#!/usr/bin/env python3
"""Verify a Predge signed record offline (Python 3.8+).

usage: python3 verify_record.py FILE [--keys FILE_OR_URL] [--offline]

FILE is a full API response (the envelope is under "attestation"), a bare
envelope, or an evidence pack (the envelope fields at the top level).
Checks, in order:
  1. canonical rebuilt from payload equals canonical  (CANONICALIZATION.md)
  2. content_hash = sha256(canonical), when the file carries content_hash
  3. ed25519 signature over canonical
  4. envelope_signature, when present
  5. public_key is listed and active in predge-keys.json (skipped with --offline)
Exit status 0 only when every check that ran passed.
Signature checks need `cryptography` or `PyNaCl`; without either they are
reported as skipped and the exit status is 2.
"""
import hashlib
import json
import sys
import urllib.request

KEYS_URL = "https://api.predge.io/.well-known/predge-keys.json"


def canonical(value):
    """The Predge rule: sorted keys at every level, no whitespace, UTF-8, no ASCII escaping."""
    return json.dumps(value, sort_keys=True, separators=(",", ":"), ensure_ascii=False)


def envelope_of(doc):
    if isinstance(doc.get("attestation"), dict):
        return doc["attestation"]
    return doc


def ed25519_verify(pub_hex, sig_hex, message):
    try:
        from cryptography.exceptions import InvalidSignature
        from cryptography.hazmat.primitives.asymmetric.ed25519 import Ed25519PublicKey
        try:
            Ed25519PublicKey.from_public_bytes(bytes.fromhex(pub_hex)).verify(bytes.fromhex(sig_hex), message)
            return True
        except (InvalidSignature, ValueError):
            return False
    except ImportError:
        pass
    try:
        from nacl.exceptions import BadSignatureError
        from nacl.signing import VerifyKey
        try:
            VerifyKey(bytes.fromhex(pub_hex)).verify(message, bytes.fromhex(sig_hex))
            return True
        except (BadSignatureError, ValueError):
            return False
    except ImportError:
        return None


def load_keys(src):
    if src.startswith("http://") or src.startswith("https://"):
        with urllib.request.urlopen(src, timeout=10) as r:
            return json.load(r)
    with open(src, encoding="utf-8") as f:
        return json.load(f)


def main(argv):
    if not argv or argv[0].startswith("-"):
        print(__doc__)
        return 64
    path, keys_src, offline = argv[0], KEYS_URL, "--offline" in argv
    if "--keys" in argv:
        keys_src = argv[argv.index("--keys") + 1]
    with open(path, encoding="utf-8") as f:
        env = envelope_of(json.load(f))

    results = []
    canon = env["canonical"]
    results.append(("payload rebuilds canonical", canonical(env["payload"]) == canon))
    digest = hashlib.sha256(canon.encode("utf-8")).hexdigest()
    if "content_hash" in env:
        results.append(("content_hash = sha256(canonical)", env["content_hash"] == digest))
    results.append(("signature over canonical", ed25519_verify(env["public_key"], env["signature"], canon.encode("utf-8"))))
    if "envelope_signature" in env:
        rest = {k: v for k, v in env.items() if k != "envelope_signature"}
        results.append(("envelope_signature", ed25519_verify(env["public_key"], env["envelope_signature"], canonical(rest).encode("utf-8"))))
    if not offline:
        try:
            keys = load_keys(keys_src).get("keys", [])
        except Exception as e:  # network or TLS trouble: say so, do not pass the check
            print(f"could not read the key set from {keys_src}: {e}; download it and pass --keys FILE")
            keys = []
        listed = any(k.get("active") and str(k.get("public_key", "")).lower() == env["public_key"].lower() for k in keys)
        results.append(("key listed and active in predge-keys.json", listed))

    print("content_hash (sha256 of canonical):", digest)
    print("kid:", env["public_key"][:16])
    for name, ok in results:
        print(f"{'PASS' if ok else ('SKIP' if ok is None else 'FAIL')}  {name}")
    if any(ok is False for _, ok in results):
        return 1
    if any(ok is None for _, ok in results):
        print("install `cryptography` or `PyNaCl` to check signatures")
        return 2
    return 0


if __name__ == "__main__":
    sys.exit(main(sys.argv[1:]))