Implement mathematical operators

* count - emits the number of items emitted by the upstream
* index - emits `Tuple2<Long, T>` for each item from the upstream. The first element of the tuple is the index (0-based), and the second if the item
* min / max - emits the min/max item from the upstream, using Java comparator
* top(x) - emits the top x items from the upstream, a new ranking is emitted every time it changes.
* sum - emits the sum of all the items emitted by the upstream
* average - emits the average of all the items emitted by the upstream

bom/pom.xml

@@ -55,6 +55,11 @@
                 <artifactId>mutiny-test-utils</artifactId>
                 <version>${project.version}</version>
             </dependency>
+            <dependency>
+                <groupId>io.smallrye.reactive</groupId>
+                <artifactId>mutiny-math</artifactId>
+                <version>${project.version}</version>
+            </dependency>
         </dependencies>
     </dependencyManagement>
 

math/README.md

@@ -0,0 +1,31 @@
+# Mutiny Math Operators
+
+This library provides a set of _operators_ for [Mutiny](https://smallrye.io/smallrye-mutiny).
+
+You can use these operators using the `plug` method offered by Mutiny:
+
+```java
+Multi<Long> counts = Multi.createFrom().items("a", "b", "c", "d", "e")
+                            .plug(Math.count())
+```
+
+These operators provide streams (`Multi`) emitting new values when the computed value changes. To get the last value, use `collect().last()`:
+
+```java
+String max = Multi.createFrom().items("e", "b", "c", "f", "g", "e")
+                .plug(Math.max())
+                .collect().last()
+                .await().indefinitely();
+```
+
+The `io.smallrye.math.Math` class provides the entry point to the offered operators:
+
+* count - emits the number of items emitted by the upstream
+* index - emits `Tuple2<Long, T>` for each item from the upstream. The first element of the tuple is the index (0-based), and the second if the item 
+* min / max - emits the min/max item from the upstream, using Java comparator
+* top(x) - emits the top x items from the upstream, a new ranking is emitted every time it changes.
+* sum - emits the sum of all the items emitted by the upstream
+* average - emits the average of all the items emitted by the upstream
+
+
+

math/pom.xml

@@ -0,0 +1,149 @@
+<?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">
+    <modelVersion>4.0.0</modelVersion>
+
+    <parent>
+        <groupId>io.smallrye.reactive</groupId>
+        <artifactId>mutiny-project</artifactId>
+        <version>999-SNAPSHOT</version>
+    </parent>
+
+    <name>SmallRye Mutiny :: Math Operators</name>
+    <artifactId>mutiny-math</artifactId>
+
+    <dependencies>
+        <dependency>
+            <groupId>io.smallrye.reactive</groupId>
+            <artifactId>mutiny</artifactId>
+        </dependency>
+
+        <dependency>
+            <groupId>io.smallrye.reactive</groupId>
+            <artifactId>reactive-streams-junit5-tck</artifactId>
+            <version>${project.version}</version>
+            <type>test-jar</type>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.reactivestreams</groupId>
+            <artifactId>reactive-streams-tck</artifactId>
+            <version>${reactive-streams.version}</version>
+            <scope>test</scope>
+            <exclusions>
+                <exclusion>
+                    <groupId>junit</groupId>
+                    <artifactId>junit</artifactId>
+                </exclusion>
+            </exclusions>
+        </dependency>
+
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-engine</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-api</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-surefire-plugin</artifactId>
+                <executions>
+                    <execution>
+                        <id>default-test</id>
+                        <goals>
+                            <goal>test</goal>
+                        </goals>
+                        <configuration>
+                            <!-- Disable TestNG -->
+                            <testNGArtifactName>none:none</testNGArtifactName>
+                        </configuration>
+                    </execution>
+                </executions>
+            </plugin>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-javadoc-plugin</artifactId>
+                <executions>
+                    <execution>
+                        <id>attach-javadocs</id>
+                        <goals>
+                            <goal>jar</goal>
+                        </goals>
+                    </execution>
+                </executions>
+            </plugin>
+            <plugin>
+                <groupId>org.moditect</groupId>
+                <artifactId>moditect-maven-plugin</artifactId>
+                <executions>
+                    <execution>
+                        <id>add-module-infos</id>
+                        <phase>package</phase>
+                        <goals>
+                            <goal>add-module-info</goal>
+                        </goals>
+                        <configuration>
+                            <module>
+                                <moduleInfoFile>src/main/module/module-info.java</moduleInfoFile>
+                            </module>
+                        </configuration>
+                    </execution>
+                </executions>
+            </plugin>
+            <plugin>
+                <groupId>org.jboss.jandex</groupId>
+                <artifactId>jandex-maven-plugin</artifactId>
+            </plugin>
+            <plugin>
+                <groupId>org.revapi</groupId>
+                <artifactId>revapi-maven-plugin</artifactId>
+            </plugin>
+        </plugins>
+    </build>
+
+    <profiles>
+        <profile>
+            <activation>
+                <jdk>[9,)</jdk>
+            </activation>
+            <id>java-9+</id>
+            <build>
+                <plugins>
+                    <plugin>
+                        <groupId>org.apache.maven.plugins</groupId>
+                        <artifactId>maven-javadoc-plugin</artifactId>
+                        <executions>
+                            <execution>
+                                <id>attach-javadocs</id>
+                                <goals>
+                                    <goal>jar</goal>
+                                </goals>
+                            </execution>
+                        </executions>
+                        <configuration>
+                            <!-- wonderful reliability of javadoc used with modules breaking on non exposed packages -->
+                            <source>8</source>
+                            <release>8</release>
+                            <detectJavaApiLink>false</detectJavaApiLink>
+                        </configuration>
+                    </plugin>
+                </plugins>
+            </build>
+        </profile>
+    </profiles>
+
+</project>

