# Godot 3 — 类型声明可选，语法不统一
var health = 100
var speed: float = 5.0
func take_damage(amount):
    health -= amount

# Godot 4 — 类型声明统一，更严格
var health: int = 100
var speed: float = 5.0
func take_damage(amount: int) -> void:
    health -= amount

# Godot 3
export(int) var health = 100
export(float, 0, 100, 0.1) var speed = 5.0
export(String, FILE, "*.json") var config_path = ""
export(Array, String) var tags = []
export(NodePath) var target_path

# Godot 4
@export var health: int = 100
@export_range(0, 100, 0.1) var speed: float = 5.0
@export_file("*.json") var config_path: String = ""
@export var tags: Array[String] = []
@export var target_path: NodePath

# Godot 3
onready var sprite = $Sprite
onready var timer = $Timer

# Godot 4
@onready var sprite: Sprite2D = $Sprite2D
@onready var timer: Timer = $Timer

# Godot 3 — 信号声明
signal health_changed(old_value, new_value)
signal died()

# Godot 4 — 信号声明（相同）
signal health_changed(old_value: int, new_value: int)
signal died()

# Godot 3 — 连接信号
connect("health_changed", self, "_on_health_changed")
emit_signal("health_changed", old_health, new_health)

# Godot 4 — 连接信号
health_changed.connect(_on_health_changed)
health_changed.emit(old_health, new_health)

# Godot 3 — 断开信号
disconnect("health_changed", self, "_on_health_changed")

# Godot 4 — 断开信号
health_changed.disconnect(_on_health_changed)

# Godot 3
func delayed_action():
    yield(get_tree().create_timer(2.0), "timeout")
    print("2 秒后执行")

func load_data():
    var result = yield(http_request, "request_completed")
    print(result)

# Godot 4
func delayed_action():
    await get_tree().create_timer(2.0).timeout
    print("2 秒后执行")

func load_data():
    var result = await http_request.request_completed
    print(result)

# Godot 3 — 匿名函数不支持，需要写具名函数
func _ready():
    get_tree().create_timer(2.0).connect("timeout", self, "_on_timer_timeout")

func _on_timer_timeout():
    print("计时结束")

# Godot 4 — 支持 Lambda
func _ready():
    get_tree().create_timer(2.0).timeout.connect(func():
        print("计时结束")
    )

    # 带参数的 Lambda
    health_changed.connect(func(old_val, new_val):
        print("生命值从 %d 变为 %d" % [old_val, new_val])
    )

# Godot 3 — KinematicBody
extends KinematicBody

var velocity = Vector3.ZERO
const GRAVITY = -9.8

func _physics_process(delta):
    velocity.y += GRAVITY * delta
    var input = Input.get_vector("left", "right", "forward", "back")
    velocity.x = input.x * speed
    velocity.z = input.y * speed
    velocity = move_and_slide(velocity, Vector3.UP)

# Godot 4 — CharacterBody3D
extends CharacterBody3D

const SPEED = 5.0
const JUMP_VELOCITY = 4.5

func _physics_process(delta):
    # 重力
    if not is_on_floor():
        velocity.y -= ProjectSettings.get_setting("physics/3d/default_gravity") * delta

    # 跳跃
    if Input.is_action_just_pressed("jump") and is_on_floor():
        velocity.y = JUMP_VELOCITY

    # 移动
    var input_dir = Input.get_vector("left", "right", "forward", "back")
    var direction = (transform.basis * Vector3(input_dir.x, 0, input_dir.y)).normalized()

    if direction:
        velocity.x = direction.x * SPEED
        velocity.z = direction.z * SPEED
    else:
        velocity.x = move_toward(velocity.x, 0, SPEED * delta)
        velocity.z = move_toward(velocity.z, 0, SPEED * delta)

    move_and_slide()

# Godot 3
func _physics_process(delta):
    var collision = move_and_collide(velocity * delta)
    if collision:
        velocity = velocity.slide(collision.normal)

# Godot 4
func _physics_process(delta):
    var collision = move_and_collide(velocity * delta)
    if collision:
        velocity = velocity.slide(collision.get_normal())

# Godot 3
$AnimationPlayer.play("run")
$AnimationPlayer.connect("animation_finished", self, "_on_anim_finished")

# Godot 4
$AnimationPlayer.play("run")
$AnimationPlayer.animation_finished.connect(_on_anim_finished)

# Godot 3
var state_machine = $AnimationTree.get("parameters/playback")
state_machine.travel("run")

# Godot 4 — AnimationMixer 替代 AnimationTree 的部分功能
@onready var anim_tree: AnimationTree = $AnimationTree

func _ready():
    var state_machine = anim_tree.get("parameters/playback") as AnimationNodeStateMachinePlayback
    state_machine.travel("run")

