main.go

package main

import (
	"fmt"
	"os"
	"sort"
	"text/tabwriter"
	"time"
)

type Track struct {
	Title string
	Artist string
	Album string
	Year int
	Length time.Duration
}

var tracks = []*Track{
	{"Go","Delilah", "From the Roots Up", 2012, length("3m38s")},
	{"Go", "Moby", "Moby", 1992, length("3m37s")},
	{"Go Ahead", "Alicia Keys", "As I Am", 2007, length("4m36s")},
	{"Ready 2 Go", "Martin Solveig", "Smash", 2011, length("4m24s")},
}

func length(s string) time.Duration{
	d,err:=time.ParseDuration(s)
	if err!=nil{
		panic(s)
	}
	return d
}

func printTracks(tracks []*Track){
	const format = "%v\t%v\t%v\t%v\t%v\t\n"

	tw := new(tabwriter.Writer).Init(os.Stdout,0,8,2,' ',0)
	fmt.Fprintf(tw,format,"Title","Artist","Album","Year","Length")
	fmt.Fprintf(tw,format,"-----","-----","-----","-----","-----")
	for _,t := range tracks{
		fmt.Fprintf(tw,format,t.Title,t.Artist,t.Album,t.Year,t.Length)
	}
	tw.Flush()
}

//For sorting we need new type
type byArtist []*Track

func(x byArtist) Len() int { return len(x)}
func(x byArtist) Less(i,j int) bool {return x[i].Artist<x[j].Artist}
func(x byArtist) Swap(i,j int) {x[i],x[j]=x[j],x[i]}

type byYear []*Track

func (x byYear) Len() int {return len(x)}
func (x byYear) Less(i,j int) bool { return x[i].Year<x[j].Year}
func (x byYear) Swap(i,j int) {x[i],x[j]=x[j],x[i]}

type customSort struct {
	t []*Track
	less func(x,y *Track) bool
}
func (x customSort) Len() int {return len(x.t)}
func (x customSort) Less(i,j int) bool {return x.less(x.t[i],x.t[j])}
func (x customSort) Swap(i,j int) {x.t[i],x.t[j]=x.t[j],x.t[i]}

func main(){
	//printTracks(tracks)
	/*sort.Sort(byArtist(tracks))//прямой порядок
	printTracks(tracks)
	sort.Sort(sort.Reverse(byArtist(tracks)))//обратный порядок
	printTracks(tracks)
	sort.Sort(byYear(tracks))
	printTracks(tracks)
	sort.Sort(sort.Reverse(byYear(tracks)))
	printTracks(tracks)*/

	sort.Sort(customSort{tracks,func(x,y *Track) bool{
		if x.Title != y.Title{
			return x.Title < y.Title
		}
		if x.Year != y.Year{
			return x.Year < y.Year
		}
		if x.Length != y.Length{
			return x.Length < y.Length
		}
		return false
	}})
	printTracks(tracks)
	ok := sort.IsSorted(customSort{tracks, func(x,y *Track) bool{
		if x.Title != y.Title{
			return x.Title < y.Title
		}
		if x.Year != y.Year{
			return x.Year < y.Year
		}
		if x.Length != y.Length{
			return x.Length < y.Length
		}
		return false
	}})
	fmt.Println(ok)
}