public partial class AnimationController : Node3D
{
	[Export] public Skeleton3D Skeleton { get; set; }
	[Export] public BoneAttachment3D RootBone { get; set; }

	// Contains all the bones in the skeleton, keyed by name (e.g. "LowerArm_L").
	Dictionary<string, BoneAttachment3D> _bones = [];

	// Whether the player's body is currently turning to match up with the camera rotation.
	bool _isTurning = false;

	// Current amount the body is turned due to walking sideways.
	float _bodyYaw = 0.0f;

	CharacterBody3D _player;
	MovementController _movementController;
	CameraController _cameraController;
	Camera3D _camera;
	Transform3D _cameraDefaultTransform;

	AnimationTree _animTree;
	Animation _walkForwardAnim;
	Animation _walkBackwardAnim;

	public override void _Ready()
	{
		_player = GetParent<CharacterBody3D>();
		_movementController = _player.GetNode<MovementController>("MovementController");
		_cameraController   = _player.GetNode<CameraController>("CameraController");
		_camera = _cameraController.Camera;
		_cameraDefaultTransform = _camera.Transform;

		_animTree = GetNode<AnimationTree>("AnimationTree");
		_walkForwardAnim  = _animTree.GetAnimation("walk_forward");
		_walkBackwardAnim = _animTree.GetAnimation("walk_backward");

		void AddBone(BoneAttachment3D bone)
			{ bone.OverridePose = true; _bones[bone.Name] = bone; }
		AddBone(RootBone);
		foreach (var child in RootBone.FindChildren("*", "BoneAttachment3D"))
			AddBone((BoneAttachment3D)child);
	}

	public override void _Process(double delta)
	{
		ResetTransforms();
		HandleTurning(delta);
		HandleLookingAnimation(delta);
		HandleWalkingAnimation(delta);
	}

	void ResetTransforms()
	{
		foreach (var bone in _bones.Values)
			bone.Transform = Skeleton.GetBonePose(bone.BoneIdx);
		_camera.Transform = _cameraDefaultTransform;
	}

	void HandleTurning(double delta)
	{
		const float TurnBegin = 60.0f; // Start turning when camera is rotated this much.
		const float TurnEnd   =  5.0f; // Stop turning when body is this close to camera rotation.
		const float TurnSpeed =  6.0f;

		var yaw = _cameraController.CurrentYaw; // Camera yaw relative to player yaw.
		var isMoving = _movementController.RealMoveSpeed > 0.01f;
		_isTurning = isMoving || (Abs(yaw) > DegToRad(TurnBegin));

		if (_isTurning) {
			var yawDelta = Sign(yaw) * Min(Abs(yaw), Abs(yaw) * TurnSpeed * (float)delta);
			_cameraController.CurrentYaw -= (float)yawDelta;
			_player.RotateY(yawDelta);

			if (Abs(_cameraController.CurrentYaw) < DegToRad(TurnEnd))
				_isTurning = false;
		}
	}

	void HandleLookingAnimation(double delta)
	{
		const float PitchFactorLowerBody = 0.05f;
		const float PitchFactorUpperBody = 0.20f;
		const float PitchFactorNeck = 0.25f;
		const float PitchFactorHead = 0.35f;

		var pitch = _cameraController.CurrentPitch;
		_bones["LowerBody"].RotateX(pitch * PitchFactorLowerBody);
		_bones["UpperBody"].RotateX(-pitch * PitchFactorUpperBody);
		_bones["Neck"].RotateX(-pitch * PitchFactorNeck);
		_bones["Head"].RotateX(-pitch * PitchFactorHead);
		_bones["UpperArm_L"].RotateX(pitch * (PitchFactorLowerBody + PitchFactorUpperBody) / 2);
		_bones["UpperArm_R"].RotateX(pitch * (PitchFactorLowerBody + PitchFactorUpperBody) / 2);
		_camera.RotateX(pitch * (1 - PitchFactorLowerBody - PitchFactorUpperBody - PitchFactorNeck - PitchFactorHead));

		const float YawFactorLowerBody = 0.06f;
		const float YawFactorUpperBody = 0.18f;
		const float YawFactorNeck = 0.2f;
		const float YawFactorHead = 0.3f;

		var yaw = _cameraController.CurrentYaw;
		_bones["LowerBody"].GlobalRotate(Vector3.Up, yaw * YawFactorLowerBody);
		_bones["UpperBody"].GlobalRotate(Vector3.Up, yaw * YawFactorUpperBody);
		_bones["Neck"].GlobalRotate(Vector3.Up, yaw * YawFactorNeck);
		_bones["Head"].GlobalRotate(Vector3.Up, yaw * YawFactorHead);
		_camera.GlobalRotate(Vector3.Up, yaw * (1 - YawFactorLowerBody - YawFactorUpperBody - YawFactorNeck - YawFactorHead));

		// How much of the "ideal" camera rotation (rather than animation rotation) should be applied.
		const float CameraFactorIdealPitch = 0.7f;
		const float CameraFactorIdealYaw   = 0.8f;
		const float CameraFactorIdealRoll  = 0.9f;

		var global_yaw = _player.Rotation.Y + yaw;
		var cameraRotation = _camera.GlobalRotation;
		cameraRotation.X = LerpAngle(cameraRotation.X, pitch, CameraFactorIdealPitch);
		cameraRotation.Y = LerpAngle(cameraRotation.Y, global_yaw, CameraFactorIdealYaw);
		cameraRotation.Z = LerpAngle(cameraRotation.Z, 0, CameraFactorIdealRoll);
		_camera.GlobalRotation = cameraRotation;
	}

	void HandleWalkingAnimation(double delta)
	{
		var input = Input.GetVector("move_strafe_left", "move_strafe_right", "move_forward", "move_back");
		var isOnFloor = _movementController.TimeSinceOnFloor < 0.25f;
		var isMoving = _movementController.RealMoveSpeed > 0.01f;
		var isMovingForward = input.Y <= 0;

		var walkState = (isOnFloor && isMoving) ? "move" : "idle";
		var walkDirection = isMovingForward ? "forward" : "backward";
		var walkSpeed = _movementController.RealMoveSpeed / _movementController.MaxSpeed;
		var targetBodyYaw = -(isMovingForward ? Vector2.Up : Vector2.Down).AngleTo(input);

		_animTree.Set("parameters/walk_state/transition_request", walkState);
		_animTree.Set("parameters/walk_direction/transition_request", walkDirection);

		var prevWalkSpeed = (float)_animTree.Get("parameters/walk_speed/blend_amount");
		_animTree.Set("parameters/walk_speed/blend_amount", Lerp(prevWalkSpeed, walkSpeed, 10 * (float)delta));

		const float YAW_FACTOR_LOWER_BODY = 0.25f;
		const float YAW_FACTOR_UPPER_BODY = 0.25f;
		const float YAW_FACTOR_NECK       = 0.50f;

		_bodyYaw += (targetBodyYaw - _bodyYaw) * (float)delta * 6;

		_bones["Root"].GlobalRotate(Vector3.Up, _bodyYaw);
		_bones["LowerBody"].GlobalRotate(Vector3.Up, -_bodyYaw * YAW_FACTOR_LOWER_BODY);
		_bones["UpperBody"].GlobalRotate(Vector3.Up, -_bodyYaw * YAW_FACTOR_UPPER_BODY);
		_bones["Neck"].GlobalRotate(Vector3.Up, -_bodyYaw * YAW_FACTOR_NECK);
	}
}