# Bedrock-API Platform Integrations

## Integration Overview

| Platform | Status | API Type | Auth Method | Streaming | Special Features |
|----------|--------|----------|-------------|-----------|------------------|
| Spotify | Full | Partner API | OAuth 2.0 | No | Full discography, high-quality metadata |
| SoundCloud | Full | api-v2 | Client ID | Yes | Progressive MP3, batch hydration, /resolve |
| Deezer | Full | Public API | None | No | Concurrent fetching, no auth required |
| YouTube Music | Full | Innertube | Cookies | Yes | 7-client fallback, itag priority, WEB_REMIX |
| Yandex Music | Stub | N/A | N/A | No | Placeholder only |
| VK Music | Stub | N/A | N/A | No | Placeholder only |

**Active Integrations**: 4  
**Stub Integrations**: 2

## Spotify Integration

### API Details

**File**: `providers/spotify.go`  
**Library**: `spotapi-go` (submodule wrapping `zmb3/spotify/v2`)  
**API Type**: Spotify Partner API (not Web API)  
**Authentication**: OAuth 2.0 Client Credentials flow

### Authentication

**Environment Variables**:
```
SPOTIFY_CLIENT_ID=your_client_id
SPOTIFY_CLIENT_SECRET=your_client_secret
```

**OAuth Flow**:
```go
func NewSpotifyProvider() *SpotifyProvider {
    clientID := os.Getenv("SPOTIFY_CLIENT_ID")
    clientSecret := os.Getenv("SPOTIFY_CLIENT_SECRET")
    
    if clientID == "" || clientSecret == "" {
        log.Println("[spotify] Credentials not configured, provider disabled")
        return nil
    }
    
    auth := spotifyauth.New(
        spotifyauth.WithClientID(clientID),
        spotifyauth.WithClientSecret(clientSecret),
    )
    
    ctx := context.Background()
    token, err := auth.Token(ctx)
    if err != nil {
        log.Printf("[spotify] Auth failed: %v", err)
        return nil
    }
    
    client := spotify.New(auth.Client(ctx, token))
    
    return &SpotifyProvider{
        client: client,
        auth:   auth,
    }
}
```

**Token Refresh**: Handled automatically by `spotapi-go` wrapper

### Search Implementation

**Track Search**:
```go
func (p *SpotifyProvider) SearchTracks(ctx context.Context, query string, limit int32) ([]*pb.Track, error) {
    results, err := p.client.Search(ctx, query, spotify.SearchTypeTrack, spotify.Limit(int(limit)))
    if err != nil {
        return nil, fmt.Errorf("spotify search: %w", err)
    }
    
    tracks := make([]*pb.Track, 0, len(results.Tracks.Tracks))
    for _, t := range results.Tracks.Tracks {
        tracks = append(tracks, &pb.Track{
            Id:        fmt.Sprintf("spotify:track:%s", t.ID),
            Title:     t.Name,
            Artist:    t.Artists[0].Name,
            ArtistId:  fmt.Sprintf("spotify:artist:%s", t.Artists[0].ID),
            Album:     t.Album.Name,
            AlbumId:   fmt.Sprintf("spotify:album:%s", t.Album.ID),
            Duration:  int32(t.Duration / 1000), // ms to seconds
            CoverUrl:  getCoverURL(t.Album.Images),
            Year:      extractYear(t.Album.ReleaseDate),
            Explicit:  t.Explicit,
            Platform:  pb.Platform_SPOTIFY,
        })
    }
    
    return tracks, nil
}
```

**Album Search**: Similar pattern, uses `spotify.SearchTypeAlbum`  
**Artist Search**: Similar pattern, uses `spotify.SearchTypeArtist`  
**Playlist Search**: Similar pattern, uses `spotify.SearchTypePlaylist`

### Metadata Retrieval

**Get Track**:
```go
func (p *SpotifyProvider) GetTrack(ctx context.Context, id string) (*pb.Track, error) {
    track, err := p.client.GetTrack(ctx, spotify.ID(id))
    if err != nil {
        return nil, fmt.Errorf("get track: %w", err)
    }
    
    return &pb.Track{
        Id:        fmt.Sprintf("spotify:track:%s", track.ID),
        Title:     track.Name,
        Artist:    track.Artists[0].Name,
        ArtistId:  fmt.Sprintf("spotify:artist:%s", track.Artists[0].ID),
        Album:     track.Album.Name,
        AlbumId:   fmt.Sprintf("spotify:album:%s", track.Album.ID),
        Duration:  int32(track.Duration / 1000),
        CoverUrl:  getCoverURL(track.Album.Images),
        Year:      extractYear(track.Album.ReleaseDate),
        Explicit:  track.Explicit,
        Isrc:      track.ExternalIDs.ISRC,
        Platform:  pb.Platform_SPOTIFY,
    }, nil
}
```

