Download REST API endpoints (#72)

* backend and frontend hotfixes, see message

Improved rendering on the frontend by cutting unecessary useStates.
Backend side, downloads now auto resume even on application kill.

* download rest api endpoints, general code refactor

* download request json mappings

server/rest/service.go

@@ -0,0 +1,38 @@
+package rest
+
+import (
+	"context"
+	"errors"
+
+	"github.com/marcopeocchi/yt-dlp-web-ui/server/internal"
+)
+
+type Service struct {
+	db *internal.MemoryDB
+	mq *internal.MessageQueue
+}
+
+func (s *Service) Exec(req internal.DownloadRequest) (string, error) {
+	p := &internal.Process{
+		Url:    req.URL,
+		Params: req.Params,
+		Output: internal.DownloadOutput{
+			Path:     req.Path,
+			Filename: req.Rename,
+		},
+	}
+
+	id := s.db.Set(p)
+	s.mq.Publish(p)
+
+	return id, nil
+}
+
+func (s *Service) Running(ctx context.Context) (*[]internal.ProcessResponse, error) {
+	select {
+	case <-ctx.Done():
+		return nil, errors.New("context cancelled")
+	default:
+		return s.db.All(), nil
+	}
+}