<?php
/**
 * 一致性hash分布式算法
 * @param $key
 * @return int
 * 实现步骤
 * 1.先将0~ 是32位最大带符号整数（0x7FFFFFFF） 想象成一个闭环
 * 2.将服务器列表通过hash算法分布在 圆环之中
 * 3.将key值也分布在圆环之中
 * 4.通过_isSorted判断服务器是否需要进行倒序排序 排序后遍历服务器 找到最近的服务器 返回
 * hash算法是不保证平衡的 为了尽量保证平衡性 我们应该加入虚拟节点数 将一个服务器节点虚拟化成为多个 较大程度上保证了平衡性
 */
class FlexiHash{
  private $_serverList = array();
  private $_isSorted = false;
  private $_virtual_node_num = 20;//虚拟节点数 服务器越少 增加的虚拟节点数应该越多
  //通过hash算法返回一个整数值
  protected function myHash($key){
    $md5 = substr(md5($key),0,8);
    $seed = 31; //种子值
    $hash=0;
    for($i=0;$i<8;$i++){
      $hash = $hash*$seed+ord($md5{$i}); //ord 返回ascii值
      $i++;
    }
    return $hash&0x7FFFFFFF; //0x7FFFFFFF表示最大值
  }
  //添加服务器
  function addServer($server){
    $hash =$this->myHash($server. '#1');
    if(!isset($this->_serverList[$hash])) {
      for ($i = 1; $i <= $this->_virtual_node_num; $i++) {
        $hash = $this->myHash($server . '#' . $i);
        $this->_serverList[$hash] = $server;
      }
    }
    $this->_isSorted = false;
    return true;
  }
  //删除服务器
  function removeServer($server){
    for ($i = 1; $i <= $this->_virtual_node_num; $i++) {
      $hash = $this->myHash($server . '#' . $i);
      unset($this->_serverList[$hash]);
    }
    $this->_isSorted = false;
    return true;
  }
  //获取服务器
  function lookup($key){
    $hash =$this->myHash($key);
    if(!$this->_isSorted){
      krsort($this->_serverList,SORT_NUMERIC);
      $this->_isSorted = true;
    }
    foreach($this->_serverList as $pos=>$server){
      if($hash >= $pos) return $server;
    }
    return end($this->_serverList);
  }
  public function getServerList(){
    krsort($this->_serverList,SORT_NUMERIC);
    return $this->_serverList;
  }
}
//demo test
$hserver = new FlexiHash();
//添加服务器
$hserver->addServer('192.168.1.1');
$hserver->addServer('192.168.1.2');
$hserver->addServer('192.168.1.3');
$hserver->addServer('192.168.1.4');
$hserver->addServer('192.168.1.5');
$key1='Key1111';
$key2='Key2222';
$key2='Key3333';
$key2='Key4444';
$key2='Key5555';
$key2='Key6666';
echo "save key1 in server: ".$hserver->lookup($key1).PHP_EOL;
echo "save key2 in server: ".$hserver->lookup($key2).PHP_EOL;
echo "save key1 in server: ".$hserver->lookup($key3).PHP_EOL;
echo "save key2 in server: ".$hserver->lookup($key4).PHP_EOL;
echo "save key1 in server: ".$hserver->lookup($key5).PHP_EOL;
echo "save key2 in server: ".$hserver->lookup($key6).PHP_EOL;
echo "================================================".PHP_EOL;
//移除服务器 key值将自动转义到下一台服务器
$hserver->removeServer('192.168.1.4');
echo "save key1 in server: ".$hserver->lookup($key1).PHP_EOL;
echo "save key2 in server: ".$hserver->lookup($key2).PHP_EOL;
echo "save key1 in server: ".$hserver->lookup($key3).PHP_EOL;
echo "save key2 in server: ".$hserver->lookup($key4).PHP_EOL;
echo "save key1 in server: ".$hserver->lookup($key5).PHP_EOL;
echo "save key2 in server: ".$hserver->lookup($key6).PHP_EOL;
echo "================================================".PHP_EOL;
//恢复故障服务器 key值将恢复原来服务器
$hserver->addServer('192.168.1.4');
echo "save key1 in server: ".$hserver->lookup($key1).PHP_EOL;
echo "save key2 in server: ".$hserver->lookup($key2).PHP_EOL;
echo "save key1 in server: ".$hserver->lookup($key3).PHP_EOL;
echo "save key2 in server: ".$hserver->lookup($key4).PHP_EOL;
echo "save key1 in server: ".$hserver->lookup($key5).PHP_EOL;
echo "save key2 in server: ".$hserver->lookup($key6).PHP_EOL;