Godot Scene Management

# additive_ui_layering.gd
# Managing multiple UI layouts without replacing the whole scene
extends Node

# EXPERT NOTE: Don't change the entire scene for just a menu. 
# Load UI scenes as children of a persistent 'UI' node.

func open_menu(path: String):
	var scene = load(path).instantiate()
	add_child(scene)
	# Pause game logic if it's a pause menu
	get_tree().paused = true

func close_menu(menu: Node):
	menu.queue_free()
	get_tree().paused = false

# skills/scene-management/code/async_scene_manager.gd
extends Node

## Async Scene Manager Expert Pattern
## Implements Threaded Loading with Progress Tracking and Data Payloads.

signal loading_progress(progress: float)
signal loading_complete(scene_resource: PackedScene)

var _target_scene_path: String = ""
var _scene_payload: Dictionary = {}

# 1. Threaded Loading Request
# Expert logic: NEVER use 'change_scene_to_file' for large levels.
func load_scene(path: String, payload: Dictionary = {}) -> void:
    _target_scene_path = path
    _scene_payload = payload
    
    # Start the threaded load
    var err = ResourceLoader.load_threaded_request(path)
    if err != OK:
        push_error("Failed to start loading: ", path)
        return
        
    set_process(true)

func _process(_delta: float) -> void:
    # 2. Async Progress Tracking
    # Professional pattern: Poll status to update UI loading bars.
    var progress = []
    var status = ResourceLoader.load_threaded_get_status(_target_scene_path, progress)
    
    match status:
        ResourceLoader.THREAD_LOAD_IN_PROGRESS:
            loading_progress.emit(progress[0])
            
        ResourceLoader.THREAD_LOAD_LOADED:
            _finalize_load()
            
        ResourceLoader.THREAD_LOAD_FAILED:
            set_process(false)
            push_error("Threaded load failed for: ", _target_scene_path)

func _finalize_load() -> void:
    set_process(false)
    var new_scene_res = ResourceLoader.load_threaded_get(_target_scene_path)
    var new_scene = new_scene_res.instantiate()
    
    # 3. Scene Payload System (Data Injection)
    # Standardize how to pass complex data before _ready().
    if new_scene.has_method("initialize"):
        new_scene.initialize(_scene_payload)
        
    get_tree().root.add_child(new_scene)
    get_tree().current_scene.queue_free()
    get_tree().current_scene = new_scene
    
    loading_complete.emit(new_scene_res)

## EXPERT NOTE:
## Use 'Memory Profiling': Inside the loading screen, call 
## 'Performance.get_monitor(Performance.MEMORY_STATIC)' and 
## 'print_stray_nodes()' to detect memory leaks during scene swaps.
## For 'scene-management', implement a 'Background Pre-loading' 
## system that starts loading the next level while the player 
## is still finishing the current one, hidden behind a 'Victory' 
## or 'Dialogue' UI to mask the transition entirely.
## NEVER hardcode scene paths; use a 'Registry' resource that 
## maps 'LEVEL_1' to the actual '.tscn' path.

# background_resource_loader.gd
# Async resource loading with progress tracking
extends Node

# EXPERT NOTE: For large levels, use ResourceLoader.load_threaded_request 
# to prevent the game from freezing while loading a new scene.

var _pending_scene: String = ""

func load_scene(path: String):
	_pending_scene = path
	var error = ResourceLoader.load_threaded_request(path)
	if error != OK:
		push_error("Failed to start loading: " + path)

func _process(_delta: float) -> void:
	if _pending_scene == "": return
	
	var progress = []
	var status = ResourceLoader.load_threaded_get_status(_pending_scene, progress)
	
	match status:
		ResourceLoader.THREAD_LOAD_IN_PROGRESS:
			# Update loading bar: progress[0]
			pass
		ResourceLoader.THREAD_LOAD_LOADED:
			var scene = ResourceLoader.load_threaded_get(_pending_scene)
			get_tree().change_scene_to_packed(scene)
			_pending_scene = ""
		ResourceLoader.THREAD_LOAD_FAILED:
			_pending_scene = ""

# dynamic_script_attachment.gd
# Attaching scripts to nodes at runtime [Modding System]
extends Node

func apply_script_to_node(node: Node, script_path: String):
	var script = load(script_path)
	if script is Script:
		node.set_script(script)
		# Re-run _ready if needed, or call init
		node.notification(NOTIFICATION_READY)

# node_path_safe_retrieval.gd
# Robust node path handling to prevent 'Null Instance' errors
extends Node

# EXPERT NOTE: Avoid hardcoded Nodepaths like get_node("../../Player") 
# as they break if the hierarchy changes. Use @onready and Unique Names.

@onready var player = %Player # Using Scene Unique Name (%)

func _ready() -> void:
	if not player:
		push_error("Critical error: Player not found in scene!")

# node_unparent_reparent.gd
# Safely moving nodes between scene hierarchies
extends Node

# PROBLEM: Reparenting mid-frame can cause issues with 
# transform synchronization.

func reparent_node(node: Node, new_parent: Node):
	# Preserve global transform during reparenting
	var global_xform = node.global_transform if node is Node2D or node is Node3D else null
	
	node.get_parent().remove_child(node)
	new_parent.add_child(node)
	
	if global_xform:
		node.global_transform = global_xform

# persistent_data_preservation.gd
# Using an Autoload for scene-crossing variables [State Management]
extends Node

# EXPERT NOTE: Values in a Scene are lost when get_tree().change_scene is called. 
# Use a Singleton (Autoload) to keep state.

