Implement notifications service with shared messaging and email drivers (#36)

backend/notifications/email/driver.go

@@ -0,0 +1,79 @@
+package email
+
+import (
+	"context"
+	"net/http"
+	"net/mail"
+	"os"
+	"strings"
+	"time"
+
+	"git.sendico.io/tech/sxchnge/notifications/model"
+	merrors "git.sendico.io/tech/sxchnge/shared/errors"
+	sharedmodel "git.sendico.io/tech/sxchnge/shared/model"
+	"github.com/go-viper/mapstructure/v2"
+)
+
+type Driver string
+
+const (
+	SendGrid Driver = "sendgrid"
+	Resend   Driver = "resend"
+)
+
+type Config = sharedmodel.DriverConfig[Driver]
+type Settings struct {
+	APIKeyEnv     string `mapstructure:"api_key_env"`
+	SenderAddress string `mapstructure:"sender_address"`
+	SenderName    string `mapstructure:"sender_name"`
+}
+
+// Outcome describes provider acceptance, never recipient delivery or reading.
+type Outcome struct {
+	State      model.State
+	Code       string
+	RetryAfter time.Duration
+}
+type Sender interface {
+	Send(context.Context, string, model.Email) Outcome
+}
+
+type client struct {
+	http     *http.Client
+	key      string
+	settings Settings
+	endpoint string
+}
+
+func New(config Config) (Sender, error) {
+	var s Settings
+	decoder, err := mapstructure.NewDecoder(&mapstructure.DecoderConfig{Result: &s, ErrorUnused: true, TagName: "mapstructure"})
+	if err != nil {
+		return nil, merrors.InternalWrap(err, "create driver settings decoder")
+	}
+	if err = decoder.Decode(config.Settings); err != nil {
+		return nil, merrors.InvalidArgument("invalid email driver settings")
+	}
+	if !ValidAddress(s.SenderAddress) || strings.ContainsAny(s.SenderName, "\r\n") {
+		return nil, merrors.InvalidArgument("invalid sender")
+	}
+	key := os.Getenv(s.APIKeyEnv)
+	if s.APIKeyEnv == "" || strings.TrimSpace(key) == "" || strings.ContainsAny(key, "\r\n") {
+		return nil, merrors.FailedPrecondition("email API key environment variable is missing")
+	}
+	c := client{http: &http.Client{Timeout: 20 * time.Second, CheckRedirect: func(*http.Request, []*http.Request) error { return http.ErrUseLastResponse }}, key: key, settings: s}
+	switch config.Driver {
+	case SendGrid:
+		c.endpoint = "https://api.sendgrid.com/v3/mail/send"
+		return &sendgrid{c}, nil
+	case Resend:
+		c.endpoint = "https://api.resend.com/emails"
+		return &resend{c}, nil
+	default:
+		return nil, merrors.InvalidArgument("unsupported email driver")
+	}
+}
+func ValidAddress(s string) bool {
+	a, err := mail.ParseAddress(s)
+	return err == nil && a.Address == s && !strings.ContainsAny(s, "\r\n") && len(s) <= 254
+}