Add Named Slots support for multi-slot component content projection

pom.xml

@@ -4,7 +4,7 @@
 
     <groupId>de.morphbit</groupId>
     <artifactId>thymeleaf-component-dialect</artifactId>
-    <version>0.1.0-SNAPSHOT</version>
+    <version>0.1.1-SNAPSHOT</version>
     <packaging>jar</packaging>
 
     <name>thymeleaf-component-dialect</name>

src/main/java/de/morphbit/thymeleaf/processor/ComponentNamedElementProcessor.java

@@ -1,12 +1,12 @@
-/* 
+/*
  * Copyright 2017, Danny Rottstegge
- * 
+ *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
- * 
+ *
  *     http://www.apache.org/licenses/LICENSE-2.0
- * 
+ *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
@@ -29,11 +29,17 @@
 import org.thymeleaf.context.ITemplateContext;
 import org.thymeleaf.engine.AttributeNames;
 import org.thymeleaf.model.IAttribute;
+import org.thymeleaf.model.ICloseElementTag;
 import org.thymeleaf.model.IElementTag;
 import org.thymeleaf.model.IModel;
 import org.thymeleaf.model.IModelFactory;
+import org.thymeleaf.model.IOpenElementTag;
 import org.thymeleaf.model.IProcessableElementTag;
+import org.thymeleaf.model.IStandaloneElementTag;
+import org.thymeleaf.model.ITemplateEnd;
 import org.thymeleaf.model.ITemplateEvent;
+import org.thymeleaf.model.ITemplateStart;
+import org.thymeleaf.model.IText;
 import org.thymeleaf.processor.element.AbstractElementModelProcessor;
 import org.thymeleaf.processor.element.IElementModelStructureHandler;
 import org.thymeleaf.standard.StandardDialect;
@@ -42,7 +48,9 @@
 public class ComponentNamedElementProcessor extends AbstractElementModelProcessor {
 
 	private static final String FRAGMENT_ATTRIBUTE = "fragment";
-	private static final String REPLACE_CONTENT_TAG = "tc:content";
+	private static final String CONTENT_TAG = "tc:content";
+	private static final String SLOT_TAG = "tc:slot";
+	private static final String NAME_ATTR = "name";
 
 	private static final int PRECEDENCE = 350;
 	private static final Pattern REPLACE_PATTERN = Pattern.compile(".*\\?\\[([\\w.\\-_]*)\\].*");
@@ -52,7 +60,7 @@ public class ComponentNamedElementProcessor extends AbstractElementModelProcesso
 
 	/**
 	 * Constructor
-	 * 
+	 *
 	 * @param dialectPrefix
 	 *            Dialect prefix (tc)
 	 * @param tagName
@@ -86,7 +94,13 @@ protected void doProcess(ITemplateContext context, IModel model, IElementModelSt
 		model.reset();
 
 		IModel replacedFragmentModel = replaceAllAttributeValues(attributes, context, fragmentModel);
-		model.addModel(mergeModels(replacedFragmentModel, componentModel, REPLACE_CONTENT_TAG));
+
+		IModelFactory modelFactory = context.getModelFactory();
+		Map<String, IModel> namedSlots = new HashMap<>();
+		IModel defaultContent = modelFactory.createModel();
+		extractSlots(componentModel, namedSlots, defaultContent, modelFactory);
+
+		model.addModel(mergeSlots(replacedFragmentModel, namedSlots, defaultContent, modelFactory));
 
 		processVariables(attributes, context, structureHandler, excludeAttributes);
 	}
@@ -138,41 +152,143 @@ private boolean isDynamicAttribute(String attribute, String prefix) {
 		return attribute.startsWith(prefix + ":") || attribute.startsWith("data-" + prefix + "-");
 	}
 
-	private IModel mergeModels(IModel base, IModel insert, String replaceTag) {
-		IModel mergedModel = insertModel(base, insert, replaceTag);
-		mergedModel = removeTag(mergedModel, replaceTag);
-		mergedModel = removeTag(mergedModel, replaceTag);
-		return mergedModel;
+	private void extractSlots(IModel model, Map<String, IModel> namedSlots, IModel defaultContent,
+			IModelFactory modelFactory) {
+		int i = 0;
+		int size = model.size();
+
+		while (i < size) {
+			ITemplateEvent event = model.get(i);
+			String elementName = getElementName(event);
+
+			if (SLOT_TAG.equals(elementName) && event instanceof IOpenElementTag openTag) {
+				String slotName = openTag.getAttributeValue(NAME_ATTR);
+				IModel slotContent = modelFactory.createModel();
+				i++;
+				int depth = 1;
+				while (i < size) {
+					event = model.get(i);
+					elementName = getElementName(event);
+					if (SLOT_TAG.equals(elementName) && event instanceof IOpenElementTag) {
+						depth++;
+					} else if (SLOT_TAG.equals(elementName) && event instanceof ICloseElementTag) {
+						depth--;
+						if (depth == 0) {
+							i++;
+							break;
+						}
+					}
+					slotContent.add(event);
+					i++;
+				}
+				if (slotName != null && !slotName.isEmpty()) {
+					namedSlots.put(slotName, slotContent);
+				} else {
+					for (int j = 0; j < slotContent.size(); j++) {
+						defaultContent.add(slotContent.get(j));
+					}
+				}
+			} else {
+				defaultContent.add(event);
+				i++;
+			}
+		}
 	}
 
