#!/usr/bin/env bash
set -euo pipefail

# Verify CASAN H5 append-only hash-chain audit log.
# Usage:
#   verify-audit-chain.sh [audit-jsonl]

SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
PROJECT_ROOT="$(cd "$SCRIPT_DIR/../../.." && pwd)"
AUDIT_LOG="${1:-$PROJECT_ROOT/.specify/logs/audit/audit.jsonl}"

if [[ ! -f "$AUDIT_LOG" ]]; then
  echo "AUDIT_CHAIN_MISSING file=$AUDIT_LOG" >&2
  exit 1
fi

COMPUTED_HEAD="$(python3 - "$AUDIT_LOG" <<'PY'
import hashlib
import json
import sys

path = sys.argv[1]
previous = ""
count = 0

with open(path, encoding="utf-8") as f:
    for line_no, line in enumerate(f, 1):
        if not line.strip():
            continue
        record = json.loads(line)
        expected_previous = record.get("previous_record_hash", "")
        if expected_previous != previous:
            raise SystemExit(
                f"AUDIT_CHAIN_BROKEN line={line_no} expected_previous={previous} actual_previous={expected_previous}"
            )

        core = "|".join(
            [
                record.get("timestamp", ""),
                record.get("trace_id", ""),
                record.get("action", ""),
                record.get("actor", ""),
                record.get("risk_level", ""),
                record.get("decision", ""),
                record.get("approval_status", ""),
                record.get("approver", ""),
                record.get("input_hash", ""),
                record.get("output_hash", ""),
                expected_previous,
            ]
        )
        expected_hash = hashlib.sha256(core.encode()).hexdigest()
        actual_hash = record.get("record_hash", "")
        if expected_hash != actual_hash:
            raise SystemExit(
                f"AUDIT_HASH_MISMATCH line={line_no} expected={expected_hash} actual={actual_hash}"
            )
        previous = actual_hash
        count += 1

# Emit count and head on stderr (human) and the head on stdout (captured).
sys.stderr.write(f"AUDIT_CHAIN_INTEGRITY_OK records={count}\n")
sys.stdout.write(previous)
PY
)"

# --- External anchor verification ---
# Recomputing a forged chain yields a different head; the stored head signature
# was produced with a private key the forger does not have, so it will not match.
AUDIT_DIR="$(dirname "$AUDIT_LOG")"
HEAD_FILE="$AUDIT_DIR/audit-head.txt"
HEAD_SIG="$AUDIT_DIR/audit-head.sig"
AUDIT_PUB="$PROJECT_ROOT/.specify/level5/central-governance/audit-public.pem"

if [[ -f "$HEAD_FILE" && -f "$HEAD_SIG" && -f "$AUDIT_PUB" ]] && command -v openssl >/dev/null 2>&1; then
  STORED_HEAD="$(cat "$HEAD_FILE")"
  if [[ "$STORED_HEAD" != "$COMPUTED_HEAD" ]]; then
    echo "AUDIT_HEAD_MISMATCH computed=$COMPUTED_HEAD stored=$STORED_HEAD" >&2
    exit 1
  fi
  if ! openssl dgst -sha256 -verify "$AUDIT_PUB" -signature "$HEAD_SIG" "$HEAD_FILE" >/dev/null 2>&1; then
    echo "AUDIT_HEAD_SIGNATURE_INVALID head=$COMPUTED_HEAD" >&2
    exit 1
  fi
  echo "AUDIT_CHAIN_VALID anchor=signed last_hash=$COMPUTED_HEAD"
else
  echo "AUDIT_CHAIN_VALID anchor=unsigned last_hash=$COMPUTED_HEAD"
fi