From fe1009187c3e2b3bd1e3375154a15d6f6cf8777b Mon Sep 17 00:00:00 2001
From: DieGurke <maxi@kske.dev>
Date: Tue, 7 Dec 2021 19:13:51 +0100
Subject: [PATCH 01/12] New change interface and changeManager class

---
 src/main/java/dev/kske/undoredo/Change.java   |  33 ++++++
 .../java/dev/kske/undoredo/ChangeManager.java | 100 ++++++++++++++++++
 2 files changed, 133 insertions(+)
 create mode 100644 src/main/java/dev/kske/undoredo/Change.java
 create mode 100644 src/main/java/dev/kske/undoredo/ChangeManager.java

diff --git a/src/main/java/dev/kske/undoredo/Change.java b/src/main/java/dev/kske/undoredo/Change.java
new file mode 100644
index 0000000..6f88984
--- /dev/null
+++ b/src/main/java/dev/kske/undoredo/Change.java
@@ -0,0 +1,33 @@
+package dev.kske.undoredo;
+
+/**
+ * Base interface for changes to be registered in an undo manager.
+ * 
+ * @author Maximilian K&auml;fer
+ * @since 0.0.1
+ */
+public interface Change {
+
+	/**
+	 * Performs the action implemented by this change.
+	 *
+	 * @since 0.0.1
+	 */
+	void apply();
+
+	/**
+	 * Inverts this change.
+	 * 
+	 * @implSpec This method is not supposed to alter the state of this change, but rather to create
+	 *           a new complementary change.
+	 * @return the inverted change
+	 * @since 0.0.1
+	 */
+	Change invert();
+
+	/**
+	 * @return whether the application of this change would result in an identical state
+	 * @since 0.0.1
+	 */
+	boolean isIdentity();
+}
diff --git a/src/main/java/dev/kske/undoredo/ChangeManager.java b/src/main/java/dev/kske/undoredo/ChangeManager.java
new file mode 100644
index 0000000..8f2812e
--- /dev/null
+++ b/src/main/java/dev/kske/undoredo/ChangeManager.java
@@ -0,0 +1,100 @@
+package dev.kske.undoredo;
+
+import java.util.*;
+
+/**
+ * @param <C> the change types to store in this change manager
+ * @author Maximilian K&auml;fer
+ * @since 0.0.1
+ */
+public final class ChangeManager<C extends Change> {
+
+	private final List<C> changes = new LinkedList<>();
+
+	private int	index;
+	private int	markedIndex;
+
+	/**
+	 * Adds a change to the changes list.
+	 * 
+	 * @param change the change to add
+	 * @since 0.0.1
+	 */
+	public void addChange(C change) {
+		change.apply();
+		changes.add(change);
+	}
+
+	/**
+	 * Undoes the change at the current index position.
+	 * 
+	 * @return whether the operation could be executed due to one being currently available
+	 * @since 0.1.0
+	 */
+	public boolean undo() {
+		if (isUndoAvailable()) {
+			changes.get(index).invert().apply();
+			--index;
+			return true;
+		}
+		return false;
+	}
+
+	/**
+	 * Applies the change that was undone before.
+	 * 
+	 * @return whether the operation could be executed due to one being currently available
+	 * @since 0.0.1
+	 */
+	public boolean redo() {
+		if (isRedoAvailable()) {
+			changes.get(index + 1).apply();
+			++index;
+			return true;
+		}
+		return false;
+	}
+
+	/**
+	 * Marks the current index.
+	 * 
+	 * @since 0.0.1
+	 */
+	public void mark() {
+		markedIndex = index;
+	}
+
+	/**
+	 * @return whether the current index was marked
+	 * @since 0.0.1
+	 */
+	public boolean isAtMarkedIndex() {
+		return markedIndex == index;
+	}
+
+	/**
+	 * @return whether the undo operation is currently available
+	 * @since 0.0.1
+	 */
+	public boolean isUndoAvailable() {
+		return index > 0;
+	}
+
+	/**
+	 * @return whether the redo operation is currently available.
+	 * @since 0.0.1
+	 */
+	public boolean isRedoAvailable() {
+		return index < changes.size() - 1;
+	}
+
+	/**
+	 * Provides an unmodifiable view of the changes stored in this change manager.
+	 * 
+	 * @return all stored changes
+	 * @since 0.0.1
+	 */
+	public List<C> getChanges() {
+		return Collections.unmodifiableList(changes);
+	}
+}

From acb25c312060a0009d37e46a4e4a65d7bf1200e8 Mon Sep 17 00:00:00 2001
From: kske <kai@kske.dev>
Date: Wed, 8 Dec 2021 10:35:09 +0100
Subject: [PATCH 02/12] Improve ChangeManager Javadoc

---
 .../java/dev/kske/undoredo/ChangeManager.java | 32 +++++++++++--------
 1 file changed, 18 insertions(+), 14 deletions(-)

diff --git a/src/main/java/dev/kske/undoredo/ChangeManager.java b/src/main/java/dev/kske/undoredo/ChangeManager.java
index 8f2812e..6d520c2 100644
--- a/src/main/java/dev/kske/undoredo/ChangeManager.java
+++ b/src/main/java/dev/kske/undoredo/ChangeManager.java
@@ -3,7 +3,11 @@ package dev.kske.undoredo;
 import java.util.*;
 
 /**
- * @param <C> the change types to store in this change manager
+ * A change manager keeps track of subsequent changes and allows un- and redoing them. A specific
+ * change can be marked using {@link #mark()} to keep track of a saved state in the application that
+ * uses the manager.
+ *
+ * @param <C> the change type to store in this change manager
  * @author Maximilian K&auml;fer
  * @since 0.0.1
  */
@@ -15,8 +19,8 @@ public final class ChangeManager<C extends Change> {
 	private int	markedIndex;
 
 	/**
-	 * Adds a change to the changes list.
-	 * 
+	 * Applies the given change and appends it to the change list.
+	 *
 	 * @param change the change to add
 	 * @since 0.0.1
 	 */
@@ -26,9 +30,9 @@ public final class ChangeManager<C extends Change> {
 	}
 
