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

# CASAN H5 — Signed/JWT approval verifier (Approval-identity MVP · C4 / V20).
#
# Problem: high-risk approval used to trust a plain env var (CASAN_APPROVER=bob) —
# anyone who can set the env can "approve". This binds an approval to a REGISTERED
# reviewer's cryptographic identity: the reviewer must SIGN this exact request with
# their private key, AND their role must be authorized for the action class.
#
# The signed assertion is:  casan-approval|v1|<action>|<actor>|<input_sha256>|<approver_id>
# — so a signature for one request/reviewer cannot be replayed for another.
#
# Usage:
#   approval-verify.sh <action> <actor> <input-file> <approver-id> <sig-file>
#   CASAN_APPROVAL_JWT=<rs256-jwt> approval-verify.sh <action> <actor> <input-file> <approver-id> -
# Registry (line format, no yaml dep):
#   reviewer <id> <role> <pubkey-file>
#   action   <action-name|default> <comma,roles>
# Env: CASAN_REVIEWERS_FILE (default governance/reviewers.registry)
#      CASAN_REVIEWERS_DIR  (default governance/reviewers) — base dir for pubkey-file
#      CASAN_APPROVAL_JWT   (optional RS256 IdP token)
#      CASAN_IDP_PUBLIC_KEY (default central-governance/idp-public.pem)
#      CASAN_IDP_JWKS_URL   (optional OIDC JWKS endpoint; overrides public key)
#      CASAN_TRUSTED_TIME / CASAN_TRUSTED_TIME_FILE (SEC-22/ARCH-06: trusted time
#        source for JWT `exp` instead of the manipulable local clock; file
#        unreadable = fail-closed)
# Exit: 0 ok (prints "APPROVAL_OK role=<role>"), 3 deny (reason on stderr), 64 usage.

SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
source "$SCRIPT_DIR/casan-paths.sh"
PROJECT_ROOT="$CASAN_APP_ROOT"
GOV_DIR="$CASAN_GOVERNANCE_ROOT"
REVIEWERS_FILE="${CASAN_REVIEWERS_FILE:-$GOV_DIR/reviewers.registry}"
REVIEWERS_DIR="${CASAN_REVIEWERS_DIR:-$GOV_DIR/reviewers}"

ACTION="${1:-}"; ACTOR="${2:-}"; INPUT_FILE="${3:-}"; APPROVER="${4:-}"; SIG_FILE="${5:-}"
if [[ -z "$ACTION" || -z "$ACTOR" || -z "$INPUT_FILE" || -z "$APPROVER" ]]; then
  echo "Usage: approval-verify.sh <action> <actor> <input-file> <approver-id> <sig-file>" >&2
  exit 64
fi

deny() { echo "APPROVAL_DENIED reason=$1 approver=$APPROVER action=$ACTION" >&2; exit 3; }

# SEC-30 (X-06): one-time-use. A verified approval token (JWT or offline signature)
# is valid for its whole exp window, so it could be REPLAYED. Record a per-token
# nonce (sha256 of the token/signature) and reject any repeat. Active in enforced
# mode or when an explicit nonce ledger is configured (dev default: off).
sha_stdin() {
  if command -v sha256sum >/dev/null 2>&1; then sha256sum | awk '{print $1}'
  else shasum -a 256 | awk '{print $1}'; fi
}
record_nonce_or_deny() {
  local nonce="$1"
  [[ "${CASAN_PROFILE:-}" == "prod" || -n "${CASAN_APPROVAL_NONCE_FILE:-}" ]] || return 0
  local ledger="${CASAN_APPROVAL_NONCE_FILE:-$CASAN_STATE_ROOT/logs/level5/approval-nonces.txt}"
  mkdir -p "$(dirname "$ledger")" 2>/dev/null || true
  if [[ -f "$ledger" ]] && grep -qxF "$nonce" "$ledger" 2>/dev/null; then
    deny "approval_replayed(nonce=${nonce:0:12}…)"
  fi
  printf '%s\n' "$nonce" >> "$ledger" || deny "nonce_ledger_unwritable"
}