-	private IModel insertModel(IModel base, IModel insert, String replaceTag) {
-		IModel clonedModel = base.cloneModel();
-		int index = findTagIndex(base, replaceTag, IElementTag.class);
-		if (index > -1) {
-			clonedModel.insertModel(index, insert);
+	private IModel mergeSlots(IModel fragmentModel, Map<String, IModel> namedSlots, IModel defaultContent,
+			IModelFactory modelFactory) {
+		IModel result = modelFactory.createModel();
+		int i = 0;
+		int size = fragmentModel.size();
+
+		while (i < size) {
+			ITemplateEvent event = fragmentModel.get(i);
+			String elementName = getElementName(event);
+
+			if (CONTENT_TAG.equals(elementName)) {
+				String contentName = null;
+				if (event instanceof IProcessableElementTag processableTag) {
+					contentName = processableTag.getAttributeValue(NAME_ATTR);
+				}
+
+				if (event instanceof IStandaloneElementTag) {
+					IModel slotContent = resolveSlotContent(contentName, namedSlots, defaultContent, null);
+					if (slotContent != null) {
+						result.addModel(slotContent);
+					}
+					i++;
+				} else if (event instanceof IOpenElementTag) {
+					IModel fallbackContent = modelFactory.createModel();
+					i++;
+					int depth = 1;
+					while (i < size) {
+						event = fragmentModel.get(i);
+						elementName = getElementName(event);
+						if (CONTENT_TAG.equals(elementName) && event instanceof IOpenElementTag) {
+							depth++;
+						} else if (CONTENT_TAG.equals(elementName) && event instanceof ICloseElementTag) {
+							depth--;
+							if (depth == 0) {
+								i++;
+								break;
+							}
+						}
+						fallbackContent.add(event);
+						i++;
+					}
+					IModel slotContent = resolveSlotContent(contentName, namedSlots, defaultContent, fallbackContent);
+					if (slotContent != null) {
+						result.addModel(slotContent);
+					}
+				} else {
+					i++;
+				}
+			} else if (event instanceof ITemplateStart || event instanceof ITemplateEnd) {
+				i++;
+			} else {
+				result.add(event);
+				i++;
+			}
 		}
-		return clonedModel;
+
+		return result;
 	}
 
-	private IModel removeTag(IModel model, final String tag) {
-		IModel clonedModel = model.cloneModel();
-		int index = findTagIndex(model, tag, IElementTag.class);
-		if (index > -1) {
-			clonedModel.remove(index);
+	private IModel resolveSlotContent(String contentName, Map<String, IModel> namedSlots, IModel defaultContent,
+			IModel fallbackContent) {
+		if (contentName != null && !contentName.isEmpty()) {
+			IModel slotContent = namedSlots.get(contentName);
+			if (slotContent != null && !isEmptyOrWhitespace(slotContent)) {
+				return slotContent;
+			}
+			return fallbackContent;
+		} else {
+			if (defaultContent != null && !isEmptyOrWhitespace(defaultContent)) {
+				return defaultContent;
+			}
+			return fallbackContent;
 		}
-		return clonedModel;
 	}
 
-	private int findTagIndex(IModel model, final String search, Class<?> clazz) {
-		int size = model.size();
-		ITemplateEvent event = null;
-		for (int i = 0; i < size; i++) {
-			event = model.get(i);
-			if ((clazz == null || clazz.isInstance(event)) && event.toString().contains(search)) {
-				return i;
+	private boolean isEmptyOrWhitespace(IModel model) {
+		for (int i = 0; i < model.size(); i++) {
+			ITemplateEvent event = model.get(i);
+			if (event instanceof IText text) {
+				if (!text.getText().trim().isEmpty()) {
+					return false;
+				}
+			} else if (event instanceof IElementTag) {
+				return false;
 			}
 		}
-		return -1;
+		return true;
+	}
+
+	private String getElementName(ITemplateEvent event) {
+		if (event instanceof IElementTag elementTag) {
+			return elementTag.getElementCompleteName();
+		}
+		return null;
 	}
 
 	private IModel replaceAllAttributeValues(Map<String, String> attributes, ITemplateContext context, IModel model) {

