#!/usr/bin/env bash
# Shared tamper-evident appender for the central tool-call audit log
# (.specify/logs/audit/tool-calls.jsonl).
#
# Every record is chained: record_hash = SHA-256(previous_record_hash | core),
# where core is the canonical (sorted-key) JSON of the record minus record_hash.
# After each append the chain head is signed with the audit RSA key, so a
# re-forged chain (recomputed hashes) cannot produce a valid head signature
# without the private key. Used by both agent-metrics.sh and tool-registry-gate.sh
# so the combined audit is tamper-evident regardless of which writer appended.
#
# Production note: the private key must live off-repo (KMS/HSM); it is local
# here only for self-contained demonstration.

append_tool_audit() {
  local record_json="$1"
  local project_root="$2"
  local audit_dir="$CASAN_STATE_ROOT/logs/audit"
  local log="$audit_dir/tool-calls.jsonl"
  mkdir -p "$audit_dir"

  local head
  head="$(python - "$log" "$record_json" <<'PY'
import hashlib, json, sys
log, rec_json = sys.argv[1], sys.argv[2]
rec = json.loads(rec_json)
prev = ""
try:
    with open(log, encoding="utf-8") as f:
        lines = [l for l in f if l.strip()]
    if lines:
        prev = json.loads(lines[-1]).get("record_hash", "")
except FileNotFoundError:
    pass
rec.pop("record_hash", None)
rec["previous_record_hash"] = prev
core = json.dumps(rec, sort_keys=True, separators=(",", ":"))
rec["record_hash"] = hashlib.sha256((prev + "|" + core).encode()).hexdigest()
with open(log, "a", encoding="utf-8") as f:
    f.write(json.dumps(rec) + "\n")
sys.stdout.write(rec["record_hash"])
PY
)"

  command -v openssl >/dev/null 2>&1 || return 0
  # Private signing key lives OFF-REPO (default ~/.casan/audit-keys); only the
  # public key is committed, for verification. Production: replace with KMS/HSM.
  local pub_dir="$CASAN_GOVERNANCE_ROOT"
  local priv_dir="${CASAN_AUDIT_KEY_DIR:-$HOME/.casan/audit-keys}"
  local priv="$priv_dir/audit-private.pem" pub="$pub_dir/audit-public.pem"
  mkdir -p "$pub_dir" "$priv_dir"
  if [[ ! -f "$priv" ]]; then
    openssl genpkey -algorithm RSA -pkeyopt rsa_keygen_bits:2048 -out "$priv" 2>/dev/null
    chmod 600 "$priv"
  fi
  # Always re-export the matching public key so a persisted off-repo private key
  # never drifts out of sync with a freshly checked-out audit-public.pem on CI
  # runners (see governance-check.sh for the full rationale).
  openssl rsa -in "$priv" -pubout -out "$pub" 2>/dev/null || true
  printf '%s' "$head" > "$audit_dir/tool-calls-head.txt"
  openssl dgst -sha256 -sign "$priv" -out "$audit_dir/tool-calls-head.sig" "$audit_dir/tool-calls-head.txt" 2>/dev/null || true
}