#!/usr/bin/env node
/**
 * render_math.js — Batch LaTeX-math renderer for the IHUFT MkDocs build.
 *
 * Reads a JSON array of math expressions from stdin and writes a JSON array
 * of rendered HTML strings to stdout.  Each input item has the shape:
 *
 *     { "tex": "<LaTeX source>", "display": <bool> }
 *
 * Each output item has the shape:
 *
 *     { "ok": true,  "html": "<rendered HTML>" }      // success
 *     { "ok": false, "error": "<KaTeX error msg>" }   // failure
 *
 * Invoked by hooks/math_prerender.py.  All math in a page is rendered in a
 * single subprocess call so that the per-page overhead of spawning Node is
 * amortised across all equations on the page.
 *
 * KaTeX produces both an HTML representation (for visual rendering) and an
 * MathML representation that includes the original LaTeX source in an
 * `<annotation encoding="application/x-tex">` element.  This means the LaTeX
 * source travels with the rendered math and can be recovered by users for
 * copy-and-paste, without any extra plumbing.
 */

const fs = require('fs');
const path = require('path');

// Resolve KaTeX from the local node_tools tree regardless of cwd.
const KATEX_PATH = path.resolve(__dirname, '..', 'node_tools', 'node_modules', 'katex');
const katex = require(KATEX_PATH);

// Common macros the IHUFT proposal relies on but that KaTeX does not bundle
// by default.  Extend this object as new macros appear in the source.
const MACROS = {
    // None at present.  KaTeX already supports \tag, \boxed, \aligned,
    // \begin{aligned}, \operatorname, \mathrm, \mathfrak, \mathcal,
    // \mathbb, \mathbf, \longleftrightarrow, \longrightarrow, \Vert,
    // \hookrightarrow, \blacksquare, etc., out of the box.
};

function renderItem(item) {
    try {
        const html = katex.renderToString(item.tex, {
            displayMode: !!item.display,
            output: 'htmlAndMathml',
            throwOnError: false,
            strict: 'ignore',
            trust: true,
            macros: MACROS,
        });
        return { ok: true, html: html };
    } catch (err) {
        return { ok: false, error: String(err && err.message || err) };
    }
}

function main() {
    let raw;
    try {
        raw = fs.readFileSync(0, 'utf-8');
    } catch (err) {
        console.error('render_math.js: failed to read stdin:', err.message);
        process.exit(2);
    }

    let items;
    try {
        items = JSON.parse(raw);
    } catch (err) {
        console.error('render_math.js: invalid JSON on stdin:', err.message);
        process.exit(2);
    }

    if (!Array.isArray(items)) {
        console.error('render_math.js: expected a JSON array of math items');
        process.exit(2);
    }

    const results = items.map(renderItem);
    process.stdout.write(JSON.stringify(results));
}

main();