## AvatarLoader - glTF/GLB import, skeleton merge, and skin re-targeting.
##
## Loads base body and attachment GLB assets, extracts skeletons and meshes,
## and re-targets attachment skins to the canonical skeleton by bone name.
##
## Per the avatar architecture spec (§6.2, §6.3):
## - The base body carries the canonical skeleton.
## - Attachments are skinned to the same skeleton by name-based re-targeting.
## - Static accessories are parented to their mount bone.
## - Body-part slots hide the corresponding base mesh.

class_name AvatarLoader
extends Node


# ---------------------------------------------------------------------------
# Constants
# ---------------------------------------------------------------------------

## Maximum number of attachments allowed in the accessory slot.
const MAX_ACCESSORY_COUNT := 8

## Skeleton bone names that form the canonical rig (§3.1).
const CANONICAL_BONES := [
	"Root",
	"Hips",
	"Spine",
	"Chest",
	"Neck",
	"Head",
	"HeadTop",
	"Jaw",
	"LeftEye",
	"RightEye",
	"LeftShoulder",
	"LeftUpperArm",
	"LeftLowerArm",
	"LeftHand",
	"RightShoulder",
	"RightUpperArm",
	"RightLowerArm",
	"RightHand",
	"LeftUpperLeg",
	"LeftLowerLeg",
	"LeftFoot",
	"RightUpperLeg",
	"RightLowerLeg",
	"RightFoot",
]


# ---------------------------------------------------------------------------
# Signals
# ---------------------------------------------------------------------------

## Emitted when a base body has been loaded successfully.
signal base_body_loaded(avatar_node: Node3D)

## Emitted when an attachment has been loaded and merged.
signal attachment_loaded(slot_id: String, attachment_node: Node3D)

## Emitted on error during loading.
signal load_error(error_msg: String)


# ---------------------------------------------------------------------------
# State
# ---------------------------------------------------------------------------

## The fully assembled avatar node (Skeleton3D + meshes + attachments).
var avatar_node: Node3D = null

## The Skeleton3D belonging to the avatar.
var skeleton: Skeleton3D = null

## Mapping of bone name -> bone index in the skeleton.
var _bone_index_map: Dictionary = {}

## Loaded base body meshes, keyed by slot id.
var _base_meshes: Dictionary = {}

## Loaded attachment nodes, keyed by slot id.
var _attachments: Dictionary = {}

## Whether the base body has been loaded.
var is_base_loaded: bool = false

## The avatar catalog reference (set by AvatarSystem).
var catalog: AvatarCatalog = null


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

## Initialize the loader with a reference to the avatar catalog.
func init_loader(cat: AvatarCatalog) -> void:
	catalog = cat


## Load the base body asset identified by [param base_body_id].
## Returns the AvatarNode3D on success, or null on failure.
func load_base_body(base_body_id: String) -> Node3D:
	if catalog == null:
		load_error.emit("AvatarCatalog not set on AvatarLoader")
		return null

	var asset_meta = catalog.resolve(base_body_id)
	if asset_meta == null:
		load_error.emit("Unknown base_body asset: %s" % base_body_id)
		return null

	if asset_meta.type != "base_body":
		load_error.emit("Asset '%s' is not a base_body, got '%s'" % [
			base_body_id, asset_meta.type])
		return null

	var path: String = asset_meta.path
	var glb_data: PackedByteArray = _load_file(path)
	if glb_data.is_empty():
		load_error.emit("Failed to read GLB file: %s" % path)
		return null

	avatar_node = _parse_glb_as_avatar(glb_data, path)
	if avatar_node == null:
		load_error.emit("Failed to parse GLB: %s" % path)
		return null

	skeleton = avatar_node.get_node_or_null("Skeleton3D") as Skeleton3D
	if skeleton == null:
		load_error.emit("No Skeleton3D found in base body: %s" % path)
		avatar_node.queue_free()
		return null

	# Build bone index map for fast lookups.
	_bone_index_map.clear()
	for i in skeleton.get_bone_count():
		var bone_name: String = skeleton.get_bone_name(i)
		if not bone_name.is_empty():
			_bone_index_map[bone_name] = i

	# Extract base body meshes and store them.
	_extract_base_meshes(avatar_node)

	is_base_loaded = true
	base_body_loaded.emit(avatar_node)
	return avatar_node


## Load and merge an attachment into the avatar.
## [param slot_id] is the slot to equip into.
## [param asset_id] is the catalog id of the attachment.
## Returns the attachment Node3D on success, or null on failure.
func load_attachment(slot_id: String, asset_id: String) -> Node3D:
	if not is_base_loaded:
		load_error.emit("Cannot load attachment: base body not loaded")
		return null

	if catalog == null:
		load_error.emit("AvatarCatalog not set on AvatarLoader")
		return null

	var asset_meta = catalog.resolve(asset_id)
	if asset_meta == null:
		load_error.emit("Unknown attachment asset: %s" % asset_id)
		return null

	if asset_meta.type != "attachment":
		load_error.emit("Asset '%s' is not an attachment, got '%s'" % [
			asset_id, asset_meta.type])
		return null

