Theme Editor: support loading/resolving base properties

flatlaf-theme-editor/src/main/java/com/formdev/flatlaf/themeeditor/FlatThemeEditorPane.java

@@ -19,8 +19,10 @@ package com.formdev.flatlaf.themeeditor;
 import java.awt.BorderLayout;
 import java.awt.Color;
 import java.awt.Font;
+import java.io.File;
 import java.io.IOException;
 import java.nio.charset.StandardCharsets;
+import java.util.List;
 import javax.swing.JLayer;
 import javax.swing.JPanel;
 import org.fife.ui.rsyntaxtextarea.AbstractTokenMakerFactory;
@@ -94,6 +96,10 @@ class FlatThemeEditorPane
 		return font.deriveFont( (float) newFontSize );
 	}
 
+	void setBaseFiles( List<File> baseFiles ) {
+		textArea.propertiesSupport.setBaseFiles( baseFiles );
+	}
+
 	void load( FileLocation loc ) throws IOException {
 		textArea.load( loc, StandardCharsets.ISO_8859_1 );
 	}

flatlaf-theme-editor/src/main/java/com/formdev/flatlaf/themeeditor/FlatThemeFileEditor.java

@@ -16,10 +16,15 @@
 
 package com.formdev.flatlaf.themeeditor;
 
-import java.awt.*;
+import java.awt.BorderLayout;
+import java.awt.Container;
+import java.awt.Dimension;
+import java.awt.Toolkit;
 import java.awt.event.KeyEvent;
 import java.io.File;
 import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
 import javax.swing.*;
 import org.fife.ui.rsyntaxtextarea.FileLocation;
 import com.formdev.flatlaf.FlatLightLaf;
@@ -39,12 +44,17 @@ public class FlatThemeFileEditor
 			? args[0]
 			: "theme-editor-test.properties" ); // TODO
 
+		List<File> baseFiles = new ArrayList<>();
+		for( int i = 1; i < args.length; i++ )
+			baseFiles.add( new File( args[i] ) );
+
 		SwingUtilities.invokeLater( () -> {
 			FlatLightLaf.install();
 			FlatInspector.install( "ctrl alt shift X" );
 
 			FlatThemeFileEditor frame = new FlatThemeFileEditor();
 
+			frame.themeEditorArea.setBaseFiles( baseFiles );
 			try {
 				frame.themeEditorArea.load( FileLocation.create( file ) );
 			} catch( IOException ex ) {

flatlaf-theme-editor/src/main/java/com/formdev/flatlaf/themeeditor/FlatThemePropertiesSupport.java

@@ -17,9 +17,12 @@
 package com.formdev.flatlaf.themeeditor;
 
 import java.awt.Color;
+import java.io.File;
+import java.io.FileInputStream;
 import java.io.IOException;
 import java.io.StringReader;
 import java.util.HashMap;
+import java.util.List;
 import java.util.Map;
 import java.util.Properties;
 import java.util.function.Function;
@@ -42,11 +45,15 @@ class FlatThemePropertiesSupport
 	private Properties propertiesCache;
 	private final Map<Integer, Object> parsedValueCache = new HashMap<>();
 
+	private File[] baseFiles;
+	private long[] baseFilesLastModified;
+	private Properties[] basePropertiesCache;
+
 	FlatThemePropertiesSupport( FlatSyntaxTextArea textArea ) {
 		this.textArea = textArea;
 
 		propertiesGetter = key -> {
-			return getProperties().getProperty( key );
+			return getProperty( key );
 		};
 		resolver = v -> {
 			return resolveValue( v );
@@ -55,6 +62,14 @@ class FlatThemePropertiesSupport
 		textArea.getDocument().addDocumentListener( this );
 	}
 
+	void setBaseFiles( List<File> baseFiles ) {
+		int size = baseFiles.size();
+		this.baseFiles = baseFiles.toArray( new File[size] );
+
+		baseFilesLastModified = new long[size];
+		basePropertiesCache = new Properties[size];
+	}
+
 	private String resolveValue( String value ) {
 		return UIDefaultsLoaderAccessor.resolveValue( value, propertiesGetter );
 	}
@@ -102,6 +117,37 @@ class FlatThemePropertiesSupport
 		}
 	}
 
+	private String getProperty( String key ) {
+		// look in current text area
+		String value = getProperties().getProperty( key );
+		if( value != null )
+			return value;
+
+		if( baseFiles == null )
+			return null;
+
+		// look in base properties files
+		for( int i = 0; i < baseFiles.length; i++ ) {
+			long lastModified = baseFiles[i].lastModified();
+			if( baseFilesLastModified[i] != lastModified ) {
+				// (re)load base properties file
+				baseFilesLastModified[i] = lastModified;
+				basePropertiesCache[i] = new Properties();
+				try {
+					basePropertiesCache[i].load( new FileInputStream( baseFiles[i] ) );
+				} catch( IOException ex ) {
+					ex.printStackTrace(); //TODO
+				}
+			}
+
+			value = basePropertiesCache[i].getProperty( key );
+			if( value != null )
+				return value;
+		}
+
+		return null;
+	}
+
 	private Properties getProperties() {
 		if( propertiesCache != null )
 			return propertiesCache;