 	/**
-	 * Undoes the change at the current index position.
-	 * 
-	 * @return whether the operation could be executed due to one being currently available
+	 * Undoes the current change.
+	 *
+	 * @return whether an action was performed
 	 * @since 0.1.0
 	 */
 	public boolean undo() {
@@ -42,8 +46,8 @@ public final class ChangeManager<C extends Change> {
 
 	/**
 	 * Applies the change that was undone before.
-	 * 
-	 * @return whether the operation could be executed due to one being currently available
+	 *
+	 * @return whether an action was performed
 	 * @since 0.0.1
 	 */
 	public boolean redo() {
@@ -56,8 +60,8 @@ public final class ChangeManager<C extends Change> {
 	}
 
 	/**
-	 * Marks the current index.
-	 * 
+	 * Marks the current change.
+	 *
 	 * @since 0.0.1
 	 */
 	public void mark() {
@@ -65,7 +69,7 @@ public final class ChangeManager<C extends Change> {
 	}
 
 	/**
-	 * @return whether the current index was marked
+	 * @return whether the current change is marked
 	 * @since 0.0.1
 	 */
 	public boolean isAtMarkedIndex() {
@@ -73,7 +77,7 @@ public final class ChangeManager<C extends Change> {
 	}
 
 	/**
-	 * @return whether the undo operation is currently available
+	 * @return whether a change is present that can be undone
 	 * @since 0.0.1
 	 */
 	public boolean isUndoAvailable() {
@@ -81,7 +85,7 @@ public final class ChangeManager<C extends Change> {
 	}
 
 	/**
-	 * @return whether the redo operation is currently available.
+	 * @return whether a change is present that can be redone
 	 * @since 0.0.1
 	 */
 	public boolean isRedoAvailable() {
@@ -90,7 +94,7 @@ public final class ChangeManager<C extends Change> {
 
 	/**
 	 * Provides an unmodifiable view of the changes stored in this change manager.
-	 * 
+	 *
 	 * @return all stored changes
 	 * @since 0.0.1
 	 */

From dc74b78d200539108e93db557dfaf0f972dd7ccb Mon Sep 17 00:00:00 2001
From: kske <kai@kske.dev>
Date: Wed, 8 Dec 2021 10:42:55 +0100
Subject: [PATCH 03/12] Add Jenkinsfile

---
 Jenkinsfile | 40 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)
 create mode 100644 Jenkinsfile

diff --git a/Jenkinsfile b/Jenkinsfile
new file mode 100644
index 0000000..61004d1
--- /dev/null
+++ b/Jenkinsfile
@@ -0,0 +1,40 @@
+pipeline {
+	agent any
+
+	options {
+		ansiColor('xterm')
+	}
+
+	stages {
+		stage('Build') {
+			steps {
+				sh 'mvn -DskipTests clean package'
+			}
+		}
+		stage('Test') {
+			steps {
+				sh 'mvn test'
+			}
+			post {
+				always {
+					junit 'target/surefire-reports/*.xml'
+				}
+			}
+		}
+		stage('SonarQube Analysis') {
+			when {
+				branch 'develop'
+			}
+			steps {
+				withSonarQubeEnv('KSKE SonarQube') {
+					sh 'mvn org.sonarsource.scanner.maven:sonar-maven-plugin:3.9.1.2184:sonar'
+				}
+			}
+		}
+	}
+	post {
+		success {
+			archiveArtifacts artifacts: 'target/undo-redo-*.jar'
+		}
+	}
+}

From bb7c1690b26ff8076296ba1478791eacae96f97e Mon Sep 17 00:00:00 2001
From: kske <kai@kske.dev>
Date: Fri, 10 Dec 2021 18:39:57 +0100
Subject: [PATCH 04/12] Add change manager unit test skeleton

---
 pom.xml                                       |  3 +
 .../dev/kske/undoredo/ChangeManagerTest.java  | 76 +++++++++++++++++++
 2 files changed, 79 insertions(+)
 create mode 100644 src/test/java/dev/kske/undoredo/ChangeManagerTest.java

diff --git a/pom.xml b/pom.xml
index f32663d..8fce4ef 100644
--- a/pom.xml
+++ b/pom.xml
@@ -165,6 +165,9 @@
 				<groupId>org.apache.maven.plugins</groupId>
 				<artifactId>maven-surefire-plugin</artifactId>
 				<version>3.0.0-M5</version>
+				<configuration>
+					<argLine>--add-opens dev.kske.undoredo/dev.kske.undoredo=ALL-UNNAMED</argLine>
+				</configuration>
 			</plugin>
 			
 		</plugins>
diff --git a/src/test/java/dev/kske/undoredo/ChangeManagerTest.java b/src/test/java/dev/kske/undoredo/ChangeManagerTest.java
new file mode 100644
index 0000000..0d4cbc0
--- /dev/null
+++ b/src/test/java/dev/kske/undoredo/ChangeManagerTest.java
@@ -0,0 +1,76 @@
+package dev.kske.undoredo;
+
+import static org.junit.jupiter.api.Assertions.fail;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * @author Kai S. K. Engelbart
+ * @since 0.0.1
+ */
+class ChangeManagerTest {
+
+	/**
+	 * Test method for {@link dev.kske.undoredo.ChangeManager#addChange(dev.kske.undoredo.Change)}.
+	 */
+	@Test
+	void testAddChange() {
+		fail("Not yet implemented");
+	}
+
+	/**
+	 * Test method for {@link dev.kske.undoredo.ChangeManager#undo()}.
+	 */
+	@Test
+	void testUndo() {
+		fail("Not yet implemented");
+	}
+
+	/**
+	 * Test method for {@link dev.kske.undoredo.ChangeManager#redo()}.
+	 */
+	@Test
+	void testRedo() {
+		fail("Not yet implemented");
+	}
+
+	/**
+	 * Test method for {@link dev.kske.undoredo.ChangeManager#mark()}.
+	 */
+	@Test
+	void testMark() {
+		fail("Not yet implemented");
+	}
+
+	/**
+	 * Test method for {@link dev.kske.undoredo.ChangeManager#isAtMarkedIndex()}.
+	 */
+	@Test
+	void testIsAtMarkedIndex() {
+		fail("Not yet implemented");
+	}
+
+	/**
+	 * Test method for {@link dev.kske.undoredo.ChangeManager#isUndoAvailable()}.
+	 */
+	@Test
+	void testIsUndoAvailable() {
+		fail("Not yet implemented");
+	}
+
+	/**
+	 * Test method for {@link dev.kske.undoredo.ChangeManager#isRedoAvailable()}.
+	 */
+	@Test
+	void testIsRedoAvailable() {
+		fail("Not yet implemented");
+	}
+
+	/**
+	 * Test method for {@link dev.kske.undoredo.ChangeManager#getChanges()}.
+	 */
+	@Test
+	void testGetChanges() {
+		fail("Not yet implemented");
+	}
+}

