## AvatarVisualizer
##
## Builds the render tree from an AvatarLoadout.
##
## Responsibilities:
##   - Create a root Node3D (or Node2D for 2D mode) as the avatar container.
##   - For each slot in the loadout, call AvatarLoader.load_slot() and attach
##     the resulting Skeleton3D / MeshInstance3D tree to the root.
##   - Apply skin-tone overrides to all MeshInstance3D nodes.
##   - Apply a single Skeleton3D root (the "body" skeleton) and retarget all
##     limb skeletons to it using the bone-map from AvatarSlotRegistry.
##   - Expose `get_root()` for the caller to attach to the scene tree.
##   - Expose `clear()` to destroy the tree and free resources.
##
## Usage:
##   var viz = AvatarVisualizer.new()
##   viz.load_loadout(loadout)
##   avatar_node.add_child(viz.get_root())
##
## The visualizer owns the Skeleton3D and MeshInstance3D trees it creates.
## The caller owns the root node's placement in the scene tree.

class_name AvatarVisualizer
extends Object


## Emitted when the visualizer has finished building the render tree.
signal build_complete
## Emitted when the visualizer has been cleared.
signal cleared


# ---------------------------------------------------------------------------
# Public API
# ---------------------------------------------------------------------------

## The root node that holds the avatar render tree.
## Set this to the desired parent before calling load_loadout().
var root: Node3D = null

## The Skeleton3D that serves as the body skeleton.
## All limb skeletons are retargeted to this skeleton's bone hierarchy.
var body_skeleton: Skeleton3D = null

## The AvatarLoadout currently loaded (null if none).
var current_loadout: AvatarLoadout = null

## Whether the visualizer is currently building (true during load_loadout).
var is_building: bool = false


# ---------------------------------------------------------------------------
# Core
# ---------------------------------------------------------------------------

## Load an AvatarLoadout and build the render tree.
##
## If [param root] is null, a new Node3D is created and assigned.
## If [param loadout] is null or invalid, the current tree is cleared.
func load_loadout(loadout: AvatarLoadout, root_node: Node3D = null) -> void:
	# Clear any previous tree.
	clear()

	if loadout == null or not loadout.is_valid():
		build_complete.emit()
		return

	current_loadout = loadout
	is_building = true

	# Create root if not provided.
	if root_node != null:
		root = root_node
	else:
		root = Node3D.new()
		root.name = "AvatarVisualizer"

	# Create the body skeleton.
	body_skeleton = Skeleton3D.new()
	body_skeleton.name = "AvatarBody"
	root.add_child(body_skeleton)

	# Build each slot's contribution.
	for slot_def in AvatarSlotRegistry.get_slot_definitions():
		var slot_key: String = slot_def.slot_key
		var slot_item: AvatarLoadout.SlotItem = loadout.slots.get(slot_key)

		if slot_item == null or slot_item.asset_id == "":
			# Slot is empty — create a placeholder.
			_add_placeholder_slot(slot_def)
			continue

		# Load the slot's asset.
		var slot_result: AvatarLoader.SlotResult = await AvatarLoader.load_slot(
			slot_item,
			slot_def,
			loadout.skin_tone,
		)

		if slot_result == null:
			push_warning("AvatarVisualizer: failed to load slot '%s' (%s)" % [slot_key, slot_item.asset_id])
			_add_placeholder_slot(slot_def)
			continue

		# Attach the loaded tree to the root.
		_attach_slot_tree(slot_result, slot_def)

	# Retarget limb skeletons to the body skeleton.
	_retarget_limbs()

	# Apply skin-tone override to all meshes.
	_apply_skin_tone(loadout.skin_tone)

	is_building = false
	build_complete.emit()


## Clear the render tree and free resources.
func clear() -> void:
	if root != null:
		root.queue_free()
		root = null
		body_skeleton = null
		current_loadout = null
		cleared.emit()


## Get the root node.
func get_root() -> Node3D:
	return root


## Get a specific slot's Skeleton3D (if it has one).
func get_slot_skeleton(slot_key: String) -> Skeleton3D:
	if body_skeleton == null:
		return null
	var bones := body_skeleton.get_bone_count()
	for i in range(bones):
		var bone_name: String = body_skeleton.get_bone_name(i)
		if bone_name == slot_key:
			return body_skeleton
	return null


## Get all MeshInstance3D nodes in the render tree.
func get_all_mesh_instances() -> Array[MeshInstance3D]:
	var meshes: Array[MeshInstance3D] = []
	if root == null:
		return meshes
	_collect_meshes(root, meshes)
	return meshes


## Get all Skeleton3D nodes in the render tree.
func get_all_skeletons() -> Array[Skeleton3D]:
	var skeletons: Array[Skeleton3D] = []
	if root == null:
		return skeletons
	_collect_skeletons(root, skeletons)
	return skeletons


