global using global::System;

global using global::System.Collections.Generic;

global using global::System.IO;

global using global::System.Linq;

global using global::System.Net.Http;

global using global::System.Threading;

global using global::System.Threading.Tasks;

​

// Now let's use the API

​

Playlist rockPlaylist = new Playlist("My rock playlist");

Song s1 = new Song("Fuel", "Metallica", TimeSpan.FromMinutes(4));

Song s2 = new Song("With or without you", "U2", TimeSpan.FromMinutes(3));

rockPlaylist.AddSong(s1);

rockPlaylist.AddSong(s2);

​

Playlist pop = new Playlist("Pop of the 90s");

Song s3 = new Song("Torn", "Natalie Imbruglia", TimeSpan.FromMinutes(3));

pop.AddSong(s3);

pop.AddSong(new Song("Hit me baby one more time", "Britney Spears", TimeSpan.FromSeconds(243)));

pop.AddSong(s2); // why not?

Console.WriteLine($"Total length of rock playlist: {rockPlaylist.GetTotalLength()}");

Console.WriteLine($"Total length of pop playlist: {pop.GetTotalLength()}");

​

​

rockPlaylist.Print();

pop.Print();

​

class Song

{

    public string Name { get; }

    public string Artist { get; }

    public TimeSpan Length { get; }

​

    public Song(string name, string artistName, TimeSpan length)

    {

        Name = name;

        Artist = artistName;

        Length = length;

    }

​

    public void Play()

    {

        Console.WriteLine($"Playing song {Name} by {Artist}");

    }

}

​

class Playlist

{

    // we need a way to keep a track of all the songs, a List will do

    private List<Song> _songs = new List<Song>();

    public string Name; 

​

    public Playlist(string name)

    {

        Name = name;

    }

​

    public void AddSong(Song s)

    {

        _songs.Add(s);

    }

​

    public void RemoveSong(Song s)

    {

        // this has a few bugs, but let's keep it simple now

        foreach (var song in _songs)

        {

            if (s == song)

            {

                _songs.Remove(s);

                return;

            }

        }

​

        Console.WriteLine($"Song {s.Name} not found in playlist {Name}");

        throw new InvalidOperationException("Song not found in playlist");

    }

​

    public TimeSpan GetTotalLength()

    {

        TimeSpan totalLength = new TimeSpan();

        foreach (var song in _songs)

        {

            totalLength += song.Length;

        }

        return totalLength;

    }

​

    public void Print()

    {

        Console.WriteLine($"Playlist: {Name}");

        foreach (Song song in _songs)

        {

            Console.WriteLine($"- {song.Name} by {song.Artist} ({song.Length})");

        }

    }

}