/*
    * Copyright 2015 The Netty Project
    *
    * The Netty Project licenses this file to you 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:
    *
    *   https://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.netty5.util.internal;
  
  import java.util.AbstractQueue;
  import java.util.Arrays;
  import java.util.Comparator;
  import java.util.Iterator;
  import java.util.NoSuchElementException;
  
  import static io.netty5.util.internal.PriorityQueueNode.INDEX_NOT_IN_QUEUE;
  import static java.util.Objects.requireNonNull;
  
  /**
   * A priority queue which uses natural ordering of elements. Elements are also required to be of type
   * {@link PriorityQueueNode} for the purpose of maintaining the index in the priority queue.
   * @param <T> The object that is maintained in the queue.
   */
  public final class DefaultPriorityQueue<T extends PriorityQueueNode> extends AbstractQueue<T>
                                                                       implements PriorityQueue<T> {
      private static final PriorityQueueNode[] EMPTY_ARRAY = new PriorityQueueNode[0];
      private final Comparator<T> comparator;
      private T[] queue;
      private int size;
  
      @SuppressWarnings("unchecked")
      public DefaultPriorityQueue(Comparator<T> comparator, int initialSize) {
          this.comparator = requireNonNull(comparator, "comparator");
          queue = (T[]) (initialSize != 0 ? new PriorityQueueNode[initialSize] : EMPTY_ARRAY);
      }
  
      @Override
      public int size() {
          return size;
      }
  
      @Override
      public boolean isEmpty() {
          return size == 0;
      }
  
      @Override
      public boolean contains(Object o) {
          if (!(o instanceof PriorityQueueNode)) {
              return false;
          }
          PriorityQueueNode node = (PriorityQueueNode) o;
          return contains(node, node.priorityQueueIndex(this));
      }
  
      @Override
      public boolean containsTyped(T node) {
          return contains(node, node.priorityQueueIndex(this));
      }
  
      @Override
      public void clear() {
          for (int i = 0; i < size; ++i) {
              T node = queue[i];
              if (node != null) {
                  node.priorityQueueIndex(this, INDEX_NOT_IN_QUEUE);
                  queue[i] = null;
              }
          }
          size = 0;
      }
  
      @Override
      public void clearIgnoringIndexes() {
          size = 0;
      }
  
      @Override
      public boolean offer(T e) {
          if (e.priorityQueueIndex(this) != INDEX_NOT_IN_QUEUE) {
              throw new IllegalArgumentException("e.priorityQueueIndex(): " + e.priorityQueueIndex(this) +
                      " (expected: " + INDEX_NOT_IN_QUEUE + ") + e: " + e);
          }
  
          // Check that the array capacity is enough to hold values by doubling capacity.
          if (size >= queue.length) {
              // Use a policy which allows for a 0 initial capacity. Same policy as JDK's priority queue, double when
              // "small", then grow by 50% when "large".
              queue = Arrays.copyOf(queue, queue.length + ((queue.length < 64) ?
                                                           (queue.length + 2) :
                                                           (queue.length >>> 1)));
         }
 
         bubbleUp(size++, e);
         return true;
     }
 
     @Override
     public T poll() {
         if (size == 0) {
             return null;
         }
         T result = queue[0];
         result.priorityQueueIndex(this, INDEX_NOT_IN_QUEUE);
 
         T last = queue[--size];
         queue[size] = null;
         if (size != 0) { // Make sure we don't add the last element back.
             bubbleDown(0, last);
         }
 
         return result;
     }
 
     @Override
     public T peek() {
         return (size == 0) ? null : queue[0];
     }
 
     @SuppressWarnings("unchecked")
     @Override
     public boolean remove(Object o) {
         final T node;
         try {
             node = (T) o;
         } catch (ClassCastException e) {
             return false;
         }
         return removeTyped(node);
     }
 
     @Override
     public boolean removeTyped(T node) {
         int i = node.priorityQueueIndex(this);
         if (!contains(node, i)) {
             return false;
         }
 
         node.priorityQueueIndex(this, INDEX_NOT_IN_QUEUE);
         if (--size == 0 || size == i) {
             // If there are no node left, or this is the last node in the array just remove and return.
             queue[i] = null;
             return true;
         }
 
