Playlist Soundness

What’s up, friend?!
I’m so pumped you’re joining us.
We’ve got a sick project we could totally use your help on!

See, someone’s giving us amazing recommendations for songs to play.
But they’re not just coming in as songs.
Sometimes they’re an album containing a array of songs.
And sometimes they’re a playlist with a method that returns an array of songs.

We’d like you to write a function for us that takes in an array of those items and returns a result playlist.
The result playlist should keep track of which songs appear under each artist, the in-order list of songs, and the total length of time across the playlist?

Can you do this for us, please?
Friend?

Setup

In one terminal, run the TypeScript compiler via the tsc script.
For example, to start the TypeScript compiler in watch mode:

npm run tsc -- --watch

In another terminal, run Jest via the test script.
For example, to start tests in watch mode:

npm run test -- --watch

Specification

Your code should export an unrollPlaylist function with an explicit return type annotation.

Parameters:

1. items: An array where each element is either a Song, Album, or Playlist

   See ./index.test.ts for examples of data.

Return type: an object with…

• artists: Object with artist names keyed to the array of songs they’re credited on
• songs: An array of Songs
• time: Total length of time across all songs

Notes

• Don’t import code from one step into another.

代码

export interface Song {
	artist: string | string[];
	length: number;
	name: string;
	type: "song";
}

export interface Album {
	songs: Song[];
	type: "album";
}

export interface Playlist {
	resolve(): Song[];
	type: "playlist";
}

export type PlaylistItem = Album | Song | Playlist;

export interface Artists {
	[i: string]: string[];
}

export interface UnrolledPlaylist {
	artists: Artists;
	songs: string[];
	time: number;
}

export function unrollPlaylist(items: PlaylistItem[]): UnrolledPlaylist {
	const artists: Artists = {};
	const songs: string[] = [];
	let time = 0;

	function addSong(song: Song) {
		const songArtists =
			typeof song.artist === "string" ? [song.artist] : song.artist;

		for (const artist of songArtists) {
			artists[artist] ??= [];
			artists[artist].push(song.name);
		}

		time += song.length;
		songs.push(song.name);
	}

	for (const item of items) {
		switch (item.type) {
			case "song":
				addSong(item);
				break;

			case "album":
				item.songs.forEach(addSong);
				break;

			case "playlist":
				item.resolve().forEach(addSong);
				break;
		}
	}

	return { artists, songs, time };
}


let items : PlaylistItem[] = [
    {
        songs: [
            {
                artist: ["Queen"],
                length: 223,
                name: "Death On Two Legs (Dedicated to...)",
                type: "song",
            },
            {
                artist: "Tenacious D",
                length: 247,
                name: "Tribute",
                type: "song",
            },
            {
                artist: ["Queen"],
                length: 68,
                name: "Lazing on a Sunday Afternoon",
                type: "song",
            },
        ],
        type: "album",
    },
]

let unrolledPlaylist: UnrolledPlaylist = unrollPlaylist(items)
console.log(unrolledPlaylist)

输出

{
  artists: {
    Queen: [
      'Death On Two Legs (Dedicated to...)',
      'Lazing on a Sunday Afternoon'
    ],
    'Tenacious D': [ 'Tribute' ]
  },
  songs: [
    'Death On Two Legs (Dedicated to...)',
    'Tribute',
    'Lazing on a Sunday Afternoon'
  ],
  time: 538
}