feat: add ACTIVE_THEME global and set_active_theme() to config

tests/test_config.py

@@ -7,6 +7,8 @@ import tempfile
 from pathlib import Path
 from unittest.mock import patch
 
+import pytest
+
 from engine import config
 
 
@@ -160,3 +162,55 @@ class TestSetFontSelection:
         config.set_font_selection(font_path=None, font_index=None)
         assert original_path == config.FONT_PATH
         assert original_index == config.FONT_INDEX
+
+
+class TestActiveTheme:
+    """Tests for ACTIVE_THEME global and set_active_theme function."""
+
+    def test_active_theme_initially_none(self):
+        """ACTIVE_THEME should be None at module start."""
+        # Reset to None to test initial state
+        original = config.ACTIVE_THEME
+        config.ACTIVE_THEME = None
+        try:
+            assert config.ACTIVE_THEME is None
+        finally:
+            config.ACTIVE_THEME = original
+
+    def test_set_active_theme_green(self):
+        """Setting green theme works correctly."""
+        config.set_active_theme("green")
+        assert config.ACTIVE_THEME is not None
+        assert config.ACTIVE_THEME.name == "green"
+        assert len(config.ACTIVE_THEME.main_gradient) == 12
+        assert len(config.ACTIVE_THEME.message_gradient) == 12
+
+    def test_set_active_theme_default(self):
+        """Default theme is green when not specified."""
+        config.set_active_theme()
+        assert config.ACTIVE_THEME is not None
+        assert config.ACTIVE_THEME.name == "green"
+
+    def test_set_active_theme_invalid(self):
+        """Invalid theme_id raises KeyError."""
+        with pytest.raises(KeyError):
+            config.set_active_theme("nonexistent")
+
+    def test_set_active_theme_all_themes(self):
+        """Verify orange and purple themes work."""
+        # Test orange
+        config.set_active_theme("orange")
+        assert config.ACTIVE_THEME.name == "orange"
+
+        # Test purple
+        config.set_active_theme("purple")
+        assert config.ACTIVE_THEME.name == "purple"
+
+    def test_set_active_theme_idempotent(self):
+        """Calling set_active_theme multiple times works."""
+        config.set_active_theme("green")
+        first_theme = config.ACTIVE_THEME
+        config.set_active_theme("green")
+        second_theme = config.ACTIVE_THEME
+        assert first_theme.name == second_theme.name
+        assert first_theme.name == "green"