         // Move the last element where node currently lives in the array.
         T moved = queue[i] = queue[size];
         queue[size] = null;
         // priorityQueueIndex will be updated below in bubbleUp or bubbleDown
 
         // Make sure the moved node still preserves the min-heap properties.
         if (comparator.compare(node, moved) < 0) {
             bubbleDown(i, moved);
         } else {
             bubbleUp(i, moved);
         }
         return true;
     }
 
     @Override
     public void priorityChanged(T node) {
         int i = node.priorityQueueIndex(this);
         if (!contains(node, i)) {
             return;
         }
 
         // Preserve the min-heap property by comparing the new priority with parents/children in the heap.
         if (i == 0) {
             bubbleDown(i, node);
         } else {
             // Get the parent to see if min-heap properties are violated.
             int iParent = (i - 1) >>> 1;
             T parent = queue[iParent];
             if (comparator.compare(node, parent) < 0) {
                 bubbleUp(i, node);
             } else {
                 bubbleDown(i, node);
             }
         }
     }
 
     @Override
     public Object[] toArray() {
         return Arrays.copyOf(queue, size);
     }
 
     @SuppressWarnings("unchecked")
     @Override
     public <X> X[] toArray(X[] a) {
         if (a.length < size) {
             return (X[]) Arrays.copyOf(queue, size, a.getClass());
         }
         System.arraycopy(queue, 0, a, 0, size);
         if (a.length > size) {
             a[size] = null;
         }
         return a;
     }
 
     /**
      * This iterator does not return elements in any particular order.
      */
     @Override
     public Iterator<T> iterator() {
         return new PriorityQueueIterator();
     }
 
     private final class PriorityQueueIterator implements Iterator<T> {
         private int index;
 
         @Override
         public boolean hasNext() {
             return index < size;
         }
 
         @Override
         public T next() {
             if (index >= size) {
                 throw new NoSuchElementException();
             }
 
             return queue[index++];
         }
 
         @Override
         public void remove() {
             throw new UnsupportedOperationException("remove");
         }
     }
 
     private boolean contains(PriorityQueueNode node, int i) {
         return i >= 0 && i < size && node.equals(queue[i]);
     }
 
     private void bubbleDown(int k, T node) {
         final int half = size >>> 1;
         while (k < half) {
             // Compare node to the children of index k.
             int iChild = (k << 1) + 1;
             T child = queue[iChild];
 
             // Make sure we get the smallest child to compare against.
             int rightChild = iChild + 1;
             if (rightChild < size && comparator.compare(child, queue[rightChild]) > 0) {
                 child = queue[iChild = rightChild];
             }
             // If the bubbleDown node is less than or equal to the smallest child then we will preserve the min-heap
             // property by inserting the bubbleDown node here.
             if (comparator.compare(node, child) <= 0) {
                 break;
             }
 
             // Bubble the child up.
             queue[k] = child;
             child.priorityQueueIndex(this, k);
 
             // Move down k down the tree for the next iteration.
             k = iChild;
         }
 
         // We have found where node should live and still satisfy the min-heap property, so put it in the queue.
         queue[k] = node;
         node.priorityQueueIndex(this, k);
     }
 
     private void bubbleUp(int k, T node) {
         while (k > 0) {
             int iParent = (k - 1) >>> 1;
             T parent = queue[iParent];
 
             // If the bubbleUp node is less than the parent, then we have found a spot to insert and still maintain
             // min-heap properties.
             if (comparator.compare(node, parent) >= 0) {
                 break;
             }
 
             // Bubble the parent down.
             queue[k] = parent;
             parent.priorityQueueIndex(this, k);
 
             // Move k up the tree for the next iteration.
             k = iParent;
         }
 
         // We have found where node should live and still satisfy the min-heap property, so put it in the queue.
         queue[k] = node;
         node.priorityQueueIndex(this, k);
     }
 }