yandex-music-api-go/internal/client/tracks.go

// Package client provides methods for interacting with Yandex Music API endpoints.
package client

import (
	"context"
	"crypto/md5"
	"encoding/xml"
	"fmt"

	"gitea.mrixs.me/Mrixs/yandex-music-api-go/internal/models"
	"gitea.mrixs.me/Mrixs/yandex-music-api-go/internal/utils"
)

const downloadSignSalt = "XGRlBW9FXlekgbPrRHuSiA"

// downloadInfoXML represents the XML response from download_info_url.
type downloadInfoXML struct {
	Host string `xml:"host"`
	Path string `xml:"path"`
	Ts   string `xml:"ts"`
	S    string `xml:"s"`
}

// resolveDownloadURL downloads the XML from downloadInfoURL, parses host/path/ts/s,
// computes the MD5 signature, and returns the signed download URL:
// https://{host}/get-mp3/{sign}/{ts}{path}
func resolveDownloadURL(ctx context.Context, downloadInfoURL string, ri models.RequestInterface) (string, error) {
	data, err := ri.Download(ctx, downloadInfoURL)
	if err != nil {
		return "", err
	}

	var xmlData downloadInfoXML
	if err := xml.Unmarshal(data, &xmlData); err != nil {
		return "", fmt.Errorf("failed to parse download info XML: %w", err)
	}

	if xmlData.Path == "" || xmlData.S == "" {
		return "", utils.NewYandexMusicError("invalid download info XML: missing path or s", utils.ErrBadRequest)
	}

	sign := fmt.Sprintf("%x", md5.Sum([]byte(downloadSignSalt+xmlData.Path[1:]+xmlData.S)))

	return fmt.Sprintf("https://%s/get-mp3/%s/%s%s", xmlData.Host, sign, xmlData.Ts, xmlData.Path), nil
}

// GetTracks gets tracks by their IDs (GET /tracks).
// Returns a slice of Track pointers, or nil if no IDs are provided.
func (c *Client) GetTracks(ctx context.Context, trackIDs []string) ([]*models.Track, error) {
	if len(trackIDs) == 0 {
		return nil, nil
	}

	params := map[string]string{
		"track-ids": joinIDs(trackIDs),
	}

	var result []models.Track
	if err := c.request.Get(ctx, "/tracks", params, &result); err != nil {
		return nil, err
	}

	tracks := make([]*models.Track, len(result))
	for i := range result {
		result[i].SetClient(c)
		tracks[i] = &result[i]
	}
	return tracks, nil
}

// GetTrack gets a single track by ID using GetTracks.
// Returns an error if no track is found with the given ID.
func (c *Client) GetTrack(ctx context.Context, trackID string) (*models.Track, error) {
	tracks, err := c.GetTracks(ctx, []string{trackID})
	if err != nil {
		return nil, err
	}
	if len(tracks) == 0 {
		return nil, utils.NewYandexMusicError("track not found", utils.ErrNotFound)
	}
	return tracks[0], nil
}

// GetTrackDownloadInfo gets download info for a track (GET /tracks/{track_id}/download-info).
// The quality parameter specifies the desired audio quality (e.g., "mp3").
func (c *Client) GetTrackDownloadInfo(ctx context.Context, trackID, quality string) ([]models.DownloadInfo, error) {
	params := map[string]string{
		"track_id": trackID,
	}
	if quality != "" {
		params["quality"] = quality
	}

	var result []models.DownloadInfo
	if err := c.request.Get(ctx, fmt.Sprintf("/tracks/%s/download-info", trackID), params, &result); err != nil {
		return nil, err
	}
	return result, nil
}

// GetTrackDownloadURL returns a signed direct download URL for a track.
// It fetches download info, finds a matching entry, downloads the XML from its
// download_info_url, parses host/path/ts/s, computes the MD5 signature, and
// returns https://{host}/get-mp3/{sign}/{ts}{path}.
func (c *Client) GetTrackDownloadURL(ctx context.Context, trackID, format string, bitrate int) (string, error) {
	info, err := c.GetTrackDownloadInfo(ctx, trackID, format)
	if err != nil {
		return "", err
	}

	// Find matching download info
	var di *models.DownloadInfo
	for i := range info {
		if info[i].Codec == format && (bitrate == 0 || info[i].Bitrate == bitrate) {
			di = &info[i]
			break
		}
	}
	if di == nil && len(info) > 0 {
		di = &info[0]
	}
	if di == nil {
		return "", utils.NewYandexMusicError("no download info available", utils.ErrNotFound)
	}

	if di.URL != "" {
		return di.URL, nil
	}

	if di.DownloadInfoURL == "" {
		return "", utils.NewYandexMusicError("no download URL available", utils.ErrNotFound)
	}

	return resolveDownloadURL(ctx, di.DownloadInfoURL, c.request)
}

// DownloadTrack downloads a track by ID.
// It first fetches download info, finds a matching format/bitrate, resolves the
// signed URL if needed, then downloads the file content.
func (c *Client) DownloadTrack(ctx context.Context, trackID, format string, bitrate int) ([]byte, error) {
	info, err := c.GetTrackDownloadInfo(ctx, trackID, format)
	if err != nil {
		return nil, err
	}

	// Find matching download info
	var di *models.DownloadInfo
	for i := range info {
		if info[i].Codec == format && (bitrate == 0 || info[i].Bitrate == bitrate) {
			di = &info[i]
			break
		}
	}
	if di == nil && len(info) > 0 {
		di = &info[0]
	}
	if di == nil {
		return nil, utils.NewYandexMusicError("no download info available", utils.ErrNotFound)
	}

	url := di.URL
	if url == "" {
		if di.DownloadInfoURL == "" {
			return nil, utils.NewYandexMusicError("no download URL available", utils.ErrNotFound)
		}
		url, err = resolveDownloadURL(ctx, di.DownloadInfoURL, c.request)
		if err != nil {
			return nil, err
		}
	}

	return c.request.Download(ctx, url)
}

// SearchResult represents search results containing tracks.
type SearchResult struct {
	Tracks *SearchTracksResult `json:"tracks"`
}

// SearchTracksResult represents track search results with total count and results list.
type SearchTracksResult struct {
	Total   int            `json:"total"`
	Results []models.Track `json:"results"`
}

func joinIDs(ids []string) string {
	result := ""
	for i, id := range ids {
		if i > 0 {
			result += ","
		}
		result += id
	}
	return result
}