Query albums by genre

tests/in_memory_music_service.ts

@@ -1,7 +1,6 @@
 import { option as O } from "fp-ts";
 import { pipe } from "fp-ts/lib/function";
 
-
 import {
   MusicService,
   Credentials,
@@ -13,33 +12,20 @@ import {
   AlbumQuery,
   slice2,
   asResult,
-  ArtistSummary,
+  artistToArtistSummary,
+  albumToAlbumSummary,
   Album,
-  AlbumSummary
 } from "../src/music_service";
 
-export const artistToArtistSummary = (
-  it: Artist
-): ArtistSummary => ({
-  id: it.id,
-  name: it.name,
-  image: it.image,
-});
-
-export const albumToAlbumSummary = (
-  it: Album
-): AlbumSummary => ({
-  id: it.id,
-  name: it.name,
-  year: it.year,
-  genre: it.genre,
-});
-
 type P<T> = (t: T) => boolean;
 const all: P<any> = (_: any) => true;
-const artistWithId = (id: string): P<Artist> => (artist: Artist) =>
+
+const albumByArtist = (id: string): P<[Artist, Album]> => ([artist, _]) =>
   artist.id === id;
 
+const albumWithGenre = (genre: string): P<[Artist, Album]> => ([_, album]) =>
+  album.genre === genre;
+
 export class InMemoryMusicService implements MusicService {
   users: Record<string, string> = {};
   artists: Artist[] = [];
@@ -76,24 +62,40 @@ export class InMemoryMusicService implements MusicService {
         pipe(
           this.artists.find((it) => it.id === id),
           O.fromNullable,
-          O.map(it => Promise.resolve(it)),
+          O.map((it) => Promise.resolve(it)),
           O.getOrElse(() => Promise.reject(`No artist with id '${id}'`))
         ),
       albums: (q: AlbumQuery) =>
         Promise.resolve(
-          this.artists.filter(
-            pipe(
-              O.fromNullable(q.artistId),
-              O.map(artistWithId),
-              O.getOrElse(() => all)
+          this.artists
+            .flatMap((artist) => artist.albums.map((album) => [artist, album]))
+            .filter(
+              pipe(
+                pipe(
+                  O.fromNullable(q.artistId), 
+                  O.map(albumByArtist)
+                ),
+                O.alt(() =>
+                  pipe(
+                    O.fromNullable(q.genre), 
+                    O.map(albumWithGenre)
+                  )
+                ),
+                O.getOrElse(() => all)
+              )
             )
-          )
         )
-          .then((artists) => artists.flatMap((it) => it.albums))
-          .then(it => it.map(albumToAlbumSummary))
+          .then((matches) => matches.map(([_, album]) => album as Album))
+          .then((it) => it.map(albumToAlbumSummary))
           .then(slice2(q))
           .then(asResult),
-      // album: (id: albumId) => Promise.resolve(this.artists.flatMap(it => it.albums).find(it => it.id === id))
+      album: (id: string) =>
+        pipe(
+          this.artists.flatMap((it) => it.albums).find((it) => it.id === id),
+          O.fromNullable,
+          O.map((it) => Promise.resolve(it)),
+          O.getOrElse(() => Promise.reject(`No album with id '${id}'`))
+        ),
     });
   }