From 2773d360fbed11f38c4245be61ca074daedf7bcf Mon Sep 17 00:00:00 2001
From: kske <kai@kske.dev>
Date: Sat, 11 Dec 2021 13:51:12 +0100
Subject: [PATCH 05/12] Implement change manager unit tests

---
 .../dev/kske/undoredo/ChangeManagerTest.java  | 138 +++++++++++-------
 .../java/dev/kske/undoredo/IntChange.java     |  31 ++++
 .../java/dev/kske/undoredo/IntWrapper.java    |  10 ++
 3 files changed, 124 insertions(+), 55 deletions(-)
 create mode 100644 src/test/java/dev/kske/undoredo/IntChange.java
 create mode 100644 src/test/java/dev/kske/undoredo/IntWrapper.java

diff --git a/src/test/java/dev/kske/undoredo/ChangeManagerTest.java b/src/test/java/dev/kske/undoredo/ChangeManagerTest.java
index 0d4cbc0..b3e1b72 100644
--- a/src/test/java/dev/kske/undoredo/ChangeManagerTest.java
+++ b/src/test/java/dev/kske/undoredo/ChangeManagerTest.java
@@ -1,8 +1,8 @@
 package dev.kske.undoredo;
 
-import static org.junit.jupiter.api.Assertions.fail;
+import static org.junit.jupiter.api.Assertions.*;
 
-import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.*;
 
 /**
  * @author Kai S. K. Engelbart
@@ -10,67 +10,95 @@ import org.junit.jupiter.api.Test;
  */
 class ChangeManagerTest {
 
+	ChangeManager<IntChange>	manager;
+	IntWrapper					wrapper;
+	IntChange					change;
+
+	@BeforeEach
+	void prepareChangeManager() {
+		manager	= new ChangeManager<>();
+		wrapper	= new IntWrapper();
+		change	= new IntChange(wrapper, 1);
+	}
+
 	/**
-	 * Test method for {@link dev.kske.undoredo.ChangeManager#addChange(dev.kske.undoredo.Change)}.
+	 * Tests adding a change.
+	 *
+	 * @since 0.0.1
 	 */
 	@Test
+	@Order(1)
 	void testAddChange() {
-		fail("Not yet implemented");
+		assertSame(0, wrapper.value);
+		manager.addChange(change);
+		assertSame(1, wrapper.value);
 	}
-
+	
 	/**
-	 * Test method for {@link dev.kske.undoredo.ChangeManager#undo()}.
-	 */
-	@Test
-	void testUndo() {
-		fail("Not yet implemented");
-	}
-
-	/**
-	 * Test method for {@link dev.kske.undoredo.ChangeManager#redo()}.
-	 */
-	@Test
-	void testRedo() {
-		fail("Not yet implemented");
-	}
-
-	/**
-	 * Test method for {@link dev.kske.undoredo.ChangeManager#mark()}.
-	 */
-	@Test
-	void testMark() {
-		fail("Not yet implemented");
-	}
-
-	/**
-	 * Test method for {@link dev.kske.undoredo.ChangeManager#isAtMarkedIndex()}.
-	 */
-	@Test
-	void testIsAtMarkedIndex() {
-		fail("Not yet implemented");
-	}
-
-	/**
-	 * Test method for {@link dev.kske.undoredo.ChangeManager#isUndoAvailable()}.
-	 */
-	@Test
-	void testIsUndoAvailable() {
-		fail("Not yet implemented");
-	}
-
-	/**
-	 * Test method for {@link dev.kske.undoredo.ChangeManager#isRedoAvailable()}.
-	 */
-	@Test
-	void testIsRedoAvailable() {
-		fail("Not yet implemented");
-	}
-
-	/**
-	 * Test method for {@link dev.kske.undoredo.ChangeManager#getChanges()}.
+	 * Tests the consistency of the change list.
+	 *
+	 * @since 0.0.1
 	 */
 	@Test
+	@Order(2)
 	void testGetChanges() {
-		fail("Not yet implemented");
+		assertTrue(manager.getChanges().isEmpty());
+		manager.addChange(change);
+		assertSame(1, manager.getChanges().size());
+		assertEquals(change, manager.getChanges().get(0));
+	}
+
+	/**
+	 * Test undoing a change.
+	 *
+	 * @since 0.0.1
+	 */
+	@Test
+	@Order(2)
+	void testUndo() {
+		assertFalse(manager.isUndoAvailable());
+		assertFalse(manager.undo());
+		manager.addChange(change);
+		assertTrue(manager.isUndoAvailable());
+		assertTrue(manager.undo());
+		assertFalse(manager.isUndoAvailable());
+		assertFalse(manager.undo());
+	}
+
+	/**
+	 * Tests redoing a change.
+	 *
+	 * @since 0.0.1
+	 */
+	@Test
+	@Order(4)
+	void testRedo() {
+		assertFalse(manager.isRedoAvailable());
+		assertFalse(manager.redo());
+		manager.addChange(change);
+		assertFalse(manager.isRedoAvailable());
+		assertFalse(manager.redo());
+		manager.undo();
+		assertTrue(manager.isRedoAvailable());
+		assertTrue(manager.redo());
+		assertFalse(manager.isRedoAvailable());
+		assertFalse(manager.redo());
+	}
+
+	/**
+	 * Tests marking a change.
+	 *
+	 * @since 0.0.1
+	 */
+	@Test
+	@Order(5)
+	void testMark() {
+		assertTrue(manager.isAtMarkedIndex());
+		manager.addChange(change);
+		assertFalse(manager.isAtMarkedIndex());
+		manager.mark();
+		assertTrue(manager.isAtMarkedIndex());
+		manager.undo();
+		assertFalse(manager.isAtMarkedIndex());
 	}
 }
diff --git a/src/test/java/dev/kske/undoredo/IntChange.java b/src/test/java/dev/kske/undoredo/IntChange.java
new file mode 100644
index 0000000..76299a4
--- /dev/null
+++ b/src/test/java/dev/kske/undoredo/IntChange.java
@@ -0,0 +1,31 @@
+package dev.kske.undoredo;
+
+/**
+ * @author Kai S. K. Engelbart
+ * @since 0.0.1
+ */
+class IntChange implements Change {
+	
+	private final IntWrapper wrapper;
+	private final int value;
+	
+	IntChange(IntWrapper wrapper, int value) {
+		this.wrapper = wrapper;
+		this.value = value;
+	}
+
+	@Override
+	public void apply() {
+		wrapper.value += value;
+	}
+
+	@Override
+	public Change invert() {
+		return new IntChange(wrapper, -value);
+	}
+
+	@Override
+	public boolean isIdentity() {
+		return value == 0;
+	}
+}
diff --git a/src/test/java/dev/kske/undoredo/IntWrapper.java b/src/test/java/dev/kske/undoredo/IntWrapper.java
new file mode 100644
index 0000000..bae74ef
--- /dev/null
+++ b/src/test/java/dev/kske/undoredo/IntWrapper.java
@@ -0,0 +1,10 @@
+package dev.kske.undoredo;
+
+/**
+ * @author Kai S. K. Engelbart
+ * @since 0.0.1
+ */
+class IntWrapper {
+	
+	int value;
+}

