notify/service/sendgrid/sendgrid.go

package sendgrid

import (
	"context"
	"net/http"

	"github.com/pkg/errors"
	"github.com/sendgrid/sendgrid-go"
	"github.com/sendgrid/sendgrid-go/helpers/mail"
)

// SendGrid struct holds necessary data to communicate with the SendGrid API.
type SendGrid struct {
	client            *sendgrid.Client
	senderAddress     string
	senderName        string
	receiverAddresses []string
}

// New returns a new instance of a SendGrid notification service.
// You will need a SendGrid API key.
// See https://sendgrid.com/docs/for-developers/sending-email/api-getting-started/
func New(apiKey, senderAddress, senderName string) *SendGrid {
	return &SendGrid{
		client:            sendgrid.NewSendClient(apiKey),
		senderAddress:     senderAddress,
		senderName:        senderName,
		receiverAddresses: []string{},
	}
}

// AddReceivers takes email addresses and adds them to the internal address list. The Send method will send
// a given message to all those addresses.
func (s *SendGrid) AddReceivers(addresses ...string) {
	s.receiverAddresses = append(s.receiverAddresses, addresses...)
}

// Send takes a message subject and a message body and sends them to all previously set chats. Message body supports
// html as markup language.
func (s SendGrid) Send(ctx context.Context, subject, message string) error {
	from := mail.NewEmail(s.senderName, s.senderAddress)
	content := mail.NewContent("text/html", message)

	// Create a new personalization instance to be able to add multiple receiver addresses.
	personalization := mail.NewPersonalization()
	personalization.Subject = subject

	for _, receiverAddress := range s.receiverAddresses {
		personalization.AddTos(mail.NewEmail(receiverAddress, receiverAddress))
	}

	mailMessage := mail.NewV3Mail()
	mailMessage.AddPersonalizations(personalization)
	mailMessage.AddContent(content)
	mailMessage.SetFrom(from)

	select {
	case <-ctx.Done():
		return ctx.Err()
	default:
		resp, err := s.client.Send(mailMessage)
		if err != nil {
			return errors.Wrap(err, "failed to send mail using SendGrid service")
		}

		if resp.StatusCode != http.StatusAccepted {
			return errors.New("the SendGrid endpoint did not accept the message")
		}
	}

	return nil
}