Lazy list for even lazier acceptedTypes parsing (#1940)

* Lazy list for even lazier MediaType acceptedTypes parsing
* Get rid of laziness breaker

Signed-off-by: Daniel Kec <daniel.kec@oracle.com>

common/common/src/main/java/io/helidon/common/LazyList.java

@@ -0,0 +1,46 @@
+/*
+ * Copyright (c)  2020 Oracle and/or its affiliates.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.helidon.common;
+
+import java.util.List;
+import java.util.function.Supplier;
+
+/**
+ * Wrapper for list of {@link io.helidon.common.LazyValue}s while keeping laziness.
+ *
+ * @param <T> type of the provided object
+ */
+public interface LazyList<T> extends List<T> {
+
+    /**
+     * Add another lazy item to the list.
+     *
+     * @param supplier to be invoke only when necessary
+     */
+    void add(Supplier<T> supplier);
+
+    /**
+     * Create wrapper from provided list of {@link io.helidon.common.LazyValue}s.
+     *
+     * @param lazyValues to be wrapped seamlessly while keeping laziness
+     * @param <T>        type of the provided object
+     * @return List invoking underlined {@link io.helidon.common.LazyValue}s only when raw value is needed.
+     */
+    static <T> LazyList<T> create(List<LazyValue<T>> lazyValues) {
+        return new LazyListImpl<>(lazyValues);
+    }
+}

common/common/src/main/java/io/helidon/common/LazyListImpl.java

@@ -0,0 +1,248 @@
+/*
+ * Copyright (c)  2020 Oracle and/or its affiliates.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.helidon.common;
+
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Iterator;
+import java.util.List;
+import java.util.ListIterator;
+import java.util.Objects;
+import java.util.function.Supplier;
+import java.util.stream.Collectors;
+
+class LazyListImpl<T> implements LazyList<T> {
+
+    private final List<LazyValue<T>> lazyValues = new ArrayList<>();
+    private List<T> allLoaded;
+
+    LazyListImpl(List<LazyValue<T>> lazyValues) {
+        this.lazyValues.addAll(lazyValues);
+    }
+
+    @Override
+    public void add(final Supplier<T> supplier) {
+        lazyValues.add(LazyValue.create(supplier));
+    }
+
+    private List<T> loadAll() {
+        if (allLoaded == null) {
+            allLoaded = lazyValues.stream().map(LazyValue::get).collect(Collectors.toList());
+        }
+        return allLoaded;
+    }
+
+    @Override
+    public int size() {
+        return lazyValues.size();
+    }
+
+    @Override
+    public boolean isEmpty() {
+        return lazyValues.isEmpty();
+    }
+
+    @Override
+    public boolean contains(final Object o) {
+        return lazyValues.stream()
+                .map(LazyValue::get)
+                .anyMatch(tLazyValue -> Objects.equals(o, tLazyValue));
+    }
+
+    @Override
+    public Iterator<T> iterator() {
+        Iterator<LazyValue<T>> lazyValueIterator = lazyValues.iterator();
+        return new Iterator<T>() {
+            @Override
+            public boolean hasNext() {
+                return lazyValueIterator.hasNext();
+            }
+
+            @Override
+            public T next() {
+                return lazyValueIterator.next().get();
+            }
+        };
+    }
+
+    @Override
+    public Object[] toArray() {
+        return loadAll().toArray();
+    }
+
+    @Override
+    public <T1> T1[] toArray(final T1[] a) {
+        return loadAll().toArray(a);
+    }
+
+    @Override
+    public boolean add(final T t) {
+        return lazyValues.add(LazyValue.create(t));
+    }
+
+    @Override
+    public boolean remove(final Object o) {
+        return lazyValues.removeIf(lv -> Objects.equals(o, lv.get()));
+    }
+
+    @Override
+    public boolean containsAll(final Collection<?> c) {
+        return loadAll().containsAll(c);
+    }
+
+    @Override
+    public boolean addAll(final Collection<? extends T> c) {
+        c.forEach(v -> lazyValues.add(LazyValue.create(v)));
+        return !c.isEmpty();
+    }
+
+    @Override
+    public boolean addAll(final int index, final Collection<? extends T> c) {
+        c.forEach(this::add);
+        return !c.isEmpty();
+    }
+
+    @Override
+    public boolean removeAll(final Collection<?> c) {
+        return loadAll().removeAll(c);
+    }
+
+    @Override
+    public boolean retainAll(final Collection<?> c) {
+        return loadAll().retainAll(c);
+    }
+
+    @Override
+    public void clear() {
+        lazyValues.clear();
+        if (allLoaded != null) {
+            allLoaded.clear();
+        }
+    }
+
+    @Override
+    public T get(final int index) {
+        return lazyValues.get(index).get();
+    }
+
+    @Override
+    public T set(final int index, final T element) {
+        return lazyValues.set(index, LazyValue.create(element)).get();
+    }
+
+    @Override
+    public void add(final int index, final T element) {
+        lazyValues.add(index, LazyValue.create(element));
+    }
+
+    @Override
+    public T remove(final int index) {
+        return lazyValues.remove(index).get();
+    }
+
+    @Override
+    public int indexOf(final Object o) {
+        for (int i = 0; i < lazyValues.size(); i++) {
+            LazyValue<T> lv = lazyValues.get(i);
+            if (Objects.equals(o, lv.get())) {
+                return i;
+            }
+        }
+        return -1;
+    }
+
+    @Override
+    public int lastIndexOf(final Object o) {
+        int index = -1;
+        for (int i = 0; i < lazyValues.size(); i++) {
+            LazyValue<T> lv = lazyValues.get(i);
+            if (Objects.equals(o, lv.get())) {
+                index = i;
+            }
+        }
+        return index;
+    }
+
+    @Override
+    public ListIterator<T> listIterator() {
+        return new LazyListIterator<>(lazyValues.listIterator());
+    }
+
+    @Override
+    public ListIterator<T> listIterator(final int index) {
+        return new LazyListIterator<>(lazyValues.listIterator(index));
+    }
+
+    @Override
+    public List<T> subList(final int fromIndex, final int toIndex) {
+        return new LazyListImpl<>(lazyValues.subList(fromIndex, toIndex));
+    }
+
+    private static class LazyListIterator<T> implements ListIterator<T> {
+
+        private final ListIterator<LazyValue<T>> innerIterator;
+
+        LazyListIterator(ListIterator<LazyValue<T>> innerIterator) {
+            this.innerIterator = innerIterator;
+        }
+
+        @Override
+        public boolean hasNext() {
+            return this.innerIterator.hasNext();
+        }
+
+        @Override
+        public T next() {
+            return this.innerIterator.next().get();
+        }
+
+        @Override
+        public boolean hasPrevious() {
+            return this.innerIterator.hasPrevious();
+        }
+
+        @Override
+        public T previous() {
+            return this.innerIterator.previous().get();
+        }
+
+        @Override
+        public int nextIndex() {
+            return this.innerIterator.nextIndex();
+        }
+
+        @Override
+        public int previousIndex() {
+            return this.innerIterator.previousIndex();
+        }
+
+        @Override
+        public void remove() {
+            this.innerIterator.remove();
+        }
+
+        @Override
+        public void set(final T t) {
+            this.innerIterator.set(LazyValue.create(t));
+        }
+
+        @Override
+        public void add(final T t) {
+            this.innerIterator.add(LazyValue.create(t));
+        }
+    }
+}