**Get Album** (with tracks):
```go
func (p *SpotifyProvider) GetAlbum(ctx context.Context, id string) (*pb.Album, error) {
    album, err := p.client.GetAlbum(ctx, spotify.ID(id))
    if err != nil {
        return nil, fmt.Errorf("get album: %w", err)
    }
    
    tracks := make([]*pb.Track, 0, len(album.Tracks.Tracks))
    for _, t := range album.Tracks.Tracks {
        tracks = append(tracks, &pb.Track{
            Id:       fmt.Sprintf("spotify:track:%s", t.ID),
            Title:    t.Name,
            Artist:   t.Artists[0].Name,
            Duration: int32(t.Duration / 1000),
            Platform: pb.Platform_SPOTIFY,
        })
    }
    
    return &pb.Album{
        Id:         fmt.Sprintf("spotify:album:%s", album.ID),
        Title:      album.Name,
        Artist:     album.Artists[0].Name,
        ArtistId:   fmt.Sprintf("spotify:artist:%s", album.Artists[0].ID),
        Year:       extractYear(album.ReleaseDate),
        CoverUrl:   getCoverURL(album.Images),
        TrackCount: int32(album.Tracks.Total),
        Tracks:     tracks,
        Genre:      getGenre(album.Genres),
        Label:      album.Label,
        Platform:   pb.Platform_SPOTIFY,
    }, nil
}
```

**Get Artist** (with discography):
```go
func (p *SpotifyProvider) GetArtist(ctx context.Context, id string) (*pb.Artist, error) {
    artist, err := p.client.GetArtist(ctx, spotify.ID(id))
    if err != nil {
        return nil, fmt.Errorf("get artist: %w", err)
    }
    
    // Fetch artist albums
    albumsPage, err := p.client.GetArtistAlbums(ctx, spotify.ID(id), spotify.Limit(50))
    if err != nil {
        return nil, fmt.Errorf("get artist albums: %w", err)
    }
    
    albums := make([]*pb.Album, 0, len(albumsPage.Albums))
    for _, a := range albumsPage.Albums {
        albums = append(albums, &pb.Album{
            Id:       fmt.Sprintf("spotify:album:%s", a.ID),
            Title:    a.Name,
            Year:     extractYear(a.ReleaseDate),
            CoverUrl: getCoverURL(a.Images),
            Platform: pb.Platform_SPOTIFY,
        })
    }
    
    return &pb.Artist{
        Id:        fmt.Sprintf("spotify:artist:%s", artist.ID),
        Name:      artist.Name,
        ImageUrl:  getCoverURL(artist.Images),
        Genres:    artist.Genres,
        Followers: int64(artist.Followers.Total),
        Albums:    albums,
        Platform:  pb.Platform_SPOTIFY,
    }, nil
}
```

### Streaming

**No Direct Streaming**:
```go
func (p *SpotifyProvider) GetStreamURL(ctx context.Context, id string) (string, error) {
    return "", errors.New("spotify does not provide streaming URLs via partner API")
}
```

**Bridge Resolution**: Handled by `resolver.go` (searches SoundCloud/YouTube Music for matching track)

### ID Namespacing

**Format**: `spotify:{type}:{native_id}`

**Examples**:
- Track: `spotify:track:3n3Ppam7vgaVa1iaRUc9Lp`
- Album: `spotify:album:6DEjYFkNZh67HP7R9PSZvv`
- Artist: `spotify:artist:0TnOYISbd1XYRBk9myaseg`
- Playlist: `spotify:playlist:37i9dQZF1DXcBWIGoYBM5M`

### Rate Limiting

**Spotify Limits**: 180 requests per minute (partner API)

**No Client-Side Limiting**: Relies on Spotify API returning 429 errors

**Error Handling**:
```go
if err != nil {
    if strings.Contains(err.Error(), "429") {
        return nil, errors.New("spotify rate limit exceeded")
    }
    return nil, err
}
```

### Unique Features

- **ISRC Support**: Returns International Standard Recording Code for tracks
- **Full Discography**: Artist endpoint returns all albums
- **High-Quality Metadata**: Rich metadata (genres, followers, release dates)
- **Explicit Content Flags**: Tracks marked as explicit

## SoundCloud Integration

### API Details

**File**: `providers/soundcloud.go`  
**Library**: Custom HTTP client (no official SDK)  
**API Type**: SoundCloud api-v2 (public, undocumented)  
**Authentication**: Client ID (no OAuth required)

### Client ID Rotation

**Environment Variable**:
```
SOUNDCLOUD_CLIENT_IDS=id1,id2,id3,id4
```

**Rotation Logic**:
```go
type SoundCloudProvider struct {
    clientIDs   []string
    currentID   int
    mu          sync.Mutex
    httpClient  *http.Client
}

func NewSoundCloudProvider() *SoundCloudProvider {
    clientIDsStr := os.Getenv("SOUNDCLOUD_CLIENT_IDS")
    if clientIDsStr == "" {
        log.Println("[soundcloud] Client IDs not configured, provider disabled")
        return nil
    }
    
    clientIDs := strings.Split(clientIDsStr, ",")
    
    return &SoundCloudProvider{
        clientIDs:  clientIDs,
        currentID:  0,
        httpClient: &http.Client{Timeout: 10 * time.Second},
    }
}

func (p *SoundCloudProvider) getClientID() string {
    p.mu.Lock()
    defer p.mu.Unlock()
    
    id := p.clientIDs[p.currentID]
    p.currentID = (p.currentID + 1) % len(p.clientIDs)
    
    return id
}
```

