refactoring-1

introduced pipelines and abstracted download process.go in Downloader interface

server/internal/pipes/FileWriter.go

@@ -0,0 +1,45 @@
+package pipes
+
+import (
+	"io"
+	"log/slog"
+	"os"
+)
+
+type FileWriter struct {
+	Path    string
+	IsFinal bool
+}
+
+func (f *FileWriter) Name() string { return "file-writer" }
+
+func (f *FileWriter) Connect(r io.Reader) (io.Reader, error) {
+	file, err := os.Create(f.Path)
+	if err != nil {
+		return nil, err
+	}
+
+	if f.IsFinal {
+		go func() {
+			defer file.Close()
+			if _, err := io.Copy(file, r); err != nil {
+				slog.Error("FileWriter (final) error", slog.Any("err", err))
+			}
+		}()
+		return r, nil
+	}
+
+	pr, pw := io.Pipe()
+
+	go func() {
+		defer file.Close()
+		defer pw.Close()
+
+		writer := io.MultiWriter(file, pw)
+		if _, err := io.Copy(writer, r); err != nil {
+			slog.Error("FileWriter (pipeline) error", slog.Any("err", err))
+		}
+	}()
+
+	return pr, nil
+}