# PhysicsPush —— CLIENT-GAP §3.7：受击击退，逐行移植 GameLib/PhysicsObject.cpp `CPhysicsObject`
# + GameLib/MapUtil.cpp `CEaseOutInterpolation`。单位 = Metin2 cm（平面 x / y）。
#   __PushCircle -> set_direction(normalize(victim - attacker))
#   IncreaseExternalForce(base, fExternalForce) -> increase_external_force(force[, collides])
#   PhysicsProcess：update(dt) 后 AddMovement(get_movement())
extends RefCounted

const FRAME_TIME := 0.02    # c_fFrameTime
const EPSILON := 0.001
const LOOP_VALUE := 100
const FLT_EPSILON := 1.192092896e-07

class EaseOut:
	var remaining := 0.0
	var value := 0.0
	var speed := 0.0
	var acceleration := 0.0
	var start_value := 0.0
	var last_value := 0.0

	func initialize() -> void:
		remaining = 0.0
		value = 0.0
		speed = 0.0
		acceleration = 0.0
		start_value = 0.0
		last_value = 0.0

	func setup(f_start: float, f_end: float, f_time: float) -> void:
		if absf(f_time) < FLT_EPSILON:
			f_time = 0.01
		value = f_start
		start_value = f_start
		last_value = f_start
		speed = (2.0 * (f_end - f_start)) / f_time
		acceleration = 2.0 * (f_end - f_start) / (f_time * f_time) - 2.0 * speed / f_time
		remaining = f_time

	func interpolate(dt: float) -> void:
		last_value = value
		remaining -= dt
		speed += acceleration * dt
		value += speed * dt
		if not is_playing():
			value = 0.0
			last_value = 0.0

	func is_playing() -> bool:
		return remaining > 0.0

	func changing_value() -> float:
		return value - last_value

var mass := 1.0
var friction := 0.3
var direction := Vector3.ZERO
var acceleration := Vector3.ZERO
var velocity := Vector3.ZERO
var last_position := Vector3.ZERO
var _x := EaseOut.new()
var _y := EaseOut.new()

func initialize() -> void:
	mass = 1.0
	friction = 0.3
	direction = Vector3.ZERO
	acceleration = Vector3.ZERO
	velocity = Vector3.ZERO
	last_position = Vector3.ZERO
	_x.initialize()
	_y.initialize()

func set_direction(dir: Vector2) -> void:
	direction = Vector3(dir.x, dir.y, 0.0)

func update(dt: float) -> void:
	if _x.is_playing():
		_x.interpolate(dt)
	if _y.is_playing():
		_y.interpolate(dt)

func _accumulate(pos: Vector3) -> Vector3:
	var force := 0.0
	if absf(velocity.x) < EPSILON or absf(velocity.y) < EPSILON or absf(velocity.z) < EPSILON:
		force -= mass * friction
	acceleration = direction * (force / mass)
	velocity += acceleration
	if velocity.x * direction.x < EPSILON:
		velocity.x = 0.0
		direction.x = 0.0
	if velocity.y * direction.y < EPSILON:
		velocity.y = 0.0
		direction.y = 0.0
	if velocity.z * direction.z < EPSILON:
		velocity.z = 0.0
		direction.z = 0.0
	return pos + velocity

# collides(movement: Vector2) -> bool 对应 IPhysicsWorld::isPhysicalCollision(base + movement)；
# 空 Callable = 没有物理世界（参考端 pWorld == NULL 分支）。
func increase_external_force(force: float, collides := Callable()) -> void:
	acceleration = direction * (force / mass)
	velocity = acceleration
	var movement := Vector3.ZERO
	for i in LOOP_VALUE:
		movement = _accumulate(movement)
		if collides.is_valid() and bool(collides.call(Vector2(movement.x, movement.y))):
			initialize()
			return
		if absf(velocity.x) < EPSILON and absf(velocity.y) < EPSILON and absf(velocity.z) < EPSILON:
			break
	set_last_position(Vector2(movement.x, movement.y), float(LOOP_VALUE) * FRAME_TIME)

func set_last_position(p: Vector2, blending_time: float) -> void:
	last_position = Vector3(p.x, p.y, 0.0)
	_x.setup(0.0, p.x, blending_time)
	_y.setup(0.0, p.y, blending_time)

func get_last_position() -> Vector2:
	return Vector2(last_position.x, last_position.y)

# GetXMovement / GetYMovement：本帧 ease-out 增量。
func get_movement() -> Vector2:
	return Vector2(_x.changing_value(), _y.changing_value())

func is_blending() -> bool:
	if velocity.length() != 0.0:
		return true
	return _x.is_playing() or _y.is_playing()