feat(cosmic-theme): add color schemes for qt apps

cosmic-theme/src/output/gtk4_output.rs

@@ -163,9 +163,19 @@ impl Theme {
             std::fs::create_dir_all(&config_dir).map_err(OutputError::Io)?;
         }
 
-        let mut file = File::create(config_dir.join(name)).map_err(OutputError::Io)?;
-        file.write_all(css_str.as_bytes())
-            .map_err(OutputError::Io)?;
+        let file_path = config_dir.join(name);
+        let tmp_file_path = config_dir.join(name.to_owned() + "~");
+
+        // Write to tmp_file_path first, then move it to file_path
+        let mut tmp_file = File::create(&tmp_file_path).map_err(OutputError::Io)?;
+        let res = tmp_file
+            .write_all(css_str.as_bytes())
+            .and_then(|_| tmp_file.flush())
+            .and_then(|_| std::fs::rename(&tmp_file_path, file_path));
+        if let Err(e) = res {
+            _ = std::fs::remove_file(&tmp_file_path);
+            return Err(OutputError::Io(e));
+        }
 
         Ok(())
     }