import { escapeHtml, raw, type Raw } from './html.ts';
import type { PlatformId } from '../types.ts';

/** Where an @mention or #hashtag points on each platform. */
const PROFILE_BASE: Record<PlatformId, string> = {
  x: 'https://x.com/',
  threads: 'https://www.threads.com/@',
  instagram: 'https://www.instagram.com/',
  tiktok: 'https://www.tiktok.com/@',
  bluesky: 'https://bsky.app/profile/',
  reddit: 'https://www.reddit.com/user/',
};

const TAG_BASE: Partial<Record<PlatformId, string>> = {
  x: 'https://x.com/hashtag/',
  instagram: 'https://www.instagram.com/explore/tags/',
  tiktok: 'https://www.tiktok.com/tag/',
};

const TOKEN = /(https?:\/\/[^\s<]+)|(^|\s)(@[\w.-]+)|(^|\s)(#[\w]+)/g;

function link(href: string, label: string): string {
  return `<a href="${escapeHtml(href)}" rel="noopener noreferrer nofollow" target="_blank">${escapeHtml(label)}</a>`;
}

/**
 * Turn post text into markup: escape everything, then make links, mentions
 * and hashtags clickable back to the platform they came from.
 */
export function linkify(text: string, platform: PlatformId): Raw {
  let out = '';
  let cursor = 0;

  for (const match of text.matchAll(TOKEN)) {
    const index = match.index;
    out += escapeHtml(text.slice(cursor, index));

    const [whole, url, mentionLead, mention, tagLead, tag] = match;
    if (url) {
      out += link(url, url.replace(/^https?:\/\/(www\.)?/, ''));
    } else if (mention) {
      out += escapeHtml(mentionLead ?? '') + link(PROFILE_BASE[platform] + mention.slice(1), mention);
    } else if (tag) {
      const base = TAG_BASE[platform];
      out += escapeHtml(tagLead ?? '') + (base ? link(base + tag.slice(1), tag) : escapeHtml(tag));
    } else {
      out += escapeHtml(whole);
    }

    cursor = index + whole.length;
  }

  out += escapeHtml(text.slice(cursor));
  return raw(out.replace(/\n/g, '<br>'));
}