Envelope/Backend/Service/SendNotification.go

package Service

import (
	"context"
	"os"

	firebase "firebase.google.com/go"
	"firebase.google.com/go/messaging"
	"github.com/joho/godotenv"

	"google.golang.org/api/option"
)

var (
	ctx       context.Context
	fcmClient *messaging.Client
)

func init() {
	var (
		fireBaseAuthKey string
		opts            []option.ClientOption
		app             *firebase.App
		err             error
	)

	err = godotenv.Load()
	if err != nil {
		panic(err)
	}

	fireBaseAuthKey = os.Getenv("FIREBASE_AUTH_KEY")

	opts = []option.ClientOption{
		option.WithCredentialsFile(fireBaseAuthKey),
	}

	ctx = context.TODO()

	app, err = firebase.NewApp(ctx, nil, opts...)
	if err != nil {
		panic(err)
	}

	fcmClient, err = app.Messaging(ctx)
	if err != nil {
		panic(err)
	}
}

func SendNotification(tokens []string, title string, data map[string]string) error {
	var (
		message messaging.MulticastMessage
		err     error
	)

	message = messaging.MulticastMessage{
		Notification: &messaging.Notification{
			Title: title,
		},
		Data:   data,
		Tokens: tokens,
	}

	_, err = fcmClient.SendMulticast(context.TODO(), &message)

	return err
}