## 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

# Preloaded rather than referenced by global class_name -- see avatar_loadout.gd.
const AvatarCatalog := preload("res://scripts/avatar/avatar_catalog.gd")


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

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

## The skin albedo baked into the placeholder base body by
## gen_placeholder_avatars.gd. apply_skin_tone() finds the mesh surfaces
## painted this colour (head + arms) and retints them.
const PLACEHOLDER_SKIN_ALBEDO := Color(0.96, 0.80, 0.19)

## 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
	avatar_node = _instance_glb_as_avatar(path)
	if avatar_node == null:
		load_error.emit("Failed to load base body scene: %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 = _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 attachment_node = _instance_glb_as_attachment(path, slot_id)
	if attachment_node == null:
		load_error.emit("Failed to load attachment scene: %s" % path)
		return null

	# If the attachment carries its own skin, retarget it to the canonical
	# skeleton; static props (the common case) are unaffected.
	_retarget_skin(attachment_node)

	# Check if this attachment has multi-bone children (e.g. Attach_LeftUpperLeg, Attach_Hips).
	var multi_bone_children: Array[Node] = []
	for child in attachment_node.get_children():
		var cname := child.name
		if cname.begins_with("Attach_") or cname.begins_with("attach_"):
			var target_bone := cname.substr(7)
			if skeleton.find_bone(target_bone) != -1:
				multi_bone_children.append(child)

	var mount_node: Node3D
	if not multi_bone_children.is_empty():
		var created_bas: Array[BoneAttachment3D] = []
		for child in multi_bone_children:
			var target_bone := child.name.substr(7)
			var ba := BoneAttachment3D.new()
			ba.name = "Mount_%s_%s" % [slot_id, target_bone]
			ba.bone_name = target_bone
			skeleton.add_child(ba)
			attachment_node.remove_child(child)
			ba.add_child(child)
			created_bas.append(ba)

		skeleton.add_child(attachment_node)
		attachment_node.set_meta("bone_attachments", created_bas)
		attachment_node.tree_exiting.connect(func():
			for ba in created_bas:
				if is_instance_valid(ba) and not ba.is_queued_for_deletion():
					ba.queue_free()
		)
		mount_node = attachment_node
	else:
		# Single mount bone via a BoneAttachment3D so it follows the skeleton.
		# Falls back to a plain skeleton child if the mount bone is missing.
		var mount_bone: String = asset_meta.get("mount_bone", "")
		if mount_bone.is_empty():
			mount_bone = _slot_to_mount_bone(slot_id)
		if not mount_bone.is_empty() and skeleton.find_bone(mount_bone) != -1:
			var ba := BoneAttachment3D.new()
			ba.name = "Mount_%s" % slot_id if slot_id != "accessory" else "Mount_accessory_%s" % asset_id
			ba.bone_name = mount_bone
			skeleton.add_child(ba)
			ba.add_child(attachment_node)
			mount_node = ba
		else:
			skeleton.add_child(attachment_node)
			mount_node = attachment_node

	# Store the top-level mount node so unload can free the whole unit.
	if slot_id == "accessory":
		var list: Array = _attachments.get("accessory", [])
		list.append(mount_node)
		_attachments["accessory"] = list
	else:
		if _attachments.has(slot_id) and is_instance_valid(_attachments[slot_id]):
			_attachments[slot_id].queue_free()
		_attachments[slot_id] = mount_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":
		for node in _attachments.get("accessory", []):
			if is_instance_valid(node):
				if node.has_meta("bone_attachments"):
					for ba in node.get_meta("bone_attachments"):
						if is_instance_valid(ba):
							ba.queue_free()
				node.queue_free()
		_attachments.erase("accessory")
	else:
		var node = _attachments.get(slot_id)
		if is_instance_valid(node):
			if node.has_meta("bone_attachments"):
				for ba in node.get_meta("bone_attachments"):
					if is_instance_valid(ba):
						ba.queue_free()
			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


## Retint the base body's skin surfaces (the ones the generator painted
## PLACEHOLDER_SKIN_ALBEDO -- head + arms) to [param color]. A no-op if the
## colour is unset (transparent). Real segmented bodies will do this per mesh.
func apply_skin_tone(color: Color) -> void:
	if color.a <= 0.0:
		return
	if avatar_node == null or not is_instance_valid(avatar_node):
		return
	var skel := avatar_node.get_node_or_null("Skeleton3D") as Skeleton3D
	if skel == null:
		return
	for child in skel.get_children():
		if not (child is MeshInstance3D):
			continue
		var mi := child as MeshInstance3D
		if mi.mesh == null:
			continue
		for s in mi.mesh.get_surface_count():
			var mat := mi.get_active_material(s)
			if mat is BaseMaterial3D and \
					(mat as BaseMaterial3D).albedo_color.is_equal_approx(PLACEHOLDER_SKIN_ALBEDO):
				var tinted := StandardMaterial3D.new()
				tinted.albedo_color = color
				tinted.roughness = 0.9
				mi.set_surface_override_material(s, tinted)


