leftpad.js

#!/usr/bin/env node
/**
 * Usage:
 *   export OPENAI_API_KEY="..."
 *   node leftpad-via-chatgpt.js "hello" 12 "*"
 *
 * Args:
 *   1) input string (default: "hello")
 *   2) target width  (default: 10)
 *   3) pad char      (default: " ")
 */

const input = process.argv[2] ?? "hello";
const width = Number(process.argv[3] ?? 10);
const padChar = (process.argv[4] ?? " ").toString();

if (!Number.isFinite(width) || width < 0) {
  console.error("Width must be a non-negative number.");
  process.exit(1);
}
if (padChar.length === 0) {
  console.error("Pad char must be at least 1 character.");
  process.exit(1);
}

const apiKey = process.env.OPENAI_API_KEY;
if (!apiKey) {
  console.error("Missing OPENAI_API_KEY env var.");
  process.exit(1);
}

async function main() {
  const prompt = [
    "You are a helpful coding agent.",
    "Left-pad the given string to the target width using the pad character.",
    "Return ONLY the final padded string. No quotes. No explanation.",
    `input=${JSON.stringify(input)}`,
    `width=${width}`,
    `padChar=${JSON.stringify(padChar)}`,
  ].join("\n");

  const res = await fetch("https://api.openai.com/v1/chat/completions", {
    method: "POST",
    headers: {
      "Authorization": `Bearer ${apiKey}`,
      "Content-Type": "application/json",
    },
    body: JSON.stringify({
      model: "gpt-4o-mini",
      messages: [{ role: "user", content: prompt }],
      temperature: 0,
    }),
  });

  if (!res.ok) {
    const text = await res.text();
    throw new Error(`HTTP ${res.status}: ${text}`);
  }

  const data = await res.json();
  const out = data.choices?.[0]?.message?.content ?? "";
  process.stdout.write(out.trimEnd() + "\n");
}

main().catch((err) => {
  console.error(err?.stack || String(err));
  process.exit(1);
});