nikoksr/notify

package telegram

import (
    "context"
    "fmt"

    tgbotapi "github.com/go-telegram-bot-api/telegram-bot-api"
)

const (
    ModeMarkdown = tgbotapi.ModeMarkdown
    ModeHTML     = tgbotapi.ModeHTML
)

// HTML is the default mode.
//
//nolint:gochecknoglobals // I agree with the linter, won't bother fixing this now, will be fixed in v2.
var parseMode = ModeHTML

// Telegram struct holds necessary data to communicate with the Telegram API.
type Telegram struct {
    client  *tgbotapi.BotAPI
    chatIDs []int64
}

// New returns a new instance of a Telegram notification service.
// For more information about telegram api token:
//
//    -> https://pkg.go.dev/github.com/go-telegram-bot-api/telegram-bot-api#NewBotAPI
func New(apiToken string) (*Telegram, error) {
    client, err := tgbotapi.NewBotAPI(apiToken)
    if err != nil {
        return nil, err
    }

    t := &Telegram{
        client:  client,
        chatIDs: []int64{},
    }

    return t, nil
}

// SetClient set a new custom BotAPI instance.
// For example allowing you to use NewBotAPIWithClient:
//
//    -> https://pkg.go.dev/github.com/go-telegram-bot-api/telegram-bot-api#NewBotAPIWithClient
func (t *Telegram) SetClient(client *tgbotapi.BotAPI) {
    t.client = client
}

// SetParseMode sets the parse mode for the message body.
// For more information about telegram constants:
//
//    -> https://pkg.go.dev/github.com/go-telegram-bot-api/telegram-bot-api#pkg-constants
func (t *Telegram) SetParseMode(mode string) {
    parseMode = mode
}

// AddReceivers takes Telegram chat IDs and adds them to the internal chat ID list. The Send method will send
// a given message to all those chats.
func (t *Telegram) AddReceivers(chatIDs ...int64) {
    t.chatIDs = append(t.chatIDs, chatIDs...)
}

// Send takes a message subject and a message body and sends them to all previously set chats. Message body supports
// html as markup language.
func (t Telegram) Send(ctx context.Context, subject, message string) error {
    fullMessage := subject + "\n" + message // Treating subject as message title

    msg := tgbotapi.NewMessage(0, fullMessage)
    msg.ParseMode = parseMode

    for _, chatID := range t.chatIDs {
        select {
        case <-ctx.Done():
            return ctx.Err()
        default:
            msg.ChatID = chatID
            if _, err := t.client.Send(msg); err != nil {
                return fmt.Errorf("send message to chat %d: %w", chatID, err)
            }
        }
    }

    return nil
}