From ee6015b35371f9a6d4dc29aa78aec2ff2c0515ee Mon Sep 17 00:00:00 2001
From: kske <kai@kske.dev>
Date: Sat, 11 Dec 2021 14:01:31 +0100
Subject: [PATCH 06/12] Fix index handling in change manager

---
 src/main/java/dev/kske/undoredo/ChangeManager.java | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/src/main/java/dev/kske/undoredo/ChangeManager.java b/src/main/java/dev/kske/undoredo/ChangeManager.java
index 6d520c2..4d45bd5 100644
--- a/src/main/java/dev/kske/undoredo/ChangeManager.java
+++ b/src/main/java/dev/kske/undoredo/ChangeManager.java
@@ -15,8 +15,8 @@ public final class ChangeManager<C extends Change> {
 
 	private final List<C> changes = new LinkedList<>();
 
-	private int	index;
-	private int	markedIndex;
+	private int	index		= -1;
+	private int	markedIndex	= -1;
 
 	/**
 	 * Applies the given change and appends it to the change list.
@@ -27,6 +27,7 @@ public final class ChangeManager<C extends Change> {
 	public void addChange(C change) {
 		change.apply();
 		changes.add(change);
+		++index;
 	}
 
 	/**
@@ -81,7 +82,7 @@ public final class ChangeManager<C extends Change> {
 	 * @since 0.0.1
 	 */
 	public boolean isUndoAvailable() {
-		return index > 0;
+		return index > -1;
 	}
 
 	/**

From f82df2b979fe0fe4648c9582b19e6e29e4c10d6b Mon Sep 17 00:00:00 2001
From: DieGurke <maxi@kske.dev>
Date: Sat, 11 Dec 2021 17:30:44 +0100
Subject: [PATCH 07/12] Extracted ChangeManager interface from concrete
 implementation

---
 .../java/dev/kske/undoredo/ChangeManager.java | 54 +++------------
 .../kske/undoredo/UnlimitedChangeManager.java | 69 +++++++++++++++++++
 .../dev/kske/undoredo/ChangeManagerTest.java  |  2 +-
 3 files changed, 81 insertions(+), 44 deletions(-)
 create mode 100644 src/main/java/dev/kske/undoredo/UnlimitedChangeManager.java

diff --git a/src/main/java/dev/kske/undoredo/ChangeManager.java b/src/main/java/dev/kske/undoredo/ChangeManager.java
index 4d45bd5..25e73f6 100644
--- a/src/main/java/dev/kske/undoredo/ChangeManager.java
+++ b/src/main/java/dev/kske/undoredo/ChangeManager.java
@@ -1,6 +1,6 @@
 package dev.kske.undoredo;
 
-import java.util.*;
+import java.util.List;
 
 /**
  * A change manager keeps track of subsequent changes and allows un- and redoing them. A specific
@@ -9,14 +9,10 @@ import java.util.*;
  *
  * @param <C> the change type to store in this change manager
  * @author Maximilian K&auml;fer
+ * @author Kai S. K. Engelbart
  * @since 0.0.1
  */
-public final class ChangeManager<C extends Change> {
-
-	private final List<C> changes = new LinkedList<>();
-
-	private int	index		= -1;
-	private int	markedIndex	= -1;
+public interface ChangeManager<C extends Change> {
 
 	/**
 	 * Applies the given change and appends it to the change list.
@@ -24,11 +20,7 @@ public final class ChangeManager<C extends Change> {
 	 * @param change the change to add
 	 * @since 0.0.1
 	 */
-	public void addChange(C change) {
-		change.apply();
-		changes.add(change);
-		++index;
-	}
+	void addChange(C change);
 
