extends Area2D

signal collected

## 钥匙中心到"脚底"的距离：射线从脚底出发，落地时钥匙正好站在表面上
const FOOT_OFFSET := 7.0
const STEP := 1.0 / 60.0
const MAX_STEPS := 240

enum State { IDLE, THROWN, LANDED }

## 关卡里那把钥匙原本是用 TerrainBase 的一块地砖画的。
## 这个开关让钥匙对象在开场时把脚下那块占位地砖擦掉，避免两个钥匙重叠。
@export var erase_placeholder_on_ready: bool = true
## 落地后多久才允许再次被捡起
@export var settle_time: float = 0.4
## 飞行时用哪几层做落地判定。玩家投掷时会把它设成玩家自己的 collision_mask，
## 所以"钥匙能落在哪"严格等于"玩家能站在哪"。
@export var flight_mask: int = 1

var state: State = State.IDLE
var velocity := Vector2.ZERO

var _settle := 0.0


func _ready() -> void:
	body_entered.connect(_on_body_entered)
	if erase_placeholder_on_ready:
		_erase_placeholder_tile()
	_start_idle()


func _physics_process(_delta: float) -> void:
	if state == State.LANDED:
		_settle += STEP
		if _settle >= settle_time:
			_start_idle()
		return
	if state != State.THROWN:
		return

	var g := gravity()
	var motion := velocity * STEP
	var from := global_position + Vector2(0.0, FOOT_OFFSET)
	var query := PhysicsRayQueryParameters2D.create(from, from + motion, flight_mask)
	var hit := get_world_2d().direct_space_state.intersect_ray(query)
	if hit.is_empty():
		global_position += motion
		velocity.y += g * STEP
	else:
		global_position = hit["position"] - Vector2(0.0, FOOT_OFFSET)
		velocity = Vector2.ZERO
		state = State.LANDED
		_settle = 0.0


# ---------------------------------------------------------------- 对外接口

func launch(v: Vector2) -> void:
	velocity = v
	state = State.THROWN
	monitoring = false
	_settle = 0.0


func _start_idle() -> void:
	state = State.IDLE
	velocity = Vector2.ZERO
	monitoring = true


func _on_body_entered(body: Node2D) -> void:
	if state != State.IDLE:
		return
	if body.has_method("collect_key"):
		body.collect_key()
		collected.emit()
		queue_free()


# ---------------------------------------------------------------- 轨迹模拟

static func gravity() -> float:
	return float(ProjectSettings.get_setting("physics/2d/default_gravity", 980.0))


## 和 _physics_process 里的推进方式完全一致，玩家用它来画预览弧线，
## 所以预览落点和真正落点会重合。mask 就是玩家的碰撞掩码。
static func simulate_trajectory(
		space: PhysicsDirectSpaceState2D,
		start: Vector2,
		vel: Vector2,
		mask: int,
		max_steps: int = MAX_STEPS) -> Dictionary:
	var points := PackedVector2Array()
	var p := start
	var v := vel
	var g := gravity()
	points.append(p)
	for i in max_steps:
		var next := p + v * STEP
		var query := PhysicsRayQueryParameters2D.create(
				p + Vector2(0.0, FOOT_OFFSET), next + Vector2(0.0, FOOT_OFFSET), mask)
		var hit := space.intersect_ray(query)
		if not hit.is_empty():
			var landing: Vector2 = hit["position"] - Vector2(0.0, FOOT_OFFSET)
			points.append(landing)
			return {"points": points, "landed": true, "landing": landing}
		p = next
		v.y += g * STEP
		points.append(p)
	return {"points": points, "landed": false, "landing": p}


# ---------------------------------------------------------------- 清理占位地砖

func _erase_placeholder_tile() -> void:
	var root: Node = owner if owner != null else get_parent()
	if root == null:
		return
	for layer in root.find_children("*", "TileMapLayer", true, false):
		var cell: Vector2i = layer.local_to_map(layer.to_local(global_position))
		if layer.get_cell_source_id(cell) != -1:
			layer.erase_cell(cell)