import katex from "katex";

/**
 * Renders $…$ / $$…$$ / \( \) / \[ \] segments of a plain-text field (abstracts, findings) to KaTeX HTML.
 * Text outside math is HTML-escaped. Used on the server only; output is trusted markup built from escaped input.
 */
export function renderMath(text: string): { html: string; hasMath: boolean } {
  const esc = (s: string) => s.replace(/&/g, "&amp;").replace(/</g, "&lt;").replace(/>/g, "&gt;");
  const re = /\$\$([\s\S]+?)\$\$|\\\[([\s\S]+?)\\\]|\\\(([\s\S]+?)\\\)|\$([^$\n]+?)\$/g;
  let out = "";
  let last = 0;
  let hasMath = false;
  for (const m of text.matchAll(re)) {
    const idx = m.index ?? 0;
    out += esc(text.slice(last, idx));
    const display = m[1] !== undefined || m[2] !== undefined;
    const src = (m[1] ?? m[2] ?? m[3] ?? m[4] ?? "").trim();
    try {
      const html = katex.renderToString(src, {
        displayMode: display,
        throwOnError: false,
        output: "htmlAndMathml",
        strict: "ignore",
      });
      out += display
        ? `<span class="math-display">${html}</span>`
        : `<span class="math-inline">${html}</span>`;
      hasMath = true;
    } catch {
      out += esc(m[0]);
    }
    last = idx + m[0].length;
  }
  out += esc(text.slice(last));
  return { html: out, hasMath };
}