<?php

function parseAdditionalAttributes($additionalAttributesString)
{
    if (empty($additionalAttributesString)) {
        return [];
    }

    $attributes = [];
    $length = strlen($additionalAttributesString);
    $i = 0;

    while ($i < $length) {
        // 寻找下一个属性名（字母数字下划线组成）
        if (preg_match('/([a-zA-Z0-9_]+)=/', $additionalAttributesString, $matches, PREG_OFFSET_CAPTURE, $i)) {
            $attributeName = $matches[1][0];
            $nameStart = $matches[1][1];
            $valueStart = $nameStart + strlen($attributeName) + 1; // +1 for '='

            // 寻找下一个属性开始位置来确定当前属性值的结束位置
            $nextAttrPos = null;
            if (preg_match('/,([a-zA-Z0-9_]+)=/', $additionalAttributesString, $nextMatches, PREG_OFFSET_CAPTURE, $valueStart)) {
                $nextAttrPos = $nextMatches[0][1]; // 逗号的位置
            }

            // 提取属性值
            if ($nextAttrPos !== null) {
                $value = substr($additionalAttributesString, $valueStart, $nextAttrPos - $valueStart);
                $i = $nextAttrPos + 1; // 跳过逗号
            } else {
                // 最后一个属性，取到字符串末尾
                $value = substr($additionalAttributesString, $valueStart);
                $i = $length; // 结束循环
            }
            //去掉导入数据中的_X000D_
            $attributes[mb_strtolower(trim($attributeName))] = preg_replace('/_x([0-9a-fA-F]{4})_/', '', trim($value));
            ;
        } else {
            // 没有找到更多属性，结束
            break;
        }
    }

    return $attributes;
}


$attribute = 'document_date=9/27/19,document_version=1.1.0,document_path=/media/files/minireview/MRDX20359CN-Airway_Epithelial_Cells.pdf,parent_skus=00218,05001,05021,05022,05008,05040,00218CA.2';

$str = '';
foreach (parseAdditionalAttributes($attribute) as $key => $value) {
    $str .= $key . '=' . $value . ',';
}

echo rtrim($str, ',').PHP_EOL;