Golang Service Provision Pattern

main.go

package main

// Service Provision Pattern
// taken from https://github.com/andygrunwald/go-jira/blob/main/cloud/jira.go

// test this code in
// https://go.dev/play/p/-BUVpELm5u8


import (
	"log"
	"os"
)

// Concrete type that provides access
// to the shared client
// It will be cast to the actual service
// providing some kind of struct polymorphism
type service struct {
	client *Client
}

// Client that will aggregate the services
type Client struct {
  // common service that will provide
  // a shared instance of the client
	common   service
  
  // dependencies
  // this are private to hide them
  // from other instances
	logger   *log.Logger
	http     *log.Logger
  
  // services instantiated with the
  // common instance
	ServiceA *ServiceA
	ServiceB *ServiceB
}

func (c *Client) Log(origin string, message string) {
	oldPrefix := c.logger.Prefix()
	c.logger.SetPrefix(origin + " ")
	defer c.logger.SetPrefix(oldPrefix)
	c.logger.Printf("%s", message)
}

func (c *Client) Do(url string) {
	c.http.Printf("%s", url)
}

type ServiceA service
type ServiceB service

func (s *ServiceA) LogA(msg string) {
	s.client.Log("A", msg)
}
func (s *ServiceB) LogB(msg string) {
	s.client.Log("B", msg)
}

func (s *ServiceA) CallAPI() {
	s.client.Do("http://example.com/api/v1/")
}

func NewClient() *Client {
	c := &Client{
		logger: log.New(os.Stdout, "", log.LstdFlags),
		http:   log.New(os.Stdout, "HTTP ", log.LstdFlags),
	}
	c.ServiceA = (*ServiceA)(&c.common)
	c.ServiceB = (*ServiceB)(&c.common)
	c.common.client = c
	return c
}

func main() {
	c := NewClient()
	c.ServiceA.LogA("hello")
	c.ServiceB.LogB("hello")
	c.ServiceA.CallAPI()
}