Add Telegram Messenger notifications

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

notifier.go

@@ -1,9 +1,26 @@
 package main
 
-import "time"
+import (
+	"fmt"
+	"time"
+)
 
 // Notifier interface to notify when a product becomes available or is sold out again
 type Notifier interface {
 	NotifyWhenAvailable(string, string, float64, string, string) error
 	NotifyWhenNotAvailable(string, time.Duration) error
 }
+
+// formatPrice using internationalization rules
+// euro sign is placed after the value
+// default the currency, or symbol if applicable, is placed before the value
+func formatPrice(value float64, currency string) string {
+	switch {
+	case currency == "EUR":
+		return fmt.Sprintf("%.2f€", value)
+	case currency == "USD":
+		return fmt.Sprintf("$%.2f", value)
+	default:
+		return fmt.Sprintf("%s%.2f", currency, value)
+	}
+}