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

# CASAN Plan-16 SEC-24 (SC-05/06, offline) — supply-chain integrity for build files.
#
# Two harness-side controls that need no network:
#   * image-pin: Dockerfiles / CI workflow files must pin container images by DIGEST
#     (`@sha256:...`), never a floating tag (`:latest`, `:20`, or no tag) — a floating
#     tag lets a malicious image be swapped in under the same name.
#   * sign / verify: a CI workflow (or any build file) is signed and verified on load;
#     a tampered, forged, or UNSIGNED file is REFUSED (fail-closed).
#
# (Live CVE/OSV scanning and real image scanning need infra and remain planned.)
#
# Usage:
#   supply-chain-integrity.sh image-pin <file> [<file> ...]
#   supply-chain-integrity.sh sign      <file> <priv-key>
#   supply-chain-integrity.sh verify    <file> <pub-key>
# Exit: 0 ok · 2 violation (unpinned image / tampered-forged sig) · 3 missing/unsigned/openssl · 64 usage.

CMD="${1:-}"; shift || true

case "$CMD" in
  image-pin)
    [[ "$#" -ge 1 ]] || { echo "usage: supply-chain-integrity.sh image-pin <file>..." >&2; exit 64; }
    for f in "$@"; do [[ -f "$f" ]] || { echo "IMAGE_PIN_MISSING file=$f" >&2; exit 3; }; done
    python3 - "$@" <<'PY'
import re, sys
bad = []
# image refs from Dockerfile `FROM x` and workflow/compose `image: x`
pat = re.compile(r'^\s*(?:FROM\s+|image:\s*["\']?)([^\s"\']+)', re.IGNORECASE)
for path in sys.argv[1:]:
    for i, line in enumerate(open(path, encoding="utf-8", errors="replace"), 1):
        m = pat.match(line)
        if not m:
            continue
        ref = m.group(1).strip()
        low = ref.lower()
        if low in ("scratch",):
            continue
        # bare single token with no registry path and no tag = local build stage -> ok
        if "/" not in ref and ":" not in ref and "." not in ref and "@" not in ref:
            continue
        if "@sha256:" in ref:
            continue  # digest-pinned -> ok
        bad.append(f"{path}:{i} unpinned image '{ref}' (use @sha256:<digest>)")
if bad:
    for b in bad:
        sys.stderr.write("IMAGE_UNPINNED " + b + "\n")
    raise SystemExit(2)
print("IMAGE_PIN_OK all images digest-pinned")
PY
    ;;
  sign)
    F="${1:-}"; KEY="${2:-}"
    command -v openssl >/dev/null 2>&1 || { echo "OPENSSL_UNAVAILABLE" >&2; exit 3; }
    [[ -f "$F" && -f "$KEY" ]] || { echo "usage: supply-chain-integrity.sh sign <file> <priv-key>" >&2; exit 64; }
    openssl dgst -sha256 -sign "$KEY" -out "$F.sig" "$F" 2>/dev/null \
      && { echo "WORKFLOW_SIGNED file=$F"; exit 0; }
    echo "WORKFLOW_SIGN_FAILED file=$F" >&2; exit 2
    ;;
  verify)
    F="${1:-}"; KEY="${2:-}"
    command -v openssl >/dev/null 2>&1 || { echo "OPENSSL_UNAVAILABLE" >&2; exit 3; }
    [[ -f "$F" ]] || { echo "WORKFLOW_MISSING file=$F" >&2; exit 3; }
    [[ -f "$KEY" ]] || { echo "WORKFLOW_PUBKEY_MISSING key=$KEY" >&2; exit 3; }
    [[ -f "$F.sig" ]] || { echo "WORKFLOW_UNSIGNED file=$F — refusing (fail-closed)" >&2; exit 3; }
    if openssl dgst -sha256 -verify "$KEY" -signature "$F.sig" "$F" >/dev/null 2>&1; then
      echo "WORKFLOW_VERIFIED file=$F"; exit 0
    fi
    echo "WORKFLOW_INVALID file=$F — tampered or forged" >&2; exit 2
    ;;
  *)
    echo "Usage: supply-chain-integrity.sh {image-pin <file>...|sign <file> <priv>|verify <file> <pub>}" >&2
    exit 64
    ;;
esac