refactor: consolidate download domain into download package

internal/download/bpm.go

@@ -0,0 +1,154 @@
+package download
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"io"
+	"net/http"
+	neturl "net/url"
+	"regexp"
+	"strconv"
+	"strings"
+
+	"github.com/PuerkitoBio/goquery"
+)
+
+var (
+	bpmRegex  = regexp.MustCompile(`tempo of <span[^>]*>(\d+) BPM`)
+	keyRegex  = regexp.MustCompile(`with a <span[^>]*>([A-G](?:♯|#|♭|b)?(?:/[A-G](?:♯|#|♭|b)?)?)</span> key`)
+	modeRegex = regexp.MustCompile(`a  <span[^>]*>([a-z]+)</span> mode`)
+)
+
+func fetchBPM(ctx context.Context, httpClient *http.Client, artist, title, duration string) (bpmKey, error) {
+	trackURL, err := findTrackURL(ctx, httpClient, artist, title, duration)
+	if err != nil {
+		return bpmKey{}, err
+	}
+
+	html, err := fetchBPMPage(ctx, httpClient, trackURL)
+	if err != nil {
+		return bpmKey{}, err
+	}
+
+	return parseBPM(html)
+}
+
+func findTrackURL(ctx context.Context, httpClient *http.Client, artist, title, duration string) (string, error) {
+	const rootURL = "https://songbpm.com"
+
+	values := neturl.Values{}
+	values.Add("query", fmt.Sprintf("%s %s", artist, title))
+
+	req, err := http.NewRequestWithContext(ctx, "POST", rootURL+"/searches", bytes.NewBufferString(values.Encode()))
+	if err != nil {
+		return "", err
+	}
+	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+	req.Header.Set("Origin", rootURL)
+
+	resp, err := httpClient.Do(req)
+	if err != nil {
+		return "", err
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		return "", fmt.Errorf("unexpected status code: %d", resp.StatusCode)
+	}
+
+	doc, err := goquery.NewDocumentFromReader(resp.Body)
+	if err != nil {
+		return "", err
+	}
+
+	wantDuration, err := strconv.Atoi(duration)
+	if err != nil {
+		return "", fmt.Errorf("invalid duration: %w", err)
+	}
+
+	lowerTitle := strings.ToLower(title)
+	lowerArtist := strings.ToLower(artist)
+
+	var matchURL string
+	doc.Find("a.flex.flex-col").EachWithBreak(func(_ int, sel *goquery.Selection) bool {
+		text := strings.ToLower(sel.Text())
+		if !strings.Contains(text, lowerTitle) || !strings.Contains(text, lowerArtist) {
+			return true
+		}
+
+		durationStr := strings.TrimSpace(sel.Find("div.flex-1.flex-col.items-center").Eq(1).Find("span.text-2xl").Text())
+		parts := strings.Split(durationStr, ":")
+		if len(parts) != 2 {
+			return true
+		}
+		minutes, err := strconv.Atoi(parts[0])
+		if err != nil {
+			return true
+		}
+		seconds, err := strconv.Atoi(parts[1])
+		if err != nil {
+			return true
+		}
+
+		const toleranceSec = 2
+		foundDuration := minutes*60 + seconds
+		if foundDuration <= wantDuration-toleranceSec || foundDuration >= wantDuration+toleranceSec {
+			return true
+		}
+
+		matchURL = sel.AttrOr("href", "")
+		return false
+	})
+
+	if matchURL == "" {
+		return "", fmt.Errorf("no data found")
+	}
+
+	return rootURL + matchURL, nil
+}
+
+func fetchBPMPage(ctx context.Context, httpClient *http.Client, url string) (string, error) {
+	req, err := http.NewRequestWithContext(ctx, "GET", url, nil)
+	if err != nil {
+		return "", err
+	}
+
+	resp, err := httpClient.Do(req)
+	if err != nil {
+		return "", err
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		return "", fmt.Errorf("unexpected status code: %d", resp.StatusCode)
+	}
+
+	body, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return "", err
+	}
+
+	return string(body), nil
+}
+
+func parseBPM(html string) (bpmKey, error) {
+	bpmMatch := bpmRegex.FindStringSubmatch(html)
+	keyMatch := keyRegex.FindStringSubmatch(html)
+	modeMatch := modeRegex.FindStringSubmatch(html)
+
+	if len(bpmMatch) != 2 || len(keyMatch) != 2 || len(modeMatch) != 2 {
+		return bpmKey{}, fmt.Errorf("no data found")
+	}
+
+	bpm := bpmMatch[1]
+	key := strings.SplitN(keyMatch[1], "/", 2)[0]
+	key = strings.ReplaceAll(key, "\u266f", "#")
+	key = strings.ReplaceAll(key, "\u266d", "b")
+
+	if modeMatch[1] == "minor" {
+		key += "m"
+	}
+
+	return bpmKey{BPM: bpm, Key: key}, nil
+}