1 files changed, 140 insertions, 0 deletions
diff --git a/internal/tts/gemini.go b/internal/tts/gemini.go
new file mode 100644
index 0000000..1836be4
--- /dev/null
+++ b/internal/tts/gemini.go
@@ -0,0 +1,140 @@
+package tts
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"strings"
+
+	"google.golang.org/genai"
+
+	"codeberg.org/snonux/comicforge/internal/provider"
+)
+
+const (
+	// DefaultModel is the Gemini TTS model used for narration.
+	DefaultModel = "gemini-2.5-flash-preview-tts"
+)
+
+// GeminiConfig configures the Gemini TTS provider.
+type GeminiConfig struct {
+	APIKey string
+	Model  string
+	Voice  string
+}
+
+// GeminiProvider generates MP3 audio with Gemini TTS.
+type GeminiProvider struct {
+	client *genai.Client
+	model  string
+	voice  string
+	err    error
+}
+
+var _ provider.TTSProvider = (*GeminiProvider)(nil)
+
+// NewGeminiProvider creates a Gemini TTS provider.
+func NewGeminiProvider(cfg *GeminiConfig) *GeminiProvider {
+	g := &GeminiProvider{model: DefaultModel}
+	if cfg == nil {
+		g.err = fmt.Errorf("tts config is required")
+		return g
+	}
+	g.model = defaultOr(cfg.Model, DefaultModel)
+	g.voice = cfg.Voice
+	if strings.TrimSpace(cfg.APIKey) == "" {
+		g.err = fmt.Errorf("Google API key is required for TTS")
+		return g
+	}
+	client, err := genai.NewClient(context.Background(), &genai.ClientConfig{
+		APIKey:  cfg.APIKey,
+		Backend: genai.BackendGeminiAPI,
+	})
+	if err != nil {
+		g.err = fmt.Errorf("create Gemini client: %w", err)
+		return g
+	}
+	g.client = client
+	return g
+}
+
+// Name returns the provider name.
+func (g *GeminiProvider) Name() string { return "gemini" }
+
+// IsAvailable reports whether the provider was initialized successfully.
+func (g *GeminiProvider) IsAvailable() error {
+	if g == nil {
+		return fmt.Errorf("tts provider is nil")
+	}
+	return g.err
+}
+
+// GenerateAudio writes MP3 audio for the provided text to outputFile.
+func (g *GeminiProvider) GenerateAudio(ctx context.Context, text, outputFile string) error {
+	if g == nil {
+		return fmt.Errorf("tts provider is nil")
+	}
+	if ctx == nil {
+		ctx = context.Background()
+	}
+	if g.err != nil {
+		return g.err
+	}
+	if strings.TrimSpace(text) == "" {
+		return fmt.Errorf("text is required")
+	}
+	if strings.TrimSpace(outputFile) == "" {
+		return fmt.Errorf("output file is required")
+	}
+	voiceName := g.voice
+	if strings.TrimSpace(voiceName) == "" {
+		voiceName = "Aoede"
+	}
+
+	speechCfg := &genai.SpeechConfig{
+		VoiceConfig: &genai.VoiceConfig{
+			PrebuiltVoiceConfig: &genai.PrebuiltVoiceConfig{VoiceName: voiceName},
+		},
+		LanguageCode: "bg-BG",
+	}
+	resp, err := g.client.Models.GenerateContent(ctx, g.model, genai.Text(text), &genai.GenerateContentConfig{
+		ResponseModalities: []string{"AUDIO"},
+		SpeechConfig:       speechCfg,
+	})
+	if err != nil {
+		return fmt.Errorf("generate audio: %w", err)
+	}
+	data, mimeType, err := extractAudio(resp)
+	if err != nil {
+		return err
+	}
+	if strings.TrimSpace(outputFile) == "" {
+		return fmt.Errorf("output file is required")
+	}
+	if err := os.WriteFile(outputFile, data, 0o644); err != nil {
+		return fmt.Errorf("write audio: %w", err)
+	}
+	if mimeType != "" && !strings.HasPrefix(mimeType, "audio/") {
+		return fmt.Errorf("unexpected audio mime type %q", mimeType)
+	}
+	return nil
+}
+
+func extractAudio(resp *genai.GenerateContentResponse) ([]byte, string, error) {
+	if resp == nil || len(resp.Candidates) == 0 || resp.Candidates[0] == nil || resp.Candidates[0].Content == nil {
+		return nil, "", fmt.Errorf("no audio returned")
+	}
+	for _, part := range resp.Candidates[0].Content.Parts {
+		if part != nil && part.InlineData != nil && len(part.InlineData.Data) > 0 {
+			return part.InlineData.Data, part.InlineData.MIMEType, nil
+		}
+	}
+	return nil, "", fmt.Errorf("audio payload missing")
+}
+
+func defaultOr(value, fallback string) string {
+	if strings.TrimSpace(value) != "" {
+		return value
+	}
+	return fallback
+}