telegrambot/src/telegram.ts

import { z } from 'zod'

/** Telegram Bot API sendMessage text limit. */
export const TELEGRAM_TEXT_MAX = 4096

export const SendMessageBodySchema = z.object({
  text: z.string().trim().min(1).max(TELEGRAM_TEXT_MAX),
  /** Override default chat from env (group or private). */
  chatId: z.string().trim().min(1).optional(),
  /** Forum topic id; omit to use env default (if any). Pass null to force no topic. */
  messageThreadId: z.number().int().positive().nullable().optional(),
  disableWebPagePreview: z.boolean().optional().default(true),
})

export type SendMessageBody = z.infer<typeof SendMessageBodySchema>

export interface TelegramSendResult {
  ok: true
  messageId: number
}

export class TelegramApiError extends Error {
  constructor(
    readonly status: number,
    readonly detail: string,
  ) {
    super(`Telegram sendMessage failed: status=${status}`)
    this.name = 'TelegramApiError'
  }
}

export async function sendTelegramMessage(input: {
  botToken: string
  chatId: string
  text: string
  messageThreadId?: number
  disableWebPagePreview: boolean
  fetchImpl?: typeof fetch
}): Promise<TelegramSendResult> {
  const fetchImpl = input.fetchImpl ?? fetch
  const payload: Record<string, unknown> = {
    chat_id: input.chatId,
    text: input.text,
    disable_web_page_preview: input.disableWebPagePreview,
  }
  if (input.messageThreadId !== undefined) {
    payload.message_thread_id = input.messageThreadId
  }

  const response = await fetchImpl(
    `https://api.telegram.org/bot${input.botToken}/sendMessage`,
    {
      method: 'POST',
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify(payload),
    },
  )

  if (!response.ok) {
    const detail = await response.text().catch(() => '')
    throw new TelegramApiError(response.status, detail.slice(0, 300))
  }

  const json = (await response.json()) as {
    ok?: boolean
    result?: { message_id?: number }
  }
  const messageId = json.result?.message_id
  if (!json.ok || typeof messageId !== 'number') {
    throw new TelegramApiError(502, 'Unexpected Telegram API response')
  }

  return { ok: true, messageId }
}