 	/**
 	 * Undoes the current change.
@@ -36,14 +28,7 @@ public final class ChangeManager<C extends Change> {
 	 * @return whether an action was performed
 	 * @since 0.1.0
 	 */
-	public boolean undo() {
-		if (isUndoAvailable()) {
-			changes.get(index).invert().apply();
-			--index;
-			return true;
-		}
-		return false;
-	}
+	boolean undo();
 
 	/**
 	 * Applies the change that was undone before.
@@ -51,47 +36,32 @@ public final class ChangeManager<C extends Change> {
 	 * @return whether an action was performed
 	 * @since 0.0.1
 	 */
-	public boolean redo() {
-		if (isRedoAvailable()) {
-			changes.get(index + 1).apply();
-			++index;
-			return true;
-		}
-		return false;
-	}
+	boolean redo();
 
 	/**
 	 * Marks the current change.
 	 *
 	 * @since 0.0.1
 	 */
-	public void mark() {
-		markedIndex = index;
-	}
+	void mark();
 
 	/**
 	 * @return whether the current change is marked
 	 * @since 0.0.1
 	 */
-	public boolean isAtMarkedIndex() {
-		return markedIndex == index;
-	}
+	boolean isAtMarkedIndex();
 
 	/**
 	 * @return whether a change is present that can be undone
 	 * @since 0.0.1
 	 */
-	public boolean isUndoAvailable() {
-		return index > -1;
-	}
+	boolean isUndoAvailable();
 
 	/**
 	 * @return whether a change is present that can be redone
 	 * @since 0.0.1
 	 */
-	public boolean isRedoAvailable() {
-		return index < changes.size() - 1;
-	}
+	boolean isRedoAvailable();
 
 	/**
 	 * Provides an unmodifiable view of the changes stored in this change manager.
@@ -99,7 +69,5 @@ public final class ChangeManager<C extends Change> {
 	 * @return all stored changes
 	 * @since 0.0.1
 	 */
-	public List<C> getChanges() {
-		return Collections.unmodifiableList(changes);
-	}
+	List<C> getChanges();
 }
diff --git a/src/main/java/dev/kske/undoredo/UnlimitedChangeManager.java b/src/main/java/dev/kske/undoredo/UnlimitedChangeManager.java
new file mode 100644
index 0000000..d927ee7
--- /dev/null
+++ b/src/main/java/dev/kske/undoredo/UnlimitedChangeManager.java
@@ -0,0 +1,69 @@
+package dev.kske.undoredo;
+
+import java.util.*;
+
+/**
+ * @param <C> the change type to store in this change manager
+ * @author Maximilian K&auml;fer
+ * @author Kai S. K. Engelbart
+ * @since 0.0.1
+ */
+public final class UnlimitedChangeManager<C extends Change> implements ChangeManager<C> {
+
+	private final List<C> changes = new LinkedList<>();
+
+	private int	index		= -1;
+	private int	markedIndex	= -1;
+
+	@Override
+	public void addChange(C change) {
+		change.apply();
+		changes.add(change);
+		++index;
+	}
+
+	@Override
+	public boolean undo() {
+		if (isUndoAvailable()) {
+			changes.get(index).invert().apply();
+			--index;
+			return true;
+		}
+		return false;
+	}
+
+	@Override
+	public boolean redo() {
+		if (isRedoAvailable()) {
+			changes.get(index + 1).apply();
+			++index;
+			return true;
+		}
+		return false;
+	}
+
+	@Override
+	public void mark() {
+		markedIndex = index;
+	}
+
+	@Override
+	public boolean isAtMarkedIndex() {
+		return markedIndex == index;
+	}
+
+	@Override
+	public boolean isUndoAvailable() {
+		return index > -1;
+	}
+
+	@Override
+	public boolean isRedoAvailable() {
+		return index < changes.size() - 1;
+	}
+
+	@Override
+	public List<C> getChanges() {
+		return Collections.unmodifiableList(changes);
+	}
+}
diff --git a/src/test/java/dev/kske/undoredo/ChangeManagerTest.java b/src/test/java/dev/kske/undoredo/ChangeManagerTest.java
index b3e1b72..db18ba5 100644
--- a/src/test/java/dev/kske/undoredo/ChangeManagerTest.java
+++ b/src/test/java/dev/kske/undoredo/ChangeManagerTest.java
@@ -16,7 +16,7 @@ class ChangeManagerTest {
 
 	@BeforeEach
 	void prepareChangeManager() {
-		manager	= new ChangeManager<>();
+		manager	= new UnlimitedChangeManager<>();
 		wrapper	= new IntWrapper();
 		change	= new IntChange(wrapper, 1);
 	}

From c411eace810e267892c749fd949d69a301b1db15 Mon Sep 17 00:00:00 2001
From: kske <kai@kske.dev>
Date: Sat, 11 Dec 2021 17:55:49 +0100
Subject: [PATCH 08/12] Convert to multi-module project

---
 .gitignore                                    |  7 ++++--
 .project                                      |  6 -----
 .classpath => core/.classpath                 |  0
 core/.project                                 | 23 +++++++++++++++++++
 core/pom.xml                                  | 15 ++++++++++++
 .../main/java/dev/kske/undoredo/Change.java   |  0
 .../java/dev/kske/undoredo/ChangeManager.java |  0
 .../kske/undoredo/UnlimitedChangeManager.java |  0
 .../java/dev/kske/undoredo/package-info.java  |  0
 {src => core/src}/main/java/module-info.java  |  0
 .../dev/kske/undoredo/ChangeManagerTest.java  |  0
 .../java/dev/kske/undoredo/IntChange.java     |  0
 .../java/dev/kske/undoredo/IntWrapper.java    |  0
 pom.xml                                       |  8 ++++++-
 14 files changed, 50 insertions(+), 9 deletions(-)
 rename .classpath => core/.classpath (100%)
 create mode 100644 core/.project
 create mode 100644 core/pom.xml
 rename {src => core/src}/main/java/dev/kske/undoredo/Change.java (100%)
 rename {src => core/src}/main/java/dev/kske/undoredo/ChangeManager.java (100%)
 rename {src => core/src}/main/java/dev/kske/undoredo/UnlimitedChangeManager.java (100%)
 rename {src => core/src}/main/java/dev/kske/undoredo/package-info.java (100%)
 rename {src => core/src}/main/java/module-info.java (100%)
 rename {src => core/src}/test/java/dev/kske/undoredo/ChangeManagerTest.java (100%)
 rename {src => core/src}/test/java/dev/kske/undoredo/IntChange.java (100%)
 rename {src => core/src}/test/java/dev/kske/undoredo/IntWrapper.java (100%)