**Purpose**: Avoid rate limiting by rotating through multiple client IDs

### Search Implementation

**Track Search**:
```go
func (p *SoundCloudProvider) SearchTracks(ctx context.Context, query string, limit int32) ([]*pb.Track, error) {
    url := fmt.Sprintf("https://api-v2.soundcloud.com/search/tracks?q=%s&limit=%d&client_id=%s",
        url.QueryEscape(query),
        limit,
        p.getClientID(),
    )
    
    resp, err := p.httpClient.Get(url)
    if err != nil {
        return nil, fmt.Errorf("soundcloud search: %w", err)
    }
    defer resp.Body.Close()
    
    var result struct {
        Collection []struct {
            ID          int64  `json:"id"`
            Title       string `json:"title"`
            User        struct {
                Username string `json:"username"`
            } `json:"user"`
            ArtworkURL  string `json:"artwork_url"`
            Duration    int32  `json:"duration"` // milliseconds
            Genre       string `json:"genre"`
            PlayCount   int64  `json:"playback_count"`
        } `json:"collection"`
    }
    
    if err := json.NewDecoder(resp.Body).Decode(&result); err != nil {
        return nil, fmt.Errorf("decode response: %w", err)
    }
    
    tracks := make([]*pb.Track, 0, len(result.Collection))
    for _, t := range result.Collection {
        tracks = append(tracks, &pb.Track{
            Id:        fmt.Sprintf("soundcloud:track:%d", t.ID),
            Title:     t.Title,
            Artist:    t.User.Username,
            Duration:  t.Duration / 1000, // ms to seconds
            CoverUrl:  t.ArtworkURL,
            Genre:     t.Genre,
            PlayCount: t.PlayCount,
            Platform:  pb.Platform_SOUNDCLOUD,
        })
    }
    
    return tracks, nil
}
```

### Batch Hydration

**Purpose**: Fetch full track details for multiple IDs in single request

**Implementation**:
```go
func (p *SoundCloudProvider) hydrateTracks(ctx context.Context, ids []string) ([]*pb.Track, error) {
    // SoundCloud allows up to 30 IDs per request
    const batchSize = 30
    
    var allTracks []*pb.Track
    
    for i := 0; i < len(ids); i += batchSize {
        end := i + batchSize
        if end > len(ids) {
            end = len(ids)
        }
        
        batch := ids[i:end]
        url := fmt.Sprintf("https://api-v2.soundcloud.com/tracks?ids=%s&client_id=%s",
            strings.Join(batch, ","),
            p.getClientID(),
        )
        
        resp, err := p.httpClient.Get(url)
        if err != nil {
            return nil, fmt.Errorf("hydrate batch: %w", err)
        }
        defer resp.Body.Close()
        
        var tracks []struct {
            ID       int64  `json:"id"`
            Title    string `json:"title"`
            Duration int32  `json:"duration"`
            // ... other fields
        }
        
        if err := json.NewDecoder(resp.Body).Decode(&tracks); err != nil {
            return nil, fmt.Errorf("decode batch: %w", err)
        }
        
        for _, t := range tracks {
            allTracks = append(allTracks, &pb.Track{
                Id:       fmt.Sprintf("soundcloud:track:%d", t.ID),
                Title:    t.Title,
                Duration: t.Duration / 1000,
                Platform: pb.Platform_SOUNDCLOUD,
            })
        }
    }
    
    return allTracks, nil
}
```

**Use Case**: Playlist retrieval (fetch details for all track IDs in playlist)

### Stream URL Resolution

**Progressive MP3 Selection**:
```go
func (p *SoundCloudProvider) GetStreamURL(ctx context.Context, id string) (string, error) {
    // Get track info
    trackURL := fmt.Sprintf("https://api-v2.soundcloud.com/tracks/%s?client_id=%s",
        id,
        p.getClientID(),
    )
    
    resp, err := p.httpClient.Get(trackURL)
    if err != nil {
        return "", fmt.Errorf("get track: %w", err)
    }
    defer resp.Body.Close()
    
    var track struct {
        Media struct {
            Transcodings []struct {
                URL    string `json:"url"`
                Format struct {
                    Protocol string `json:"protocol"`
                    MimeType string `json:"mime_type"`
                } `json:"format"`
            } `json:"transcodings"`
        } `json:"media"`
    }
    
    if err := json.NewDecoder(resp.Body).Decode(&track); err != nil {
        return "", fmt.Errorf("decode track: %w", err)
    }
    
    // Select progressive MP3 transcoding
    for _, t := range track.Media.Transcodings {
        if t.Format.Protocol == "progressive" && strings.Contains(t.Format.MimeType, "mp3") {
            // Fetch actual stream URL from transcoding URL
            streamResp, err := p.httpClient.Get(fmt.Sprintf("%s?client_id=%s", t.URL, p.getClientID()))
            if err != nil {
                continue
            }
            defer streamResp.Body.Close()
            
            var streamData struct {
                URL string `json:"url"`
            }
            
            if err := json.NewDecoder(streamResp.Body).Decode(&streamData); err != nil {
                continue
            }
            
            return streamData.URL, nil
        }
    }
    
    return "", errors.New("no progressive stream found")
}
```

