import os


def load_class_map(filename, root=''):
    class_map_path = filename
    if not os.path.exists(class_map_path):
        class_map_path = os.path.join(root, filename)
        assert os.path.exists(class_map_path), 'Cannot locate specified class map file (%s)' % filename
    class_map_ext = os.path.splitext(filename)[-1].lower()
    if class_map_ext == '.txt':
        with open(class_map_path) as f:
            class_to_idx = {v.strip(): k for k, v in enumerate(f)}
    else:
        assert False, 'Unsupported class map extension'
    return class_to_idx