//! A simple plugin and component for a basic flying camera in Bevy.
//! Movement system is based on Minecraft, flying along the horizontal plane no matter the mouse's vertical angle, with two extra buttons for moving vertically.
//!
//! Defalt keybinds are:
//! - W / A / S / D - Move along the horizontal plane
//! - Shift - Move downward
//! - Space - Move upward
//!
//! # Example
//! ```rust
//! use bevy::prelude::*;
//! use bevy_fly_camera::{FlyCamera, FlyCameraPlugin};
//!
//! fn setup(mut commands: Commands) {
//!		commands
//! 		.spawn(Camera3dComponents::default())
//! 		.with(FlyCamera::default());
//! }
//!
//! fn main() {
//!		App::build()
//! 		.add_plugins(DefaultPlugins)
//! 		.add_startup_system(setup.system())
//! 		.add_plugin(FlyCameraPlugin)
//! 		.run();
//! }
//! ```
//!
//! There's also a basic piece of example code included in `/examples/basic.rs`
use bevy::{input::mouse::MouseMotion, prelude::*};

/// A set of options for initializing a FlyCamera.
/// Attach this component to a [`Camera3dComponents`](https://docs.rs/bevy/0.1.3/bevy/prelude/struct.Camera3dComponents.html) bundle to control it with your mouse and keyboard.
/// # Example
/// ```no_run
/// fn setup(mut commands: Commands) {
///		commands
/// 		.spawn(Camera3dComponents::default())
/// 		.with(FlyCamera::default());
/// }

pub struct FlyCamera {
	/// The speed the FlyCamera moves at. Defaults to `1.0`
	pub speed: f32,
	/// The maximum speed the FlyCamera can move at. Defaults to `0.5`
	pub max_speed: f32,
	/// The sensitivity of the FlyCamera's motion based on mouse movement. Defaults to `3.0`
	pub sensitivity: f32,
	/// The amount of deceleration to apply to the camera's motion. Defaults to `1.0`
	pub friction: f32,
	/// The current pitch of the FlyCamera in degrees. This value is always up-to-date, enforced by [FlyCameraPlugin](struct.FlyCameraPlugin.html)
	pub pitch: f32,
	/// The current pitch of the FlyCamera in degrees. This value is always up-to-date, enforced by [FlyCameraPlugin](struct.FlyCameraPlugin.html)
	pub yaw: f32,
	/// The current velocity of the FlyCamera. This value is always up-to-date, enforced by [FlyCameraPlugin](struct.FlyCameraPlugin.html)
	pub velocity: Vec3,
	/// Key used to move forward. Defaults to `W`
	pub key_forward: KeyCode,
	/// Key used to move backward. Defaults to `S
	pub key_backward: KeyCode,
	/// Key used to move left. Defaults to `A`
	pub key_left: KeyCode,
	/// Key used to move right. Defaults to `D`
	pub key_right: KeyCode,
	/// Key used to move up. Defaults to `Space`
	pub key_up: KeyCode,
	/// Key used to move forward. Defaults to `LShift`
	pub key_down: KeyCode,
	/// If `false`, disable keyboard control of the camera. Defaults to `true`
	pub enabled: bool,
}
impl Default for FlyCamera {
	fn default() -> Self {
		Self {
			speed: 1.5,
			max_speed: 0.5,
			sensitivity: 3.0,
			friction: 1.0,
			pitch: 0.0,
			yaw: 0.0,
			velocity: Vec3::zero(),
			key_forward: KeyCode::W,
			key_backward: KeyCode::S,
			key_left: KeyCode::A,
			key_right: KeyCode::D,
			key_up: KeyCode::Space,
			key_down: KeyCode::LShift,
			enabled: true,
		}
	}
}

fn forward_vector(rotation: &Quat) -> Vec3 {
	rotation.mul_vec3(Vec3::unit_z()).normalize()
}

fn forward_walk_vector(rotation: &Quat) -> Vec3 {
	let f = forward_vector(rotation);
	let f_flattened = Vec3::new(f.x(), 0.0, f.z()).normalize();
	f_flattened
}

