Ability to set image as GDM background

Closes #40.

tweaks/gdm/tweak.py

@@ -0,0 +1,86 @@
+import os.path
+import shutil
+import subprocess
+from argparse import ArgumentParser
+from scripts import config
+from scripts.utils.is_photo import is_photo, NotSupportedPhotoExtension
+
+def define_arguments(parser: ArgumentParser):
+    gdm_args = parser.add_argument_group("GDM tweaks")
+    gdm_args.add_argument("--gdm-image", type=str, nargs="?", help="Set GDM background image")
+    gdm_args.add_argument("--gdm-blur", type=int, nargs="?", help="Blur GDM background image (px)")
+    gdm_args.add_argument("--gdm-darken", type=int, choices=range(0, 100), help="Darken GDM background image (%)", metavar="(0 - 100)")
+    gdm_args.add_argument("--gdm-lighten",  type=int, choices=range(0, 100), help="Lighten GDM background image", metavar="(0 - 100)")
+
+
+def apply_tweak(args, theme, colors):
+    if args.gdm_image:
+        gdm_image = GDMImage(args.gdm_image, config.temp_folder, args.gdm_blur)
+
+        destination_dir = os.path.join(config.temp_folder, config.gdm_folder, config.raw_theme_folder)
+        os.makedirs(destination_dir, exist_ok=True)
+
+        gdm_image.copy_image(destination_dir)
+
+        theme += f"""
+            .login-dialog {{
+                background-image: url("{gdm_image.image_name}");
+                background-size: cover;
+                {f"box-shadow: inset 0 0 0 9999px rgba(0, 0, 0, {args.gdm_darken/100});" if args.gdm_darken else ""}
+                {f"box-shadow: inset 0 0 0 9999px rgba(255, 255, 255, {args.gdm_lighten/100});" if args.gdm_lighten else ""}
+            }}
+        """
+
+
+class GDMImage:
+    """
+    Class to apply effects to GDM background image
+    """
+
+    image_name: str
+
+    def __init__(self, path: str, temp_folder: str, blur: int = None):
+        self.path = path
+
+        extension = path.split(".")[-1]
+        if not is_photo(extension):
+            raise NotSupportedPhotoExtension(extension)
+
+        self.image_name = f"gdm-image.{extension}"
+        self.destination_dir = temp_folder
+        self.destination_file = os.path.join(self.destination_dir, self.image_name)
+
+        if not os.path.exists(self.destination_file):
+            self._create_file()
+            self._magick_tweaks(blur)
+
+    def copy_image(self, destination: str):
+        dest_path = os.path.join(destination, self.image_name)
+        shutil.copyfile(self.destination_file, dest_path)
+
+    def _create_file(self):
+        os.makedirs(self.destination_dir, exist_ok=True)
+        shutil.copyfile(self.path, self.destination_file)
+
+    def _magick_tweaks(self, blur: int = None):
+        if not shutil.which("magick"):
+            print("Warning: ImageMagick not found. Image effects will be skipped.")
+            return
+
+        file = self.destination_file
+
+        modified = False
+        command = ["magick", file]
+
+        if blur:
+            command.extend(["-blur", f"0x{blur}"])
+            modified = True
+
+        if modified:
+            print("Applying image filters... This may take a while.")
+            output_file = file
+            command.append(output_file)
+            try:
+                subprocess.run(command, check=True)
+            except subprocess.CalledProcessError:
+                print(f"Error: Failed to apply image effects to {file}")