# ---------------------------------------------------------------------------
# Internal helpers
# ---------------------------------------------------------------------------

## Add a placeholder (empty) skeleton for a slot that has no asset.
func _add_placeholder_slot(slot_def: AvatarSlotRegistry.SlotDefinition) -> void:
	if body_skeleton == null:
		return

	var bone_name: String = slot_def.slot_key
	var bone_id: int = body_skeleton.add_bone(bone_name)

	# Set the bone's rest pose to identity (placeholder).
	var rest := Transform3D()
	rest.origin = slot_def.default_offset
	body_skeleton.set_bone_rest(bone_id, rest)

	# Set parent to root (bone 0 is the root bone).
	body_skeleton.set_bone_parent(bone_id, 0)


## Attach a loaded slot's tree to the root.
func _attach_slot_tree(result: AvatarLoader.SlotResult, slot_def: AvatarSlotRegistry.SlotDefinition) -> void:
	if result.skeleton == null:
		return

	# Add the skeleton as a child of the body skeleton.
	# The skeleton's bones will be merged into the body skeleton during retargeting.
	result.skeleton.name = "%s_skeleton" % slot_def.slot_key
	result.skeleton.visible = true
	root.add_child(result.skeleton)


## Retarget all limb skeletons to the body skeleton.
func _retarget_limbs() -> void:
	if body_skeleton == null:
		return

	# Collect all child Skeleton3D nodes (limb skeletons).
	var limb_skeletons: Array[Skeleton3D] = []
	for child in root.get_children():
		if child is Skeleton3D and child != body_skeleton:
			limb_skeletons.append(child as Skeleton3D)

	# For each limb skeleton, merge its bones into the body skeleton.
	for limb in limb_skeletons:
		_merge_skeleton_into_body(limb)
		limb.queue_free()


## Merge a limb skeleton's bones into the body skeleton.
func _merge_skeleton_into_body(limb: Skeleton3D) -> void:
	if limb == null or body_skeleton == null:
		return

	var limb_bone_count: int = limb.get_bone_count()
	var start_id: int = body_skeleton.get_bone_count()

	for i in range(limb_bone_count):
		var bone_name: String = limb.get_bone_name(i)
		var bone_id: int = body_skeleton.add_bone(bone_name)

		# Copy the rest transform.
		var rest: Transform3D = limb.get_bone_rest(i)
		body_skeleton.set_bone_rest(bone_id, rest)

		# Copy the parent.
		var parent_id: int = limb.get_bone_parent(i)
		if parent_id >= 0:
			# Map parent ID to body skeleton.
			if parent_id == 0:
				# Root of limb skeleton -> parent is the body root.
				body_skeleton.set_bone_parent(bone_id, 0)
			else:
				# Offset by start_id to map to body skeleton bones.
				body_skeleton.set_bone_parent(bone_id, start_id + parent_id)
		else:
			body_skeleton.set_bone_parent(bone_id, 0)

		# Copy custom bone data (if any).
		var custom_data_count: int = limb.get_bone_custom_data_count(i)
		for j in range(custom_data_count):
			var data: Variant = limb.get_bone_custom_data(i, j)
			body_skeleton.set_bone_custom_data(bone_id, j, data)

		# Copy mesh connections.
		var mesh_count: int = limb.get_bone_mesh_count(i)
		for m in range(mesh_count):
			var mesh: MeshInstance3D = limb.get_bone_mesh(i, m)
			if mesh != null:
				# Re-parent mesh to body skeleton.
				mesh.skeleton = body_skeleton
				mesh.skeleton_path = body_skeleton.get_path()
				body_skeleton.add_bone_mesh(bone_id, mesh)


## Apply skin-tone override to all MeshInstance3D nodes.
func _apply_skin_tone(skin_tone: Color) -> void:
	if skin_tone == Color.TRANSPARENT:
		return

	var meshes: Array[MeshInstance3D] = get_all_mesh_instances()
	for mesh_instance in meshes:
		if mesh_instance.material_override == null:
			mesh_instance.material_override = StandardMaterial3D.new()
		var mat: StandardMaterial3D = mesh_instance.material_override
		mat.albedo_color = skin_tone


## Recursively collect all MeshInstance3D nodes.
func _collect_meshes(node: Node, result: Array[MeshInstance3D]) -> void:
	if node is MeshInstance3D:
		result.append(node as MeshInstance3D)
	for child in node.get_children():
		_collect_meshes(child, result)


## Recursively collect all Skeleton3D nodes.
func _collect_skeletons(node: Node, result: Array[Skeleton3D]) -> void:
	if node is Skeleton3D:
		result.append(node as Skeleton3D)
	for child in node.get_children():
		_collect_skeletons(child, result)