feat(agents): Add Deezer API artist image provider agent (#4180)

* feat(agents): Add Deezer API artist image provider agent

* fix(agents): Use proper naming convention of consts

* fix(agents): Check if json test data can be read

* fix(agents): Use underscores for unused function arguments

* fix(agents): Move int literal to deezerArtistSearchLimit const

* feat: add Deezer configuration option to disable it.

Signed-off-by: Deluan <deluan@navidrome.org>

---------

Signed-off-by: Deluan <deluan@navidrome.org>
Co-authored-by: Deluan Quintão <deluan@navidrome.org>

core/agents/deezer/client_test.go

@@ -0,0 +1,68 @@
+package deezer
+
+import (
+	"bytes"
+	"context"
+	"io"
+	"net/http"
+	"os"
+
+	. "github.com/onsi/ginkgo/v2"
+	. "github.com/onsi/gomega"
+)
+
+var _ = Describe("client", func() {
+	var httpClient *fakeHttpClient
+	var client *client
+
+	BeforeEach(func() {
+		httpClient = &fakeHttpClient{}
+		client = newClient(httpClient)
+	})
+
+	Describe("ArtistImages", func() {
+		It("returns artist images from a successful request", func() {
+			f, err := os.Open("tests/fixtures/deezer.search.artist.json")
+			Expect(err).To(BeNil())
+			httpClient.mock("https://api.deezer.com/search/artist", http.Response{Body: f, StatusCode: 200})
+
+			artists, err := client.searchArtists(context.TODO(), "Michael Jackson", 20)
+			Expect(err).To(BeNil())
+			Expect(artists).To(HaveLen(17))
+			Expect(artists[0].Name).To(Equal("Michael Jackson"))
+			Expect(artists[0].PictureXl).To(Equal("https://cdn-images.dzcdn.net/images/artist/97fae13b2b30e4aec2e8c9e0c7839d92/1000x1000-000000-80-0-0.jpg"))
+		})
+
+		It("fails if artist was not found", func() {
+			httpClient.mock("https://api.deezer.com/search/artist", http.Response{
+				StatusCode: 200,
+				Body:       io.NopCloser(bytes.NewBufferString(`{"data":[],"total":0}`)),
+			})
+
+			_, err := client.searchArtists(context.TODO(), "Michael Jackson", 20)
+			Expect(err).To(MatchError(ErrNotFound))
+		})
+	})
+})
+
+type fakeHttpClient struct {
+	responses   map[string]*http.Response
+	lastRequest *http.Request
+}
+
+func (c *fakeHttpClient) mock(url string, response http.Response) {
+	if c.responses == nil {
+		c.responses = make(map[string]*http.Response)
+	}
+	c.responses[url] = &response
+}
+
+func (c *fakeHttpClient) Do(req *http.Request) (*http.Response, error) {
+	c.lastRequest = req
+	u := req.URL
+	u.RawQuery = ""
+	if resp, ok := c.responses[u.String()]; ok {
+		return resp, nil
+	}
+	panic("URL not mocked: " + u.String())
+}