feat: backend service

backend/internal/mail/errors.go

@@ -0,0 +1,27 @@
+package mail
+
+import "errors"
+
+// Sentinel errors emitted by Service methods. Handlers translate them
+// into HTTP responses; tests match on them with errors.Is.
+var (
+	// ErrDeliveryNotFound is returned by AdminGetDelivery and AdminResend
+	// when the supplied delivery_id does not name a row.
+	ErrDeliveryNotFound = errors.New("mail: delivery not found")
+
+	// ErrResendOnSent is returned by AdminResend when the targeted row
+	// is in the terminal `sent` state. The admin contract maps this to
+	// 409 Conflict; resending an already-delivered mail would push a
+	// duplicate copy to the recipient.
+	ErrResendOnSent = errors.New("mail: cannot resend a sent delivery")
+
+	// ErrUnknownTemplate is returned by EnqueueTemplate when the
+	// supplied template_id is not registered in the inline template
+	// catalog. A typo at the producer is the typical cause.
+	ErrUnknownTemplate = errors.New("mail: unknown template")
+
+	// ErrInvalidRecipient is returned by EnqueueLoginCode and
+	// EnqueueTemplate when the supplied recipient address is empty or
+	// fails go-mail's RFC 5322 validation.
+	ErrInvalidRecipient = errors.New("mail: invalid recipient address")
+)