import type { ReactNode } from 'react';
import type { Person } from './types';

/** Room-wide mention tokens, always offered alongside members. */
export const SPECIAL_MENTIONS = ['channel', 'here'];

function esc(s: string): string {
  return s.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
}

/** The @token currently being typed at the end of the draft (caret-at-end), or null. */
export function trailingMentionQuery(draft: string): string | null {
  const m = draft.match(/(?:^|\s)@([\w]*)$/);
  return m ? (m[1] ?? '') : null;
}

/** Replace the trailing @query with `@insert ` (keeping the leading boundary). */
export function insertMention(draft: string, insert: string): string {
  return draft.replace(/(^|\s)@([\w]*)$/, (_full, lead: string) => `${lead}@${insert} `);
}

/** Resolve the opaque mention userId list from the final text + known members. */
export function resolveMentions(text: string, members: Person[]): string[] {
  const ids = new Set<string>();
  for (const p of members) if (text.includes(`@${p.name}`)) ids.add(p.id);
  if (/@channel\b/.test(text) || /@here\b/.test(text)) for (const p of members) ids.add(p.id);
  return [...ids];
}

/** Render text with @mentions (member names + @channel/@here) wrapped for highlighting. */
export function highlightMentions(text: string, memberNames: string[]): ReactNode[] {
  // Longest-first so "@Sofia Ramirez" wins over a bare "@Sofia".
  const names = [...new Set([...memberNames, ...SPECIAL_MENTIONS])].filter(Boolean).sort((a, b) => b.length - a.length);
  if (names.length === 0) return [text];
  const re = new RegExp(`@(${names.map(esc).join('|')})`, 'g');
  const out: ReactNode[] = [];
  let last = 0;
  let key = 0;
  let m: RegExpExecArray | null;
  while ((m = re.exec(text)) !== null) {
    if (m.index > last) out.push(text.slice(last, m.index));
    out.push(
      <span key={`m${key++}`} className="miu-mention">
        {m[0]}
      </span>,
    );
    last = m.index + m[0].length;
  }
  if (last < text.length) out.push(text.slice(last));
  return out.length > 0 ? out : [text];
}