math/revapi.json

@@ -0,0 +1,37 @@
+[ {
+  "extension" : "revapi.java",
+  "id" : "java",
+  "configuration" : {
+    "missing-classes" : {
+      "behavior" : "report",
+      "ignoreMissingAnnotations" : false
+    },
+    "filter" : {
+      "packages" : {
+        "regex" : true,
+        "include" : [ "io\\.smallrye\\.mutiny\\.math(\\..+)?" ]
+      }
+    }
+  }
+}, {
+  "extension" : "revapi.differences",
+  "id" : "breaking-changes",
+  "configuration" : {
+    "criticality" : "highlight",
+    "minSeverity" : "POTENTIALLY_BREAKING",
+    "minCriticality" : "documented",
+    "differences" : [
+
+    ]
+  }
+}, {
+  "extension" : "revapi.reporter.json",
+  "configuration" : {
+    "minSeverity" : "POTENTIALLY_BREAKING",
+    "minCriticality" : "documented",
+    "output" : "target/compatibility.json",
+    "indent" : true,
+    "append" : false,
+    "keepEmptyFile" : true
+  }
+} ]

math/src/main/java/io/smallrye/mutiny/math/AverageOperator.java

@@ -0,0 +1,30 @@
+package io.smallrye.mutiny.math;
+
+import java.util.function.Function;
+
+import io.smallrye.mutiny.Multi;
+
+/**
+ * Average operator emitting the current count.
+ * Everytime it gets an item from upstream, it emits the <em>average</em> of the already received items.
+ * If the stream emits the completion event without having emitting any item before, 0 is emitted, following by the
+ * completion event.
+ * If the upstream emits a failure, the failure is propagated.
+ */
+public class AverageOperator<T extends Number>
+        implements Function<Multi<T>, Multi<Double>> {
+
+    private double sum = 0;
+    private long count = 0;
+
+    @Override
+    public Multi<Double> apply(Multi<T> multi) {
+        return multi
+                .onItem().transform(x -> {
+                    count = count + 1;
+                    sum = sum + x.doubleValue();
+                    return sum / count;
+                })
+                .onCompletion().ifEmpty().continueWith(0.0);
+    }
+}

math/src/main/java/io/smallrye/mutiny/math/CountOperator.java

@@ -0,0 +1,30 @@
+package io.smallrye.mutiny.math;
+
+import java.util.function.Function;
+
+import io.smallrye.mutiny.Multi;
+
+/**
+ * Count operator emitting the current count.
+ * Everytime it gets an item from upstream, it emits the <em>count</em>.
+ * If the stream emits the completion event without having emitting any item before, 0 is emitted, following by the
+ * completion event.
+ * If the upstream emits a failure, the failure is propagated.
+ *
+ * @param <T> type of the incoming items.
+ */
+public class CountOperator<T>
+        implements Function<Multi<T>, Multi<Long>> {
+
+    private long count = 0;
+
+    @Override
+    public Multi<Long> apply(Multi<T> multi) {
+        return multi
+                .onItem().transform(x -> {
+                    count = count + 1;
+                    return count;
+                })
+                .onCompletion().ifEmpty().continueWith(0L);
+    }
+}

math/src/main/java/io/smallrye/mutiny/math/IndexOperator.java

@@ -0,0 +1,26 @@
+package io.smallrye.mutiny.math;
+
+import java.util.function.Function;
+
+import io.smallrye.mutiny.Multi;
+import io.smallrye.mutiny.tuples.Tuple2;
+
+/**
+ * Index operator emitting a {@link io.smallrye.mutiny.tuples.Tuple2 Tuple2<Long, T>}, with the index (0-based) of the
+ * element
+ * and the element from upstream.
+ * If the upstream emits a failure, the failure is propagated.
+ *
+ * @param <T> type of the incoming items.
+ */
+public class IndexOperator<T>
+        implements Function<Multi<T>, Multi<Tuple2<Long, T>>> {
+
+    private long index = 0;
+
+    @Override
+    public Multi<Tuple2<Long, T>> apply(Multi<T> multi) {
+        return multi
+                .onItem().transform(x -> Tuple2.of(index++, x));
+    }
+}