fn strafe_vector(rotation: &Quat) -> Vec3 {
	// Rotate it 90 degrees to get the strafe direction
	Quat::from_rotation_y(90.0f32.to_radians())
		.mul_vec3(forward_walk_vector(rotation))
		.normalize()
}

fn movement_axis(
	input: &Res<Input<KeyCode>>,
	plus: KeyCode,
	minus: KeyCode,
) -> f32 {
	let mut axis = 0.0;
	if input.pressed(plus) {
		axis += 1.0;
	}
	if input.pressed(minus) {
		axis -= 1.0;
	}
	axis
}

fn camera_movement_system(
	time: Res<Time>,
	keyboard_input: Res<Input<KeyCode>>,
	mut query: Query<(&mut FlyCamera, &mut Transform)>,
) {
	for (mut options, mut transform) in query.iter_mut() {
		let (axis_h, axis_v, axis_float) = if options.enabled {
			(
				movement_axis(&keyboard_input, options.key_right, options.key_left),
				movement_axis(
					&keyboard_input,
					options.key_backward,
					options.key_forward,
				),
				movement_axis(&keyboard_input, options.key_up, options.key_down),
			)
		} else {
			(0.0, 0.0, 0.0)
		};

		let rotation = transform.rotation;
		let accel: Vec3 = (strafe_vector(&rotation) * axis_h)
			+ (forward_walk_vector(&rotation) * axis_v)
			+ (Vec3::unit_y() * axis_float);
		let accel: Vec3 = if accel.length() != 0.0 {
			accel.normalize() * options.speed
		} else {
			Vec3::zero()
		};

		let friction: Vec3 = if options.velocity.length() != 0.0 {
			options.velocity.normalize() * -1.0 * options.friction
		} else {
			Vec3::zero()
		};

		options.velocity += accel * time.delta_seconds;

		// clamp within max speed
		if options.velocity.length() > options.max_speed {
			options.velocity = options.velocity.normalize() * options.max_speed;
		}

		let delta_friction = friction * time.delta_seconds;

		options.velocity = if (options.velocity + delta_friction).signum()
			!= options.velocity.signum()
		{
			Vec3::zero()
		} else {
			options.velocity + delta_friction
		};

		transform.translation += options.velocity;
	}
}

#[derive(Default)]
struct State {
	mouse_motion_event_reader: EventReader<MouseMotion>,
}

fn mouse_motion_system(
	time: Res<Time>,
	mut state: ResMut<State>,
	mouse_motion_events: Res<Events<MouseMotion>>,
	mut query: Query<(&mut FlyCamera, &mut Transform)>,
) {
	let mut delta: Vec2 = Vec2::zero();
	for event in state.mouse_motion_event_reader.iter(&mouse_motion_events) {
		delta += event.delta;
	}
	if delta == Vec2::zero() {
		return;
	}

	for (mut options, mut transform) in query.iter_mut() {
		if !options.enabled {
			continue;
		}
		options.yaw -= delta.x() * options.sensitivity * time.delta_seconds;
		options.pitch += delta.y() * options.sensitivity * time.delta_seconds;

		if options.pitch > 89.9 {
			options.pitch = 89.9;
		}
		if options.pitch < -89.9 {
			options.pitch = -89.9;
		}
		// println!("pitch: {}, yaw: {}", options.pitch, options.yaw);

		let yaw_radians = options.yaw.to_radians();
		let pitch_radians = options.pitch.to_radians();

		transform.rotation = Quat::from_axis_angle(Vec3::unit_y(), yaw_radians)
			* Quat::from_axis_angle(-Vec3::unit_x(), pitch_radians);
	}
}

/**
Include this plugin to add the systems for the FlyCamera bundle.

```no_run
fn main() {
	App::build().add_plugin(FlyCameraPlugin);
}
```

**/

pub struct FlyCameraPlugin;

impl Plugin for FlyCameraPlugin {
	fn build(&self, app: &mut AppBuilder) {
		app
			.init_resource::<State>()
			.add_system(camera_movement_system.system())
			.add_system(mouse_motion_system.system());
	}
}