**Stream Types**:
- **Progressive**: Direct HTTP download (preferred)
- **HLS**: HTTP Live Streaming (not used)

**Bitrate**: Typically 128 kbps MP3

### URL Resolution

**Purpose**: Convert SoundCloud URLs to track IDs

**Implementation**:
```go
func (p *SoundCloudProvider) ResolveURL(ctx context.Context, trackURL string) (string, error) {
    resolveURL := fmt.Sprintf("https://api-v2.soundcloud.com/resolve?url=%s&client_id=%s",
        url.QueryEscape(trackURL),
        p.getClientID(),
    )
    
    resp, err := p.httpClient.Get(resolveURL)
    if err != nil {
        return "", fmt.Errorf("resolve url: %w", err)
    }
    defer resp.Body.Close()
    
    var result struct {
        ID int64 `json:"id"`
    }
    
    if err := json.NewDecoder(resp.Body).Decode(&result); err != nil {
        return "", fmt.Errorf("decode response: %w", err)
    }
    
    return fmt.Sprintf("%d", result.ID), nil
}
```

**Example**:
```
Input:  https://soundcloud.com/artist/track-name
Output: 1234567890
```

### Rate Limiting

**SoundCloud Limits**: Undocumented (estimated 1000 requests/hour per client ID)

**Mitigation**: Client ID rotation (4 IDs = 4000 requests/hour)

**Error Handling**:
```go
if resp.StatusCode == 429 {
    log.Printf("[soundcloud] Rate limit hit, rotating client ID")
    return p.SearchTracks(ctx, query, limit) // Retry with next client ID
}
```

### Unique Features

- **Client ID Rotation**: Automatic rotation to avoid rate limits
- **Batch Hydration**: Fetch 30 tracks in single request
- **URL Resolution**: Convert web URLs to track IDs
- **Progressive Streaming**: Direct MP3 download (no HLS complexity)

## Deezer Integration

### API Details

**File**: `providers/deezer.go`  
**Library**: Custom HTTP client (no official Go SDK)  
**API Type**: Deezer Public API  
**Authentication**: None required

### Search Implementation

**Track Search**:
```go
func (p *DeezerProvider) SearchTracks(ctx context.Context, query string, limit int32) ([]*pb.Track, error) {
    url := fmt.Sprintf("https://api.deezer.com/search/track?q=%s&limit=%d",
        url.QueryEscape(query),
        limit,
    )
    
    resp, err := http.Get(url)
    if err != nil {
        return nil, fmt.Errorf("deezer search: %w", err)
    }
    defer resp.Body.Close()
    
    var result struct {
        Data []struct {
            ID       int64  `json:"id"`
            Title    string `json:"title"`
            Artist   struct {
                ID   int64  `json:"id"`
                Name string `json:"name"`
            } `json:"artist"`
            Album struct {
                ID    int64  `json:"id"`
                Title string `json:"title"`
                Cover string `json:"cover_medium"`
            } `json:"album"`
            Duration int32 `json:"duration"` // seconds (not milliseconds)
        } `json:"data"`
    }
    
    if err := json.NewDecoder(resp.Body).Decode(&result); err != nil {
        return nil, fmt.Errorf("decode response: %w", err)
    }
    
    tracks := make([]*pb.Track, 0, len(result.Data))
    for _, t := range result.Data {
        tracks = append(tracks, &pb.Track{
            Id:       fmt.Sprintf("deezer:track:%d", t.ID),
            Title:    t.Title,
            Artist:   t.Artist.Name,
            ArtistId: fmt.Sprintf("deezer:artist:%d", t.Artist.ID),
            Album:    t.Album.Title,
            AlbumId:  fmt.Sprintf("deezer:album:%d", t.Album.ID),
            Duration: t.Duration, // Already in seconds
            CoverUrl: t.Album.Cover,
            Platform: pb.Platform_DEEZER,
        })
    }
    
    return tracks, nil
}
```

