bunker/server/internal/application/service.go

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 necessary 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
}