// Telegram Mini App deep-link "start parameters", mirroring the connector's Go
// scheme (platform/telegram/internal/deeplink): a one-character kind prefix plus a
// value —
//   g<game uuid>        open that game
//   i<invitation uuid>  open that invitation
//   f<6-digit code>     redeem that friend code
// An empty or unrecognised parameter opens the lobby.

export type DeepLink =
  | { kind: 'lobby' }
  | { kind: 'game'; id: string }
  | { kind: 'invitation'; id: string }
  | { kind: 'friendCode'; code: string };

/** parseStartParam classifies a Telegram start parameter into a routing target. */
export function parseStartParam(param: string | undefined | null): DeepLink {
  if (!param) return { kind: 'lobby' };
  const value = param.slice(1);
  if (!value) return { kind: 'lobby' };
  switch (param[0]) {
    case 'g':
      return { kind: 'game', id: value };
    case 'i':
      return { kind: 'invitation', id: value };
    case 'f':
      return { kind: 'friendCode', code: value };
    default:
      return { kind: 'lobby' };
  }
}

/** gameParam builds the start parameter that opens a game. */
export const gameParam = (id: string): string => 'g' + id;
/** invitationParam builds the start parameter that opens an invitation. */
export const invitationParam = (id: string): string => 'i' + id;
/** friendCodeParam builds the start parameter that redeems a friend code. */
export const friendCodeParam = (code: string): string => 'f' + code;

function envVar(name: string): string | undefined {
  return (import.meta.env as Record<string, string | undefined>)[name];
}

/**
 * telegramBase returns the Mini App link base (e.g. https://t.me/<bot>/<app>) for a
 * bot language: VITE_TELEGRAM_LINK_EN / _RU when lang is en/ru, else the
 * language-agnostic VITE_TELEGRAM_LINK. Returns null when none is configured, so a
 * shared link points at the same bot the player signed in through.
 */
function telegramBase(lang: string): string | null {
  const byLang =
    lang === 'ru' ? envVar('VITE_TELEGRAM_LINK_RU') : lang === 'en' ? envVar('VITE_TELEGRAM_LINK_EN') : undefined;
  return byLang || envVar('VITE_TELEGRAM_LINK') || null;
}

/**
 * botUsername extracts the bot's @username (without the @) from the configured Mini App
 * link for a bot language: the first path segment of https://t.me/<bot>/<app>. Returns
 * null when no base is configured or the link carries no path, so callers can fall back
 * when they cannot point at a specific bot.
 */
export function botUsername(lang = ''): string | null {
  const base = telegramBase(lang);
  if (!base) return null;
  try {
    const seg = new URL(base).pathname.split('/').filter(Boolean)[0];
    return seg || null;
  } catch {
    return null;
  }
}

/**
 * shareLink wraps a deep-link start parameter in a t.me Mini App link for the given
 * bot language (the session's service language). Returns null when no base is
 * configured, so callers can hide the share affordance.
 */
export function shareLink(param: string, lang = ''): string | null {
  const base = telegramBase(lang);
  if (!base) return null;
  const sep = base.includes('?') ? '&' : '?';
  return `${base}${sep}startapp=${encodeURIComponent(param)}`;
}