	# Check slot exclusivity for accessory slot.
	if slot_id == "accessory":
		var current_accessories: Array[String] = _attachments.get("accessory", [])
		if current_accessories.size() >= MAX_ACCESSORY_COUNT:
			load_error.emit("Accessory slot full (%d/%d)" % [
				MAX_ACCESSORY_COUNT, MAX_ACCESSORY_COUNT])
			return null

	var path: String = asset_meta.path
	var glb_data: PackedByteArray = _load_file(path)
	if glb_data.is_empty():
		load_error.emit("Failed to read GLB file: %s" % path)
		return null

	var attachment_node = _parse_glb_as_attachment(glb_data, path, slot_id)
	if attachment_node == null:
		load_error.emit("Failed to parse attachment GLB: %s" % path)
		return null

	# Retarget skin to the canonical skeleton.
	_retarget_skin(attachment_node)

	# Parent static accessories to their mount bone.
	_parent_attachment(attachment_node, slot_id, asset_meta)

	# Store reference.
	if slot_id == "accessory":
		var list: Array[String] = _attachments.get("accessory", [])
		list.append(asset_id)
		_attachments["accessory"] = list
	else:
		_attachments[slot_id] = attachment_node

	attachment_loaded.emit(slot_id, attachment_node)
	return attachment_node


## Remove an attachment from the given slot.
func unload_attachment(slot_id: String) -> void:
	if slot_id == "accessory":
		var list: Array[String] = _attachments.get("accessory", [])
		for asset_id in list:
			var node = _attachments.get(asset_id)
			if node and node is Node:
				node.queue_free()
		_attachments.erase("accessory")
	else:
		var node = _attachments.get(slot_id)
		if node and node is Node:
			node.queue_free()
		_attachments.erase(slot_id)


## Hide or show the base mesh for a given body-part slot.
func set_base_mesh_visible(slot_id: String, visible: bool) -> void:
	var mesh = _base_meshes.get(slot_id)
	if mesh and mesh is Node3D:
		mesh.visible = visible


## Get the current loadout as a dictionary (for serialization).
func get_current_loadout() -> Dictionary:
	var loadout: Dictionary = {
		"base_body": "",
		"slots": {},
	}

	# Determine base body id from catalog.
	if is_base_loaded and catalog != null:
		# Walk through catalog to find which base_body loaded.
		for id in catalog.get_all_ids():
			var meta = catalog.resolve(id)
			if meta and meta.type == "base_body":
				loadout.base_body = id
				break

	# Collect equipped attachments.
	for slot_id in _attachments:
		if slot_id == "accessory":
			loadout.slots[slot_id] = _attachments[slot_id] as Array
		else:
			var node = _attachments[slot_id]
			if node is Node3D:
				# Find the asset id by matching the node's name.
				var aid: String = node.name
				loadout.slots[slot_id] = aid

	return loadout


## Reset the avatar to an unloaded state.
func reset() -> void:
	if avatar_node and avatar_node is Node:
		avatar_node.queue_free()

	avatar_node = null
	skeleton = null
	_bone_index_map.clear()
	_base_meshes.clear()
	_attachments.clear()
	is_base_loaded = false


# ---------------------------------------------------------------------------
# Internal: GLB Parsing
# ---------------------------------------------------------------------------

## Parse a GLB byte array into an avatar Node3D structure.
## Creates: Avatar (Node3D) -> Skeleton3D + BodyMeshes + AttachmentPoints
func _parse_glb_as_avatar(glb_data: PackedByteArray, path: String) -> Node3D:
	var avatar := Node3D.new()
	avatar.name = "Avatar"

	# Create the skeleton container.
	var skeleton_node := Skeleton3D.new()
	skeleton_node.name = "Skeleton3D"
	skeleton_node.position = Vector3(0, 0, 0)
	avatar.add_child(skeleton_node)

	# Create attachment points container.
	var attach_points := Node3D.new()
	attach_points.name = "AttachmentPoints"
	avatar.add_child(attach_points)

	# Create body meshes container.
	var body_meshes := Node3D.new()
	body_meshes.name = "BodyMeshes"
	avatar.add_child(body_meshes)

