"""Reject analysis caches whose inputs or implementation have changed."""
import hashlib
import json
from pathlib import Path


def digest(path):
    result = hashlib.sha256()
    with Path(path).open('rb') as stream:
        for block in iter(lambda: stream.read(1024 * 1024), b''):
            result.update(block)
    return result.hexdigest()


def provenance(inputs):
    paths = [Path(path).resolve() for path in inputs]
    paths.append(Path(__file__).resolve())
    return {str(path): digest(path) for path in sorted(set(paths))}


def verified_cache(path, inputs):
    """An unverified legacy cache must be rebuilt in a new analysis directory.

    Fail closed rather than silently mixing a new recording with archived
    arrays, split identities or reports. Never delete archived evidence here.
    """
    path = Path(path)
    if not path.exists():
        return False
    manifest = Path(str(path) + '.provenance.json')
    if manifest.exists():
        saved = json.loads(manifest.read_text())
        if (saved.get('inputs') == provenance(inputs)
                and saved.get('cache_sha256') == digest(path)):
            return True
    raise ValueError(
        f'Unverified or stale analysis cache: {path}. '
        'Use a new analysis output directory and rebuild upstream stages; '
        'retain the archived directory for reproducing previous reports.')


def record_cache(path, inputs):
    path = Path(path)
    manifest = Path(str(path) + '.provenance.json')
    manifest.write_text(json.dumps(
        {'inputs': provenance(inputs), 'cache_sha256': digest(path)},
        indent=2) + '\n')