### Concurrent Artist Data Fetching

**Get Artist** (parallel goroutines):
```go
func (p *DeezerProvider) GetArtist(ctx context.Context, id string) (*pb.Artist, error) {
    var (
        wg        sync.WaitGroup
        mu        sync.Mutex
        artist    *pb.Artist
        albums    []*pb.Album
        topTracks []*pb.Track
        errors    []error
    )
    
    wg.Add(3)
    
    // Fetch artist info
    go func() {
        defer wg.Done()
        
        url := fmt.Sprintf("https://api.deezer.com/artist/%s", id)
        resp, err := http.Get(url)
        if err != nil {
            mu.Lock()
            errors = append(errors, err)
            mu.Unlock()
            return
        }
        defer resp.Body.Close()
        
        var data struct {
            ID        int64    `json:"id"`
            Name      string   `json:"name"`
            Picture   string   `json:"picture_medium"`
            NbFan     int64    `json:"nb_fan"`
        }
        
        json.NewDecoder(resp.Body).Decode(&data)
        
        mu.Lock()
        artist = &pb.Artist{
            Id:        fmt.Sprintf("deezer:artist:%d", data.ID),
            Name:      data.Name,
            ImageUrl:  data.Picture,
            Followers: data.NbFan,
            Platform:  pb.Platform_DEEZER,
        }
        mu.Unlock()
    }()
    
    // Fetch artist albums
    go func() {
        defer wg.Done()
        
        url := fmt.Sprintf("https://api.deezer.com/artist/%s/albums", id)
        resp, err := http.Get(url)
        if err != nil {
            mu.Lock()
            errors = append(errors, err)
            mu.Unlock()
            return
        }
        defer resp.Body.Close()
        
        var data struct {
            Data []struct {
                ID      int64  `json:"id"`
                Title   string `json:"title"`
                Cover   string `json:"cover_medium"`
                ReleaseDate string `json:"release_date"`
            } `json:"data"`
        }
        
        json.NewDecoder(resp.Body).Decode(&data)
        
        mu.Lock()
        for _, a := range data.Data {
            albums = append(albums, &pb.Album{
                Id:       fmt.Sprintf("deezer:album:%d", a.ID),
                Title:    a.Title,
                CoverUrl: a.Cover,
                Year:     extractYear(a.ReleaseDate),
                Platform: pb.Platform_DEEZER,
            })
        }
        mu.Unlock()
    }()
    
    // Fetch artist top tracks
    go func() {
        defer wg.Done()
        
        url := fmt.Sprintf("https://api.deezer.com/artist/%s/top?limit=10", id)
        resp, err := http.Get(url)
        if err != nil {
            mu.Lock()
            errors = append(errors, err)
            mu.Unlock()
            return
        }
        defer resp.Body.Close()
        
        var data struct {
            Data []struct {
                ID    int64  `json:"id"`
                Title string `json:"title"`
            } `json:"data"`
        }
        
        json.NewDecoder(resp.Body).Decode(&data)
        
        mu.Lock()
        for _, t := range data.Data {
            topTracks = append(topTracks, &pb.Track{
                Id:       fmt.Sprintf("deezer:track:%d", t.ID),
                Title:    t.Title,
                Platform: pb.Platform_DEEZER,
            })
        }
        mu.Unlock()
    }()
    
    wg.Wait()
    
    if len(errors) > 0 {
        return nil, errors[0]
    }
    
    artist.Albums = albums
    // topTracks not included in response (no field in Artist proto)
    
    return artist, nil
}
```

**Performance**: 3 API calls in parallel instead of sequential (3x faster)

### Streaming

**No Public Streaming**:
```go
func (p *DeezerProvider) GetStreamURL(ctx context.Context, id string) (string, error) {
    return "", errors.New("deezer public API does not provide streaming URLs")
}
```

**Note**: Deezer has streaming API, but requires paid partnership (not public)

### Duration Handling

**Deezer Returns Seconds** (not milliseconds like Spotify):
```go
track := &pb.Track{
    Duration: deezerTrack.Duration, // Already in seconds, no conversion needed
}
```

### Rate Limiting

**Deezer Limits**: 50 requests per 5 seconds (public API)

**No Client-Side Limiting**: Relies on Deezer API returning 403 errors

**Error Handling**:
```go
if resp.StatusCode == 403 {
    return nil, errors.New("deezer rate limit exceeded")
}
```

### Unique Features

- **No Authentication**: Public API, no credentials required
- **Concurrent Fetching**: Artist data fetched in parallel
- **Fan Count**: Returns follower count (nb_fan field)
- **Simple Integration**: No OAuth, no client IDs, just HTTP GET

## YouTube Music Integration

### API Details

**File**: `providers/youtube.go`  
**Library**: `github.com/kkdai/youtube/v2`  
**API Type**: YouTube Innertube API (internal, undocumented)  
**Authentication**: Cookies (optional, for age-restricted content)

### 7-Client Fallback Pool

**Client Configurations**:
```go
var youtubeClients = []struct {
    name   string
    config youtube.ClientConfig
}{
    {
        name: "TVHTML5_SIMPLY_EMBEDDED",
        config: youtube.ClientConfig{
            ClientName:    "TVHTML5_SIMPLY_EMBEDDED_PLAYER",
            ClientVersion: "2.0",
        },
    },
    {
        name: "TVHTML5",
        config: youtube.ClientConfig{
            ClientName:    "TVHTML5",
            ClientVersion: "7.20230622",
        },
    },
    {
        name: "ANDROID_VR_1",
        config: youtube.ClientConfig{
            ClientName:    "ANDROID_VR",
            ClientVersion: "1.37.35",
            AndroidSDKVersion: 30,
        },
    },
    {
        name: "ANDROID_VR_2",
        config: youtube.ClientConfig{
            ClientName:    "ANDROID_VR",
            ClientVersion: "1.38.50",
            AndroidSDKVersion: 31,
        },
    },
    {
        name: "ANDROID",
        config: youtube.ClientConfig{
            ClientName:    "ANDROID",
            ClientVersion: "18.20.39",
            AndroidSDKVersion: 33,
        },
    },
    {
        name: "IOS",
        config: youtube.ClientConfig{
            ClientName:    "IOS",
            ClientVersion: "18.20.3",
            DeviceModel:   "iPhone14,5",
        },
    },
    {
        name: "WEB",
        config: youtube.ClientConfig{
            ClientName:    "WEB",
            ClientVersion: "2.20230622.01.00",
        },
    },
}
```

