refactor(downloader): improve structure and readability

internal/downloader/metadata.go

@@ -0,0 +1,92 @@
+package downloader
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"net/http"
+
+	"github.com/mathismqn/godeez/internal/deezer"
+	"github.com/mathismqn/godeez/internal/provider"
+)
+
+type metadataResult struct {
+	bpmKey   provider.BPMKey
+	genre    string
+	warnings []string
+}
+
+type metadataFetcher struct {
+	httpClient *http.Client
+}
+
+func newMetadataFetcher(httpClient *http.Client) *metadataFetcher {
+	return &metadataFetcher{
+		httpClient: httpClient,
+	}
+}
+
+func (mf *metadataFetcher) fetch(ctx context.Context, song *deezer.Song, opts Options) metadataResult {
+	result := metadataResult{
+		bpmKey:   provider.BPMKey{},
+		genre:    "",
+		warnings: []string{},
+	}
+
+	if !opts.BPM && !opts.Genre {
+		return result
+	}
+
+	bmpChan := make(chan provider.BPMKey, 1)
+	bmpErrChan := make(chan error, 1)
+	genreChan := make(chan string, 1)
+	genreErrChan := make(chan error, 1)
+
+	if opts.BPM {
+		go func() {
+			p := provider.BPMProvider{}
+			bmpKey, err := p.Fetch(ctx, mf.httpClient, song.Artist, song.Title, song.Duration)
+			if err != nil {
+				bmpErrChan <- err
+			} else {
+				bmpChan <- bmpKey
+			}
+		}()
+	}
+
+	if opts.Genre {
+		go func() {
+			p := provider.GenreProvider{}
+			genre, err := p.Fetch(ctx, mf.httpClient, song.Artist, song.GetTitle())
+			if err != nil {
+				genreErrChan <- err
+			} else {
+				genreChan <- genre
+			}
+		}()
+	}
+
+	if opts.BPM {
+		select {
+		case bmpKey := <-bmpChan:
+			result.bpmKey = bmpKey
+		case err := <-bmpErrChan:
+			if !errors.Is(err, context.Canceled) {
+				result.warnings = append(result.warnings, fmt.Sprintf("failed to fetch BPM and key: %v", err))
+			}
+		}
+	}
+
+	if opts.Genre {
+		select {
+		case genre := <-genreChan:
+			result.genre = genre
+		case err := <-genreErrChan:
+			if !errors.Is(err, context.Canceled) {
+				result.warnings = append(result.warnings, fmt.Sprintf("failed to fetch genre: %v", err))
+			}
+		}
+	}
+
+	return result
+}