task zz: add Voices()/BuildAttribution() to Provider interface [OCP]

Extend audio.Provider with Voices() []string and BuildAttribution() string
so all provider-specific behaviour is encapsulated in the implementation
rather than scattered as switch-cases across callers.

Add package-level VoicesFor(name) and BuildAttributionFor(name, params)
for callers (processor, GUI) that need these before constructing a
Provider instance. Add AttributionParamsFrom(config, word, ...) so
callers can build AttributionParams from the flat Config without a manual
provider switch. Implement both new interface methods in OpenAIProvider
and GeminiProvider. Update all Provider mock/fake types in tests.

Migrate audioVoicesForProvider() and saveAudioAttribution() in both
processor.go and gui/generator.go to use the new package-level helpers,
replacing the 10+ duplicated switch blocks.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

5 files changed, 88 insertions, 4 deletions

diff --git a/internal/audio/attribution.go b/internal/audio/attribution.go
index 7c3cda2..57f8c1d 100644
--- a/internal/audio/attribution.go
+++ b/internal/audio/attribution.go
@@ -18,6 +18,34 @@ type AttributionParams struct {
 	GeneratedAt   time.Time
 }
 
+// AttributionParamsFrom builds an AttributionParams from a flat Config and the
+// word being transcribed, reading provider-appropriate sub-config fields to
+// eliminate the need for callers to switch on config.Provider themselves.
+func AttributionParamsFrom(config *Config, word, instruction, processedText string, generatedAt time.Time) AttributionParams {
+	base := AttributionParams{
+		Word:          word,
+		Instruction:   instruction,
+		ProcessedText: processedText,
+		GeneratedAt:   generatedAt,
+	}
+	if config == nil {
+		return base
+	}
+	switch strings.ToLower(strings.TrimSpace(config.Provider)) {
+	case "gemini":
+		g := geminiAudioConfigFrom(config)
+		base.Model = g.TTSModel
+		base.Voice = g.Voice
+		base.Speed = g.Speed
+	default:
+		o := openAIAudioConfigFrom(config)
+		base.Model = o.Model
+		base.Voice = o.Voice
+		base.Speed = o.Speed
+	}
+	return base
+}
+
 // AttributionPath returns the sidecar attribution file path for a generated audio file.
 func AttributionPath(audioFile string) string {
 	return strings.TrimSuffix(audioFile, filepath.Ext(audioFile)) + "_attribution.txt"
diff --git a/internal/audio/gemini_provider.go b/internal/audio/gemini_provider.go
index bda01f5..5100c5e 100644
--- a/internal/audio/gemini_provider.go
+++ b/internal/audio/gemini_provider.go
@@ -97,6 +97,16 @@ func (p *GeminiProvider) Name() string {
 	return "gemini"
 }
 
+// Voices returns the list of Gemini voices supported by the app.
+func (p *GeminiProvider) Voices() []string {
+	return GeminiVoices
+}
+
+// BuildAttribution returns the Gemini attribution text for a generated audio file.
+func (p *GeminiProvider) BuildAttribution(params AttributionParams) string {
+	return BuildGeminiAttribution(params)
+}
+
 // IsAvailable checks if the Google API key is configured.
 func (p *GeminiProvider) IsAvailable() error {
 	if p == nil || strings.TrimSpace(p.config.APIKey) == "" {
diff --git a/internal/audio/openai_provider.go b/internal/audio/openai_provider.go
index 9c6d3a4..e6212f8 100644
--- a/internal/audio/openai_provider.go
+++ b/internal/audio/openai_provider.go
@@ -147,6 +147,16 @@ func (p *OpenAIProvider) IsAvailable() error {
 	return nil
 }
 
+// Voices returns the list of OpenAI voices supported by the app.
+func (p *OpenAIProvider) Voices() []string {
+	return OpenAIVoices
+}
+
+// BuildAttribution returns the OpenAI attribution text for a generated audio file.
+func (p *OpenAIProvider) BuildAttribution(params AttributionParams) string {
+	return BuildOpenAIAttribution(params)
+}
+
 // preprocessBulgarianText prepares Bulgarian text for clearer TTS pronunciation
 func (p *OpenAIProvider) preprocessBulgarianText(text string) string {
 	return openAIProcessedText(text)
diff --git a/internal/audio/provider.go b/internal/audio/provider.go
index fac0cd9..60be848 100644
--- a/internal/audio/provider.go
+++ b/internal/audio/provider.go
@@ -3,18 +3,27 @@ package audio
 import (
 	"context"
 	"fmt"
+	"strings"
 )
 
-// Provider defines the interface for text-to-speech providers
+// Provider defines the interface for text-to-speech providers.
+// All provider-specific behavior (voices, attribution) is encapsulated here
+// so callers never need to switch on the provider name (OCP).
 type Provider interface {
-	// GenerateAudio generates audio from text and saves it to the specified file
+	// GenerateAudio generates audio from text and saves it to the specified file.
 	GenerateAudio(ctx context.Context, text string, outputFile string) error
 
-	// Name returns the provider name
+	// Name returns the provider name.
 	Name() string
 
-	// IsAvailable checks if the provider is properly configured and available
+	// IsAvailable checks if the provider is properly configured and available.
 	IsAvailable() error
+
+	// Voices returns the list of voice names supported by this provider.
+	Voices() []string
+
+	// BuildAttribution returns the attribution text for a generated audio file.
+	BuildAttribution(params AttributionParams) string
 }
 
 // OpenAIAudioConfig holds settings specific to the OpenAI TTS backend.
@@ -58,6 +67,25 @@ type Config struct {
 	GeminiSpeed    float64 // Prompt hint for desired speech speed
 }
 
+// VoicesFor returns the voice list for the named provider. This is a
+// convenience for callers that need voices before constructing a Provider.
+func VoicesFor(providerName string) []string {
+	if strings.ToLower(strings.TrimSpace(providerName)) == "gemini" {
+		return GeminiVoices
+	}
+	return OpenAIVoices
+}
+
+// BuildAttributionFor builds the attribution text for the named provider
+// without requiring a Provider instance. Use Provider.BuildAttribution when
+// you already have an instance.
+func BuildAttributionFor(providerName string, params AttributionParams) string {
+	if strings.ToLower(strings.TrimSpace(providerName)) == "gemini" {
+		return BuildGeminiAttribution(params)
+	}
+	return BuildOpenAIAttribution(params)
+}
+
 // openAIAudioConfigFrom extracts the OpenAI-specific sub-config from the flat Config.
 // A nil Config produces a zero-value OpenAIAudioConfig.
 func openAIAudioConfigFrom(c *Config) OpenAIAudioConfig {
diff --git a/internal/audio/provider_test.go b/internal/audio/provider_test.go
index 5702016..9b8037c 100644
--- a/internal/audio/provider_test.go
+++ b/internal/audio/provider_test.go
@@ -28,6 +28,14 @@ func (m *mockProvider) IsAvailable() error {
 	return m.availableErr
 }
 
+func (m *mockProvider) Voices() []string {
+	return nil
+}
+
+func (m *mockProvider) BuildAttribution(params AttributionParams) string {
+	return ""
+}
+
 func TestDefaultProviderConfig(t *testing.T) {
 	config := DefaultProviderConfig()