Introduce gRPC-based snapshot client and server functionality.

Implemented gRPC client and server for snapshot management, enabling remote operations like listing, fetching, and downloading snapshots. Updated interfaces to support the new gRPC implementation and integrated server start functionality into the API.

api.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"unprism.ru/KRBL/agate/grpc"
 
 	"unprism.ru/KRBL/agate/store"
 )
@@ -171,7 +172,74 @@ func (a *Agate) Close() error {
 }
 
 // StartServer starts a gRPC server to share snapshots.
-// This is a placeholder for future implementation.
 func (a *Agate) StartServer(ctx context.Context, address string) error {
-	return errors.New("server functionality not implemented yet")
+	_, err := grpc.RunServer(ctx, a.manager, address)
+	if err != nil {
+		return fmt.Errorf("failed to start server: %w", err)
+	}
+
+	// We don't store the server reference because we don't have a way to stop it yet
+	// In a future version, we could add a StopServer method
+
+	return nil
+}
+
+// ConnectRemote connects to a remote snapshot server.
+// Returns a client that can be used to interact with the remote server.
+func (a *Agate) ConnectRemote(address string) (*grpc.SnapshotClient, error) {
+	client, err := grpc.ConnectToServer(address)
+	if err != nil {
+		return nil, fmt.Errorf("failed to connect to remote server: %w", err)
+	}
+
+	return client, nil
+}
+
+// GetRemoteSnapshotList retrieves a list of snapshots from a remote server.
+func (a *Agate) GetRemoteSnapshotList(ctx context.Context, address string) ([]store.SnapshotInfo, error) {
+	client, err := a.ConnectRemote(address)
+	if err != nil {
+		return nil, err
+	}
+	defer client.Close()
+
+	return client.ListSnapshots(ctx)
+}
+
+// GetRemoteSnapshot downloads a snapshot from a remote server.
+// If localParentID is provided, it will be used to optimize the download by skipping files that already exist locally.
+func (a *Agate) GetRemoteSnapshot(ctx context.Context, address string, snapshotID string, localParentID string) error {
+	client, err := a.ConnectRemote(address)
+	if err != nil {
+		return err
+	}
+	defer client.Close()
+
+	// Create a temporary directory for the downloaded snapshot
+	tempDir := filepath.Join(a.options.WorkDir, "temp", snapshotID)
+	if err := os.MkdirAll(tempDir, 0755); err != nil {
+		return fmt.Errorf("failed to create temporary directory: %w", err)
+	}
+
+	// Download the snapshot
+	if err := client.DownloadSnapshot(ctx, snapshotID, tempDir, localParentID); err != nil {
+		return fmt.Errorf("failed to download snapshot: %w", err)
+	}
+
+	// Get the snapshot details to create a local copy
+	details, err := client.FetchSnapshotDetails(ctx, snapshotID)
+	if err != nil {
+		return fmt.Errorf("failed to get snapshot details: %w", err)
+	}
+
+	// Create a local snapshot from the downloaded files
+	_, err = a.manager.CreateSnapshot(ctx, tempDir, details.Name, localParentID)
+	if err != nil {
+		return fmt.Errorf("failed to create local snapshot: %w", err)
+	}
+
+	// Clean up the temporary directory
+	os.RemoveAll(tempDir)
+
+	return nil
 }