BAEL-1155 crdt (#2659)

* BAEL-1155 crdt

* BAEL-1155 fix pom

libraries/pom.xml

@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
     <parent>
         <artifactId>parent-modules</artifactId>
         <groupId>com.baeldung</groupId>
@@ -487,7 +487,7 @@
             <artifactId>vavr</artifactId>
             <version>${vavr.version}</version>
         </dependency>
-        
+
         <!-- Retrofit -->
         <dependency>
             <groupId>com.squareup.retrofit2</groupId>
@@ -503,7 +503,7 @@
             <groupId>com.squareup.retrofit2</groupId>
             <artifactId>adapter-rxjava</artifactId>
             <version>${retrofit.version}</version>
-        </dependency>        
+        </dependency>
         <dependency>
             <groupId>com.squareup.okhttp3</groupId>
             <artifactId>logging-interceptor</artifactId>
@@ -596,6 +596,11 @@
             <artifactId>jgrapht-core</artifactId>
             <version>1.0.1</version>
         </dependency>
+        <dependency>
+           <groupId>com.netopyr.wurmloch</groupId>
+            <artifactId>wurmloch-crdt</artifactId>
+            <version>${crdt.version}</version>
+        </dependency>
     </dependencies>
     <repositories>
         <repository>
@@ -617,6 +622,7 @@
         </repository>
     </repositories>
     <properties>
+        <crdt.version>0.1.0</crdt.version>
         <multiverse.version>0.7.0</multiverse.version>
         <cglib.version>3.2.4</cglib.version>
         <commons-lang.version>3.6</commons-lang.version>
@@ -669,6 +675,6 @@
         <protonpack.version>1.14</protonpack.version>
         <unit-ri.version>1.0.3</unit-ri.version>
         <cache.version>1.0.0</cache.version>
-    	<hazelcast.version>3.8.4</hazelcast.version>
+        <hazelcast.version>3.8.4</hazelcast.version>
     </properties>
 </project>

libraries/src/test/java/com/baeldung/crdt/CRDTTest.java

@@ -0,0 +1,153 @@
+package com.baeldung.crdt;
+
+import com.netopyr.wurmloch.crdt.GCounter;
+import com.netopyr.wurmloch.crdt.GSet;
+import com.netopyr.wurmloch.crdt.LWWRegister;
+import com.netopyr.wurmloch.crdt.PNCounter;
+import com.netopyr.wurmloch.store.LocalCrdtStore;
+import org.junit.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class CRDTTest {
+
+    @Test
+    public void givenGrowOnlySet_whenTwoReplicasDiverge_thenShouldMergeItWithoutAConflict() {
+        //given
+        final LocalCrdtStore crdtStore1 = new LocalCrdtStore();
+        final LocalCrdtStore crdtStore2 = new LocalCrdtStore();
+        crdtStore1.connect(crdtStore2);
+
+        final GSet<String> replica1 = crdtStore1.createGSet("ID_1");
+        final GSet<String> replica2 = crdtStore2.<String>findGSet("ID_1").get();
+
+        //when
+        replica1.add("apple");
+        replica2.add("banana");
+
+        //then
+        assertThat(replica1).contains("apple", "banana");
+        assertThat(replica2).contains("apple", "banana");
+
+        //when
+        crdtStore1.disconnect(crdtStore2);
+
+        replica1.add("strawberry");
+        replica2.add("pear");
+
+
+        assertThat(replica1).contains("apple", "banana", "strawberry");
+        assertThat(replica2).contains("apple", "banana", "pear");
+
+        crdtStore1.connect(crdtStore2);
+
+        //then
+        assertThat(replica1).contains("apple", "banana", "strawberry", "pear");
+        assertThat(replica2).contains("apple", "banana", "strawberry", "pear");
+    }
+
+    @Test
+    public void givenIncrementOnlyCounter_whenTwoReplicasDiverge_thenShouldMergeIt() {
+        //given
+        final LocalCrdtStore crdtStore1 = new LocalCrdtStore();
+        final LocalCrdtStore crdtStore2 = new LocalCrdtStore();
+        crdtStore1.connect(crdtStore2);
+
+        final GCounter replica1 = crdtStore1.createGCounter("ID_1");
+        final GCounter replica2 = crdtStore2.findGCounter("ID_1").get();
+
+        //when
+        replica1.increment();
+        replica2.increment(2L);
+
+        //then
+        assertThat(replica1.get()).isEqualTo(3L);
+        assertThat(replica2.get()).isEqualTo(3L);
+
+        //when
+        crdtStore1.disconnect(crdtStore2);
+
+        replica1.increment(3L);
+        replica2.increment(5L);
+
+
+        assertThat(replica1.get()).isEqualTo(6L);
+        assertThat(replica2.get()).isEqualTo(8L);
+
+        crdtStore1.connect(crdtStore2);
+
+        // then
+        assertThat(replica1.get()).isEqualTo(11L);
+        assertThat(replica2.get()).isEqualTo(11L);
+    }
+
+    @Test
+    public void givenPNCounter_whenReplicasDiverge_thenShouldMergeWithoutAConflict() {
+        // given
+        final LocalCrdtStore crdtStore1 = new LocalCrdtStore();
+        final LocalCrdtStore crdtStore2 = new LocalCrdtStore();
+        crdtStore1.connect(crdtStore2);
+
+        final PNCounter replica1 = crdtStore1.createPNCounter("ID_1");
+        final PNCounter replica2 = crdtStore2.findPNCounter("ID_1").get();
+
+        //when
+        replica1.increment();
+        replica2.decrement(2L);
+
+        //then
+        assertThat(replica1.get()).isEqualTo(-1L);
+        assertThat(replica2.get()).isEqualTo(-1L);
+
+        //when
+        crdtStore1.disconnect(crdtStore2);
+
+        replica1.decrement(3L);
+        replica2.increment(5L);
+
+        assertThat(replica1.get()).isEqualTo(-4L);
+        assertThat(replica2.get()).isEqualTo(4L);
+
+        crdtStore1.connect(crdtStore2);
+
+        //then
+        assertThat(replica1.get()).isEqualTo(1L);
+        assertThat(replica2.get()).isEqualTo(1L);
+    }
+
+    @Test
+    public void givenLastWriteWinsStrategy_whenReplicasDiverge_thenAfterMergeShouldKeepOnlyLastValue() {
+        //given
+        final LocalCrdtStore crdtStore1 = new LocalCrdtStore("N_1");
+        final LocalCrdtStore crdtStore2 = new LocalCrdtStore("N_2");
+        crdtStore1.connect(crdtStore2);
+
+        final LWWRegister<String> replica1 = crdtStore1.createLWWRegister("ID_1");
+        final LWWRegister<String> replica2 = crdtStore2.<String>findLWWRegister("ID_1").get();
+
+        //when
+        replica1.set("apple");
+        replica2.set("banana");
+
+        // then
+        assertThat(replica1.get()).isEqualTo("banana");
+        assertThat(replica2.get()).isEqualTo("banana");
+
+
+        // when
+        crdtStore1.disconnect(crdtStore2);
+
+        replica1.set("strawberry");
+        replica2.set("pear");
+
+
+        assertThat(replica1.get()).isEqualTo("strawberry");
+        assertThat(replica2.get()).isEqualTo("pear");
+
+        crdtStore1.connect(crdtStore2);
+
+        //then
+        assertThat(replica1.get()).isEqualTo("pear");
+        assertThat(replica2.get()).isEqualTo("pear");
+    }
+}