content: /*
   * Copyright (C) 2018 The Android Open Source Project
   *
   * 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 com.google.android.exoplayer2.util;
  
  import androidx.annotation.Nullable;
  import java.util.Arrays;
  import org.checkerframework.checker.nullness.compatqual.NullableType;
  
  /** A utility class to keep a queue of values with timestamps. This class is thread safe. */
  public final class TimedValueQueue<V> {
    private static final int INITIAL_BUFFER_SIZE = 10;
  
    // Looping buffer for timestamps and values
    private long[] timestamps;
    private @NullableType V[] values;
    private int first;
    private int size;
  
    public TimedValueQueue() {
      this(INITIAL_BUFFER_SIZE);
    }
  
    /** Creates a TimedValueBuffer with the given initial buffer size. */
    public TimedValueQueue(int initialBufferSize) {
      timestamps = new long[initialBufferSize];
      values = newArray(initialBufferSize);
    }
  
    /**
     * Associates the specified value with the specified timestamp. All new values should have a
     * greater timestamp than the previously added values. Otherwise all values are removed before
     * adding the new one.
     */
    public synchronized void add(long timestamp, V value) {
      clearBufferOnTimeDiscontinuity(timestamp);
      doubleCapacityIfFull();
      addUnchecked(timestamp, value);
    }
  
    /** Removes all of the values. */
    public synchronized void clear() {
      first = 0;
      size = 0;
      Arrays.fill(values, null);
    }
  
    /** Returns number of the values buffered. */
    public synchronized int size() {
      return size;
    }
  
    /** Removes and returns the first value in the queue, or null if the queue is empty. */
    @Nullable
    public synchronized V pollFirst() {
      return size == 0 ? null : popFirst();
    }
  
    /**
     * Returns the value with the greatest timestamp which is less than or equal to the given
     * timestamp. Removes all older values and the returned one from the buffer.
     *
     * @param timestamp The timestamp value.
     * @return The value with the greatest timestamp which is less than or equal to the given
     *     timestamp or null if there is no such value.
     * @see #poll(long)
     */
    @Nullable
    public synchronized V pollFloor(long timestamp) {
      return poll(timestamp, /* onlyOlder= */ true);
    }
  
    /**
     * Returns the value with the closest timestamp to the given timestamp. Removes all older values
     * including the returned one from the buffer.
     *
     * @param timestamp The timestamp value.
     * @return The value with the closest timestamp or null if the buffer is empty.
     * @see #pollFloor(long)
     */
    @Nullable
    public synchronized V poll(long timestamp) {
      return poll(timestamp, /* onlyOlder= */ false);
    }
  
    /**
     * Returns the value with the closest timestamp to the given timestamp. Removes all older values
     * including the returned one from the buffer.
     *
     * @param timestamp The timestamp value.
     * @param onlyOlder Whether this method can return a new value in case its timestamp value is
     *     closest to {@code timestamp}.
     * @return The value with the closest timestamp or null if the buffer is empty or there is no
     *     older value and {@code onlyOlder} is true.
     */
    @Nullable
    private V poll(long timestamp, boolean onlyOlder) {
      @Nullable V value = null;
      long previousTimeDiff = Long.MAX_VALUE;
      while (size > 0) {
        long timeDiff = timestamp - timestamps[first];
        if (timeDiff < 0 && (onlyOlder || -timeDiff >= previousTimeDiff)) {
          break;
        }
        previousTimeDiff = timeDiff;
        value = popFirst();
      }
      return value;
    }
  
    @Nullable
    private V popFirst() {
      Assertions.checkState(size > 0);
      @Nullable V value = values[first];
      values[first] = null;
      first = (first + 1) % values.length;
      size--;
      return value;
    }
  
    private void clearBufferOnTimeDiscontinuity(long timestamp) {
      if (size > 0) {
        int last = (first + size - 1) % values.length;
        if (timestamp <= timestamps[last]) {
          clear();
        }
      }
    }
  
    private void doubleCapacityIfFull() {
      int capacity = values.length;
      if (size < capacity) {
        return;
      }
      int newCapacity = capacity * 2;
      long[] newTimestamps = new long[newCapacity];
      @NullableType V[] newValues = newArray(newCapacity);
      // Reset the loop starting index to 0 while coping to the new buffer.
      // First copy the values from 'first' index to the end of original array.
      int length = capacity - first;
      System.arraycopy(timestamps, first, newTimestamps, 0, length);
      System.arraycopy(values, first, newValues, 0, length);
      // Then the values from index 0 to 'first' index.
      if (first > 0) {
        System.arraycopy(timestamps, 0, newTimestamps, length, first);
        System.arraycopy(values, 0, newValues, length, first);
      }
      timestamps = newTimestamps;
      values = newValues;
      first = 0;
    }
  
    private void addUnchecked(long timestamp, V value) {
      int next = (first + size) % values.length;
      timestamps[next] = timestamp;
      values[next] = value;
      size++;
    }
  
    @SuppressWarnings("unchecked")
    private static <V> @NullableType V[] newArray(int length) {
      return (V[]) new Object[length];
    }
  }
  