	# Create attachments container.
	var attachments_container := Node3D.new()
	attachments_container.name = "Attachments"
	avatar.add_child(attachments_container)

	# Parse the GLB and extract skeleton + meshes.
	var gltf_document := GLTFDocument.new()
	var gltf_state := GLTFState.new()

	var parse_result := gltf_document.append_from_buffer(glb_data, "", gltf_state)
	if parse_result != OK:
		push_error("GLB parse error: %s" % error_string(parse_result))
		avatar.queue_free()
		return null

	# Generate the actual scene tree from the parsed GLTF state.
	var scene_root := gltf_document.generate_scene(gltf_state)
	if scene_root == null:
		push_error("Failed to generate scene from GLB: %s" % path)
		avatar.queue_free()
		return null

	# Merge GLB nodes into our avatar structure (recurses into children).
	if scene_root is Node3D:
		_merge_node_into_avatar(scene_root, avatar, body_meshes,
			attach_points, attachments_container)

	return avatar


## Parse a GLB byte array into an attachment Node3D.
func _parse_glb_as_attachment(glb_data: PackedByteArray, path: String,
		slot_id: String) -> Node3D:

	var gltf_document := GLTFDocument.new()
	var gltf_state := GLTFState.new()

	var parse_result := gltf_document.append_from_buffer(glb_data, "", gltf_state)
	if parse_result != OK:
		push_error("GLB parse error: %s" % error_string(parse_result))
		return null

	var scene_root := gltf_document.generate_scene(gltf_state)
	if scene_root == null:
		push_error("Failed to generate scene from attachment GLB: %s" % path)
		return null

	var attachment := Node3D.new()
	attachment.name = "%s_%s" % [slot_id, path.get_file().get_basename()]

	if scene_root is Node3D:
		attachment.add_child(scene_root.duplicate())

	return attachment


## Merge a GLB node tree into the avatar's container structure.
func _merge_node_into_avatar(node: Node3D, avatar: Node3D,
		body_meshes: Node3D, attach_points: Node3D,
		attachments_container: Node3D) -> void:

	var node_name := node.name

	# Identify skeleton nodes.
	if node is Skeleton3D:
		var src_skel := node as Skeleton3D
		var dst_skel := avatar.get_node_or_null("Skeleton3D") as Skeleton3D
		if dst_skel:
			# Copy bones from source skeleton to destination.
			for i in src_skel.get_bone_count():
				var bone_name := src_skel.get_bone_name(i)
				var bone_pose := src_skel.get_bone_pose(i)
				var parent_idx := src_skel.get_bone_parent(i)
				if dst_skel.has_bone(bone_name):
					# Bone already exists (canonical).
					dst_skel.set_bone_pose(i, bone_pose)
					if parent_idx >= 0:
						var parent_name := src_skel.get_bone_name(parent_idx)
						var dst_parent_idx := dst_skel.find_bone(parent_name)
						if dst_parent_idx >= 0:
							dst_skel.set_bone_parent(i, dst_parent_idx)
				else:
					# Add new bone.
					var new_idx := dst_skel.add_bone(bone_name)
					dst_skel.set_bone_pose(new_idx, bone_pose)
					if parent_idx >= 0:
						var parent_name := src_skel.get_bone_name(parent_idx)
						var dst_parent_idx := dst_skel.find_bone(parent_name)
						if dst_parent_idx >= 0:
							dst_skel.set_bone_parent(new_idx, dst_parent_idx)
		# Skinned meshes are commonly children of the skeleton node in a GLB
		# export, not siblings — fall through to the recursion below instead
		# of returning, so they still get merged in.
		for child in src_skel.get_children():
			if child is Node3D:
				_merge_node_into_avatar(child, avatar, body_meshes,
					attach_points, attachments_container)
		return

	# Identify attachment point nodes (empty nodes named attach_*).
	if node_name.begins_with("attach_"):
		var cloned := node.duplicate()
		cloned.name = node_name
		attach_points.add_child(cloned)
		return

	# Identify mesh nodes.
	if node is MeshInstance3D:
		var mesh_inst := node as MeshInstance3D
		var cloned := mesh_inst.duplicate() as MeshInstance3D
		# Determine which container to place it in.
		if node_name == "Body" or node_name.ends_with("_Mesh"):
			body_meshes.add_child(cloned)
		else:
			attachments_container.add_child(cloned)
		return

	# For other nodes, recurse into children.
	for child in node.get_children():
		if child is Node3D:
			_merge_node_into_avatar(child, avatar, body_meshes,
				attach_points, attachments_container)


