"""Load only the explicitly allowed, hash-verified local preprocessing code."""
import hashlib
import importlib
from pathlib import Path

ROOT=Path(__file__).resolve().parent
ALLOWED={'command_normalizer':set(),'command_canonicalizer':{'command_normalizer.py'},'command_normalizer_v2':set(),'command_canonicalizer_v2':{'command_normalizer_v2.py'}}


def load_preprocessor(metadata):
    name=metadata.get('module')
    if name not in ALLOWED:raise ValueError('Unrecognized input preprocessing module')
    file=ROOT/(name+'.py')
    if hashlib.sha256(file.read_bytes()).hexdigest()!=metadata.get('sha256'):raise ValueError('Input preprocessing source mismatch')
    dependencies=metadata.get('dependencies',{})
    if set(dependencies)!=ALLOWED[name]:raise ValueError('Input preprocessing dependencies mismatch')
    for filename,expected in dependencies.items():
        if hashlib.sha256((ROOT/filename).read_bytes()).hexdigest()!=expected:raise ValueError('Input preprocessing dependency source mismatch')
    module=importlib.import_module(name)
    if Path(module.__file__).resolve()!=file or module.VERSION!=metadata.get('version'):raise ValueError('Input preprocessing module identity mismatch')
    return module.normalize_state