Example of php implementing the sunday algorithm of string matching algorithm

<?php
/*
 *@param $pattern 模式串
 *@param $text 待匹配串
 */
function mySunday($pattern = '',$text = ''){
    if(!$pattern || !$text) return false;
    $pattern_len = mb_strlen($pattern);
    $text_len = mb_strlen($text);
    if($pattern_len >= $text_len) return false;
    $i = 0;
    for($i = 0; $i < $pattern_len; $i++){ //组装以pattern中的字符为下标的数组
        $shift[$pattern[$i]] = $pattern_len - $i;
    }
    while($i <= $text_len - $pattern_len){
        $nums = 0;     //匹配上的字符个数
        while($pattern[$nums] == $text[$i + $nums]){
            $nums++;
            if($nums == $pattern_len){
                return "The first match index is $i\n";
            }
        }
        if($i + $pattern_len < $text_len && isset($shift[$text[$i + $pattern_len]])){ //判断模式串后一位字符是否在模式串中
            $i += $shift[$text[$i + $pattern_len]];      //对齐该字符
        }else{
            $i += $pattern_len;      //直接滑动pattern_len位
        }
    }
}
$text = "I am testing mySunday on sunday!";
$pattern = "sunday";
echo mySunday($pattern,$text);