#!/usr/bin/env python3
# SPDX-License-Identifier: AGPL-3.0-or-later
# BENCH-AUTO-401-019: Offline VEX proof bundle verifier

"""
Offline verification of VEX proof bundles without network access.

Validates:
- DSSE envelope structure
- Payload type and format
- Evidence hash references
- Justification catalog membership
- CAS hash verification

Usage:
    python bench/tools/verify.py --bundle PATH [--cas-root PATH] [--catalog PATH]
"""

import argparse
import base64
import hashlib
import json
import sys
from pathlib import Path
from typing import Any


class VerificationResult:
    """Result of a verification check."""

    def __init__(self, passed: bool, message: str, details: str = ""):
        self.passed = passed
        self.message = message
        self.details = details

    def __str__(self):
        status = "\033[0;32m✓\033[0m" if self.passed else "\033[0;31m✗\033[0m"
        result = f"{status} {self.message}"
        if self.details:
            result += f"\n    {self.details}"
        return result


def sha256_hex(data: bytes) -> str:
    """Compute SHA-256 hash."""
    return hashlib.sha256(data).hexdigest()


def blake3_hex(data: bytes) -> str:
    """Compute BLAKE3-256 hash (fallback to SHA-256)."""
    try:
        import blake3
        return "blake3:" + blake3.blake3(data).hexdigest()
    except ImportError:
        return "sha256:" + sha256_hex(data)


def load_json(path: Path) -> dict | None:
    """Load JSON file."""
    try:
        with open(path, 'r', encoding='utf-8') as f:
            return json.load(f)
    except (json.JSONDecodeError, FileNotFoundError) as e:
        return None


def verify_dsse_structure(dsse: dict) -> list[VerificationResult]:
    """Verify DSSE envelope structure."""
    results = []

    # Check required fields
    if "payloadType" not in dsse:
        results.append(VerificationResult(False, "Missing payloadType"))
    else:
        results.append(VerificationResult(True, f"payloadType: {dsse['payloadType']}"))

    if "payload" not in dsse:
        results.append(VerificationResult(False, "Missing payload"))
    else:
        results.append(VerificationResult(True, "payload present"))

    if "signatures" not in dsse or not dsse["signatures"]:
        results.append(VerificationResult(False, "Missing or empty signatures"))
    else:
        sig_count = len(dsse["signatures"])
        results.append(VerificationResult(True, f"Found {sig_count} signature(s)"))

        # Check for placeholder signatures
        for i, sig in enumerate(dsse["signatures"]):
            sig_value = sig.get("sig", "")
            if sig_value.startswith("PLACEHOLDER"):
                results.append(VerificationResult(
                    False,
                    f"Signature {i} is placeholder",
                    "Bundle needs actual signing before deployment"
                ))
            else:
                keyid = sig.get("keyid", "unknown")
                results.append(VerificationResult(True, f"Signature {i} keyid: {keyid}"))

    return results


def decode_payload(dsse: dict) -> tuple[dict | None, list[VerificationResult]]:
    """Decode DSSE payload."""
    results = []

    payload_b64 = dsse.get("payload", "")
    if not payload_b64:
        results.append(VerificationResult(False, "Empty payload"))
        return None, results

    try:
        payload_bytes = base64.b64decode(payload_b64)
        payload = json.loads(payload_bytes)
        results.append(VerificationResult(True, "Payload decoded successfully"))
        return payload, results
    except Exception as e:
        results.append(VerificationResult(False, f"Failed to decode payload: {e}"))
        return None, results


def verify_openvex(payload: dict) -> list[VerificationResult]:
    """Verify OpenVEX document structure."""
    results = []

    # Check OpenVEX context
    context = payload.get("@context", "")
    if "openvex" in context.lower():
        results.append(VerificationResult(True, f"OpenVEX context: {context}"))
    else:
        results.append(VerificationResult(False, f"Unexpected context: {context}"))

    # Check statements
    statements = payload.get("statements", [])
    if not statements:
        results.append(VerificationResult(False, "No VEX statements"))
    else:
        results.append(VerificationResult(True, f"Contains {len(statements)} statement(s)"))

        for i, stmt in enumerate(statements):
            vuln = stmt.get("vulnerability", {})
            vuln_id = vuln.get("name", vuln.get("@id", "unknown"))
            status = stmt.get("status", "unknown")
            results.append(VerificationResult(
                True,
                f"Statement {i}: {vuln_id} -> {status}"
            ))

    return results


def verify_evidence_hashes(payload: dict, cas_root: Path | None) -> list[VerificationResult]:
    """Verify evidence hash references against CAS."""
    results = []

    statements = payload.get("statements", [])
    for stmt in statements:
        impact = stmt.get("impact_statement", "")
        if "Evidence hash:" in impact:
            hash_value = impact.split("Evidence hash:")[1].strip()
            results.append(VerificationResult(True, f"Evidence hash: {hash_value[:16]}..."))

