add support for Nemo file manager

relative-xopp-background

@@ -52,6 +52,7 @@ def main():
 
 
 NAUTILUS_SELECTION = 'NAUTILUS_SCRIPT_SELECTED_FILE_PATHS'
+NEMO_SELECTION = 'NEMO_SCRIPT_SELECTED_FILE_PATHS'
 SCRIPT_NAME = 'relative-xopp-background'
 
 
@@ -64,14 +65,10 @@ def parse_args() -> List[Path]:
 
     # get list of selected paths
     selected_paths: List[Path] = []
-    selected_files_str = getenv(NAUTILUS_SELECTION)
-    if selected_files_str:
-        selected_files = selected_files_str.split('\n')
-        # if last filename is empty, remove it
-        if len(selected_files[-1]) < 1:
-            selected_files = selected_files[:-1]
-        selected_paths = [Path(file) for file in selected_files]
-    else:
+    selected_paths += selection_from_env(NAUTILUS_SELECTION)
+    selected_paths += selection_from_env(NEMO_SELECTION)
+    # if no selected files from NAUTILUS or NEMO were added
+    if len(selected_paths) == 0:
         selected_paths = [Path(file) for file in argv[1:]]
 
     # for each selected path
@@ -91,7 +88,22 @@ def parse_args() -> List[Path]:
             if path.suffix == '.xopp':
                 xopp_files.append(path.absolute())
 
-    return xopp_files
+    # don't return duplicates
+    return list(set(xopp_files))
+
+
+def selection_from_env(key: str) -> List[Path]:
+    """
+    Splits the value of environment key "key" by newlines and returns each element as Path object.
+    """
+    newline_delimited_selection = getenv(key)
+    if newline_delimited_selection:
+        selected_files = newline_delimited_selection.split('\n')
+        # if last filename is empty, remove it
+        if len(selected_files[-1]) < 1:
+            selected_files = selected_files[:-1]
+        return [Path(file) for file in selected_files]
+    return []
 
 
 def usage():