**Fallback Logic**:
```go
func (p *YouTubeProvider) GetStreamURL(ctx context.Context, id string) (string, error) {
    for _, clientConfig := range youtubeClients {
        client := youtube.Client{Config: clientConfig.config}
        
        if p.cookies != "" {
            client.HTTPClient = &http.Client{
                Transport: &cookieTransport{cookies: p.cookies},
            }
        }
        
        video, err := client.GetVideoContext(ctx, id)
        if err != nil {
            log.Printf("[youtube] Client %s failed: %v", clientConfig.name, err)
            continue
        }
        
        // Check for cipher (encrypted stream)
        if len(video.Formats) > 0 && video.Formats[0].Cipher != "" {
            log.Printf("[youtube] Client %s returned ciphered stream, skipping", clientConfig.name)
            continue
        }
        
        // Select best format
        streamURL := p.selectBestFormat(video.Formats)
        if streamURL != "" {
            log.Printf("[youtube] Client %s succeeded", clientConfig.name)
            return streamURL, nil
        }
    }
    
    // All clients failed, fallback to SoundCloud
    log.Println("[youtube] All clients failed, falling back to SoundCloud")
    return p.fallbackToSoundCloud(ctx, id)
}
```

**Why 7 Clients**: Different clients have different capabilities and restrictions. Some work for age-restricted content, some avoid ciphered streams, some have better format availability.

### Itag Priority (Audio Quality)

**Format Selection**:
```go
func (p *YouTubeProvider) selectBestFormat(formats youtube.FormatList) string {
    // Priority: 251 (opus, ~160kbps) > 140 (aac, ~128kbps)
    itagPriority := []int{251, 140}
    
    for _, itag := range itagPriority {
        for _, format := range formats {
            if format.ItagNo == itag {
                return format.URL
            }
        }
    }
    
    // Fallback: first audio-only format
    for _, format := range formats {
        if strings.Contains(format.MimeType, "audio") && !strings.Contains(format.MimeType, "video") {
            return format.URL
        }
    }
    
    return ""
}
```

**Itag Reference**:
- **251**: Opus audio, ~160 kbps (best quality)
- **140**: AAC audio, ~128 kbps (good quality, better compatibility)

### Metadata Client (WEB_REMIX)

**Search Implementation**:
```go
func (p *YouTubeProvider) SearchTracks(ctx context.Context, query string, limit int32) ([]*pb.Track, error) {
    // Use WEB_REMIX client (YouTube Music, not regular YouTube)
    client := youtube.Client{
        Config: youtube.ClientConfig{
            ClientName:    "WEB_REMIX",
            ClientVersion: "1.20231122.01.00",
        },
    }
    
    // YouTube Music search endpoint
    searchURL := "https://music.youtube.com/youtubei/v1/search"
    
    payload := map[string]interface{}{
        "context": map[string]interface{}{
            "client": map[string]interface{}{
                "clientName":    "WEB_REMIX",
                "clientVersion": "1.20231122.01.00",
            },
        },
        "query": query,
    }
    
    // Make request, parse music-specific results
    // ...
}
```

**WEB_REMIX vs WEB**: WEB_REMIX returns YouTube Music results (songs, albums, artists), WEB returns regular YouTube videos

### Cookie Support (Age-Restricted Content)

**Environment Variable**:
```
YOUTUBE_COOKIES=cookie-string
```

**Cookie Injection**:
```go
type cookieTransport struct {
    cookies string
    base    http.RoundTripper
}

func (t *cookieTransport) RoundTrip(req *http.Request) (*http.Response, error) {
    req.Header.Set("Cookie", t.cookies)
    
    base := t.base
    if base == nil {
        base = http.DefaultTransport
    }
    
    return base.RoundTrip(req)
}

func NewYouTubeProvider() *YouTubeProvider {
    cookies := os.Getenv("YOUTUBE_COOKIES")
    
    return &YouTubeProvider{
        cookies: cookies,
    }
}
```

**Use Case**: Access age-restricted music videos (requires logged-in YouTube account cookies)

### Cipher Handling

**Problem**: Some YouTube streams are encrypted (ciphered) and require JavaScript decryption

**Solution**: Skip ciphered streams, try next client

```go
if len(video.Formats) > 0 && video.Formats[0].Cipher != "" {
    log.Printf("[youtube] Client %s returned ciphered stream, skipping", clientConfig.name)
    continue // Try next client
}
```

**Fallback**: If all clients return ciphered streams, fall back to SoundCloud

### SoundCloud Fallback

**Implementation**:
```go
func (p *YouTubeProvider) fallbackToSoundCloud(ctx context.Context, videoID string) (string, error) {
    // Get video metadata
    video, err := p.getVideoMetadata(ctx, videoID)
    if err != nil {
        return "", err
    }
    
    // Search SoundCloud for "{artist} - {title}"
    query := fmt.Sprintf("%s - %s", video.Artist, video.Title)
    
    soundcloudProvider := NewSoundCloudProvider()
    tracks, err := soundcloudProvider.SearchTracks(ctx, query, 1)
    if err != nil || len(tracks) == 0 {
        return "", errors.New("soundcloud fallback failed")
    }
    
    // Get stream URL from first SoundCloud result
    return soundcloudProvider.GetStreamURL(ctx, tracks[0].Id)
}
```

