadow_normal_bias += normal_bias_step_size;
            example_text.single_mut().sections[10].value =
                format!("{:.1}", light.shadow_normal_bias);
        }
    }
}

fn adjust_directional_light_biases(
    input: Res<Input<KeyCode>>,
    mut query: Query<&mut DirectionalLight>,
    mut example_text: Query<&mut Text>,
) {
    let depth_bias_step_size = 0.01;
    let normal_bias_step_size = 0.1;
    for mut light in &mut query {
        if input.just_pressed(KeyCode::Key5) {
            light.shadow_depth_bias -= depth_bias_step_size;
            example_text.single_mut().sections[13].value =
                format!("{:.2}", light.shadow_depth_bias);
        }
        if input.just_pressed(KeyCode::Key6) {
            light.shadow_depth_bias += depth_bias_step_size;
            example_text.single_mut().sections[13].value =
                format!("{:.2}", light.shadow_depth_bias);
        }
        if input.just_pressed(KeyCode::Key7) {
            light.shadow_normal_bias -= normal_bias_step_size;
            example_text.single_mut().sections[16].value =
                format!("{:.1}", light.shadow_normal_bias);
        }
        if input.just_pressed(KeyCode::Key8) {
            light.shadow_normal_bias += normal_bias_step_size;
            example_text.single_mut().sections[16].value =
                format!("{:.1}", light.shadow_normal_bias);
        }
    }
}

#[derive(Component)]
struct CameraController {
    pub enabled: bool,
    pub sensitivity: f32,
    pub key_forward: KeyCode,
    pub key_back: KeyCode,
    pub key_left: KeyCode,
    pub key_right: KeyCode,
    pub key_up: KeyCode,
    pub key_down: KeyCode,
    pub key_run: KeyCode,
    pub walk_speed: f32,
    pub run_speed: f32,
    pub friction: f32,
    pub pitch: f32,
    pub yaw: f32,
    pub velocity: Vec3,
}

impl Default for CameraController {
    fn default() -> Self {
        Self {
            enabled: true,
            sensitivity: 0.5,
            key_forward: KeyCode::W,
            key_back: KeyCode::S,
            key_left: KeyCode::A,
            key_right: KeyCode::D,
            key_up: KeyCode::E,
            key_down: KeyCode::Q,
            key_run: KeyCode::ShiftLeft,
            walk_speed: 10.0,
            run_speed: 30.0,
            friction: 0.5,
            pitch: 0.0,
            yaw: 0.0,
            velocity: Vec3::ZERO,
        }
    }
}

fn camera_controller(
    time: Res<Time>,
    mut mouse_events: EventReader<MouseMotion>,
    key_input: Res<Input<KeyCode>>,
    mut query: Query<(&mut Transform, &mut CameraController), With<Camera>>,
) {
    let dt = time.delta_seconds();

    // Handle mouse input
    let mut mouse_delta = Vec2::ZERO;
    for mouse_event in mouse_events.iter() {
        mouse_delta += mouse_event.delta;
    }

    for (mut transform, mut options) in &mut query {
        if !options.enabled {
            continue;
        }

        // Handle key input
        let mut axis_input = Vec3::ZERO;
        if key_input.pressed(options.key_forward) {
            axis_input.z += 1.0;
        }
        if key_input.pressed(options.key_back) {
            axis_input.z -= 1.0;
        }
        if key_input.pressed(options.key_right) {
            axis_input.x += 1.0;
        }
        if key_input.pressed(options.key_left) {
            axis_input.x -= 1.0;
        }
        if key_input.pressed(options.key_up) {
            axis_input.y += 1.0;
        }
        if key_input.pressed(options.key_down) {
            axis_input.y -= 1.0;
        }

        // Apply movement update
        if axis_input != Vec3::ZERO {
            let max_speed = if key_input.pressed(options.key_run) {
                options.run_speed
            } else {
                options.walk_speed
            };
            options.velocity = axis_input.normalize() * max_speed;
        } else {
            let friction = options.friction.clamp(0.0, 1.0);
            options.velocity *= 1.0 - friction;
            if options.velocity.length_squared() < 1e-6 {
                options.velocity = Vec3::ZERO;
            }
        }
        let forward = transform.forward();
        let right = transform.right();
        transform.translation += options.velocity.x * dt * right
            + options.velocity.y * dt * Vec3::Y
            + options.velocity.z * dt * forward;

        if mouse_delta != Vec2::ZERO {
            // Apply look update
            options.pitch = (options.pitch - mouse_delta.y * 0.5 * options.sensitivity * dt)
                .clamp(-PI / 2., PI / 2.);
            options.yaw -= mouse_delta.x * options.sensitivity * dt;
            transform.rotation = Quat::from_euler(EulerRot::ZYX, 0.0, options.yaw, options.pitch);
        }
    }
}