From fd9a0a2199f48267ef02e232d4ba5e7e1b32a608 Mon Sep 17 00:00:00 2001
From: Paul Campbell <pcampbell@kemitix.net>
Date: Fri, 22 May 2020 20:51:42 +0100
Subject: [PATCH] Add StreamZipper

---
 .../net/kemitix/text/fit/StreamZipper.java    | 60 +++++++++++++++++++
 src/main/java/net/kemitix/text/fit/Tuple.java | 24 ++++++++
 .../kemitix/text/fit/StreamZipperTest.java    | 40 +++++++++++++
 3 files changed, 124 insertions(+)
 create mode 100644 src/main/java/net/kemitix/text/fit/StreamZipper.java
 create mode 100644 src/main/java/net/kemitix/text/fit/Tuple.java
 create mode 100644 src/test/java/net/kemitix/text/fit/StreamZipperTest.java

diff --git a/src/main/java/net/kemitix/text/fit/StreamZipper.java b/src/main/java/net/kemitix/text/fit/StreamZipper.java
new file mode 100644
index 0000000..4fe001a
--- /dev/null
+++ b/src/main/java/net/kemitix/text/fit/StreamZipper.java
@@ -0,0 +1,60 @@
+package net.kemitix.text.fit;
+
+
+import java.util.List;
+import java.util.function.BiFunction;
+import java.util.function.IntFunction;
+import java.util.stream.Stream;
+
+import static java.lang.Math.min;
+import static java.util.stream.IntStream.range;
+
+/**
+ * Utility to zip two {@link Stream}s together.
+ *
+ * @author Paul Campbell (pcampbell@kemitix.net)
+ */
+public final class StreamZipper {
+
+    private StreamZipper() {
+        throw new UnsupportedOperationException();
+    }
+
+    /**
+     * Zip two {@link Stream}s together.
+     *
+     * <p>The resulting stream will contain only as many items as the shortest of the two lists.</p>
+     *
+     * @param a the first List
+     * @param b the second List
+     * @param zipper the function to zip an item from each list
+     * @param <A> the type of the first list
+     * @param <B> the type of the second list
+     * @param <C> the type of the joined items
+     * @return a Stream of the joined items
+     */
+    public static <A, B, C> Stream<C> zip(
+            final List<A> a,
+            final List<B> b,
+            final BiFunction<A, B, C> zipper
+    ) {
+        return range(0, limit(a, b))
+                .mapToObj(tuple(a, b, zipper));
+    }
+
+    private static <A, B> int limit(
+            final List<A> a,
+            final List<B> b
+    ) {
+        return min(a.size(), b.size());
+    }
+
+    private static <A, B, C> IntFunction<C> tuple(
+            final List<A> a,
+            final List<B> b,
+            final BiFunction<A, B, C> zipper
+    ) {
+        return i -> zipper.apply(a.get(i), b.get(i));
+    }
+
+}
diff --git a/src/main/java/net/kemitix/text/fit/Tuple.java b/src/main/java/net/kemitix/text/fit/Tuple.java
new file mode 100644
index 0000000..086b690
--- /dev/null
+++ b/src/main/java/net/kemitix/text/fit/Tuple.java
@@ -0,0 +1,24 @@
+package net.kemitix.text.fit;
+
+public class Tuple<A, B> {
+
+    private final A partA;
+    private final B partB;
+
+    private Tuple(final A partA, final B partB) {
+        this.partA = partA;
+        this.partB = partB;
+    }
+
+    public static <A, B> Tuple<A, B> of(final A a, final B b) {
+        return new Tuple<>(a, b);
+    }
+
+    public A get1() {
+        return partA;
+    }
+
+    public B get2() {
+        return partB;
+    }
+}
diff --git a/src/test/java/net/kemitix/text/fit/StreamZipperTest.java b/src/test/java/net/kemitix/text/fit/StreamZipperTest.java
new file mode 100644
index 0000000..5ed3015
--- /dev/null
+++ b/src/test/java/net/kemitix/text/fit/StreamZipperTest.java
@@ -0,0 +1,40 @@
+package net.kemitix.text.fit;
+
+import org.assertj.core.api.WithAssertions;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+
+import java.lang.reflect.Constructor;
+import java.util.Arrays;
+import java.util.List;
+import java.util.stream.Collectors;
+
+class StreamZipperTest implements WithAssertions {
+
+    @Test
+    void privateUtilityConstructor() throws NoSuchMethodException {
+        //given
+        final Constructor<StreamZipper> constructor = StreamZipper.class.getDeclaredConstructor();
+        constructor.setAccessible(true);
+        //then
+        assertThatCode(constructor::newInstance)
+                .hasCauseInstanceOf(UnsupportedOperationException.class);
+    }
+
+    @Test
+    @DisplayName("Pair two lists together")
+    void pairItems() {
+        //when
+        final List<String> strings = Arrays.asList("One", "Two", "Three");
+        final List<Integer> integers = Arrays.asList(3, 2, 1);
+        final List<Tuple<String, Integer>> zipped =
+                StreamZipper.zip(strings, integers, Tuple::of).collect(Collectors.toList());
+        //then
+        assertThat(zipped)
+                .extracting(Tuple::get1)
+                .containsExactlyElementsOf(strings.subList(0, zipped.size()));
+        assertThat(zipped)
+                .extracting(Tuple::get2)
+                .containsExactlyElementsOf(integers.subList(0, zipped.size()));
+    }
+}