**Use Case**: When all YouTube clients fail (ciphered streams, geo-restrictions, etc.)

### Rate Limiting

**YouTube Limits**: Undocumented (estimated 10,000 requests/day for Innertube API)

**No Client-Side Limiting**: Relies on YouTube API returning 429 errors

**Error Handling**:
```go
if err != nil && strings.Contains(err.Error(), "429") {
    return nil, errors.New("youtube rate limit exceeded")
}
```

### Unique Features

- **7-Client Fallback**: Maximizes stream availability
- **Itag Priority**: Selects best audio quality
- **WEB_REMIX Metadata**: YouTube Music-specific search results
- **Cookie Support**: Access age-restricted content
- **Cipher Avoidance**: Skips encrypted streams
- **SoundCloud Fallback**: Ultimate fallback when YouTube fails

## Lyrics Integrations

### LrcLib (Synced Lyrics)

**File**: `bedrock_server/lrclib.go`  
**API**: `https://lrclib.net/api/get`  
**Authentication**: None required  
**Format**: LRC (timestamped lyrics)

**Implementation**:
```go
func (s *server) GetSyncedLyrics(ctx context.Context, req *pb.LyricsRequest) (*pb.SyncedLyricsResponse, error) {
    client := &http.Client{Timeout: 5 * time.Second}
    
    url := fmt.Sprintf("https://lrclib.net/api/get?artist_name=%s&track_name=%s&album_name=%s&duration=%d",
        url.QueryEscape(req.Artist),
        url.QueryEscape(req.Title),
        url.QueryEscape(req.Album),
        req.Duration,
    )
    
    resp, err := client.Get(url)
    if err != nil {
        return nil, fmt.Errorf("lrclib request: %w", err)
    }
    defer resp.Body.Close()
    
    if resp.StatusCode == 404 {
        return nil, errors.New("lyrics not found")
    }
    
    var result struct {
        SyncedLyrics string `json:"syncedLyrics"`
    }
    
    if err := json.NewDecoder(resp.Body).Decode(&result); err != nil {
        return nil, fmt.Errorf("decode response: %w", err)
    }
    
    // Parse LRC format
    lines := parseLRC(result.SyncedLyrics)
    
    return &pb.SyncedLyricsResponse{
        Lines:  lines,
        Source: "lrclib",
    }, nil
}

func parseLRC(lrc string) []*pb.LyricLine {
    var lines []*pb.LyricLine
    
    for _, line := range strings.Split(lrc, "\n") {
        // Parse [mm:ss.xx] timestamp
        if !strings.HasPrefix(line, "[") {
            continue
        }
        
        parts := strings.SplitN(line, "]", 2)
        if len(parts) != 2 {
            continue
        }
        
        timestamp := parseTimestamp(parts[0][1:]) // Remove leading [
        text := parts[1]
        
        lines = append(lines, &pb.LyricLine{
            Timestamp: timestamp,
            Text:      text,
        })
    }
    
    return lines
}

func parseTimestamp(ts string) int32 {
    // Parse "mm:ss.xx" format
    parts := strings.Split(ts, ":")
    if len(parts) != 2 {
        return 0
    }
    
    minutes, _ := strconv.Atoi(parts[0])
    secondsParts := strings.Split(parts[1], ".")
    seconds, _ := strconv.Atoi(secondsParts[0])
    centiseconds := 0
    if len(secondsParts) > 1 {
        centiseconds, _ = strconv.Atoi(secondsParts[1])
    }
    
    return int32(minutes*60*1000 + seconds*1000 + centiseconds*10)
}
```

**Matching**: Artist + title + album + duration (all parameters improve match accuracy)

**Timeout**: 5 seconds (fast API)

### Genius (Plain Lyrics)

**File**: `bedrock_server/genius.go`  
**Library**: `github.com/rhnvrm/lyric-api-go`  
**Authentication**: `GENIUS_ACCESS_TOKEN` environment variable  
**Format**: Plain text + annotations

**Implementation**:
```go
func (s *server) GetLyrics(ctx context.Context, req *pb.LyricsRequest) (*pb.LyricsResponse, error) {
    accessToken := os.Getenv("GENIUS_ACCESS_TOKEN")
    if accessToken == "" {
        return nil, errors.New("GENIUS_ACCESS_TOKEN not configured")
    }
    
    geniusClient := genius.NewClient(accessToken)
    
    // Search for song
    query := fmt.Sprintf("%s %s", req.Artist, req.Title)
    searchResults, err := geniusClient.Search(query)
    if err != nil {
        return nil, fmt.Errorf("genius search: %w", err)
    }
    
    if len(searchResults.Hits) == 0 {
        return nil, errors.New("lyrics not found")
    }
    
    songID := searchResults.Hits[0].Result.ID
    
    // Fetch lyrics
    lyrics, err := geniusClient.GetLyrics(songID)
    if err != nil {
        return nil, fmt.Errorf("get lyrics: %w", err)
    }
    
    // Fetch annotations
    annotations, err := geniusClient.GetAnnotations(songID)
    if err != nil {
        log.Printf("[genius] Failed to fetch annotations: %v", err)
        annotations = nil // Continue without annotations
    }
    
    pbAnnotations := make([]*pb.Annotation, 0, len(annotations))
    for _, a := range annotations {
        pbAnnotations = append(pbAnnotations, &pb.Annotation{
            Fragment:   a.Fragment,
            Annotation: a.Annotation,
        })
    }
    
    return &pb.LyricsResponse{
        Lyrics:      lyrics,
        Source:      "genius",
        Annotations: pbAnnotations,
    }, nil
}
```