## Extract base body meshes from the avatar and store them by slot.
func _extract_base_meshes(avatar: Node3D) -> void:
	var body_meshes := avatar.get_node_or_null("BodyMeshes") as Node3D
	if body_meshes == null:
		return

	for child in body_meshes.get_children():
		if child is MeshInstance3D:
			var mesh_name := child.name
			var slot_id := _mesh_name_to_slot(mesh_name)
			if slot_id != "":
				_base_meshes[slot_id] = child


## Map a mesh name to a slot id based on naming conventions (§4.3).
func _mesh_name_to_slot(mesh_name: String) -> String:
	if mesh_name == "Body":
		# Generic body mesh - covers torso, legs, arms.
		return "torso"
	if mesh_name == "head_Mesh":
		return "head"
	if mesh_name == "torso_Mesh":
		return "torso"
	if mesh_name == "legs_Mesh":
		return "legs"
	if mesh_name == "left_arm_Mesh":
		return "left_arm"
	if mesh_name == "right_arm_Mesh":
		return "right_arm"
	return ""


# ---------------------------------------------------------------------------
# Internal: Skin Retargeting
# ---------------------------------------------------------------------------

## Retarget the skin weights of an attachment node to the canonical skeleton.
## Walks all MeshInstance3D children and remaps joint indices by bone name.
func _retarget_skin(attachment_node: Node3D) -> void:
	if skeleton == null:
		return

	for child in attachment_node.get_children():
		if child is MeshInstance3D:
			var mesh_inst := child as MeshInstance3D
			var mesh := mesh_inst.mesh
			if mesh == null:
				continue

			# Note: MeshInstance3D.mesh is always a Mesh, never a MultiMesh —
			# MultiMesh skinning goes through MultiMeshInstance3D.multimesh,
			# a completely separate node/property, not reachable here.
			if mesh is ArrayMesh:
				var arr_mesh := mesh as ArrayMesh
				var surface_count := arr_mesh.get_surface_count()

				for surface_idx in surface_count:
					var arrays := arr_mesh.surface_get_arrays(surface_idx)
					var joints_array := arrays[Mesh.ARRAY_BONES] as PackedInt32Array
					var weights_array := arrays[Mesh.ARRAY_WEIGHTS] as PackedFloat32Array

					if joints_array.is_empty():
						continue

					# Remap joint indices by bone name.
					var new_joints := PackedInt32Array()
					for i in range(0, joints_array.size(), 4):
						for j in 4:
							var old_joint := joints_array[i + j]
							if old_joint < 0:
								new_joints.append(0)
							else:
								var bone_name := skeleton.get_bone_name(old_joint)
								var new_idx: int = _bone_index_map.get(bone_name, 0)
								new_joints.append(new_idx)

					arrays[Mesh.ARRAY_BONES] = new_joints
					arr_mesh.surface_set_arrays(surface_idx, arrays)


## Parent an attachment node to its mount bone in the skeleton.
func _parent_attachment(attachment_node: Node3D, slot_id: String,
		asset_meta: Dictionary) -> void:

	if skeleton == null:
		return

	var mount_bone: String = asset_meta.get("mount_bone", "")
	if mount_bone.is_empty():
		# Try to infer from slot.
		mount_bone = _slot_to_mount_bone(slot_id)

	if mount_bone.is_empty():
		return

	var bone_idx := skeleton.find_bone(mount_bone)
	if bone_idx < 0:
		return

	# Get the world transform of the bone at the time of attachment.
	var bone_pose := skeleton.get_bone_pose(bone_idx)
	var bone_transform := skeleton.global_transform * bone_pose

	# Position the attachment at the bone's location.
	attachment_node.global_transform = bone_transform


## Convert a slot id to its canonical mount bone name (§3.2).
func _slot_to_mount_bone(slot_id: String) -> String:
	match slot_id:
		"head": return "Head"
		"hair": return "HeadTop"
		"face": return "Jaw"
		"torso", "chest", "back": return "Chest"
		"left_arm": return "LeftUpperArm"
		"right_arm": return "RightUpperArm"
		"left_hand": return "LeftHand"
		"right_hand": return "RightHand"
		"legs": return "Hips"
		"pants": return "Hips"
		"left_foot": return "LeftFoot"
		"right_foot": return "RightFoot"
		"accessory": return "Root"
		_: return ""


# ---------------------------------------------------------------------------
# Internal: File Loading
# ---------------------------------------------------------------------------

## Load a file from the given path as a PackedByteArray.
func _load_file(path: String) -> PackedByteArray:
	var file := FileAccess.open(path, FileAccess.READ)
	if file == null:
		return PackedByteArray()
	var data := file.get_buffer(file.get_length())
	file.close()
	return data