How to do it...

These steps cover writing and running your application:

1. From your Terminal or console application, create a new directory called ~/projects/go-programming-cookbook/chapter13/firebase and navigate to it.
2. Run the following command:

$ go mod init github.com/PacktPublishing/Go-Programming-Cookbook-Second-Edition/chapter13/firebase

You should see a file called go.mod that contains the following content:

module github.com/PacktPublishing/Go-Programming-Cookbook-Second-Edition/chapter13/firebase

3. Create a file called client.go with the following content:

package firebase

import (
  "context"

  "cloud.google.com/go/firestore"
  "github.com/pkg/errors"
)

// Client Interface for mocking
type Client interface {
  Get(ctx context.Context, key string) (interface{}, error)
  Set(ctx context.Context, key string, value interface{}) error
  Close() error
}

// firestore.Client implements Close()
// we create Get and Set
type firebaseClient struct {
  *firestore.Client
  collection string
}

func (f *firebaseClient) Get(ctx context.Context, key string) (interface{}, error) {
  data, err := f.Collection(f.collection).Doc(key).Get(ctx)
  if err != nil {
    return nil, errors.Wrap(err, "get failed")
  }
  return data.Data(), nil
}

func (f *firebaseClient) Set(ctx context.Context, key string, value interface{}) error {
  set := make(map[string]interface{})
  set[key] = value
  _, err := f.Collection(f.collection).Doc(key).Set(ctx, set)
  return errors.Wrap(err, "set failed")
}

4. Create a file called auth.go with the following content:

package firebase

import (
  "context"

  firebase "firebase.google.com/go"
  "github.com/pkg/errors"
  "google.golang.org/api/option"
)

// Authenticate grabs oauth scopes using a generated
// service_account.json file from
// https://console.firebase.google.com/project/go-cookbook/settings/serviceaccounts/adminsdk
func Authenticate(ctx context.Context, collection string) (Client, error) {

  opt := option.WithCredentialsFile("/tmp/service_account.json")
  app, err := firebase.NewApp(ctx, nil, opt)
  if err != nil {
    return nil, errors.Wrap(err, "error initializing app")
  }

  client, err := app.Firestore(ctx)
  if err != nil {
    return nil, errors.Wrap(err, "failed to intialize filestore")
  }
  return &firebaseClient{Client: client, collection: collection}, nil
}

5. Create a new directory named example and navigate to it.
6. Create a file named main.go with the following content:

package main

import (
  "context"
  "fmt"
  "log"

  "github.com/PacktPublishing/Go-Programming-Cookbook-Second-Edition/chapter13/firebase"
)

func main() {
  ctx := context.Background()
  c, err := firebase.Authenticate(ctx, "collection")
  if err != nil {
    log.Fatalf("error initializing client: %v", err)
  }
  defer c.Close()

  if err := c.Set(ctx, "key", []string{"val1", "val2"}); err != nil {
    log.Fatalf(err.Error())
  }

  res, err := c.Get(ctx, "key")
  if err != nil {
    log.Fatalf(err.Error())
  }
  fmt.Println(res)

  if err := c.Set(ctx, "key2", []string{"val3", "val4"}); err != nil {
    log.Fatalf(err.Error())
  }

  res, err = c.Get(ctx, "key2")
  if err != nil {
    log.Fatalf(err.Error())
  }
  fmt.Println(res)
}

7. Run go run main.go.
8. You may also run go build ./example. You should see the following output:

$ go run main.go 
[val1 val2]
[val3 val4]

9. The go.mod file may be updated and the go.sum file should now be present in the top-level recipe directory.
10. If you copied or wrote your own tests, go up one directory and run go test. Ensure that all the tests pass.