import { randomBytes } from 'node:crypto';

/**
 * UUIDv7 — 48-bit Unix-ms timestamp in the high bits, 74 random bits below.
 *
 * Time-ordered, monotonic enough for our needs (idempotency keys + Stream IDs).
 * No dependency on the `uuid` package — Phase 0 keeps the foundation
 * tree-shakeable for the Python side (which uses its own implementation).
 *
 * Reference: RFC 9562 §5.7.
 */
export function uuidv7(now: number = Date.now()): string {
  const ts = BigInt(now); // milliseconds since epoch
  const bytes = randomBytes(16);

  // 48-bit timestamp (big-endian) in bytes 0..5
  bytes[0] = Number((ts >> 40n) & 0xffn);
  bytes[1] = Number((ts >> 32n) & 0xffn);
  bytes[2] = Number((ts >> 24n) & 0xffn);
  bytes[3] = Number((ts >> 16n) & 0xffn);
  bytes[4] = Number((ts >> 8n) & 0xffn);
  bytes[5] = Number(ts & 0xffn);

  // Version 7 in the high nibble of byte 6
  bytes[6] = (bytes[6]! & 0x0f) | 0x70;
  // RFC 4122 variant (10xx) in the high bits of byte 8
  bytes[8] = (bytes[8]! & 0x3f) | 0x80;

  const hex = Buffer.from(bytes).toString('hex');
  return [
    hex.slice(0, 8),
    hex.slice(8, 12),
    hex.slice(12, 16),
    hex.slice(16, 20),
    hex.slice(20, 32),
  ].join('-');
}

const UUID_V7_RE =
  /^[0-9a-f]{8}-[0-9a-f]{4}-7[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/i;

export function isUuidV7(value: string): boolean {
  return UUID_V7_RE.test(value);
}