Add lib/generators.nix

lib/generators.nix

@@ -0,0 +1,30 @@
+{ lib, pkgs, ... }:
+
+with builtins;
+with lib;
+{
+  toCSSFile = file:
+    let fileName = baseNameOf file;
+        compiledStyles =
+          pkgs.runCommand "compileScssFile"
+            { buildInputs = [ sass ]; } ''
+              mkdir "$out"
+              scss --sourcekkmap=none \
+                   --no-cache \
+                   --style compressed \
+                   --default-encoding utf-8 \
+                   "${file}" \
+                   >>"$out/${fileName}.css"
+            '';
+    in "${compiledStyles}/${fileName}";
+
+  toFilteredImage = imageFile: options:
+    let result = "result.png";
+        filteredImage =
+          pkgs.runCommand "filterWallpaper"
+            { buildInputs = [ pkgs.imagemagick ]; } ''
+              mkdir "$out"
+              convert ${options} ${imageFile} $out/${result}
+            '';
+    in "${filteredImage}/${result}";
+}