import MathJax from "mathjax";
import process from "node:process";

const MAX_MESSAGE_LENGTH = 500;

function errorMessage(error) {
  const message = error && typeof error.message === "string" ? error.message : String(error);
  return message.slice(0, MAX_MESSAGE_LENGTH);
}

function renderError(serialized) {
  const match = serialized.match(/data-mjx-error="([^"]+)"/);
  return match ? match[1].slice(0, MAX_MESSAGE_LENGTH) : "";
}

async function readStdin() {
  let input = "";
  for await (const chunk of process.stdin) {
    input += chunk;
  }
  return input;
}

function parsePayload(input) {
  const payload = JSON.parse(input || "{}");
  if (!payload || !Array.isArray(payload.expressions)) {
    throw new Error("Input JSON must contain an expressions array.");
  }
  return payload;
}

async function checkExpression(expression) {
  const index = Number(expression.index);
  const body = String(expression.body ?? "");
  const display = Boolean(expression.display);

  try {
    const svg = await MathJax.tex2svgPromise(body, { display });
    const serialized = MathJax.startup.adaptor.serializeXML(svg);
    const message = renderError(serialized);
    if (message) {
      return { index, ok: false, message };
    }
    return { index, ok: true };
  } catch (error) {
    return { index, ok: false, message: errorMessage(error) };
  }
}

async function main() {
  await MathJax.init({
    loader: { load: ["input/tex", "output/svg"] },
  });

  if (process.argv.includes("--health")) {
    await MathJax.tex2svgPromise("x", { display: false });
    process.stdout.write(`${JSON.stringify({ ok: true })}\n`);
    return;
  }

  const payload = parsePayload(await readStdin());
  const results = [];
  for (const expression of payload.expressions) {
    results.push(await checkExpression(expression));
  }
  process.stdout.write(`${JSON.stringify({ results })}\n`);
}

main().catch((error) => {
  process.stderr.write(`${errorMessage(error)}\n`);
  process.exitCode = 1;
});