util: Add a keyed list class and a sorted variant

This is inspired by C#'s KeyedCollection. The sorted variant removes the
need for an observable SortedMap.

Signed-off-by: Samuel Holland <samuel@sholland.org>

app/src/main/java/com/wireguard/android/util/Keyed.java

@@ -0,0 +1,9 @@
+package com.wireguard.android.util;
+
+/**
+ * Interface for objects that have a identifying key of the given type.
+ */
+
+public interface Keyed<K> {
+    K getKey();
+}

app/src/main/java/com/wireguard/android/util/KeyedList.java

@@ -0,0 +1,23 @@
+package com.wireguard.android.util;
+
+import java.util.Collection;
+import java.util.List;
+
+/**
+ * A list containing elements that can be looked up by key. A {@code KeyedList} cannot contain
+ * {@code null} elements.
+ */
+
+public interface KeyedList<K, E extends Keyed<? extends K>> extends List<E> {
+    boolean containsAllKeys(Collection<K> keys);
+
+    boolean containsKey(K key);
+
+    E get(K key);
+
+    E getLast(K key);
+
+    int indexOfKey(K key);
+
+    int lastIndexOfKey(K key);
+}

app/src/main/java/com/wireguard/android/util/KeyedObservableArrayList.java

@@ -0,0 +1,100 @@
+package com.wireguard.android.util;
+
+import android.databinding.ObservableArrayList;
+import android.support.annotation.NonNull;
+
+import java.util.Collection;
+import java.util.ListIterator;
+import java.util.Objects;
+
+/**
+ * ArrayList that allows looking up elements by some key property. As the key property must always
+ * be retrievable, this list cannot hold {@code null} elements. Because this class places no
+ * restrictions on the order or duplication of keys, lookup by key, as well as all list modification
+ * operations, require O(n) time.
+ */
+
+public class KeyedObservableArrayList<K, E extends Keyed<? extends K>>
+        extends ObservableArrayList<E> implements KeyedObservableList<K, E> {
+    @Override
+    public boolean add(final E e) {
+        if (e == null)
+            throw new NullPointerException();
+        return super.add(e);
+    }
+
+    @Override
+    public void add(final int index, final E e) {
+        if (e == null)
+            throw new NullPointerException();
+        super.add(index, e);
+    }
+
+    @Override
+    public boolean addAll(@NonNull final Collection<? extends E> c) {
+        if (c.contains(null))
+            throw new NullPointerException();
+        return super.addAll(c);
+    }
+
+    @Override
+    public boolean addAll(final int index, @NonNull final Collection<? extends E> c) {
+        if (c.contains(null))
+            throw new NullPointerException();
+        return super.addAll(index, c);
+    }
+
+    @Override
+    public boolean containsAllKeys(final Collection<K> keys) {
+        for (final K key : keys)
+            if (!containsKey(key))
+                return false;
+        return true;
+    }
+
+    @Override
+    public boolean containsKey(final K key) {
+        return indexOfKey(key) >= 0;
+    }
+
+    @Override
+    public E get(final K key) {
+        final int index = indexOfKey(key);
+        return index >= 0 ? get(index) : null;
+    }
+
+    @Override
+    public E getLast(final K key) {
+        final int index = lastIndexOfKey(key);
+        return index >= 0 ? get(index) : null;
+    }
+
+    @Override
+    public int indexOfKey(final K key) {
+        final ListIterator<E> iterator = listIterator();
+        while (iterator.hasNext()) {
+            final int index = iterator.nextIndex();
+            if (Objects.equals(iterator.next().getKey(), key))
+                return index;
+        }
+        return -1;
+    }
+
+    @Override
+    public int lastIndexOfKey(final K key) {
+        final ListIterator<E> iterator = listIterator(size());
+        while (iterator.hasPrevious()) {
+            final int index = iterator.previousIndex();
+            if (Objects.equals(iterator.previous().getKey(), key))
+                return index;
+        }
+        return -1;
+    }
+
+    @Override
+    public E set(final int index, final E e) {
+        if (e == null)
+            throw new NullPointerException();
+        return super.set(index, e);
+    }
+}

