Add the possibility to keep the actual value to the UploadWidget

It looks ever-more like FileWithPreviewWidget, but I'm a bit afraid to
touch this one; seems there is a lot of legacy around it that I would
not want to break.

wcs/qommon/form.py

@@ -314,22 +314,36 @@ class UploadedFile:
         return self.get_file().read()
 
 
-class UploadWidget(FileWidget):
-    def __init__(self, name, directory=None, filename=None, validation=None, **kwargs):
+class UploadWidget(CompositeWidget):
+    def __init__(self, name, value=None, directory=None, filename=None,
+            validation=None, **kwargs):
+        super(CompositeWidget, self).__init__(name, **kwargs)
+        del kwargs['title']
+        kwargs.pop('hint')
+        self.value = value
         self.directory = directory or 'uploads'
         self.filename = filename
         self.validation = validation
-        super(UploadWidget, self).__init__(name, **kwargs)
+        if value:
+            self.add(CheckboxWidget, 'orexisting',
+                            title = _('Use previous file.'), value=True);
+            self.widgets[-1].render_br = False
+            self.add(FileWidget, 'file', title = _('Or upload a new one'), **kwargs)
+        else:
+            self.add(FileWidget, 'file', **kwargs)
 
     def _parse(self, request):
-        super(UploadWidget, self)._parse(request)
-        if not self.value:
-            return
-        if self.validation:
-            valid, msg = self.validation(self.value)
-            if not valid:
-                self.error = msg
-        self.value = UploadedFile(self.directory, self.filename, self.value)
+        if self.value and self.get('orexisting'):
+            pass
+        elif self.get('file'):
+            upload = self.get('file')
+            self.value = UploadedFile(self.directory, self.filename, upload)
+            if self.validation:
+                valid, msg = self.validation(upload)
+                if not valid:
+                    self.error = msg
+        else:
+            self.value = None
 
 class FileWithPreviewWidget(CompositeWidget):
     """Widget that proposes a File Upload widget but that stores the file