src/test/java/de/morphbit/thymeleaf/dialect/NamedSlotTest.java

@@ -0,0 +1,86 @@
+package de.morphbit.thymeleaf.dialect;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import de.morphbit.thymeleaf.base.AbstractThymeleafComponentDialectTest;
+import org.junit.jupiter.api.Test;
+import org.thymeleaf.context.Context;
+
+public class NamedSlotTest extends AbstractThymeleafComponentDialectTest {
+
+	@Test
+	public void itShouldDistributeContentToNamedSlots() {
+		String html = processThymeleafFile("named_slots.html", new Context());
+
+		assertNotNull(html);
+
+		// No tc: tags should remain in output
+		assertFalse(html.contains("tc:page-layout"));
+		assertFalse(html.contains("tc:content"));
+		assertFalse(html.contains("tc:slot"));
+
+		// Layout structure should be present
+		assertTrue(html.contains("class=\"layout\""));
+		assertTrue(html.contains("class=\"header\""));
+		assertTrue(html.contains("class=\"body\""));
+		assertTrue(html.contains("class=\"footer\""));
+
+		// Named slot "header" should be in the header section
+		assertTrue(html.contains("<h1>My Page Title</h1>"));
+
+		// Named slot "footer" should be in the footer section
+		assertTrue(html.contains("<span>Copyright 2026</span>"));
+
+		// Default content should be in the body section
+		assertTrue(html.contains("<p>Main content here</p>"));
+	}
+
+	@Test
+	public void itShouldPlaceNamedSlotsInCorrectSections() {
+		String html = processThymeleafFile("named_slots.html", new Context());
+
+		assertNotNull(html);
+
+		// Verify header content is within header section
+		int headerSectionStart = html.indexOf("class=\"header\"");
+		int bodySectionStart = html.indexOf("class=\"body\"");
+		int footerSectionStart = html.indexOf("class=\"footer\"");
+		int headerContentPos = html.indexOf("My Page Title");
+		int bodyContentPos = html.indexOf("Main content here");
+		int footerContentPos = html.indexOf("Copyright 2026");
+
+		assertTrue(headerContentPos > headerSectionStart && headerContentPos < bodySectionStart,
+				"Header content should be within header section");
+		assertTrue(bodyContentPos > bodySectionStart && bodyContentPos < footerSectionStart,
+				"Body content should be within body section");
+		assertTrue(footerContentPos > footerSectionStart, "Footer content should be within footer section");
+	}
+
+	@Test
+	public void itShouldOverrideDefaultContentWithNamedSlot() {
+		String html = processThymeleafFile("named_slots_default_content.html", new Context());
+
+		assertNotNull(html);
+
+		// Named slot "header" should override the default
+		assertTrue(html.contains("<b>Custom Header</b>"));
+		assertFalse(html.contains("Default Header"));
+
+		// Default slot should contain custom body content
+		assertTrue(html.contains("<p>Custom body content</p>"));
+		assertFalse(html.contains("Default Body"));
+	}
+
+	@Test
+	public void itShouldUseFallbackContentWhenNoSlotProvided() {
+		String html = processThymeleafFile("named_slots_fallback.html", new Context());
+
+		assertNotNull(html);
+
+		// No slots provided, so default content should be used
+		assertTrue(html.contains("Default Header"));
+		assertTrue(html.contains("Default Body"));
+	}
+}

src/test/resources/templates/components/layout_component.html

@@ -0,0 +1,29 @@
+<!DOCTYPE html>
+<html xmlns:th="http://www.thymeleaf.org" xmlns:tc="http://www.morphbit.com/thymeleaf/component">
+<head>
+</head>
+<body>
+
+    <div th:fragment="page-layout" class="layout">
+        <header class="header">
+            <tc:content name="header"></tc:content>
+        </header>
+        <main class="body">
+            <tc:content></tc:content>
+        </main>
+        <footer class="footer">
+            <tc:content name="footer"></tc:content>
+        </footer>
+    </div>
+
+    <div th:fragment="card-with-defaults" class="card">
+        <div class="card-header">
+            <tc:content name="header">Default Header</tc:content>
+        </div>
+        <div class="card-body">
+            <tc:content>Default Body</tc:content>
+        </div>
+    </div>
+
+</body>
+</html>

src/test/resources/templates/named_slots.html

@@ -0,0 +1,17 @@
+<!DOCTYPE html>
+<html
+    xmlns:th="http://www.thymeleaf.org"
+    xmlns:tc="http://www.morphbit.com/thymeleaf/component">
+<head>
+    <title>Test</title>
+</head>
+<body>
+
+    <tc:page-layout>
+        <tc:slot name="header"><h1>My Page Title</h1></tc:slot>
+        <tc:slot name="footer"><span>Copyright 2026</span></tc:slot>
+        <p>Main content here</p>
+    </tc:page-layout>
+
+</body>
+</html>