Refactoring with DDD Lite

Author: roblaszczak

README.md

@@ -1,5 +1,7 @@
 # Wild Workouts
 
+*The idea for this series, is to apply DDD by refactoring. This process is in progress! Please check articles, to know the current progress.*
+
 Wild Workouts is an example project that we created to show how to build Go applications that are **easy to develop, maintain, and fun to work with, especially in the long term!**
 
 No application is perfect from the beginning. With over a dozen coming articles, we will uncover what issues you can find in the current implementation. We will also show how to fix these issues and achieve clean implementation by refactoring.
@@ -11,7 +13,8 @@ No application is perfect from the beginning. With over a dozen coming articles,
 3. [**Robust gRPC communication on Google Cloud Run (but not only!)**](https://threedots.tech/post/robust-grpc-google-cloud-run/?utm_source=github.com)
 4. [**You should not build your own authentication. Let Firebase do it for you.**](https://threedots.tech/post/firebase-cloud-run-authentication/?utm_source=github.com)
 5. [**Business Applications in Go: Things to know about DRY**](https://threedots.tech/post/things-to-know-about-dry/?utm_source=github.com)
-6. *More articles are on the way!*
+6. [**When microservices in Go are not enough: introduction to DDD Lite**](https://threedots.tech/post/ddd-lite-in-go-introduction/?utm_source=github.com)
+7. *More articles are on the way!*
 
 ### Directories
 

api/protobuf/trainer.proto

@@ -6,7 +6,9 @@ import "google/protobuf/timestamp.proto";
 
 service TrainerService {
   rpc IsHourAvailable(IsHourAvailableRequest) returns (IsHourAvailableResponse) {}
-  rpc UpdateHour(UpdateHourRequest) returns (EmptyResponse) {}
+  rpc ScheduleTraining(UpdateHourRequest) returns (EmptyResponse) {}
+  rpc CancelTraining(UpdateHourRequest) returns (EmptyResponse) {}
+  rpc MakeHourAvailable(UpdateHourRequest) returns (EmptyResponse) {}
 }
 
 message IsHourAvailableRequest {
@@ -19,9 +21,6 @@ message IsHourAvailableResponse {
 
 message UpdateHourRequest {
   google.protobuf.Timestamp time = 1;
-
-  bool has_training_scheduled = 2;
-  bool available = 3;
 }
 
 message EmptyResponse {}

docker/app/start.sh

@@ -1 +1 @@
-go run *.go
+go run .

internal/common/genproto/trainer/trainer.pb.go

@@ -0,0 +1,74 @@
+package hour
+
+import "github.com/pkg/errors"
+
+// Availability is enum.
+//
+// Using struct instead of `type Availability string` for enums allows us to ensure,
+// that we have full control of what values are possible.
+// With `type Availability string` you are able to create `Availability("i_can_put_anything_here")`
+type Availability struct {
+	a string
+}
+
+// Every type in Go have zero value. In that case it's `Availability{}`.
+// It's always a good idea to check if provided value is not zero!
+func (h Availability) IsZero() bool {
+	return h == Availability{}
+}
+
+var (
+	Available         = Availability{"available"}
+	NotAvailable      = Availability{"not_available"}
+	TrainingScheduled = Availability{"training_scheduled"}
+)
+
+var (
+	ErrTrainingScheduled   = errors.New("unable to modify hour, because scheduled training")
+	ErrNoTrainingScheduled = errors.New("training is not scheduled")
+	ErrHourNotAvailable    = errors.New("hour is not available")
+)
+
+func (h Hour) IsAvailable() bool {
+	return h.availability == Available
+}
+
+func (h Hour) HasTrainingScheduled() bool {
+	return h.availability == TrainingScheduled
+}
+
+func (h *Hour) MakeNotAvailable() error {
+	if h.HasTrainingScheduled() {
+		return ErrTrainingScheduled
+	}
+
+	h.availability = NotAvailable
+	return nil
+}
+
+func (h *Hour) MakeAvailable() error {
+	if h.HasTrainingScheduled() {
+		return ErrTrainingScheduled
+	}
+
+	h.availability = Available
+	return nil
+}
+
+func (h *Hour) ScheduleTraining() error {
+	if !h.IsAvailable() {
+		return ErrHourNotAvailable
+	}
+
+	h.availability = TrainingScheduled
+	return nil
+}
+
+func (h *Hour) CancelTraining() error {
+	if !h.HasTrainingScheduled() {
+		return ErrNoTrainingScheduled
+	}
+
+	h.availability = Available
+	return nil
+}