/**
 * Utility functions for generating and validating room codes.
 *
 * Room codes are 6 uppercase ASCII letters (A-Z). They are generated from a
 * combination of the current timestamp and a random component so that codes
 * are effectively unique without requiring a server round-trip.
 */

const ROOM_CODE_LENGTH = 6;
const ROOM_CODE_CHARS = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
const ROOM_CODE_REGEX = /^[A-Z]{6}$/;

/**
 * Generates a 6-character uppercase room code.
 *
 * The code is derived from `Date.now()` combined with `Math.random()` so that
 * two codes generated at different times (or by different clients at the same
 * millisecond) are extremely unlikely to collide.
 */
export function generateRoomCode(): string {
  const seed = Date.now() + Math.floor(Math.random() * 1_000_000);
  let code = "";
  let remaining = seed;
  for (let i = 0; i < ROOM_CODE_LENGTH; i++) {
    // Mix in additional randomness per character to avoid sequential patterns
    const idx =
      (remaining + Math.floor(Math.random() * ROOM_CODE_CHARS.length)) %
      ROOM_CODE_CHARS.length;
    code += ROOM_CODE_CHARS[idx];
    remaining = Math.floor(remaining / ROOM_CODE_CHARS.length) + Date.now();
  }
  return code;
}

/**
 * Returns true when `code` is a syntactically valid room code (exactly 6
 * uppercase ASCII letters).
 */
export function isValidRoomCode(code: string): boolean {
  return ROOM_CODE_REGEX.test(code);
}