diff --git a/.gitignore b/.gitignore
index 731eb43..6cfda9f 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,2 +1,5 @@
-/target/
-/.settings/
+# Maven build directories
+target/
+
+# Eclipse settings directories
+.settings/
diff --git a/.project b/.project
index 9c30c27..1f09710 100644
--- a/.project
+++ b/.project
@@ -5,11 +5,6 @@
 	<projects>
 	</projects>
 	<buildSpec>
-		<buildCommand>
-			<name>org.eclipse.jdt.core.javabuilder</name>
-			<arguments>
-			</arguments>
-		</buildCommand>
 		<buildCommand>
 			<name>org.eclipse.m2e.core.maven2Builder</name>
 			<arguments>
@@ -17,7 +12,6 @@
 		</buildCommand>
 	</buildSpec>
 	<natures>
-		<nature>org.eclipse.jdt.core.javanature</nature>
 		<nature>org.eclipse.m2e.core.maven2Nature</nature>
 	</natures>
 </projectDescription>
diff --git a/.classpath b/core/.classpath
similarity index 100%
rename from .classpath
rename to core/.classpath
diff --git a/core/.project b/core/.project
new file mode 100644
index 0000000..49781d8
--- /dev/null
+++ b/core/.project
@@ -0,0 +1,23 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<projectDescription>
+	<name>undo-redo-core</name>
+	<comment></comment>
+	<projects>
+	</projects>
+	<buildSpec>
+		<buildCommand>
+			<name>org.eclipse.jdt.core.javabuilder</name>
+			<arguments>
+			</arguments>
+		</buildCommand>
+		<buildCommand>
+			<name>org.eclipse.m2e.core.maven2Builder</name>
+			<arguments>
+			</arguments>
+		</buildCommand>
+	</buildSpec>
+	<natures>
+		<nature>org.eclipse.jdt.core.javanature</nature>
+		<nature>org.eclipse.m2e.core.maven2Nature</nature>
+	</natures>
+</projectDescription>
diff --git a/core/pom.xml b/core/pom.xml
new file mode 100644
index 0000000..4cfd653
--- /dev/null
+++ b/core/pom.xml
@@ -0,0 +1,15 @@
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
+	<modelVersion>4.0.0</modelVersion>
+
+	<artifactId>undo-redo-core</artifactId>
+	<name>Undo-Redo Core</name>
+	
+	<parent>
+		<groupId>dev.kske</groupId>
+		<artifactId>undo-redo</artifactId>
+		<version>0.0.1-SNAPSHOT</version>
+	</parent>
+
+</project>
diff --git a/src/main/java/dev/kske/undoredo/Change.java b/core/src/main/java/dev/kske/undoredo/Change.java
similarity index 100%
rename from src/main/java/dev/kske/undoredo/Change.java
rename to core/src/main/java/dev/kske/undoredo/Change.java
diff --git a/src/main/java/dev/kske/undoredo/ChangeManager.java b/core/src/main/java/dev/kske/undoredo/ChangeManager.java
similarity index 100%
rename from src/main/java/dev/kske/undoredo/ChangeManager.java
rename to core/src/main/java/dev/kske/undoredo/ChangeManager.java
diff --git a/src/main/java/dev/kske/undoredo/UnlimitedChangeManager.java b/core/src/main/java/dev/kske/undoredo/UnlimitedChangeManager.java
similarity index 100%
rename from src/main/java/dev/kske/undoredo/UnlimitedChangeManager.java
rename to core/src/main/java/dev/kske/undoredo/UnlimitedChangeManager.java
diff --git a/src/main/java/dev/kske/undoredo/package-info.java b/core/src/main/java/dev/kske/undoredo/package-info.java
similarity index 100%
rename from src/main/java/dev/kske/undoredo/package-info.java
rename to core/src/main/java/dev/kske/undoredo/package-info.java
diff --git a/src/main/java/module-info.java b/core/src/main/java/module-info.java
similarity index 100%
rename from src/main/java/module-info.java
rename to core/src/main/java/module-info.java
diff --git a/src/test/java/dev/kske/undoredo/ChangeManagerTest.java b/core/src/test/java/dev/kske/undoredo/ChangeManagerTest.java
similarity index 100%
rename from src/test/java/dev/kske/undoredo/ChangeManagerTest.java
rename to core/src/test/java/dev/kske/undoredo/ChangeManagerTest.java
diff --git a/src/test/java/dev/kske/undoredo/IntChange.java b/core/src/test/java/dev/kske/undoredo/IntChange.java
similarity index 100%
rename from src/test/java/dev/kske/undoredo/IntChange.java
rename to core/src/test/java/dev/kske/undoredo/IntChange.java
diff --git a/src/test/java/dev/kske/undoredo/IntWrapper.java b/core/src/test/java/dev/kske/undoredo/IntWrapper.java
similarity index 100%
rename from src/test/java/dev/kske/undoredo/IntWrapper.java
rename to core/src/test/java/dev/kske/undoredo/IntWrapper.java
diff --git a/pom.xml b/pom.xml
index 8fce4ef..f04ca06 100644
--- a/pom.xml
+++ b/pom.xml
@@ -6,10 +6,15 @@
 	<groupId>dev.kske</groupId>
 	<artifactId>undo-redo</artifactId>
 	<version>0.0.1-SNAPSHOT</version>
+	<packaging>pom</packaging>
 
