package main

import (
	"compress/gzip"
	"fmt"
	"io"
	"os"
	"sync"
)

/*
	@Ref: https://livebook.manning.com/book/go-in-practice/chapter-3/65
	1. Practice gzip compress
	2. How to use wait group
	3. os.Args[1:] can stream in multiple files to the program without writing a walk function. Command: go run main.go ./testdata/*
	4. Passing the filename to each goroutine can make sure the correct file is executed as it's scheduled

*/
func main() {

	// Single thread
	// for _, file := range os.Args[1:] {

	// 	err := compress(file)
	// 	if err != nil {
	// 		os.Exit(0)
	// 	}
	// }

	// Multi threads
	wg := sync.WaitGroup{}
	var (
		i    int
		file string
	)
	for i, file = range os.Args[1:] {
		wg.Add(1)
		go func(filename string) {
			compress(filename)
			wg.Done()
		}(file)
	}

	wg.Wait()
	fmt.Printf("Compressed %d files\n", i+1)
}

func compress(filename string) error {
	in, err := os.Open(filename)
	if err != nil {
		return err
	}

	defer in.Close()

	out, err := os.Create(filename + ".gz")
	if err != nil {
		return err
	}

	defer out.Close()

	gzout := gzip.NewWriter(out)
	_, err = io.Copy(gzout, in)
	gzout.Close()

	return err
}