import { parseInlineMD } from '../plugins/markdown';
import { sanitizeText } from './sanitize';

/**
 * Room topic markdown → `m.room.topic` content (#262).
 *
 * Uses the composer's inline markdown parser (the same rules as messages: links,
 * bare URLs and `"` are handled), with one topic-specific guard: an `_` between
 * two letters/digits is literal, as in CommonMark. Topics are full of
 * `#room_alias:server`, `@user_name:server` and snake_case paths, which the
 * shared parser would otherwise turn into italics and, worse, drop from the
 * plain `topic` that every other client shows.
 */

// Spans the guard must not touch: inline code, link targets, bare URLs.
const PROTECTED = /(`[^`\n]*`|\]\([^)\n]*\)|https?:\/\/[^\s<>"]+)/;
const INTRAWORD_UNDERSCORES = /(?<=[\p{L}\p{N}])_+(?=[\p{L}\p{N}])/gu;

const escapeIntrawordUnderscores = (line: string): string =>
  line
    .split(PROTECTED)
    .map((part, i) =>
      // split() with one capture group puts the protected spans at odd indexes.
      i % 2 === 1 ? part : part.replace(INTRAWORD_UNDERSCORES, (m) => m.replace(/_/g, '\\_')),
    )
    .join('');

const ENTITIES: Record<string, string> = {
  '&amp;': '&',
  '&lt;': '<',
  '&gt;': '>',
  '&quot;': '"',
  '&#39;': "'",
};
const decodeEntities = (s: string): string =>
  s.replace(/&(?:amp|lt|gt|quot|#39);/g, (e) => ENTITIES[e]);

/** Readable plain text for `topic`: markers dropped, links kept as "text (url)". */
const htmlToPlain = (html: string): string =>
  decodeEntities(
    html
      .replace(/<a\b[^>]*\bhref="([^"]*)"[^>]*>(.*?)<\/a>/g, (_m, href: string, label: string) => {
        const text = label.replace(/<[^>]+>/g, '');
        return text === href ? href : `${text} (${href})`;
      })
      .replace(/<br>/g, '\n')
      .replace(/<[^>]+>/g, ''),
  );

export type TopicContent =
  | { topic: string }
  | { topic: string; format: 'org.matrix.custom.html'; formatted_body: string };

export function buildTopicContent(text: string): TopicContent {
  const lines = text.split('\n');
  const html = lines
    .map((line) => parseInlineMD(sanitizeText(escapeIntrawordUnderscores(line))))
    .join('<br>');
  const plainHtml = lines.map(sanitizeText).join('<br>');
  // No markdown at all: send the text as typed, without a formatted body.
  if (html === plainHtml) return { topic: text };
  return { topic: htmlToPlain(html), format: 'org.matrix.custom.html', formatted_body: html };
}