 	<name>Undo-Redo</name>
 	<description>A Java library for managing changes in an editor history.</description>
 	<url>https://git.kske.dev/kske/event-bus</url>
+	
+	<modules>
+		<module>core</module>
+	</modules>
 
 	<licenses>
 		<license>
@@ -169,7 +174,8 @@
 					<argLine>--add-opens dev.kske.undoredo/dev.kske.undoredo=ALL-UNNAMED</argLine>
 				</configuration>
 			</plugin>
-			
+
 		</plugins>
 	</build>
 </project>
+

From 4ef3c412519654f0a957a6cdce019bcf36d77cbb Mon Sep 17 00:00:00 2001
From: kske <kai@kske.dev>
Date: Sat, 11 Dec 2021 17:58:09 +0100
Subject: [PATCH 09/12] Adapt Jenkinsfile to multi-module architecture

---
 Jenkinsfile | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Jenkinsfile b/Jenkinsfile
index 61004d1..ae2c663 100644
--- a/Jenkinsfile
+++ b/Jenkinsfile
@@ -17,7 +17,7 @@ pipeline {
 			}
 			post {
 				always {
-					junit 'target/surefire-reports/*.xml'
+					junit '*/target/surefire-reports/*.xml'
 				}
 			}
 		}
@@ -34,7 +34,7 @@ pipeline {
 	}
 	post {
 		success {
-			archiveArtifacts artifacts: 'target/undo-redo-*.jar'
+			archiveArtifacts artifacts: '*/target/undo-redo-*.jar'
 		}
 	}
 }

From 93e177cc35941c5627d8174dae159540a1922327 Mon Sep 17 00:00:00 2001
From: DieGurke <maxi@kske.dev>
Date: Sat, 11 Dec 2021 18:09:47 +0100
Subject: [PATCH 10/12] Changed LinkedList to ArrayList

---
 .../src/main/java/dev/kske/undoredo/UnlimitedChangeManager.java | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/core/src/main/java/dev/kske/undoredo/UnlimitedChangeManager.java b/core/src/main/java/dev/kske/undoredo/UnlimitedChangeManager.java
index d927ee7..db958ac 100644
--- a/core/src/main/java/dev/kske/undoredo/UnlimitedChangeManager.java
+++ b/core/src/main/java/dev/kske/undoredo/UnlimitedChangeManager.java
@@ -10,7 +10,7 @@ import java.util.*;
  */
 public final class UnlimitedChangeManager<C extends Change> implements ChangeManager<C> {
 
-	private final List<C> changes = new LinkedList<>();
+	private final List<C> changes = new ArrayList<>();
 
 	private int	index		= -1;
 	private int	markedIndex	= -1;

From 23aa60e65e02f97708f40ae8c6fbdd2cd4c6e2ab Mon Sep 17 00:00:00 2001
From: kske <kai@kske.dev>
Date: Sat, 11 Dec 2021 18:18:39 +0100
Subject: [PATCH 11/12] Move everything into the core package

---
 .../java/dev/kske/undoredo/{ => core}/Change.java  |  2 +-
 .../kske/undoredo/{ => core}/ChangeManager.java    |  2 +-
 .../{ => core}/UnlimitedChangeManager.java         |  2 +-
 .../dev/kske/undoredo/{ => core}/package-info.java |  2 +-
 core/src/main/java/module-info.java                |  2 +-
 .../undoredo/{ => core}/ChangeManagerTest.java     |  4 ++--
 .../dev/kske/undoredo/{ => core}/IntChange.java    | 14 +++++++-------
 .../dev/kske/undoredo/{ => core}/IntWrapper.java   |  4 ++--
 8 files changed, 16 insertions(+), 16 deletions(-)
 rename core/src/main/java/dev/kske/undoredo/{ => core}/Change.java (95%)
 rename core/src/main/java/dev/kske/undoredo/{ => core}/ChangeManager.java (97%)
 rename core/src/main/java/dev/kske/undoredo/{ => core}/UnlimitedChangeManager.java (97%)
 rename core/src/main/java/dev/kske/undoredo/{ => core}/package-info.java (83%)
 rename core/src/test/java/dev/kske/undoredo/{ => core}/ChangeManagerTest.java (98%)
 rename core/src/test/java/dev/kske/undoredo/{ => core}/IntChange.java (70%)
 rename core/src/test/java/dev/kske/undoredo/{ => core}/IntWrapper.java (72%)

diff --git a/core/src/main/java/dev/kske/undoredo/Change.java b/core/src/main/java/dev/kske/undoredo/core/Change.java
similarity index 95%
rename from core/src/main/java/dev/kske/undoredo/Change.java
rename to core/src/main/java/dev/kske/undoredo/core/Change.java
index 6f88984..4252e03 100644
--- a/core/src/main/java/dev/kske/undoredo/Change.java
+++ b/core/src/main/java/dev/kske/undoredo/core/Change.java
@@ -1,4 +1,4 @@
-package dev.kske.undoredo;
+package dev.kske.undoredo.core;
 
 /**
  * Base interface for changes to be registered in an undo manager.
diff --git a/core/src/main/java/dev/kske/undoredo/ChangeManager.java b/core/src/main/java/dev/kske/undoredo/core/ChangeManager.java
similarity index 97%
rename from core/src/main/java/dev/kske/undoredo/ChangeManager.java
rename to core/src/main/java/dev/kske/undoredo/core/ChangeManager.java
index 25e73f6..7b887e7 100644
--- a/core/src/main/java/dev/kske/undoredo/ChangeManager.java
+++ b/core/src/main/java/dev/kske/undoredo/core/ChangeManager.java
@@ -1,4 +1,4 @@
-package dev.kske.undoredo;
+package dev.kske.undoredo.core;
 
 import java.util.List;
 
