From 1785d6ad9e532d442682f843be8958c8855017c2 Mon Sep 17 00:00:00 2001
From: Ivan Hetman <Ihromant@users.noreply.github.com>
Date: Wed, 7 Oct 2020 12:21:55 +0300
Subject: [PATCH] Collectors.toMap (#515)

Implement Collectors.toMap
---
 .../java/util/stream/TCollectors.java         | 48 +++++++++++++++++++
 .../java/util/stream/CollectorsTest.java      | 23 +++++++++
 2 files changed, 71 insertions(+)

diff --git a/classlib/src/main/java/org/teavm/classlib/java/util/stream/TCollectors.java b/classlib/src/main/java/org/teavm/classlib/java/util/stream/TCollectors.java
index 543bd9359..5b356ea32 100644
--- a/classlib/src/main/java/org/teavm/classlib/java/util/stream/TCollectors.java
+++ b/classlib/src/main/java/org/teavm/classlib/java/util/stream/TCollectors.java
@@ -17,12 +17,16 @@ package org.teavm.classlib.java.util.stream;
 
 import java.util.ArrayList;
 import java.util.Collection;
+import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
+import java.util.Map;
 import java.util.Set;
 import java.util.function.BiConsumer;
 import java.util.function.BinaryOperator;
+import java.util.function.Function;
 import java.util.function.Supplier;
+import org.teavm.classlib.java.util.TObjects;
 
 public final class TCollectors {
     private TCollectors() {
@@ -69,4 +73,48 @@ public final class TCollectors {
         return TCollector.of(StringBuilder::new, accumulator, combiner,
                 sb -> sb.insert(0, prefix).append(suffix).toString());
     }
+
+    public static <E, K, V> TCollector<E, ?, Map<K, V>> toMap(Function<? super E, ? extends K> keyMapper,
+            Function<? super E, ? extends V> valueMapper) {
+        return TCollector.of(HashMap::new,
+                (map, el) -> {
+                    K k = keyMapper.apply(el);
+                    V newV = TObjects.requireNonNull(valueMapper.apply(el));
+                    V oldV = map.putIfAbsent(k, newV);
+                    if (oldV != null) {
+                        throw new IllegalStateException(
+                                "Key " + k + " corresponds to values " + oldV + " and " + newV);
+                    }
+                },
+                (m1, m2) -> {
+                    for (Map.Entry<K, V> e : m2.entrySet()) {
+                        V newV = TObjects.requireNonNull(e.getValue());
+                        V oldV = m1.putIfAbsent(e.getKey(), newV);
+                        if (oldV != null) {
+                            throw new IllegalStateException(
+                                    "Key " + e.getKey() + " corresponds to values " + oldV + " and " + newV);
+                        }
+                    }
+                    return m1;
+                },
+                TCollector.Characteristics.IDENTITY_FINISH);
+    }
+
+    public static <E, K, V> TCollector<E, ?, Map<K, V>> toMap(Function<? super E, ? extends K> keyMapper,
+            Function<? super E, ? extends V> valueMapper, BinaryOperator<V> mergeFunction) {
+        return toMap(keyMapper, valueMapper, mergeFunction, HashMap::new);
+    }
+
+    public static <E, K, V, M extends Map<K, V>> TCollector<E, ?, M> toMap(Function<? super E, ? extends K> keyMapper,
+            Function<? super E, ? extends V> valueMapper, BinaryOperator<V> mergeFunction, Supplier<M> mapFactory) {
+        return TCollector.of(mapFactory,
+                (map, el) -> map.merge(keyMapper.apply(el), valueMapper.apply(el), mergeFunction),
+                (m1, m2) -> {
+                    for (Map.Entry<K, V> e : m2.entrySet()) {
+                        m1.merge(e.getKey(), e.getValue(), mergeFunction);
+                    }
+                    return m1;
+                },
+                TCollector.Characteristics.IDENTITY_FINISH);
+    }
 }
diff --git a/tests/src/test/java/org/teavm/classlib/java/util/stream/CollectorsTest.java b/tests/src/test/java/org/teavm/classlib/java/util/stream/CollectorsTest.java
index 9fef1929e..64c36d9cf 100644
--- a/tests/src/test/java/org/teavm/classlib/java/util/stream/CollectorsTest.java
+++ b/tests/src/test/java/org/teavm/classlib/java/util/stream/CollectorsTest.java
@@ -18,9 +18,13 @@ package org.teavm.classlib.java.util.stream;
 import static org.junit.Assert.assertEquals;
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
+import java.util.Map;
+import java.util.function.Function;
 import java.util.stream.Collectors;
+import java.util.stream.IntStream;
 import java.util.stream.Stream;
 import org.junit.Test;
 import org.junit.runner.RunWith;
@@ -55,4 +59,23 @@ public class CollectorsTest {
         Stream.of(1, 2, 3).collect(Collectors.toCollection(() -> c));
         assertEquals(Arrays.asList(1, 2, 3), c);
     }
+
+    @Test(expected = NullPointerException.class)
+    public void noNullsInToMap() {
+        Stream.of(1, 2, null).collect(Collectors.toMap(Function.identity(), Function.identity()));
+    }
+
+    @Test(expected = IllegalStateException.class)
+    public void noDuplicatesInToMap() {
+        Stream.of(1, 2, 2).collect(Collectors.toMap(Function.identity(), Function.identity()));
+    }
+
+    @Test
+    public void toMap() {
+        Map<Integer, Integer> expected = new HashMap<>();
+        IntStream.range(1, 4).forEach(i -> expected.put(i, i));
+
+        assertEquals(expected,
+                IntStream.range(1, 4).boxed().collect(Collectors.toMap(Function.identity(), Function.identity())));
+    }
 }