1 files changed, 58 insertions, 6 deletions

diff --git a/internal/audio/provider.go b/internal/audio/provider.go
index 0e863bf..fac0cd9 100644
--- a/internal/audio/provider.go
+++ b/internal/audio/provider.go
@@ -17,26 +17,76 @@ type Provider interface {
 	IsAvailable() error
 }
 
-// Config holds common configuration for audio providers.
+// OpenAIAudioConfig holds settings specific to the OpenAI TTS backend.
+// Callers that only use Gemini never need to populate these fields.
+type OpenAIAudioConfig struct {
+	Key         string
+	Model       string  // "tts-1", "tts-1-hd", or "gpt-4o-mini-tts"
+	Voice       string  // One of OpenAIVoices.
+	Speed       float64 // 0.25 to 4.0
+	Instruction string  // Voice instructions for gpt-4o-mini-tts model
+}
+
+// GeminiAudioConfig holds settings specific to the Gemini TTS backend.
+// Callers that only use OpenAI never need to populate these fields.
+type GeminiAudioConfig struct {
+	APIKey   string
+	TTSModel string  // "gemini-2.5-flash-preview-tts"
+	Voice    string  // One of GeminiVoices; empty lets the caller choose a random voice.
+	Speed    float64 // Prompt hint for desired speech speed
+}
+
+// Config holds common configuration for audio providers. Provider-specific
+// settings are grouped into OpenAI and Gemini sub-configs so callers and
+// implementations only see the fields relevant to their backend.
 type Config struct {
 	Provider     string // Provider name: "openai" or "gemini"
 	OutputDir    string // Directory for output files
 	OutputFormat string // Output format: "mp3" or "wav"
 
-	// OpenAI-specific settings
+	// OpenAI-specific settings — ignored when Provider == "gemini".
 	OpenAIKey         string
 	OpenAIModel       string  // "tts-1", "tts-1-hd", or "gpt-4o-mini-tts"
 	OpenAIVoice       string  // One of OpenAIVoices.
 	OpenAISpeed       float64 // 0.25 to 4.0
 	OpenAIInstruction string  // Voice instructions for gpt-4o-mini-tts model
 
-	// Gemini-specific settings
+	// Gemini-specific settings — ignored when Provider == "openai".
 	GoogleAPIKey   string
 	GeminiTTSModel string  // "gemini-2.5-flash-preview-tts"
 	GeminiVoice    string  // One of GeminiVoices; empty lets the caller choose a random voice.
 	GeminiSpeed    float64 // Prompt hint for desired speech speed
 }
 
+// openAIAudioConfigFrom extracts the OpenAI-specific sub-config from the flat Config.
+// A nil Config produces a zero-value OpenAIAudioConfig.
+func openAIAudioConfigFrom(c *Config) OpenAIAudioConfig {
+	if c == nil {
+		return OpenAIAudioConfig{}
+	}
+	return OpenAIAudioConfig{
+		Key:         c.OpenAIKey,
+		Model:       c.OpenAIModel,
+		Voice:       c.OpenAIVoice,
+		Speed:       c.OpenAISpeed,
+		Instruction: c.OpenAIInstruction,
+	}
+}
+
+// geminiAudioConfigFrom extracts the Gemini-specific sub-config from the flat Config.
+// A nil Config produces a zero-value GeminiAudioConfig.
+func geminiAudioConfigFrom(c *Config) GeminiAudioConfig {
+	if c == nil {
+		return GeminiAudioConfig{}
+	}
+	return GeminiAudioConfig{
+		APIKey:   c.GoogleAPIKey,
+		TTSModel: c.GeminiTTSModel,
+		Voice:    c.GeminiVoice,
+		Speed:    c.GeminiSpeed,
+	}
+}
+
 // DefaultConfig returns default configuration
 func DefaultProviderConfig() *Config {
 	return &Config{
@@ -53,7 +103,9 @@ func DefaultProviderConfig() *Config {
 	}
 }
 
-// NewProvider creates the appropriate audio provider based on configuration
+// NewProvider creates the appropriate audio provider based on configuration.
+// It extracts provider-specific sub-configs so each implementation only
+// receives the fields it needs (ISP).
 func NewProvider(config *Config) (Provider, error) {
 	if config == nil {
 		config = DefaultProviderConfig()
@@ -64,12 +116,12 @@ func NewProvider(config *Config) (Provider, error) {
 		if config.OpenAIKey == "" {
 			return nil, fmt.Errorf("OpenAI API key is required")
 		}
-		return NewOpenAIProvider(config)
+		return NewOpenAIProvider(openAIAudioConfigFrom(config), config.OutputFormat)
 	case "gemini":
 		if config.GoogleAPIKey == "" {
 			return nil, fmt.Errorf("google API key is required")
 		}
-		return NewGeminiProvider(config)
+		return NewGeminiProvider(geminiAudioConfigFrom(config), config.OutputFormat)
 	default:
 		return nil, fmt.Errorf("unknown audio provider: %s", config.Provider)
 	}