[[ -f "$INPUT_FILE" ]] || deny "input_file_missing"
[[ -f "$REVIEWERS_FILE" ]] || deny "reviewer_registry_missing"
command -v openssl >/dev/null 2>&1 || deny "openssl_unavailable"

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

INPUT_SHA="$(hash_file "$INPUT_FILE")"

# Role authorization for this action (fallback to the "default" action policy).
ROLES="$(awk -v a="$ACTION" '$1=="action" && $2==a {print $3; exit}' "$REVIEWERS_FILE")"
[[ -n "$ROLES" ]] || ROLES="$(awk '$1=="action" && $2=="default" {print $3; exit}' "$REVIEWERS_FILE")"

if [[ -n "${CASAN_APPROVAL_JWT:-}" ]]; then
  IDP_PUB="${CASAN_IDP_PUBLIC_KEY:-$GOV_DIR/idp-public.pem}"
  if [[ -n "${CASAN_IDP_JWKS_URL:-}" ]]; then
    IDP_PUB="jwks:${CASAN_IDP_JWKS_URL}"
  else
    [[ -f "$IDP_PUB" ]] || deny "idp_pubkey_missing($IDP_PUB)"
  fi
  JWT_OUT="$(
    python3 - "$CASAN_APPROVAL_JWT" "$IDP_PUB" "$APPROVER" "$ROLES" "$ACTION" "$ACTOR" "$INPUT_SHA" <<'PY'
import base64
import json
import os
import subprocess
import sys
import tempfile
import time
import urllib.request

jwt, pub, approver, roles_csv, action, actor, input_sha = sys.argv[1:8]

def die(reason):
    print(reason, file=sys.stderr)
    sys.exit(3)

def b64u_decode(part):
    try:
        return base64.urlsafe_b64decode(part + "=" * (-len(part) % 4))
    except Exception:
        die("jwt_base64_invalid")

parts = jwt.split(".")
if len(parts) != 3:
    die("jwt_shape_invalid")
header = json.loads(b64u_decode(parts[0]))
claims = json.loads(b64u_decode(parts[1]))
if header.get("alg") != "RS256":
    die("jwt_alg_not_allowed")

# SEC-22 (ARCH-06): do NOT trust the local system clock alone for expiry. When a
# trusted time source is provided (CASAN_TRUSTED_TIME seconds, or
# CASAN_TRUSTED_TIME_FILE containing seconds from a trusted timestamp authority),
# use it; an unreadable/invalid source is fail-closed (deny).
def _trusted_now():
    v = os.environ.get("CASAN_TRUSTED_TIME")
    if v:
        try:
            return int(v)
        except Exception:
            die("trusted_time_invalid")
    f = os.environ.get("CASAN_TRUSTED_TIME_FILE")
    if f:
        try:
            return int(open(f).read().strip())
        except Exception:
            die("trusted_time_file_unreadable")
    return int(time.time())

if int(claims.get("exp", 0)) <= _trusted_now():
    die("jwt_expired")
if claims.get("sub") != approver:
    die("jwt_sub_mismatch")
role = claims.get("role", "")
roles = [r for r in roles_csv.split(",") if r]
if role not in roles:
    die(f"jwt_role_not_authorized(role={role} allowed={roles_csv})")
if claims.get("action") != action:
    die("jwt_action_mismatch")
if claims.get("actor") != actor:
    die("jwt_actor_mismatch")
if claims.get("input_sha256") != input_sha:
    die("jwt_input_hash_mismatch")

sig = b64u_decode(parts[2])
signing_input = ".".join(parts[:2]).encode()

def der_len(n):
    if n < 128:
        return bytes([n])
    raw = n.to_bytes((n.bit_length() + 7) // 8, "big")
    return bytes([0x80 | len(raw)]) + raw

def der_tlv(tag, body):
    return bytes([tag]) + der_len(len(body)) + body

def der_int(n):
    raw = n.to_bytes((n.bit_length() + 7) // 8, "big") or b"\x00"
    if raw[0] & 0x80:
        raw = b"\x00" + raw
    return der_tlv(0x02, raw)