            # Verify against CAS if root provided
            if cas_root and cas_root.exists():
                # Look for reachability.json in CAS
                reach_file = cas_root / "reachability.json"
                if reach_file.exists():
                    with open(reach_file, 'rb') as f:
                        content = f.read()
                    actual_hash = blake3_hex(content)

                    if actual_hash == hash_value or hash_value in actual_hash:
                        results.append(VerificationResult(True, "Evidence hash matches CAS"))
                    else:
                        results.append(VerificationResult(
                            False,
                            "Evidence hash mismatch",
                            f"Expected: {hash_value[:32]}..., Got: {actual_hash[:32]}..."
                        ))

    return results


def verify_catalog_membership(payload: dict, catalog_path: Path) -> list[VerificationResult]:
    """Verify justification is in catalog."""
    results = []

    if not catalog_path.exists():
        results.append(VerificationResult(False, f"Catalog not found: {catalog_path}"))
        return results

    catalog = load_json(catalog_path)
    if catalog is None:
        results.append(VerificationResult(False, "Failed to load catalog"))
        return results

    # Extract catalog entries
    entries = catalog if isinstance(catalog, list) else catalog.get("entries", [])
    catalog_ids = {e.get("id", "") for e in entries}

    # Check each statement's justification
    statements = payload.get("statements", [])
    for stmt in statements:
        justification = stmt.get("justification")
        if justification:
            if justification in catalog_ids:
                results.append(VerificationResult(
                    True,
                    f"Justification '{justification}' in catalog"
                ))
            else:
                results.append(VerificationResult(
                    False,
                    f"Justification '{justification}' not in catalog"
                ))

    return results


def main():
    parser = argparse.ArgumentParser(
        description="Offline VEX proof bundle verifier"
    )
    parser.add_argument(
        "--bundle",
        type=Path,
        required=True,
        help="Path to DSSE bundle file"
    )
    parser.add_argument(
        "--cas-root",
        type=Path,
        default=None,
        help="Path to CAS evidence directory"
    )
    parser.add_argument(
        "--catalog",
        type=Path,
        default=Path("docs/benchmarks/vex-justifications.catalog.json"),
        help="Path to justification catalog"
    )

    args = parser.parse_args()

    # Resolve paths
    repo_root = Path(__file__).parent.parent.parent
    bundle_path = args.bundle if args.bundle.is_absolute() else repo_root / args.bundle
    catalog_path = args.catalog if args.catalog.is_absolute() else repo_root / args.catalog
    cas_root = args.cas_root if args.cas_root and args.cas_root.is_absolute() else (
        repo_root / args.cas_root if args.cas_root else None
    )

    print(f"Verifying: {bundle_path}")
    print("")

    all_results = []
    passed = 0
    failed = 0

    # Load DSSE bundle
    dsse = load_json(bundle_path)
    if dsse is None:
        print("\033[0;31m✗\033[0m Failed to load bundle")
        return 1

    # Verify DSSE structure
    print("DSSE Structure:")
    results = verify_dsse_structure(dsse)
    for r in results:
        print(f"  {r}")
        if r.passed:
            passed += 1
        else:
            failed += 1
    all_results.extend(results)

    # Decode payload
    print("\nPayload:")
    payload, results = decode_payload(dsse)
    for r in results:
        print(f"  {r}")
        if r.passed:
            passed += 1
        else:
            failed += 1
    all_results.extend(results)

    if payload:
        # Verify OpenVEX structure
        payload_type = dsse.get("payloadType", "")
        if "openvex" in payload_type.lower():
            print("\nOpenVEX:")
            results = verify_openvex(payload)
            for r in results:
                print(f"  {r}")
                if r.passed:
                    passed += 1
                else:
                    failed += 1
            all_results.extend(results)

        # Verify evidence hashes
        print("\nEvidence:")
        results = verify_evidence_hashes(payload, cas_root)
        for r in results:
            print(f"  {r}")
            if r.passed:
                passed += 1
            else:
                failed += 1
        all_results.extend(results)

        # Verify catalog membership
        print("\nCatalog:")
        results = verify_catalog_membership(payload, catalog_path)
        for r in results:
            print(f"  {r}")
            if r.passed:
                passed += 1
            else:
                failed += 1
        all_results.extend(results)

    # Summary
    print(f"\n{'='*40}")
    print(f"Passed: {passed}, Failed: {failed}")

    return 0 if failed == 0 else 1


if __name__ == "__main__":
    sys.exit(main())