app/src/main/java/com/wireguard/android/util/KeyedObservableList.java

@@ -0,0 +1,11 @@
+package com.wireguard.android.util;
+
+import android.databinding.ObservableList;
+
+/**
+ * A list that is both keyed and observable.
+ */
+
+public interface KeyedObservableList<K, E extends Keyed<? extends K>>
+        extends KeyedList<K, E>, ObservableList<E> {
+}

app/src/main/java/com/wireguard/android/util/SortedKeyedObservableArrayList.java

@@ -0,0 +1,106 @@
+package com.wireguard.android.util;
+
+import android.support.annotation.NonNull;
+
+import java.util.AbstractList;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.List;
+
+/**
+ * KeyedArrayList that enforces uniqueness and sorted order across the set of keys. This class uses
+ * binary search to improve lookup and replacement times to O(log(n)). However, due to the
+ * array-based nature of this class, insertion and removal of elements with anything but the largest
+ * key still require O(n) time.
+ */
+
+public class SortedKeyedObservableArrayList<K extends Comparable<? super K>,
+        E extends Keyed<? extends K>> extends KeyedObservableArrayList<K, E> {
+
+    private final transient List<K> keyList = new KeyList<>(this);
+
+    @Override
+    public boolean add(final E e) {
+        final int insertionPoint = getInsertionPoint(e);
+        if (insertionPoint < 0) {
+            // Skipping insertion is non-destructive if the new and existing objects are the same.
+            if (e == get(-insertionPoint - 1))
+                return false;
+            throw new IllegalArgumentException("Element with same key already exists in list");
+        }
+        super.add(insertionPoint, e);
+        return true;
+    }
+
+    @Override
+    public void add(final int index, final E e) {
+        final int insertionPoint = getInsertionPoint(e);
+        if (insertionPoint < 0)
+            throw new IllegalArgumentException("Element with same key already exists in list");
+        if (insertionPoint != index)
+            throw new IndexOutOfBoundsException("Wrong index given for element");
+        super.add(index, e);
+    }
+
+    @Override
+    public boolean addAll(@NonNull final Collection<? extends E> c) {
+        boolean didChange = false;
+        for (final E e : c)
+            if (add(e))
+                didChange = true;
+        return didChange;
+    }
+
+    @Override
+    public boolean addAll(int index, @NonNull final Collection<? extends E> c) {
+        for (final E e : c)
+            add(index++, e);
+        return true;
+    }
+
+    private int getInsertionPoint(final E e) {
+        return -Collections.binarySearch(keyList, e.getKey()) - 1;
+    }
+
+    @Override
+    public int indexOfKey(final K key) {
+        final int index = Collections.binarySearch(keyList, key);
+        return index >= 0 ? index : -1;
+    }
+
+    @Override
+    public int lastIndexOfKey(final K key) {
+        // There can never be more than one element with the same key in the list.
+        return indexOfKey(key);
+    }
+
+    @Override
+    public E set(final int index, final E e) {
+        if (e.getKey().compareTo(get(index).getKey()) != 0) {
+            // Allow replacement if the new key would be inserted adjacent to the replaced element.
+            final int insertionPoint = getInsertionPoint(e);
+            if (insertionPoint < index || insertionPoint > index + 1)
+                throw new IndexOutOfBoundsException("Wrong index given for element");
+        }
+        return super.set(index, e);
+    }
+
+    private static final class KeyList<K extends Comparable<? super K>,
+            E extends Keyed<? extends K>> extends AbstractList<K> {
+        private final SortedKeyedObservableArrayList<K, E> list;
+
+        private KeyList(final SortedKeyedObservableArrayList<K, E> list) {
+            this.list = list;
+        }
+
+        @Override
+        public K get(final int index) {
+            return list.get(index).getKey();
+        }
+
+        @Override
+        public int size() {
+            return list.size();
+        }
+    }
+}