## 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
# ---------------------------------------------------------------------------

## Instantiate a base-body .glb (a Godot-imported PackedScene) into an avatar
## structure:
##   Avatar (Node3D)
##     Skeleton3D          -- the canonical rig + skin-bound body meshes
##     BodyMeshes (Node3D) -- unused container, kept for compatibility
##     Attachments (Node3D)-- equipped attachment nodes (added by load_attachment)
##
## Uses load().instantiate() rather than the runtime GLTFDocument path: the
## imported .scn is the one that actually ends up in an exported build, with
## the skeleton + skin set up by Godot's import pipeline. (The raw-bytes
## GLTFDocument path -- for future user-uploaded models -- misbehaved in a
## release build: no Skeleton3D produced, so the player fell back to a capsule.)
func _instance_glb_as_avatar(path: String) -> Node3D:
	var packed = load(path)
	if not (packed is PackedScene):
		push_error("Base body is not an importable scene: %s" % path)
		return null
	var scene_root: Node = packed.instantiate()
	if not (scene_root is Node3D):
		push_error("Base body scene root is not a Node3D: %s" % path)
		scene_root.free()
		return null

	var src_skel := _find_first_skeleton(scene_root)
	if src_skel == null:
		push_error("No Skeleton3D in base body scene: %s" % path)
		scene_root.free()
		return null

	var avatar := Node3D.new()
	avatar.name = "Avatar"

	src_skel.get_parent().remove_child(src_skel)
	src_skel.name = "Skeleton3D"
	src_skel.transform = Transform3D.IDENTITY
	_clear_owner_recursive(src_skel)
	avatar.add_child(src_skel)
	scene_root.free()

	var body_meshes := Node3D.new()
	body_meshes.name = "BodyMeshes"
	avatar.add_child(body_meshes)

	var attachments_container := Node3D.new()
	attachments_container.name = "Attachments"
	avatar.add_child(attachments_container)

	return avatar


## Depth-first search for the first Skeleton3D under [param node].
func _find_first_skeleton(node: Node) -> Skeleton3D:
	if node is Skeleton3D:
		return node as Skeleton3D
	for child in node.get_children():
		var found := _find_first_skeleton(child)
		if found:
			return found
	return null


## Instantiate an attachment .glb (imported PackedScene) into a single named
## Node3D the caller can mount to a bone as one unit.
func _instance_glb_as_attachment(path: String, slot_id: String) -> Node3D:
	var packed = load(path)
	if not (packed is PackedScene):
		push_error("Attachment is not an importable scene: %s" % path)
		return null
	var scene_root: Node = packed.instantiate()
	if not (scene_root is Node3D):
		push_error("Attachment scene root is not a Node3D: %s" % path)
		scene_root.free()
		return null

	var attachment := Node3D.new()
	attachment.name = "%s_%s" % [slot_id, path.get_file().get_basename()]
	for child in scene_root.get_children().duplicate():
		scene_root.remove_child(child)
		_clear_owner_recursive(child)
		attachment.add_child(child)
	scene_root.free()
	return attachment


## generate_scene() stamps every node with the GLB root as `owner`; that
## becomes inconsistent (and noisy) once we reparent the node elsewhere.
func _clear_owner_recursive(node: Node) -> void:
	node.owner = null
	for child in node.get_children():
		_clear_owner_recursive(child)


## Index the base body's skinned meshes by slot so equipping a body-part
## attachment can hide the corresponding base mesh. generate_scene() parents
## skinned meshes under the Skeleton3D, so scan there.
func _extract_base_meshes(avatar: Node3D) -> void:
	var skel := avatar.get_node_or_null("Skeleton3D") as Skeleton3D
	if skel == null:
		return

	for child in skel.get_children():
		if child is MeshInstance3D:
			# The single "Body" placeholder mesh is registered only under
			# "torso" -- mapping it to every body-part slot would make it
			# vanish the moment any one body-part item is equipped. A real
			# multi-mesh body registers each mesh under its own slot.
			if child.name == "Body":
				_base_meshes["torso"] = child
			else:
				var slot_id := _mesh_name_to_slot(child.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)
					# Static props (the common attachment) carry no bone/weight
					# arrays at all -- nothing to retarget.
					if arrays[Mesh.ARRAY_BONES] == null or arrays[Mesh.ARRAY_WEIGHTS] == null:
						continue
					var joints_array: PackedInt32Array = arrays[Mesh.ARRAY_BONES]
					var weights_array: PackedFloat32Array = arrays[Mesh.ARRAY_WEIGHTS]

					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