/*
    * Copyright 2021 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;
  
  /**
   * Internal primitive map implementation that is specifically optimised for the runs availability map use case in
   * {@code PoolChunk}.
   */
  public final class LongLongHashMap {
      private static final int MASK_TEMPLATE = ~1;
      private int mask;
      private long[] array;
      private int maxProbe;
      private long zeroVal;
      private final long emptyVal;
  
      public LongLongHashMap(long emptyVal) {
          this.emptyVal = emptyVal;
          zeroVal = emptyVal;
          int initialSize = 32;
          array = new long[initialSize];
          mask = initialSize - 1;
          computeMaskAndProbe();
      }
  
      public long put(long key, long value) {
          if (key == 0) {
              long prev = zeroVal;
              zeroVal = value;
              return prev;
          }
  
          for (;;) {
              int index = index(key);
              for (int i = 0; i < maxProbe; i++) {
                  long existing = array[index];
                  if (existing == key || existing == 0) {
                      long prev = existing == 0? emptyVal : array[index + 1];
                      array[index] = key;
                      array[index + 1] = value;
                      for (; i < maxProbe; i++) { // Nerf any existing misplaced entries.
                          index = index + 2 & mask;
                          if (array[index] == key) {
                              array[index] = 0;
                              prev = array[index + 1];
                              break;
                          }
                      }
                      return prev;
                  }
                  index = index + 2 & mask;
              }
              expand(); // Grow array and re-hash.
          }
      }
  
      public void remove(long key) {
          if (key == 0) {
              zeroVal = emptyVal;
              return;
          }
          int index = index(key);
          for (int i = 0; i < maxProbe; i++) {
              long existing = array[index];
              if (existing == key) {
                  array[index] = 0;
                  break;
              }
              index = index + 2 & mask;
          }
      }
  
      public long get(long key) {
          if (key == 0) {
              return zeroVal;
          }
          int index = index(key);
          for (int i = 0; i < maxProbe; i++) {
              long existing = array[index];
              if (existing == key) {
                  return array[index + 1];
              }
              index = index + 2 & mask;
          }
          return emptyVal;
      }
 
     private int index(long key) {
         // Hash with murmur64, and mask.
         key ^= key >>> 33;
         key *= 0xff51afd7ed558ccdL;
         key ^= key >>> 33;
         key *= 0xc4ceb9fe1a85ec53L;
         key ^= key >>> 33;
         return (int) key & mask;
     }
 
     private void expand() {
         long[] prev = array;
         array = new long[prev.length * 2];
         computeMaskAndProbe();
         for (int i = 0; i < prev.length; i += 2) {
             long key = prev[i];
             if (key != 0) {
                 long val = prev[i + 1];
                 put(key, val);
             }
         }
     }
 
     private void computeMaskAndProbe() {
         int length = array.length;
         mask = length - 1 & MASK_TEMPLATE;
         maxProbe = (int) Math.log(length);
     }
 }