import type { LanguageModel } from "ai";
import { generateText } from "ai";

const CRON_RE = /(?:^|\s)((?:[\d*/,-]+\s+){4,5}[\d*/,-]+)(?:\s|$)/;

export function extractCron(raw: string): string {
  const cleaned = raw.replace(/`/g, "").trim();
  const match = cleaned.match(CRON_RE);
  if (match) return match[1]!.trim();
  const firstLine = cleaned.split("\n")[0]!.trim();
  if (/^[\d*/,\s-]+$/.test(firstLine)) return firstLine;
  return cleaned;
}

const CRON_SYSTEM_PROMPT =
  "Convert the following natural-language timing description to a cron expression. Reply with ONLY the cron expression, nothing else. No explanation, no markdown, no backticks. Use 5-field format (minute hour day-of-month month day-of-week).";

export async function translateToCron(model: LanguageModel, timing: string): Promise<string> {
  const { text } = await generateText({
    model,
    system: CRON_SYSTEM_PROMPT,
    prompt: timing,
  });
  if (!text?.trim()) throw new Error("LLM returned empty cron expression");
  return extractCron(text);
}