**Annotations**: Explanations of lyric meanings (unique to Genius)

**No Timeout**: Uses library default (30 seconds)

## Stub Integrations

### Yandex Music

**File**: `providers/yandex.go`

**Implementation**:
```go
type YandexProvider struct{}

func (p *YandexProvider) Name() string {
    return "yandex"
}

func (p *YandexProvider) SearchTracks(ctx context.Context, query string, limit int32) ([]*pb.Track, error) {
    return nil, errors.New("yandex provider not implemented")
}

// All other methods return errors
```

**Status**: Placeholder only, no actual implementation

**Reason**: Yandex Music API requires partnership agreement (not publicly available)

### VK Music

**File**: `providers/vk.go`

**Implementation**: Same as Yandex (stub only)

**Status**: Placeholder only, no actual implementation

**Reason**: VK Music API requires VK developer account and OAuth (complex setup)

## Integration Comparison

| Feature | Spotify | SoundCloud | Deezer | YouTube Music |
|---------|---------|------------|--------|---------------|
| **Authentication** | OAuth 2.0 | Client ID | None | Cookies (optional) |
| **Streaming** | No | Yes (MP3) | No | Yes (Opus/AAC) |
| **Search Quality** | Excellent | Good | Good | Excellent |
| **Metadata Richness** | High | Medium | Medium | High |
| **Rate Limits** | 180/min | ~1000/hr | 50/5s | ~10k/day |
| **Reliability** | High | Medium | High | Medium |
| **Unique Features** | ISRC, discography | Batch hydration | No auth | 7-client fallback |
| **Complexity** | Medium | Low | Low | High |

## Error Handling Patterns

### Provider-Level Errors

**Pattern**: Log and continue (don't fail entire request)

```go
tracks, err := provider.SearchTracks(ctx, query, limit)
if err != nil {
    log.Printf("[%s] Search failed: %v", provider.Name(), err)
    errors = append(errors, &pb.ProviderError{
        Provider: provider.Name(),
        Message:  err.Error(),
    })
    continue // Don't return, try other providers
}
```

### Partial Response Handling

**Pattern**: Return successful results even if some providers fail

```go
if len(errors) > 0 {
    if len(allTracks) == 0 {
        status = pb.ResponseStatus_ERROR
    } else {
        status = pb.ResponseStatus_PARTIAL
    }
}

return &pb.SearchTracksResponse{
    Tracks: allTracks,
    Status: status,
    Errors: errors,
}
```

### Retry Logic

**No Automatic Retries**: Failed requests are not retried

**Client Responsibility**: Clients must implement retry logic if needed

## Performance Optimization

### Parallel Queries

**All Providers Queried Simultaneously**:
```go
var wg sync.WaitGroup

for _, provider := range providers {
    wg.Add(1)
    go func(p trackProvider) {
        defer wg.Done()
        results, err := p.SearchTracks(ctx, query, limit)
        // Aggregate results
    }(provider)
}

wg.Wait()
```

**Response Time**: Limited by slowest provider (not sum of all providers)

### Connection Pooling

**HTTP Client Reuse**: Each provider maintains persistent HTTP client

```go
type SoundCloudProvider struct {
    httpClient *http.Client
}

func NewSoundCloudProvider() *SoundCloudProvider {
    return &SoundCloudProvider{
        httpClient: &http.Client{
            Timeout: 10 * time.Second,
            Transport: &http.Transport{
                MaxIdleConns:        100,
                MaxIdleConnsPerHost: 10,
                IdleConnTimeout:     90 * time.Second,
            },
        },
    }
}
```

**Benefit**: Avoid TCP handshake overhead on every request

## Integration Recommendations for Metadata Aggregator

### Adopt

- **Provider Interface Pattern**: Clean abstraction for platform-specific logic
- **Parallel Queries**: Fan-out concurrency for fast responses
- **Partial Response Handling**: Resilient to individual provider failures
- **ID Namespacing**: Prevents collisions, enables explicit routing

### Avoid

- **No Caching**: Implement Redis caching for metadata
- **No Rate Limiting**: Add client-side rate limiting per provider
- **Manual HTTP Clients**: Consider using official SDKs where available

### Enhance

- **Add More Providers**: Discogs, MusicBrainz, Last.fm, etc.
- **Implement Caching**: Cache metadata, search results, stream URLs
- **Add Circuit Breakers**: Temporarily disable failing providers
- **Add Metrics**: Track provider success rates, latencies, errors
- **Add Retry Logic**: Exponential backoff for transient failures