DartGame/game/core/dart/dart.gd

class_name Dart
extends RigidBody3D

## A single dart. Dragged from the tray, thrown at the board.
##
## Lifecycle: FROZEN -> DRAGGING -> IN_FLIGHT -> LANDED
## The scene root (main.gd) routes mouse input here; the dart does not
## hunt for the camera or raycast for itself.

signal landed(dart: Dart, hit_point: Vector3)

enum State { IDLE, DRAGGING, IN_FLIGHT, LANDED }

# --- Tuning -------------------------------------------------------------

@export_group("Drag")
## How hard the dart chases the cursor while held.
@export var drag_follow_speed: float = 20.0
## Clamp so a fast flick doesn't launch it across the room mid-drag.
@export var max_drag_speed: float = 42.0
## Tilt of the drag plane relative to the camera, in degrees.
@export_range(-180.0, 180.0) var drag_plane_angle: float = 15.0
@export var drag_linear_damp: float = 5.0
@export var drag_angular_damp: float = 10.0

@export_group("Throw")
@export var forward_impulse: float = 8.0

## Scale the raw flick velocity down. Raw mouse speed is usually too fast.
@export var throw_force_multiplier: float = 0.5
@export var max_throw_speed: float = 42.0
## Higher = more visible arc. Real gravity looks too floaty at dart scale.
@export var flight_gravity_scale: float = 2.0

@export_group("Flight")
## How fast the nose swings to face the direction of travel.
@export var nose_align_speed: float = 1.0
## Which local axis is the dart's tip. Check this against the model.
@export var forward_axis: Vector3 = Vector3.FORWARD
## Below this speed the dart is considered landed.
@export var landed_speed_threshold: float = 0.5

# --- State --------------------------------------------------------------

var state: State = State.IDLE

var _drag_plane: Plane
var _drag_offset: Vector3 = Vector3.ZERO
var _target_pos: Vector3 = Vector3.ZERO

## Sampled positions, used to compute throw velocity on release.
const HISTORY_LENGTH := 6
var _pos_history: Array[Vector3] = []
var _time_history: Array[float] = []


func _ready() -> void:
	freeze_mode = RigidBody3D.FREEZE_MODE_STATIC
	freeze = true
	add_to_group(&"dart")


# --- Public API (called by main.gd) --------------------------------------

func begin_drag(camera: Camera3D, hit_point: Vector3) -> void:
	state = State.DRAGGING
	freeze = false

	gravity_scale = 0.0          # don't sag while held
	linear_damp = drag_linear_damp
	angular_damp = drag_angular_damp

	# The plane the dart slides along while dragged. Tilted off the camera's
	# view axis so pulling back also pulls the dart down, which feels natural.
	var base_normal := camera.global_transform.basis.z
	var tilted := base_normal.rotated(
		camera.global_transform.basis.x,
		deg_to_rad(drag_plane_angle)
	)
	_drag_plane = Plane(tilted.normalized(), hit_point)
	_drag_offset = global_position - hit_point

	# Seed the target to the current position. Without this the dart drops
	# to the plane origin until the mouse first moves.
	_target_pos = global_position

	_pos_history.clear()
	_time_history.clear()


func update_drag(camera: Camera3D, mouse_pos: Vector2) -> void:
	if state != State.DRAGGING:
		return

	var ray_origin := camera.project_ray_origin(mouse_pos)
	var ray_dir := camera.project_ray_normal(mouse_pos)
	var hit = _drag_plane.intersects_ray(ray_origin, ray_dir)
	if hit != null:
		_target_pos = hit + _drag_offset

func release_drag() -> void:
	if state != State.DRAGGING:
		return
	state = State.IN_FLIGHT
	gravity_scale = flight_gravity_scale
	linear_damp = 0.0
	angular_damp = 0.0

	# The flick gives aim (up/down/left/right). It CANNOT give forward speed —
	# the drag plane faces the camera, so motion toward the board is ~zero.
	var flick := _calculate_throw_velocity() * throw_force_multiplier

	# The forward component has to come from somewhere. Use the camera's
	# forward, so "throw" always means "toward what you're looking at".
	var cam := get_viewport().get_camera_3d()
	var forward := -cam.global_transform.basis.z * forward_impulse

	var throw := flick + forward
	if throw.length() > max_throw_speed:
		throw = throw.normalized() * max_throw_speed
	linear_velocity = throw

	var raw := _calculate_throw_velocity()
	print("flick: %s  forward: %s  final: %s (%.1f m/s)" % [flick, forward, throw, throw.length()])


# --- Physics ------------------------------------------------------------

func _physics_process(delta: float) -> void:
	match state:
		State.DRAGGING:
			_process_drag()
		State.IN_FLIGHT:
			_process_flight(delta)


func _process_drag() -> void:
	# Chase the target with velocity rather than teleporting, so the dart
	# still collides with things and carries momentum into the throw.
	var to_target := _target_pos - global_position
	var desired := to_target * drag_follow_speed
	if desired.length() > max_drag_speed:
		desired = desired.normalized() * max_drag_speed

	linear_velocity = desired
	angular_velocity = angular_velocity.lerp(Vector3.ZERO, 0.2)

	_pos_history.append(global_position)
	_time_history.append(Time.get_ticks_msec() / 1000.0)
	if _pos_history.size() > HISTORY_LENGTH:
		_pos_history.pop_front()
		_time_history.pop_front()


func _process_flight(delta: float) -> void:
	if linear_velocity.length() > landed_speed_threshold:
		_align_to_velocity(delta)
	else:
		_on_landed()


func _align_to_velocity(delta: float) -> void:
	var vel_dir := linear_velocity.normalized()
	var current_forward := global_transform.basis * forward_axis
	var axis := current_forward.cross(vel_dir)

	if axis.length() < 0.001:
		return   # already aligned, or exactly opposed

	axis = axis.normalized()
	var angle := current_forward.angle_to(vel_dir)
	var step := minf(angle, nose_align_speed * delta)

	global_transform.basis = global_transform.basis.rotated(axis, step)
	global_transform.basis = global_transform.basis.orthonormalized()


func _on_landed() -> void:
	state = State.LANDED
	angular_velocity = Vector3.ZERO
	landed.emit(self, global_position)


func _calculate_throw_velocity() -> Vector3:
	if _pos_history.size() < 2:
		return linear_velocity

	var dt: float = _time_history[-1] - _time_history[0]
	if dt <= 0.0:
		return linear_velocity

	return (_pos_history[-1] - _pos_history[0]) / dt