diff --git a/core/src/main/java/dev/kske/undoredo/UnlimitedChangeManager.java b/core/src/main/java/dev/kske/undoredo/core/UnlimitedChangeManager.java
similarity index 97%
rename from core/src/main/java/dev/kske/undoredo/UnlimitedChangeManager.java
rename to core/src/main/java/dev/kske/undoredo/core/UnlimitedChangeManager.java
index db958ac..8a0ff35 100644
--- a/core/src/main/java/dev/kske/undoredo/UnlimitedChangeManager.java
+++ b/core/src/main/java/dev/kske/undoredo/core/UnlimitedChangeManager.java
@@ -1,4 +1,4 @@
-package dev.kske.undoredo;
+package dev.kske.undoredo.core;
 
 import java.util.*;
 
diff --git a/core/src/main/java/dev/kske/undoredo/package-info.java b/core/src/main/java/dev/kske/undoredo/core/package-info.java
similarity index 83%
rename from core/src/main/java/dev/kske/undoredo/package-info.java
rename to core/src/main/java/dev/kske/undoredo/core/package-info.java
index 1cda98b..b4cc131 100644
--- a/core/src/main/java/dev/kske/undoredo/package-info.java
+++ b/core/src/main/java/dev/kske/undoredo/core/package-info.java
@@ -5,4 +5,4 @@
  * @author Kai S. K. Engelbart
  * @since 0.0.1
  */
-package dev.kske.undoredo;
+package dev.kske.undoredo.core;
diff --git a/core/src/main/java/module-info.java b/core/src/main/java/module-info.java
index d8d1033..3ae73e7 100644
--- a/core/src/main/java/module-info.java
+++ b/core/src/main/java/module-info.java
@@ -7,5 +7,5 @@
  */
 module dev.kske.undoredo {
 
-	exports dev.kske.undoredo;
+	exports dev.kske.undoredo.core;
 }
diff --git a/core/src/test/java/dev/kske/undoredo/ChangeManagerTest.java b/core/src/test/java/dev/kske/undoredo/core/ChangeManagerTest.java
similarity index 98%
rename from core/src/test/java/dev/kske/undoredo/ChangeManagerTest.java
rename to core/src/test/java/dev/kske/undoredo/core/ChangeManagerTest.java
index db18ba5..4643970 100644
--- a/core/src/test/java/dev/kske/undoredo/ChangeManagerTest.java
+++ b/core/src/test/java/dev/kske/undoredo/core/ChangeManagerTest.java
@@ -1,4 +1,4 @@
-package dev.kske.undoredo;
+package dev.kske.undoredo.core;
 
 import static org.junit.jupiter.api.Assertions.*;
 
@@ -33,7 +33,7 @@ class ChangeManagerTest {
 		manager.addChange(change);
 		assertSame(1, wrapper.value);
 	}
-	
+
 	/**
 	 * Tests the consistency of the change list.
 	 *
diff --git a/core/src/test/java/dev/kske/undoredo/IntChange.java b/core/src/test/java/dev/kske/undoredo/core/IntChange.java
similarity index 70%
rename from core/src/test/java/dev/kske/undoredo/IntChange.java
rename to core/src/test/java/dev/kske/undoredo/core/IntChange.java
index 76299a4..f6e8a32 100644
--- a/core/src/test/java/dev/kske/undoredo/IntChange.java
+++ b/core/src/test/java/dev/kske/undoredo/core/IntChange.java
@@ -1,17 +1,17 @@
-package dev.kske.undoredo;
+package dev.kske.undoredo.core;
 
 /**
  * @author Kai S. K. Engelbart
  * @since 0.0.1
  */
 class IntChange implements Change {
-	
-	private final IntWrapper wrapper;
-	private final int value;
-	
+
+	private final IntWrapper	wrapper;
+	private final int			value;
+
 	IntChange(IntWrapper wrapper, int value) {
-		this.wrapper = wrapper;
-		this.value = value;
+		this.wrapper	= wrapper;
+		this.value		= value;
 	}
 
 	@Override
diff --git a/core/src/test/java/dev/kske/undoredo/IntWrapper.java b/core/src/test/java/dev/kske/undoredo/core/IntWrapper.java
similarity index 72%
rename from core/src/test/java/dev/kske/undoredo/IntWrapper.java
rename to core/src/test/java/dev/kske/undoredo/core/IntWrapper.java
index bae74ef..2b6907d 100644
--- a/core/src/test/java/dev/kske/undoredo/IntWrapper.java
+++ b/core/src/test/java/dev/kske/undoredo/core/IntWrapper.java
@@ -1,10 +1,10 @@
-package dev.kske.undoredo;
+package dev.kske.undoredo.core;
 
 /**
  * @author Kai S. K. Engelbart
  * @since 0.0.1
  */
 class IntWrapper {
-	
+
 	int value;
 }

From a4695870c4502584ab2bc09a51fc3d7315250c69 Mon Sep 17 00:00:00 2001
From: kske <kai@kske.dev>
Date: Sat, 11 Dec 2021 18:22:06 +0100
Subject: [PATCH 12/12] Fix core module name

---
 core/src/main/java/module-info.java | 2 +-
 pom.xml                             | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/core/src/main/java/module-info.java b/core/src/main/java/module-info.java
index 3ae73e7..ccaee99 100644
--- a/core/src/main/java/module-info.java
+++ b/core/src/main/java/module-info.java
@@ -5,7 +5,7 @@
  * @author Kai S. K. Engelbart
  * @since 0.0.1
  */
-module dev.kske.undoredo {
+module dev.kske.undoredo.core {
 
 	exports dev.kske.undoredo.core;
 }
diff --git a/pom.xml b/pom.xml
index f04ca06..70f0e57 100644
--- a/pom.xml
+++ b/pom.xml
@@ -171,7 +171,7 @@
 				<artifactId>maven-surefire-plugin</artifactId>
 				<version>3.0.0-M5</version>
 				<configuration>
-					<argLine>--add-opens dev.kske.undoredo/dev.kske.undoredo=ALL-UNNAMED</argLine>
+					<argLine>--add-opens dev.kske.undoredo.core/dev.kske.undoredo.core=ALL-UNNAMED</argLine>
 				</configuration>
 			</plugin>