// Тонкий клиент Bot API на fetch. URL содержит токен, поэтому ни URL, ни исходные
// ошибки fetch наружу не отдаём: тексты TelegramError собираются только из метода и ответа API.

export type TelegramErrorKind = 'retryable' | 'config';

export class TelegramError extends Error {
  constructor(
    message: string,
    readonly kind: TelegramErrorKind,
    /** HTTP-код ответа API; нет у сетевых ошибок и таймаута */
    readonly code?: number,
    readonly retryAfterSec?: number,
  ) {
    super(message);
    this.name = 'TelegramError';
  }
}

export type FetchLike = (url: string, init: RequestInit) => Promise<Response>;

export type TgUser = { id: number; is_bot: boolean; first_name: string; username?: string };
export type TgChat = { id: number; type: 'private' | 'group' | 'supergroup' | 'channel'; title?: string; is_forum?: boolean };
export type TgDocument = { file_id: string; file_name?: string; file_size?: number };
export type TgMessage = {
  message_id: number;
  message_thread_id?: number;
  from?: TgUser;
  chat: TgChat;
  text?: string;
  document?: TgDocument;
};
export type TgCallbackQuery = { id: string; from: TgUser; message?: TgMessage; data?: string };
export type TgUpdate = {
  update_id: number;
  message?: TgMessage;
  callback_query?: TgCallbackQuery;
  my_chat_member?: { chat: TgChat; from: TgUser };
};
export type TgChatMember = { status: string; can_manage_topics?: boolean };
export type InlineKeyboard = { inline_keyboard: { text: string; callback_data: string }[][] };

export type SendMessageParams = {
  chat_id: number;
  text: string;
  message_thread_id?: number;
  parse_mode?: 'HTML';
  reply_markup?: InlineKeyboard;
  disable_web_page_preview?: boolean;
};

export type TelegramClient = ReturnType<typeof createTelegramClient>;

// С VPS в РФ api.telegram.org недоступен — ходим через ретранслятор (TELEGRAM_API_BASE, см. deploy/tg-relay).
export const DEFAULT_API_BASE = 'https://api.telegram.org';

export function createTelegramClient({
  token,
  apiBase = DEFAULT_API_BASE,
  fetch = globalThis.fetch,
  timeoutMs = 5000,
}: {
  token: string;
  apiBase?: string;
  fetch?: FetchLike;
  timeoutMs?: number;
}) {
  async function request(method: string, url: string, init: RequestInit, timeout: number, signal?: AbortSignal) {
    const timeoutSignal = AbortSignal.timeout(timeout);
    try {
      return await fetch(url, { ...init, signal: signal ? AbortSignal.any([signal, timeoutSignal]) : timeoutSignal });
    } catch (err) {
      if (signal?.aborted) throw new TelegramError(`${method}: отменено`, 'retryable');
      const reason = timeoutSignal.aborted ? 'таймаут' : `сеть (${err instanceof Error ? err.name : 'unknown'})`;
      throw new TelegramError(`${method}: ${reason}`, 'retryable');
    }
  }

  async function call<T>(
    method: string,
    params: Record<string, unknown> | FormData = {},
    opts: { timeoutMs?: number; signal?: AbortSignal } = {},
  ): Promise<T> {
    const init: RequestInit =
      params instanceof FormData
        ? { method: 'POST', body: params }
        : { method: 'POST', headers: { 'content-type': 'application/json' }, body: JSON.stringify(params) };
    const res = await request(method, `${apiBase}/bot${token}/${method}`, init, opts.timeoutMs ?? timeoutMs, opts.signal);

    let body: { ok?: boolean; result?: T; description?: string; parameters?: { retry_after?: number } };
    try {
      body = (await res.json()) as typeof body;
    } catch {
      body = {};
    }
    if (res.ok && body.ok) return body.result as T;

    const description = (body.description ?? res.statusText).replaceAll(token, '***');
    const message = `${method}: ${res.status} ${description}`;
    if (res.status === 429) {
      throw new TelegramError(message, 'retryable', 429, body.parameters?.retry_after ?? 1);
    }
    if (res.status >= 500) throw new TelegramError(message, 'retryable', res.status);
    // 400/401/403/404/409: дело в настройке (чат, тема, права, токен) — повтор сам не поможет.
    throw new TelegramError(message, 'config', res.status);
  }

  return {
    call,
    getMe: () => call<TgUser>('getMe'),
    sendMessage: (params: SendMessageParams) => call<TgMessage>('sendMessage', params),
    sendDocument(params: {
      chat_id: number;
      file: { name: string; data: Uint8Array };
      caption?: string;
      message_thread_id?: number;
    }) {
      const form = new FormData();
      form.set('chat_id', String(params.chat_id));
      if (params.message_thread_id !== undefined) form.set('message_thread_id', String(params.message_thread_id));
      if (params.caption) form.set('caption', params.caption);
      form.set('document', new Blob([new Uint8Array(params.file.data)]), params.file.name);
      // Файл бэкапа может идти дольше обычного сообщения.
      return call<TgMessage>('sendDocument', form, { timeoutMs: Math.max(timeoutMs, 60_000) });
    },
    getUpdates: (
      params: { offset?: number; timeout: number; allowed_updates: string[] },
      signal?: AbortSignal,
    ) => call<TgUpdate[]>('getUpdates', params, { timeoutMs: (params.timeout + 10) * 1000, signal }),
    createForumTopic: (chat_id: number, name: string) =>
      call<{ message_thread_id: number; name: string }>('createForumTopic', { chat_id, name }),
    getChat: (chat_id: number) => call<TgChat>('getChat', { chat_id }),
    getChatMember: (chat_id: number, user_id: number) => call<TgChatMember>('getChatMember', { chat_id, user_id }),
    answerCallbackQuery: (callback_query_id: string, text?: string) =>
      call<boolean>('answerCallbackQuery', { callback_query_id, text }),
    editMessageText: (params: { chat_id: number; message_id: number; text: string; reply_markup?: InlineKeyboard }) =>
      call<TgMessage | boolean>('editMessageText', params),
    getFile: (file_id: string) => call<{ file_id: string; file_path?: string; file_size?: number }>('getFile', { file_id }),
    async downloadFile(filePath: string, maxBytes: number): Promise<Uint8Array> {
      const res = await request('downloadFile', `${apiBase}/file/bot${token}/${filePath}`, {}, 60_000);
      if (!res.ok) throw new TelegramError(`downloadFile: ${res.status}`, res.status >= 500 ? 'retryable' : 'config', res.status);
      const data = new Uint8Array(await res.arrayBuffer());
      if (data.byteLength > maxBytes) throw new TelegramError('downloadFile: файл больше лимита', 'config');
      return data;
    },
  };
}