The very basic client app, not adapted for mobiles.

client/internal/application/service.go

@@ -0,0 +1,80 @@
+package application
+
+import (
+	"errors"
+	"fmt"
+)
+
+var (
+	// ErrServiceAlreadyRegistered returns if trying to register a service with name already taken by other service.
+	ErrServiceAlreadyRegistered = errors.New("service with such name already registered")
+	// ErrServiceNotFound returns if trying to gather service with unknown name.
+	ErrServiceNotFound = errors.New("service with such name wasn't found")
+)
+
+// Service is an interface every service should conform to. Specific services will have own interface for
+// cross-service interation.
+type Service interface {
+	// Configure configures service. Called after ConnectDependencies and before LaunchStartupTasks.
+	Configure() error
+	// ConnectDependencies gets neccessary dependencies.
+	ConnectDependencies() error
+	// Initialize initializes service's internal state. Called while registering service with Application
+	// lifecycle controller.
+	Initialize() error
+	// Name returns service name.
+	Name() string
+	// LaunchStartupTasks launches tasks on application start. Called after ConnectDependencies and Configure.
+	LaunchStartupTasks() error
+	// Shutdown stops service.
+	Shutdown() error
+}
+
+// RegisterService registering service with lifecycle controller for later use in any other service.
+func (a *Application) RegisterService(srv Service) error {
+	var found bool
+
+	for _, knownService := range a.services {
+		if srv.Name() == knownService.Name() {
+			found = true
+
+			break
+		}
+	}
+
+	if found {
+		return fmt.Errorf(
+			"%w: RegisterService: check for service '%s' registration: %w",
+			errApplication,
+			srv.Name(),
+			ErrServiceAlreadyRegistered,
+		)
+	}
+
+	if err := srv.Initialize(); err != nil {
+		return fmt.Errorf("%w: RegisterService: initialize service '%s': %w", errApplication, srv.Name(), err)
+	}
+
+	a.services = append(a.services, srv)
+
+	return nil
+}
+
+// Service returns requested service.
+func (a *Application) Service(name string) Service {
+	var srv Service
+
+	for _, knownService := range a.services {
+		if knownService.Name() == name {
+			srv = knownService
+
+			break
+		}
+	}
+
+	if srv == nil {
+		return nil
+	}
+
+	return srv
+}