Listen to changes in firestore

changes.md

To authorize firebase:

  ctx := context.Background()

	opt := option.WithCredentialsFile("./serviceAccountKey.json")
	app, err := firebase.NewApp(ctx, nil, opt)
	if err != nil {
		log.Fatalf("Error %v \n", err)
	}

	client, err := app.Firestore(ctx)
	if err != nil {
		log.Fatalf("Error %v \n", err)
	}

To get the messages collections:

  iter := client.Collection("messages").Snapshots(ctx)
	if err != nil {
		log.Fatalf("Error %v \n", err)
	}
	defer iter.Stop()

	now := time.Now()

To listen for firestore changes:

   for {
		doc, err := iter.Next()
		if err != nil {
			if err == iterator.Done {
				break
			}
			log.Fatalf("Error %v \n", err)
		}
		for _, change := range doc.Changes {
			switch change.Kind {
			case firestore.DocumentAdded:
				if change.Doc.CreateTime.After(now) {
					log.Println("Document Added", change.Doc.Data())
				}
			case firestore.DocumentModified:
				if change.Doc.UpdateTime.After(now) {
					log.Println("Document modified", change.Doc.Data())
				}
			case firestore.DocumentRemoved:
				log.Println("Document removed", change.Doc.Data())
			}
		}
	}

main.go

package main

import (
	"context"
	"log"
	"time"

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

func main() {
	ctx := context.Background()

	opt := option.WithCredentialsFile("./serviceAccountKey.json")
	app, err := firebase.NewApp(ctx, nil, opt)
	if err != nil {
		log.Fatalf("Error %v \n", err)
	}

	client, err := app.Firestore(ctx)
	if err != nil {
		log.Fatalf("Error %v \n", err)
	}

	iter := client.Collection("messages").Snapshots(ctx)
	if err != nil {
		log.Fatalf("Error %v \n", err)
	}
	defer iter.Stop()

	now := time.Now()

	for {
		doc, err := iter.Next()
		if err != nil {
			if err == iterator.Done {
				break
			}
			log.Fatalf("Error %v \n", err)
		}
		for _, change := range doc.Changes {
			switch change.Kind {
			case firestore.DocumentAdded:
				if change.Doc.CreateTime.After(now) {
					log.Println("Document Added", change.Doc.Data())
				}
			case firestore.DocumentModified:
				if change.Doc.UpdateTime.After(now) {
					log.Println("Document modified", change.Doc.Data())
				}
			case firestore.DocumentRemoved:
				log.Println("Document removed", change.Doc.Data())
			}
		}
	}

	log.Printf("App created: %v \n", app)
}