Add --theme option to CLI

README.md

@@ -65,7 +65,7 @@ textual-paint
 
 ```
 $ python3 paint.py --help
-usage: paint.py [-h] [--ascii-only-icons] [--clear-screen] [filename]
+usage: paint.py [-h] [--theme THEME] [--ascii-only-icons] [--clear-screen] [filename]
 
 Paint in the terminal.
 
@@ -74,6 +74,7 @@ positional arguments:
 
 options:
   -h, --help          show this help message and exit
+  --theme THEME       Theme to use, either "light" or "dark"
   --ascii-only-icons  Use only ASCII characters for tool icons
   --clear-screen      Clear the screen before starting; useful for development, to avoid seeing fixed errors
 ```

paint.py

@@ -1136,7 +1136,10 @@ class PaintApp(App):
 # and it would create a new app instance, and all arguments would be ignored.
 app = PaintApp()
 
+# Command line arguments
+# Please keep in sync with the README
 parser = argparse.ArgumentParser(description='Paint in the terminal.')
+parser.add_argument('--theme', default='light', help='Theme to use, either "light" or "dark"')
 parser.add_argument('--ascii-only-icons', action='store_true', help='Use only ASCII characters for tool icons')
 # This flag is for development, because it's very confusing
 # to see the error message from the previous run,
@@ -1168,6 +1171,10 @@ if args.filename:
         app.filename = args.filename
 if args.clear_screen:
     os.system("cls||clear")
+if args.theme not in ["light", "dark"]:
+    print("Invalid theme. Must be either 'light' or 'dark'.")
+    sys.exit(1)
+app.dark = args.theme == "dark"
 
 if __name__ == "__main__":
     app.run()