From b77b338c7acf83768e3b180720adf7d5083fb9e0 Mon Sep 17 00:00:00 2001
From: Karl Tauber <karl@jformdesigner.com>
Date: Thu, 28 Oct 2021 19:03:13 +0200
Subject: [PATCH] Styling: support using variables (defined in properties
 files) in CSS styles

---
 .../java/com/formdev/flatlaf/FlatLaf.java     |  3 +++
 .../com/formdev/flatlaf/UIDefaultsLoader.java | 20 ++++++++++++++++++-
 .../formdev/flatlaf/ui/TestFlatStyling.java   | 14 +++++++++++++
 3 files changed, 36 insertions(+), 1 deletion(-)

diff --git a/flatlaf-core/src/main/java/com/formdev/flatlaf/FlatLaf.java b/flatlaf-core/src/main/java/com/formdev/flatlaf/FlatLaf.java
index f5311895..88338293 100644
--- a/flatlaf-core/src/main/java/com/formdev/flatlaf/FlatLaf.java
+++ b/flatlaf-core/src/main/java/com/formdev/flatlaf/FlatLaf.java
@@ -886,6 +886,9 @@ public abstract class FlatLaf
 	public static Object parseDefaultsValue( String key, String value, Class<?> valueType )
 		throws IllegalArgumentException
 	{
+		// resolve variables
+		value = UIDefaultsLoader.resolveValueFromUIManager( value );
+
 		// parse value
 		Object val = UIDefaultsLoader.parseValue( key, value, valueType, null,
 			v -> UIDefaultsLoader.resolveValueFromUIManager( v ), Collections.emptyList() );
diff --git a/flatlaf-core/src/main/java/com/formdev/flatlaf/UIDefaultsLoader.java b/flatlaf-core/src/main/java/com/formdev/flatlaf/UIDefaultsLoader.java
index b8133be7..d0ac7aa2 100644
--- a/flatlaf-core/src/main/java/com/formdev/flatlaf/UIDefaultsLoader.java
+++ b/flatlaf-core/src/main/java/com/formdev/flatlaf/UIDefaultsLoader.java
@@ -80,6 +80,8 @@ class UIDefaultsLoader
 	private static final String OPTIONAL_PREFIX = "?";
 	private static final String WILDCARD_PREFIX = "*.";
 
+	private static final String FLATLAF_VARIABLES = "FlatLaf.variables";
+
 	private static int parseColorDepth;
 
 	private static final Cache<String, Object> fontCache = new Cache<>();
@@ -244,10 +246,13 @@ class UIDefaultsLoader
 			};
 
 			// parse and add properties to UI defaults
+			Map<String, String> variables = new HashMap<>( 50 );
 			for( Map.Entry<Object, Object> e : properties.entrySet() ) {
 				String key = (String) e.getKey();
-				if( key.startsWith( VARIABLE_PREFIX ) )
+				if( key.startsWith( VARIABLE_PREFIX ) ) {
+					variables.put( key, (String) e.getValue() );
 					continue;
+				}
 
 				String value = resolveValue( (String) e.getValue(), propertiesGetter );
 				try {
@@ -256,6 +261,9 @@ class UIDefaultsLoader
 					logParseError( key, value, ex, true );
 				}
 			}
+
+			// remember variables in defaults to allow using them in styles
+			defaults.put( FLATLAF_VARIABLES, variables );
 		} catch( IOException ex ) {
 			LoggingFacade.INSTANCE.logSevere( "FlatLaf: Failed to load properties files.", ex );
 		}
@@ -299,6 +307,16 @@ class UIDefaultsLoader
 	}
 
 	static String resolveValueFromUIManager( String value ) {
+		if( value.startsWith( VARIABLE_PREFIX ) ) {
+			@SuppressWarnings( "unchecked" )
+			Map<String, String> variables = (Map<String, String>) UIManager.get( FLATLAF_VARIABLES );
+			String newValue = (variables != null) ? variables.get( value ) : null;
+			if( newValue == null )
+				throw new IllegalArgumentException( "variable '" + value + "' not found" );
+
+			return newValue;
+		}
+
 		if( !value.startsWith( PROPERTY_PREFIX ) )
 			return value;
 
diff --git a/flatlaf-core/src/test/java/com/formdev/flatlaf/ui/TestFlatStyling.java b/flatlaf-core/src/test/java/com/formdev/flatlaf/ui/TestFlatStyling.java
index 9902ed1b..ef273c83 100644
--- a/flatlaf-core/src/test/java/com/formdev/flatlaf/ui/TestFlatStyling.java
+++ b/flatlaf-core/src/test/java/com/formdev/flatlaf/ui/TestFlatStyling.java
@@ -30,6 +30,7 @@ import org.junit.jupiter.api.AfterAll;
 import org.junit.jupiter.api.BeforeAll;
 import org.junit.jupiter.api.Test;
 import com.formdev.flatlaf.icons.*;
+import com.formdev.flatlaf.util.ColorFunctions;
 
 /**
  * @author Karl Tauber
@@ -157,6 +158,19 @@ public class TestFlatStyling
 		testStyle( "arrowType", "chevron", "$Component.arrowType" );
 	}
 
+	@Test
+	void parseVariables() {
+		Color background = UIManager.getColor( "Panel.background" );
+
+		testColorStyle( background.getRGB(), "@background" );
+		testColorStyle(
+			ColorFunctions.darken( background, 0.2f ).getRGB(),
+			"darken(@background,20%)" );
+		testColorStyle(
+			ColorFunctions.saturate( ColorFunctions.darken( background, 0.2f ), 0.1f ).getRGB(),
+			"saturate(darken(@background,20%),10%)" );
+	}
+
 	private void testColorStyle( int expectedRGB, String style ) {
 		testStyle( "background", new Color( expectedRGB, (expectedRGB & 0xff000000) != 0 ), style );
 	}