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

# CASAN Plan-16 SEC-25 (SC-07, offline) — build-artifact attestation (tested==deployed).
#
# A green CI gate proves the TESTED artifact is sound, but nothing binds it to what
# is DEPLOYED — a different artifact could ship. This produces a signed attestation
# over an artifact's content hash; verification recomputes the hash and checks the
# signature, so a swapped/modified artifact (deployed != tested) or a forged
# attestation is REFUSED (fail-closed). Offline form of SLSA-style provenance;
# real signed-commit enrollment + full provenance chain need CI/key infra.
#
# Usage:
#   artifact-attest.sh attest <artifact> <priv-key>            # -> <artifact>.att (+ .att.sig)
#   artifact-attest.sh verify <artifact> <attestation> <pub>   # tested==deployed check
# Exit: 0 ok · 2 mismatch/forged/tampered · 3 missing/unsigned/openssl · 64 usage.

CMD="${1:-}"; ART="${2:-}"
command -v openssl >/dev/null 2>&1 || { echo "OPENSSL_UNAVAILABLE" >&2; exit 3; }

sha256_of() {
  if command -v sha256sum >/dev/null 2>&1; then sha256sum "$1" | awk '{print $1}'
  else shasum -a 256 "$1" | awk '{print $1}'; fi
}

case "$CMD" in
  attest)
    KEY="${3:-}"
    [[ -f "$ART" && -f "$KEY" ]] || { echo "usage: artifact-attest.sh attest <artifact> <priv-key>" >&2; exit 64; }
    H="$(sha256_of "$ART")"
    ATT="$ART.att"
    printf '{"artifact":"%s","sha256":"%s","attested_at":"%s"}\n' \
      "$(basename "$ART")" "$H" "$(date -u +%Y-%m-%dT%H:%M:%SZ)" > "$ATT"
    openssl dgst -sha256 -sign "$KEY" -out "$ATT.sig" "$ATT" 2>/dev/null \
      || { echo "ATTEST_SIGN_FAILED" >&2; exit 2; }
    echo "ARTIFACT_ATTESTED artifact=$(basename "$ART") sha256=${H:0:16}… att=$ATT"
    exit 0
    ;;
  verify)
    ATT="${3:-}"; KEY="${4:-}"
    [[ -f "$ART" ]] || { echo "ARTIFACT_MISSING file=$ART" >&2; exit 3; }
    [[ -n "$ATT" && -f "$ATT" ]] || { echo "ATTESTATION_MISSING file=$ATT — refusing (fail-closed)" >&2; exit 3; }
    [[ -f "$KEY" ]] || { echo "ATTEST_PUBKEY_MISSING key=$KEY" >&2; exit 3; }
    [[ -f "$ATT.sig" ]] || { echo "ATTESTATION_UNSIGNED file=$ATT — refusing (fail-closed)" >&2; exit 3; }
    if ! openssl dgst -sha256 -verify "$KEY" -signature "$ATT.sig" "$ATT" >/dev/null 2>&1; then
      echo "ATTESTATION_FORGED file=$ATT — tampered or wrong key" >&2; exit 2
    fi
    WANT="$(python3 -c 'import json,sys;print(json.load(open(sys.argv[1])).get("sha256",""))' "$ATT" 2>/dev/null)"
    HAVE="$(sha256_of "$ART")"
    if [[ -z "$WANT" || "$WANT" != "$HAVE" ]]; then
      echo "ARTIFACT_MISMATCH deployed!=tested want=${WANT:0:16}… have=${HAVE:0:16}…" >&2; exit 2
    fi
    echo "ARTIFACT_VERIFIED tested==deployed sha256=${HAVE:0:16}…"
    exit 0
    ;;
  *)
    echo "Usage: artifact-attest.sh {attest <artifact> <priv>|verify <artifact> <att> <pub>}" >&2
    exit 64
    ;;
esac