var player_hp: int = 100
var current_level_seed: int = 1234
var unlocked_items: Array = []

func save_state():
	# Logic to serialize variables to a config file
	pass

# scene_instancing_pooling.gd
# Object pooling for high-frequency scene instancing
extends Node

@export var scene_to_pool: PackedScene
@export var pool_size := 50

var _pool: Array = []

func _ready() -> void:
	for i in pool_size:
		var instance = scene_to_pool.instantiate()
		instance.visible = false
		instance.process_mode = Node.PROCESS_MODE_DISABLED
		add_child(instance)
		_pool.append(instance)

func spawn(pos: Vector2):
	for i in _pool:
		if i.process_mode == Node.PROCESS_MODE_DISABLED:
			i.global_position = pos
			i.visible = true
			i.process_mode = Node.PROCESS_MODE_INHERIT
			return i
	return null # Pool exhausted

# skills/scene-management/scripts/scene_pool.gd
extends Node

## Scene Pool Expert Pattern
## Object pooling for frequently spawned/destroyed scenes to reduce instantiation overhead.

class_name ScenePool

var _pool: Dictionary = {}  # PackedScene path → Array of inactive instances

func prewarm(scene_path: String, count: int) -> void:
	var scene := load(scene_path) as PackedScene
	if not scene:
		push_error("Failed to load scene: %s" % scene_path)
		return
		
	if scene_path not in _pool:
		_pool[scene_path] = []
		
	for i in range(count):
		var instance := scene.instantiate()
		instance.set_meta("_pooled", true)
		_pool[scene_path].append(instance)

func acquire(scene_path: String, parent: Node) -> Node:
	if scene_path not in _pool or _pool[scene_path].is_empty():
		# Pool empty, create new instance
		var scene := load(scene_path) as PackedScene
		var instance := scene.instantiate()
		instance.set_meta("_pooled", true)
		parent.add_child(instance)
		return instance
	
	# Reuse pooled instance
	var instance := _pool[scene_path].pop_back()
	parent.add_child(instance)
	return instance

func release(instance: Node) -> void:
	if not instance.has_meta("_pooled"):
		instance.queue_free()
		return
		
	var scene_path := instance.scene_file_path
	if scene_path.is_empty():
		instance.queue_free()
		return
		
	instance.get_parent().remove_child(instance)
	
	if scene_path not in _pool:
		_pool[scene_path] = []
	_pool[scene_path].append(instance)

func clear_pool(scene_path: String = "") -> void:
	if scene_path.is_empty():
		for path in _pool:
			for instance in _pool[path]:
				instance.queue_free()
		_pool.clear()
	elif scene_path in _pool:
		for instance in _pool[scene_path]:
			instance.queue_free()
		_pool.erase(scene_path)

## EXPERT USAGE:
## var pool := ScenePool.new()
## pool.prewarm("res://projectiles/bullet.tscn", 50)
##
## # Spawn
## var bullet := pool.acquire("res://projectiles/bullet.tscn", self)
##
## # Return to pool
## pool.release(bullet)

# skills/scene-management/scripts/scene_state_manager.gd
extends Node

## Scene State Manager Expert Pattern
## Preserves and restores scene state across transitions (player position, collected items, NPC states).

class_name SceneStateManager

var _scene_states: Dictionary = {}  # scene_path → state data

func save_current_scene() -> void:
	var current_scene := get_tree().current_scene
	if not current_scene:
		return
		
	var scene_path := current_scene.scene_file_path
	var state := {}
	
	# Save all nodes in "persist" group
	for node in get_tree().get_nodes_in_group("persist"):
		var node_data := {}
		
		if node is Node2D or node is Node3D:
			node_data["position"] = node.global_position
			
		if node.has_method("save_state"):
			node_data["custom"] = node.save_state()
			
		state[node.get_path()] = node_data
	
	_scene_states[scene_path] = state
	print("Saved state for: %s (%d nodes)" % [scene_path, state.size()])

func restore_scene(scene_path: String) -> void:
	if scene_path not in _scene_states:
		return
		
	await get_tree().process_frame  # Wait for scene to load
	
	var state: Dictionary = _scene_states[scene_path]
	
	for node_path in state:
		var node := get_tree().current_scene.get_node_or_null(node_path)
		if not node:
			continue
			
		var node_data: Dictionary = state[node_path]
		
		if "position" in node_data:
			node.global_position = node_data["position"]
			
		if "custom" in node_data and node.has_method("load_state"):
			node.load_state(node_data["custom"])
	
	print("Restored state for: %s (%d nodes)" % [scene_path, state.size()])

func clear_scene_state(scene_path: String) -> void:
	_scene_states.erase(scene_path)

func clear_all_states() -> void:
	_scene_states.clear()

## EXPERT USAGE:
## Add nodes to "persist" group + implement save_state/load_state:
##
## func save_state() -> Dictionary:
##   return {"health": health, "inventory": inventory}
##
## func load_state(data: Dictionary) -> void:
##   health = data.get("health", 100)
##   inventory = data.get("inventory", [])

# scene_transition_manager.gd
# Smooth transitions between scenes using Tweens/Shaders
extends CanvasLayer

@onready var color_rect := $ColorRect

func transition_to(scene_path: String):
	# Fade to black
	var tween = create_tween()
	await tween.tween_property(color_rect, "color:a", 1.0, 0.5).finished
	
	get_tree().change_scene_to_file(scene_path)
	
	# Fade back in
	tween = create_tween()
	tween.tween_property(color_rect, "color:a", 0.0, 0.5)

# subviewport_scene_layering.gd
# Running two different scenes in parallel using Viewports
extends SubViewportContainer

# EXPERT NOTE: Use SubViewports for Mini-maps, Split-screen, 
# or 3D UI elements rendered in a 2D world.

func _ready() -> void:
	# Ensure the viewport is correctly capturing its own world
	$SubViewport.own_world_3d = true