malice

export type CodeSegment =

  | { kind: 'text'; text: string }

  | { kind: 'inline'; text: string }

  | { kind: 'block'; text: string; lang: string | null };

const FENCE = /```([^\s`]*)[^\S\n]*\n?([\s\S]*?)\n?```/g;

const INLINE = /`([^`\n]+)`/g;

function splitInline(text: string, out: CodeSegment[]): void {

  let last = 0;

  for (const m of text.matchAll(INLINE)) {

    if (m.index > last) out.push({ kind: 'text', text: text.slice(last, m.index) });

    out.push({ kind: 'inline', text: m[1] });

    last = m.index + m[0].length;

  }

  if (last < text.length) out.push({ kind: 'text', text: text.slice(last) });

}

export function parseCode(text: string): CodeSegment[] {

  const out: CodeSegment[] = [];

  if (!text.includes('`')) {

    if (text) out.push({ kind: 'text', text });

    return out;

  }

  let last = 0;

  for (const m of text.matchAll(FENCE)) {

    splitInline(text.slice(last, m.index), out);

    out.push({ kind: 'block', text: m[2], lang: m[1] || null });

    last = m.index + m[0].length;

    if (text[last] === '\n') last += 1;

  }

  splitInline(text.slice(last), out);

  return out;

}

export function hasCode(segments: CodeSegment[]): boolean {

  return segments.some((s) => s.kind !== 'text');

}

function escapeHtml(text: string): string {

  return text.replace(/&/g, '&amp;').replace(/</g, '&lt;').replace(/>/g, '&gt;').replace(/"/g, '&quot;');

}

/** Matrix `formatted_body` for a plain body, or null when it has no code to format. */

export function codeToHtml(body: string): string | null {

  const segments = parseCode(body);

  if (!hasCode(segments)) return null;

  return segments

    .map((s) => {

      if (s.kind === 'inline') return `<code>${escapeHtml(s.text)}</code>`;

      if (s.kind === 'block') {

        const cls = s.lang ? ` class="language-${escapeHtml(s.lang)}"` : '';

        return `<pre><code${cls}>${escapeHtml(s.text)}</code></pre>`;

      }

      return escapeHtml(s.text).replace(/\n/g, '<br>');

    })

    .join('');

}