malice

import { Marked, type Token, type Tokens } from 'marked';

import type { Mention } from './mentions';

function escapeHtml(text: string): string {

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

}

function escapeRegExp(text: string): string {

  return text.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');

}

function mentionLinker(mentions: Mention[]): (escaped: string) => string {

  const byText = new Map(mentions.filter((m) => m.text).map((m) => [escapeHtml(m.text), m.user_id]));

  if (byText.size === 0) return (escaped) => escaped;

  const names = [...byText.keys()].sort((a, b) => b.length - a.length);

  const pattern = new RegExp(names.map(escapeRegExp).join('|'), 'g');

  return (escaped) =>

    escaped.replace(pattern, (name) => `<a href="https://matrix.to/#/${escapeHtml(byText.get(name)!)}">${name}</a>`);

}

function textToHtml(text: string, link: (escaped: string) => string): string {

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

}

const PLAIN_INLINE = new Set(['text', 'escape', 'br']);

function isPlain(tokens: Token[]): boolean {

  const blocks = tokens.filter((t) => t.type !== 'space');

  if (blocks.length !== 1 || blocks[0].type !== 'paragraph') return blocks.length === 0;

  return (blocks[0] as Tokens.Paragraph).tokens.every((t) => PLAIN_INLINE.has(t.type) && !('tokens' in t && t.tokens));

}

function markdownToHtml(body: string, link: (escaped: string) => string): string | null {

  const marked = new Marked({ gfm: true, breaks: true });

  marked.use({

    renderer: {

      text(token) {

        if ('tokens' in token && token.tokens) return false;

        return link('escaped' in token && token.escaped ? token.text : escapeHtml(token.text));

      },

      html(token) {

        return escapeHtml(token.text);

      },

      image(token) {

        return `<a href="${escapeHtml(token.href)}">${escapeHtml(token.text || token.href)}</a>`;

      },

      checkbox(token) {

        return token.checked ? '[x] ' : '[ ] ';

      }

    }

  });

  const tokens = marked.lexer(body);

  if (isPlain(tokens)) return null;

  return marked.parser(tokens).trim();

}

/** Matrix `formatted_body` for a composed message, or null when plain text says it all. */

export function formatBody(body: string, mentions: Mention[], markdown: boolean): string | null {

  const link = mentionLinker(mentions);

  const html = markdown ? markdownToHtml(body, link) : null;

  if (html !== null) return html;

  const plain = textToHtml(body, link);

  return plain === escapeHtml(body).replace(/\n/g, '<br>') ? null : plain;

}

export function insideOpenFence(text: string, caret: number): boolean {

  return (text.slice(0, caret).match(/^\s*```/gm)?.length ?? 0) % 2 === 1;

}