event bus pattern in go

main.go

// An event BUS is a communication pattern between subsystems
// event SOURCING is a design pattern that I would define as:
// System state is stored as an append-only sequence of events,
// current system state is the result of applying all events in order.

// this demonstrates an event bus:
package main

import (
	"fmt"
	"strconv"
	"time"
)

type event interface {
	Event() string
}

type eventDeleteEntryRequest struct {
	userID    int
	entryUUID string
}

func (e eventDeleteEntryRequest) Event() string {
	return "DeleteEntryRequest"
}

type eventDeleteEntry struct {
	entryUUID string
}

func (e eventDeleteEntry) Event() string {
	return "DeleteEntry"
}

func main() {
	// A real bus has to multiplex events, ignoring that with ugly channels
	bus := make(chan event)
	go endpointService(bus)
	go authService(bus)
	go dbService(bus)
	<-time.After(10 * time.Second)
}

func endpointService(bus chan event) {
	var i int
	for {
		i++
		req := eventDeleteEntryRequest{
			userID:    i,
			entryUUID: "covfefe" + strconv.Itoa(i),
		}
		fmt.Printf("Publishing %+v\n", req)
		bus <- req
		time.Sleep(time.Second)
	}
}

func authService(bus chan event) {
	for e := range bus {
		f, ok := e.(eventDeleteEntryRequest)
		if !ok {
			// put it back
			bus <- e
			continue
		}
		// auth logic:
		if f.userID%2 == 0 {
			// granted
			g := eventDeleteEntry{
				entryUUID: f.entryUUID,
			}
			bus <- g
		}
	}
}

func dbService(bus chan event) {
	for e := range bus {
		f, ok := e.(eventDeleteEntry)
		if !ok {
			// put it back
			bus <- e
			continue
		}
		// db logic:
		fmt.Printf("deleting %s\n", f.entryUUID)
	}
}