/*
    * Copyright 2025 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.netty.util.internal;
  
  import java.util.ArrayList;
  import java.util.List;
  
  import static io.netty.util.internal.ObjectUtil.checkPositive;
  import static java.lang.Math.max;
  import static java.lang.Math.min;
  
  /**
   * Calculate sizes in a adaptive way.
   */
  public final class AdaptiveCalculator {
      private static final int INDEX_INCREMENT = 4;
      private static final int INDEX_DECREMENT = 1;
  
      private static final int[] SIZE_TABLE;
  
      static {
          List<Integer> sizeTable = new ArrayList<Integer>();
          for (int i = 16; i < 512; i += 16) {
              sizeTable.add(i);
          }
  
          // Suppress a warning since i becomes negative when an integer overflow happens
          for (int i = 512; i > 0; i <<= 1) {
              sizeTable.add(i);
          }
  
          SIZE_TABLE = new int[sizeTable.size()];
          for (int i = 0; i < SIZE_TABLE.length; i ++) {
              SIZE_TABLE[i] = sizeTable.get(i);
          }
      }
  
      private static int getSizeTableIndex(final int size) {
          for (int low = 0, high = SIZE_TABLE.length - 1;;) {
              if (high < low) {
                  return low;
              }
              if (high == low) {
                  return high;
              }
  
              int mid = low + high >>> 1;
              int a = SIZE_TABLE[mid];
              int b = SIZE_TABLE[mid + 1];
              if (size > b) {
                  low = mid + 1;
              } else if (size < a) {
                  high = mid - 1;
              } else if (size == a) {
                  return mid;
              } else {
                  return mid + 1;
              }
          }
      }
  
      private final int minIndex;
      private final int maxIndex;
      private final int minCapacity;
      private final int maxCapacity;
      private int index;
      private int nextSize;
      private boolean decreaseNow;
  
      public AdaptiveCalculator(int minimum, int initial, int maximum) {
          checkPositive(minimum, "minimum");
          if (initial < minimum) {
              throw new IllegalArgumentException("initial: " + initial);
          }
          if (maximum < initial) {
              throw new IllegalArgumentException("maximum: " + maximum);
          }
  
          int minIndex = getSizeTableIndex(minimum);
          if (SIZE_TABLE[minIndex] < minimum) {
              this.minIndex = minIndex + 1;
          } else {
              this.minIndex = minIndex;
          }
  
          int maxIndex = getSizeTableIndex(maximum);
         if (SIZE_TABLE[maxIndex] > maximum) {
             this.maxIndex = maxIndex - 1;
         } else {
             this.maxIndex = maxIndex;
         }
 
         int initialIndex = getSizeTableIndex(initial);
         if (SIZE_TABLE[initialIndex] > initial) {
             this.index = initialIndex - 1;
         } else {
             this.index = initialIndex;
         }
         this.minCapacity = minimum;
         this.maxCapacity = maximum;
         nextSize = max(SIZE_TABLE[index], minCapacity);
     }
 
     public void record(int size) {
         if (size <= SIZE_TABLE[max(0, index - INDEX_DECREMENT)]) {
             if (decreaseNow) {
                 index = max(index - INDEX_DECREMENT, minIndex);
                 nextSize = max(SIZE_TABLE[index], minCapacity);
                 decreaseNow = false;
             } else {
                 decreaseNow = true;
             }
         } else if (size >= nextSize) {
             index = min(index + INDEX_INCREMENT, maxIndex);
             nextSize = min(SIZE_TABLE[index], maxCapacity);
             decreaseNow = false;
         }
     }
 
     public int nextSize() {
         return nextSize;
     }
 }