## Converts raw WMOLoader data into a Godot Node3D scene tree.
## Usage:
##   var data = WMOLoader.new().load_wmo(abs_path)
##   var node = WMOBuilder.build(data, "res://extracted")
##   add_child(node)
class_name WMOBuilder

static var _texture_cache: Dictionary = {}

# Returns a Node3D containing one MeshInstance3D per WMO group.
static func build(data: Dictionary, extracted_dir: String = "") -> Node3D:
	var root := Node3D.new()
	root.name = "WMO"

	if not data.has("groups"):
		return root

	var textures: PackedStringArray  = data.get("textures", PackedStringArray())
	var materials: Array             = data.get("materials", [])

	# Build Godot materials from WMO material definitions
	var godot_materials: Array[StandardMaterial3D] = []
	for mat_def in materials:
		godot_materials.append(_build_material(mat_def, textures, extracted_dir))

	# Build one MeshInstance3D per group
	var groups: Array = data.get("groups", [])
	for gi in groups.size():
		var g: Dictionary = groups[gi]
		if g.is_empty():
			continue
		var mesh_inst := _build_group_mesh(g, godot_materials)
		mesh_inst.name = "Group_%d" % gi
		root.add_child(mesh_inst)

	return root


static func _build_group_mesh(
		g: Dictionary,
		godot_mats: Array[StandardMaterial3D]) -> MeshInstance3D:

	var verts:   PackedVector3Array = g.get("vertices", PackedVector3Array())
	var normals: PackedVector3Array = g.get("normals",  PackedVector3Array())
	var uvs:     PackedVector2Array = g.get("uvs",      PackedVector2Array())
	var colors:  PackedColorArray   = g.get("colors",   PackedColorArray())
	var indices: PackedInt32Array   = g.get("indices",  PackedInt32Array())
	var batches: Array              = g.get("batches",  [])
	var mesh := ArrayMesh.new()
	if verts.is_empty() or indices.is_empty():
		var empty := MeshInstance3D.new()
		empty.mesh = mesh
		return empty

	if batches.is_empty():
		batches = [{
			"index_start": 0,
			"index_count": indices.size(),
			"material_id": -1,
		}]

	for batch_variant in batches:
		if not (batch_variant is Dictionary):
			continue
		var batch: Dictionary = batch_variant
		var idx_start: int = int(batch.get("index_start", 0))
		var idx_count: int = int(batch.get("index_count", 0))
		var mat_id: int = int(batch.get("material_id", -1))
		if idx_count <= 0 or idx_start >= indices.size():
			continue

		var batch_indices := PackedInt32Array()
		for i in range(idx_start, mini(idx_start + idx_count, indices.size()), 3):
			if i + 2 >= indices.size():
				break
			# Reverse winding for the current local basis conversion.
			batch_indices.append(indices[i + 0])
			batch_indices.append(indices[i + 2])
			batch_indices.append(indices[i + 1])
		if batch_indices.is_empty():
			continue

		var arrays := []
		arrays.resize(Mesh.ARRAY_MAX)
		arrays[Mesh.ARRAY_VERTEX] = verts
		if normals.size() == verts.size():
			arrays[Mesh.ARRAY_NORMAL] = normals
		if uvs.size() == verts.size():
			arrays[Mesh.ARRAY_TEX_UV] = uvs
		if colors.size() == verts.size():
			arrays[Mesh.ARRAY_COLOR] = colors
		arrays[Mesh.ARRAY_INDEX] = batch_indices

		mesh.add_surface_from_arrays(Mesh.PRIMITIVE_TRIANGLES, arrays)

		var surf_idx := mesh.get_surface_count() - 1
		if mat_id >= 0 and mat_id < godot_mats.size():
			mesh.surface_set_material(surf_idx, godot_mats[mat_id])

	var mi := MeshInstance3D.new()
	mi.mesh = mesh
	return mi


static func _build_material(
		mat_def: Dictionary,
		textures: PackedStringArray,
		extracted_dir: String = "") -> StandardMaterial3D:

	var mat := StandardMaterial3D.new()
	mat.cull_mode = BaseMaterial3D.CULL_DISABLED
	mat.roughness = 0.85
	mat.metallic = 0.0
	mat.shading_mode = BaseMaterial3D.SHADING_MODE_UNSHADED
	mat.specular_mode = BaseMaterial3D.SPECULAR_DISABLED
	mat.vertex_color_use_as_albedo = false

	var blend_mode: int = mat_def.get("blend_mode", 0)
	match blend_mode:
		0: mat.transparency = BaseMaterial3D.TRANSPARENCY_DISABLED
		1: mat.transparency = BaseMaterial3D.TRANSPARENCY_ALPHA_SCISSOR
		_: mat.transparency = BaseMaterial3D.TRANSPARENCY_ALPHA

	# Texture is loaded later by the scene assembler (needs BLP→Image conversion)
	# Store the path as metadata for the assembler to pick up
	var tex0_id: int = mat_def.get("texture0", -1)
	if tex0_id >= 0 and tex0_id < textures.size():
		var tex_path: String = str(textures[tex0_id]).replace("\\", "/")
		mat.set_meta("texture0_path", tex_path)
		var tex := _load_texture(tex_path, extracted_dir)
		if tex:
			mat.albedo_texture = tex
			mat.texture_filter = BaseMaterial3D.TEXTURE_FILTER_LINEAR_WITH_MIPMAPS_ANISOTROPIC

	mat.set_meta("wow_flags",      mat_def.get("flags",  0))
	mat.set_meta("wow_shader",     mat_def.get("shader", 0))

	return mat


static func _load_texture(rel_path: String, extracted_dir: String) -> Texture2D:
	if rel_path.is_empty() or extracted_dir.is_empty():
		return null

	var abs_path := ProjectSettings.globalize_path(extracted_dir.path_join(rel_path.replace("\\", "/")))
	if _texture_cache.has(abs_path):
		return _texture_cache[abs_path]

	if not ClassDB.class_exists("BLPLoader"):
		return null

	var loader = ClassDB.instantiate("BLPLoader")
	if loader == null:
		return null

	var img: Image = loader.call("load_image", abs_path)
	if img == null or img.is_empty():
		_texture_cache[abs_path] = null
		return null

	img.generate_mipmaps()
	var tex := ImageTexture.create_from_image(img)
	_texture_cache[abs_path] = tex
	return tex