Add Telegram Messenger notifications

Signed-off-by: Julien Riou <julien@riou.xyz>

notifier_telegram.go

@@ -0,0 +1,129 @@
+package main
+
+import (
+	"fmt"
+	"time"
+
+	telegram "github.com/go-telegram-bot-api/telegram-bot-api/v5"
+	log "github.com/sirupsen/logrus"
+	"gorm.io/gorm"
+)
+
+// TelegramMessage to store relationship between a Product and a Telegram notification
+type TelegramMessage struct {
+	gorm.Model
+	MessageID  int `gorm:"not null;unique"`
+	ProductURL string
+	Product    Product `gorm:"foreignKey:ProductURL"`
+}
+
+// TelegramNotifier to manage notifications to Twitter
+type TelegramNotifier struct {
+	db          *gorm.DB
+	bot         *telegram.BotAPI
+	chatID      int64
+	channelName string
+	timeout     int
+}
+
+// NewTelegramNotifier to create a Notifier with Telegram capabilities
+func NewTelegramNotifier(config *TelegramConfig, db *gorm.DB) (*TelegramNotifier, error) {
+	// create table
+	err := db.AutoMigrate(&TelegramMessage{})
+	if err != nil {
+		return nil, err
+	}
+
+	// create client
+	bot, err := telegram.NewBotAPI(config.Token)
+	if err != nil {
+		return nil, err
+	}
+	log.Debugf("connected to telegram as %s", bot.Self.UserName)
+
+	return &TelegramNotifier{
+		db:          db,
+		bot:         bot,
+		chatID:      config.ChatID,
+		channelName: config.ChannelName,
+	}, nil
+}
+
+// NotifyWhenAvailable create a Telegram message for announcing that a product is available
+// implements the Notifier interface
+func (n *TelegramNotifier) NotifyWhenAvailable(shopName string, productName string, productPrice float64, productCurrency string, productURL string) error {
+	// TODO: check if message exists in the database to avoid flood
+
+	// send message to telegram
+	formattedPrice := formatPrice(productPrice, productCurrency)
+	message := fmt.Sprintf("🟢 %s: %s for %s is available at %s", shopName, productName, formattedPrice, productURL)
+	messageID, err := n.sendMessage(message, 0)
+	if err != nil {
+		return err
+	}
+
+	// save telegram message to database
+	m := TelegramMessage{MessageID: messageID, ProductURL: productURL}
+	trx := n.db.Create(&m)
+	if trx.Error != nil {
+		return fmt.Errorf("failed to save telegram message %d to database: %s", m.MessageID, trx.Error)
+	}
+	log.Debugf("telegram message %d saved to database", m.MessageID)
+
+	return nil
+}
+
+// NotifyWhenNotAvailable create a Telegram message replying to the NotifyWhenAvailable message to say it's gone
+// implements the Notifier interface
+func (n *TelegramNotifier) NotifyWhenNotAvailable(productURL string, duration time.Duration) error {
+	// find message in the database
+	var m TelegramMessage
+	trx := n.db.Where(TelegramMessage{ProductURL: productURL}).First(&m)
+	if trx.Error != nil {
+		return fmt.Errorf("failed to find telegram message in database for product with url %s: %s", productURL, trx.Error)
+	}
+	if m.MessageID == 0 {
+		log.Warnf("telegram message for product with url %s not found, skipping close notification", productURL)
+		return nil
+	}
+
+	// format message
+	text := fmt.Sprintf("🔴 And it's gone (%s)", duration)
+
+	// send reply on telegram
+	_, err := n.sendMessage(text, m.MessageID)
+	if err != nil {
+		return fmt.Errorf("failed to reply on telegram: %s", err)
+	}
+	log.Infof("reply to telegram message %d sent", m.MessageID)
+
+	// remove message from database
+	trx = n.db.Unscoped().Delete(&m)
+	if trx.Error != nil {
+		return fmt.Errorf("failed to remove message %d from database: %s", m.MessageID, trx.Error)
+	}
+	log.Debugf("telegram message removed from database")
+	return nil
+}
+
+func (n *TelegramNotifier) sendMessage(text string, reply int) (int, error) {
+	log.Debugf("sending message %s to telegram", text)
+	var request telegram.MessageConfig
+	if n.chatID != 0 {
+		request = telegram.NewMessage(n.chatID, text)
+	} else {
+		request = telegram.NewMessageToChannel(n.channelName, text)
+	}
+	request.DisableWebPagePreview = true
+
+	if reply != 0 {
+		request.ReplyToMessageID = reply
+	}
+
+	response, err := n.bot.Send(request)
+	if err != nil {
+		return 0, err
+	}
+	log.Infof("message %d sent to telegram", response.MessageID)
+	return response.MessageID, nil
+}