const EXECUTION_ID_PATTERN = /^[A-Za-z0-9][A-Za-z0-9_-]{0,199}$/;
const MAX_EXECUTION_ID_LENGTH = 200;

interface BuildExecutionIdOptions {
  now?: Date;
  random?: number;
}

export const validateExecutionId = (
  value: unknown,
  label = "executionId",
): string => {
  if (typeof value !== "string" || !EXECUTION_ID_PATTERN.test(value)) {
    throw new Error(
      `${label} must match the canonical execution ID rule: `
      + "1-200 letters, numbers, underscores, or hyphens, beginning with a letter or number",
    );
  }
  return value;
};

export const buildExecutionId = (
  targetId: string,
  options: BuildExecutionIdOptions = {},
): string => {
  const timestamp = (options.now || new Date()).toISOString().replace(/\D/g, "");
  const random = options.random ?? Math.random();
  const nonce = random.toString(36).slice(2).padEnd(8, "0").slice(0, 8);
  const prefix = `exec-${timestamp}-${nonce}`;
  const targetBudget = MAX_EXECUTION_ID_LENGTH - prefix.length - 1;
  const targetSlug = targetId
    .replace(/[^A-Za-z0-9_-]/g, "-")
    .slice(0, targetBudget);
  return validateExecutionId(`${prefix}-${targetSlug}`);
};