<?php
/**
 * 抽奖工具
 */
class lottery_tool {
    protected static $awardsArr;
    protected static $proField = 'probability';
    protected static $proSum = 0;
    protected static $checkAward = false;
    const SUCCESS_CODE = 0;
    const FAIL_CODE = -1;
    //检查抽奖数据
    protected static function checkAwards(){
        if (!is_array(self::$awardsArr) || empty(self::$awardsArr)) {
            return self::$checkAward = false;
        }
        self::$proSum = 0;
        foreach (self::$awardsArr as $_key => $award) {
            self::$proSum += $award[self::$proField];
        }
        if (empty(self::$proSum)) {
            return self::$checkAward = false;
        }
        return self::$checkAward = true;
    }
    protected static function successRoll($rollKey){
        return array('code' => self::SUCCESS_CODE, 'roll_key' => $rollKey, 'msg' => 'roll success');
    }
    protected static function failRoll($msg = 'roll fail'){
        return array('code' => self::FAIL_CODE, 'msg' => $msg );
    }
    //抽奖
    public static function roll () {
        if (false == self::$checkAward) {
            return self::failRoll('awards data is not the right format!');
        }
        $result = mt_rand(0, self::$proSum);
        $proValue = 0;
        foreach (self::$awardsArr as $_key => $value) {
            $proValue += $value[self::$proField];
            if ($result <= $proValue) {
                return self::successRoll($_key);
            }
        }
        return self::failRoll('wrong');
    }
    //改变概率字段名
    public static function setProField($field = null) {
        if (!empty($field)) {
            self::$proField = $field;
        }
    }
    //设置奖品
    public static function setAwards($awards){
        self::$awardsArr = $awards;
        self::checkAwards();
    }
}

$awards = array(
    '0' => array('pro' => 15, 'info' => '15%的可能性'),
    '1' => array('pro' => 25, 'info' => '25%的可能性'),
    '2' => array('pro' => 40, 'info' => '40%的可能性'),
    '3' => array('pro' => 20, 'info' => '20%的可能性'),
    );
lottery_tool::setProField('pro');
lottery_tool::setAwards($awards);
$result = array();
for ($i = 10000; $i --;) {
    $result[] = lottery_tool::roll();
}
foreach ($result as $key => $value) {
    $awards[$value['roll_key']]['num'] ++;
}
echo '<pre>';
var_dump($awards);

array
  0 =>
    array
      'pro' => int 15
      'info' => string '15%的可能性' (length=15)
      'num' => int 1596
  1 =>
    array
      'pro' => int 25
      'info' => string '25%的可能性' (length=15)
      'num' => int 2484
  2 =>
    array
      'pro' => int 40
      'info' => string '40%的可能性' (length=15)
      'num' => int 3939
  3 =>
    array
      'pro' => int 20
      'info' => string '20%的可能性' (length=15)
      'num' => int 1981