package main

import (
	"fmt"
	"time"
	"sync"
)

type payloadData struct {
  Index int
}

type resultData struct {
  Res int
}

type job struct {
	Payload payloadData
	Result chan resultData
}

func worker(jobs <-chan job) {
	for {
		// get next job
		params := <-jobs

		fmt.Printf("-> index: %d\n", params.Payload.Index)

		// simulate a heavy processing
		time.Sleep(1 * time.Second)
    
		// return result
		params.Result <- resultData{Res: params.Payload.Index}
	}
}

var jobPool chan job

func main() {
 	workerCount := 5
  
 	jobPool = make(chan job)
	// start a fixed amount of workers
	for i := 0; i < workerCount; i++ {
		go worker(jobPool)
	}
  
	// needed only to wait until all go routines will complete
 	var wg sync.WaitGroup
 	for j := 0; j < 10; j++ {
   		wg.Add(1)
		
		go func(i int){
			defer wg.Done()
			
			// prepare channel for result
			c := make(chan resultData)
			// send job to worker
			jobPool <- job{Payload: payloadData{Index: i}, Result: c}
			// wait till complete
			data := <-c
			fmt.Printf("<- result: %d\n", data.Res);
		}(j)
	}
	wg.Wait()
}