refactor: move backends into the backends directory (#1279)

* refactor: move backends into the backends directory

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

* refactor: move main close to implementation for every backend

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

---------

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

backend/go/tts/piper.go

@@ -0,0 +1,49 @@
+package main
+
+// This is a wrapper to statisfy the GRPC service interface
+// It is meant to be used by the main executable that is the server for the specific backend type (falcon, gpt3, etc)
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+
+	"github.com/go-skynet/LocalAI/pkg/grpc/base"
+	pb "github.com/go-skynet/LocalAI/pkg/grpc/proto"
+	piper "github.com/mudler/go-piper"
+)
+
+type Piper struct {
+	base.SingleThread
+	piper *PiperB
+}
+
+func (sd *Piper) Load(opts *pb.ModelOptions) error {
+	if filepath.Ext(opts.ModelFile) != ".onnx" {
+		return fmt.Errorf("unsupported model type %s (should end with .onnx)", opts.ModelFile)
+	}
+	var err error
+	// Note: the Model here is a path to a directory containing the model files
+	sd.piper, err = New(opts.LibrarySearchPath)
+	return err
+}
+
+func (sd *Piper) TTS(opts *pb.TTSRequest) error {
+	return sd.piper.TTS(opts.Text, opts.Model, opts.Dst)
+}
+
+type PiperB struct {
+	assetDir string
+}
+
+func New(assetDir string) (*PiperB, error) {
+	if _, err := os.Stat(assetDir); err != nil {
+		return nil, err
+	}
+	return &PiperB{
+		assetDir: assetDir,
+	}, nil
+}
+
+func (s *PiperB) TTS(text, model, dst string) error {
+	return piper.TextToWav(text, model, s.assetDir, "", dst)
+}