def jwk_to_pem(jwk):
    n = int.from_bytes(b64u_decode(jwk["n"]), "big")
    e = int.from_bytes(b64u_decode(jwk["e"]), "big")
    rsa_pub = der_tlv(0x30, der_int(n) + der_int(e))
    alg_id = der_tlv(
        0x30,
        der_tlv(0x06, b"\x2a\x86\x48\x86\xf7\x0d\x01\x01\x01") + der_tlv(0x05, b""),
    )
    spki = der_tlv(0x30, alg_id + der_tlv(0x03, b"\x00" + rsa_pub))
    b64 = base64.encodebytes(spki).decode().replace("\n", "")
    lines = [b64[i:i+64] for i in range(0, len(b64), 64)]
    return "-----BEGIN PUBLIC KEY-----\n" + "\n".join(lines) + "\n-----END PUBLIC KEY-----\n"

pub_file = pub
with tempfile.TemporaryDirectory() as td:
    sig_path = os.path.join(td, "sig.bin")
    msg_path = os.path.join(td, "msg.txt")
    open(sig_path, "wb").write(sig)
    open(msg_path, "wb").write(signing_input)
    if pub.startswith("jwks:"):
        try:
            jwks = json.loads(urllib.request.urlopen(pub[len("jwks:"):], timeout=5).read().decode())
        except Exception:
            die("jwks_fetch_failed")
        kid = header.get("kid")
        keys = [k for k in jwks.get("keys", []) if k.get("kty") == "RSA" and (not kid or k.get("kid") == kid)]
        if not keys:
            die("jwks_key_not_found")
        pub_file = os.path.join(td, "idp-public.pem")
        open(pub_file, "w", encoding="utf-8").write(jwk_to_pem(keys[0]))
    rc = subprocess.run(
        ["openssl", "dgst", "-sha256", "-verify", pub_file, "-signature", sig_path, msg_path],
        stdout=subprocess.DEVNULL,
        stderr=subprocess.DEVNULL,
    ).returncode
if rc != 0:
    die("jwt_signature_invalid")
print(f"OK role={role}")
PY
  )" || deny "oidc_jwt_invalid(${JWT_OUT:-see_stderr})"
  ROLE="${JWT_OUT#OK role=}"
  record_nonce_or_deny "$(printf '%s' "$CASAN_APPROVAL_JWT" | sha_stdin)"
  echo "APPROVAL_OK mechanism=oidc role=$ROLE approver=$APPROVER action=$ACTION"
  exit 0
fi

[[ -n "$SIG_FILE" && -f "$SIG_FILE" ]] || deny "signature_missing"

# Reviewer lookup (first matching registered reviewer).
REV_LINE="$(awk -v id="$APPROVER" '$1=="reviewer" && $2==id {print $3" "$4; exit}' "$REVIEWERS_FILE")"
[[ -n "$REV_LINE" ]] || deny "approver_not_registered"
ROLE="${REV_LINE%% *}"
PUB_REL="${REV_LINE##* }"

case ",$ROLES," in
  *",$ROLE,"*) : ;;
  *) deny "approver_role_not_authorized(role=$ROLE action=$ACTION allowed=$ROLES)" ;;
esac

# Resolve pubkey path (absolute or relative to reviewers dir).
PUB="$PUB_REL"; [[ "$PUB" = /* ]] || PUB="$REVIEWERS_DIR/$PUB_REL"
[[ -f "$PUB" ]] || deny "approver_pubkey_missing($PUB)"

# Rebuild the exact signed assertion and verify.
MSG="casan-approval|v1|$ACTION|$ACTOR|$INPUT_SHA|$APPROVER"
TMP="$(mktemp)"; trap 'rm -f "$TMP"' EXIT
printf '%s' "$MSG" > "$TMP"
openssl dgst -sha256 -verify "$PUB" -signature "$SIG_FILE" "$TMP" >/dev/null 2>&1 \
  || deny "approval_signature_invalid"

record_nonce_or_deny "$(sha_stdin < "$SIG_FILE")"
echo "APPROVAL_OK role=$ROLE approver=$APPROVER action=$ACTION"
exit 0