# Godot 4 新的动画回调
func _ready():
    $AnimationPlayer.animation_finished.connect(_on_anim_finished)

# Godot 4 可以自动导入 Godot 3 的 .tres 文件
# 但某些格式可能需要手动调整

# 常见需要修改的资源类型：
# - SpatialMaterial → StandardMaterial3D
# - ParticlesMaterial → ParticleProcessMaterial
# - DynamicFont → 项目设置中配置默认字体
# - ShaderMaterial 中的 shader 语法变更

// Godot 3
shader_type spatial;
render_mode unshaded;

uniform sampler2D texture_albedo : hint_albedo;
uniform vec4 color : hint_color;

void fragment() {
    ALBEDO = texture(texture_albedo, UV).rgb * color.rgb;
}

// Godot 4
shader_type spatial;
render_mode unshaded;

uniform sampler2D texture_albedo : source_color;
uniform vec4 color : source_color;

void fragment() {
    ALBEDO = texture(texture_albedo, UV).rgb * color.rgb;
}

# Godot 4 内置的项目转换器
# 编辑器 → 项目 → 工具 → 升级到 Godot 4

# 转换器会自动处理：
# ✅ 节点类型重命名
# ✅ API 方法重命名
# ✅ export → @export
# ✅ onready → @onready
# ✅ 部分信号连接语法
#
# 转换器不会处理：
# ❌ 复杂的信号连接逻辑
# ❌ 自定义 Shader 语法
# ❌ GDScript 2.0 类型系统
# ❌ 第三方插件兼容性

# 使用 sed 批量替换节点名称
find . -name "*.gd" -exec sed -i 's/KinematicBody/CharacterBody3D/g' {} \;
find . -name "*.gd" -exec sed -i 's/Spatial/Node3D/g' {} \;
find . -name "*.gd" -exec sed -i 's/Sprite\b/Sprite2D/g' {} \;

# 替换导出语法
find . -name "*.gd" -exec sed -i 's/export(\(.*\))/@export/g' {} \;
find . -name "*.gd" -exec sed -i 's/onready var/@onready var/g' {} \;

# 替换方法名
find . -name "*.gd" -exec sed -i 's/\.instance()/.instantiate()/g' {} \;
find . -name "*.gd" -exec sed -i 's/rand_range/randf_range/g' {} \;
find . -name "*.gd" -exec sed -i 's/deg2rad/deg_to_rad/g' {} \;
find . -name "*.gd" -exec sed -i 's/rad2deg/rad_to_deg/g' {} \;
find . -name "*.gd" -exec sed -i 's/stepify/snapped/g' {} \;

# ❌ Godot 3 写法在 Godot 4 中报错
velocity = move_and_slide(velocity, Vector3.UP)

# ✅ Godot 4 正确写法
move_and_slide()
# velocity 已经是 CharacterBody3D 的内置属性

# ❌ Godot 3 旧语法
$Button.connect("pressed", self, "_on_button_pressed")

# ✅ Godot 4 新语法
$Button.pressed.connect(_on_button_pressed)

# Godot 4 更严格的类型检查
# ❌ 可能在运行时崩溃
var sprite = $Sprite  # 没有类型提示
sprite.rotation += 0.1  # 如果节点不存在会崩溃

# ✅ 安全做法
@onready var sprite: Sprite2D = $Sprite2D
# 或使用 get_node_or_null
var sprite = get_node_or_null("Sprite2D") as Sprite2D
if sprite:
    sprite.rotation += 0.1

# Godot 4 更严格的类型转换
# ❌ 可能失败
var node = get_node("SomeNode") as CharacterBody3D  # 如果类型不匹配返回 null

# ✅ 使用 is 检查
var node = get_node("SomeNode")
if node is CharacterBody3D:
    var character = node as CharacterBody3D
    character.velocity = Vector3.ZERO

# 1. 备份原始项目
cp -r my_game my_game_backup

# 2. 在 Godot 4 中打开项目
# 允许自动转换

# 3. 逐个修复错误
# 编辑器会标记所有错误

# 4. 全面测试

# 保留部分 Godot 3 脚本，逐步替换
# 使用兼容层：

# compatibility_layer.gd
# 封装 Godot 3 → 4 的 API 差异

static func move_and_slide_compat(body: CharacterBody3D, vel: Vector3, up: Vector3) -> Vector3:
    body.velocity = vel
    body.up_direction = up
    body.move_and_slide()
    return body.velocity

static func instance_scene(scene: PackedScene) -> Node:
    return scene.instantiate()