Used to listen to firestore documents on snapshot using golang

main.go

package main

import (
	"context"
	"fmt"
	"log"
	"os"
	"os/signal"
	"syscall"

	"cloud.google.com/go/firestore"
	"google.golang.org/api/iterator"
)

var PROJECTID string
var COLLECTION string

func getEnvOrFail(envvar string) string {
	varValue := os.Getenv(envvar)
	if varValue == "" {
		log.Fatalf("Could not fetch env variable %s", envvar)
	}
	return varValue
}

func init() {
	PROJECTID = getEnvOrFail("projectid")
	COLLECTION = getEnvOrFail("collection")
}

func snapshotListener(ctx context.Context, collection string) {
	client, err := firestore.NewClient(ctx, PROJECTID)
	if err != nil {
		log.Fatalf("trouble setting up client, %v", err)
	}
	defer client.Close()

	q := client.Collection(collection)
	qsi := q.Snapshots(ctx)
	for {
		qsnap, err := qsi.Next()
		fmt.Printf("Last read at %s with %v docs read\n", qsnap.ReadTime.String(), qsnap.Size)
		if err == iterator.Done {
			break
		}
		if err != nil {
			log.Fatalf("error with iterator %v", err)
		}
		docs := qsnap.Documents
		for {
			doc, err := docs.Next()
			if err == iterator.Done {
				break
			}
			if err != nil {
				fmt.Printf("an error occurred reading the snapshot")
			}
			fmt.Printf("Doc %s, updated at %v\n", doc.Ref.ID, doc.UpdateTime.String())
		}
	}
}

func main() {
	ctx, stop := signal.NotifyContext(context.Background(), syscall.SIGTERM)
	defer stop()

	go snapshotListener(ctx, COLLECTION)

	<-ctx.Done()
}