extends RefCounted
class_name GLBLoader

## Loads a GLB file at runtime using GLTFDocument.
## Usage:
##   var loader = GLBLoader.new()
##   var scene = loader.load("res://path/to/model.glb")
##   if scene:
##       get_tree().current_scene.add_child(scene)

static func load(glb_path: String) -> Node3D:
    print("GLBLoader: loading " + glb_path)
    
    # Check if file exists
    if not FileAccess.file_exists(glb_path):
        print("GLBLoader: file not found: " + glb_path)
        return null
    
    # Read file as bytes
    var file = FileAccess.open(glb_path, FileAccess.READ)
    if not file:
        print("GLBLoader: failed to open file")
        return null
    
    var bytes = file.get_buffer(file.get_length())
    file.close()
    
    print("GLBLoader: read %d bytes" % bytes.size())
    
    # Parse with GLTFDocument
    var gltf = GLTFDocument.new()
    var state = GLTFState.new()
    
    var err = gltf.append_from_buffer(bytes, "", state)
    if err != OK:
        print("GLBLoader: failed to parse GLB, error: %d" % err)
        return null
    
    print("GLBLoader: parsed successfully (%d animations, %d meshes)" % [
        state.animations.size(), state.meshes.size()])
    
    # Generate scene — remove_immutable_tracks=false preserves all bone
    # animation tracks (default true strips tracks where rest==pose → T-pose).
    var scene = gltf.generate_scene(state, 30, false, false)
    if not scene:
        print("GLBLoader: failed to generate scene")
        return null
    
    print("GLBLoader: generated scene: %s" % scene.name)
    return scene