<?php

namespace Heanup\Frame\Library;

/**
 * BASE62 解析类，专门针对长10进制与62进制互转
 */
class BaseConverter
{
    private static $string = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
    private static $encodeBlockSize = 7;
    private static $decodeBlockSize = 4;

    /**
     * 批量从10进制转换到62进制
     *
     * @param array $mids
     * @return array 以10进制mid为key的62进制mid数组
     */
    public static function multi_from10to62(array $mids)
    {
        $ret = array();
        foreach ($mids as $mid) {
            $ret[$mid] = self::from10to62($mid);
        }
        return $ret;
    }

    /**
     * 批量从62进制转换到10进制
     *
     * @param array $mids
     * @param bool $compat
     * @param bool $for_mid
     * @return array 以62进制mid为key的10进制mid数组
     */
    public static function multi_from62to10(array $mids, $compat = false, $for_mid = true)
    {
        $ret = array();
        foreach ($mids as $mid) {
            $ret[$mid] = self::from62to10($mid, $compat, $for_mid);
        }
        return $ret;
    }

    /**
     * 将mid从10进制转换成62进制字符串
     *
     * @param    string $mid
     * @return    string
     */
    public static function from10to62($mid)
    {
        $str = "";
        $midlen = strlen($mid);
        $segments = ceil($midlen / self::$encodeBlockSize);
        $start = $midlen;
        for ($i = 1; $i < $segments; $i += 1) {
            $start -= self::$encodeBlockSize;
            $seg = substr($mid, $start, self::$encodeBlockSize);
            $seg = self::encodeSegment($seg);
            $str = str_pad($seg, self::$decodeBlockSize, '0', STR_PAD_LEFT) . $str;
        }
        $str = self::encodeSegment(substr($mid, 0, $start)) . $str;
        return $str;
    }

    /**
     * 将62进制字符串转成10进制mid
     *
     * $compat $for_mid 参数意图不确定，直接从原作者处考过来。使用时直接使用默认参数即可。
     *
     * @param    string $str
     * @param    bool $compat
     * @param    bool $for_mid
     * @return    string
     */
    public static function from62to10($str, $compat = false, $for_mid = true)
    {
        $mid = "";
        $strlen = strlen($str);
        $segments = ceil($strlen / self::$decodeBlockSize);
        $start = $strlen;
        for ($i = 1; $i < $segments; $i += 1) {
            $start -= self::$decodeBlockSize;
            $seg = substr($str, $start, self::$decodeBlockSize);
            $seg = self::decodeSegment($seg);
            /* Note by Rodin:
             * 由于 decodeBlockSize设置为4，而 encodeBlockSize 设置为 7
             * 而 base 62里4位最大的数为 ZZZZ，对应到10进制为 14776336，比encodeBlockSize
             * 多1位……所以，将10进制转成62进制且在不足位时左补0，不会有任何问题。反之，
             * 在62转成10进制的时候就可能会出现溢出，这是个潜在的bug，不清楚为什么目前没有
             * bug爆出且当初采用了这种不标准不严谨的62进制转换法……
             * 目前常用的mid里存在类似： l4ETJ4DfL (9位)，在每segment大约出现大于 GZZZ 的串以后
             * 总位数就会不符合目前的预期……
             * 例如：
             * ZZZZZZZZZ转换成10进制会成为 611477633614776336，总位数已经达到了20位，而常见的7位
             * mid的62进制数字通常只有16位
             */
            $mid = str_pad($seg, self::$encodeBlockSize, '0', STR_PAD_LEFT) . $mid;
        }
        $mid = self::decodeSegment(substr($str, 0, $start)) . $mid;

        //判断v3、v4版本mid
        if ($for_mid) {
            $midlen = strlen($mid);
            $first = substr($mid, 0, 1);
            if ($midlen == 16 && ($first == '3' || $first == '4')) {
                return $mid;
            }
            if ($midlen == 19 && $first == '5') {
                return $mid;
            }
        }
        //end
        if ($compat && !in_array(substr($mid, 0, 3), array('109', '110', '201', '211', '221', '231', '241'))) {
            $mid = self::decodeSegment(substr($str, 0, 4)) . self::decodeSegment(substr($str, 4));
        }
        if ($for_mid) {
            if (substr($mid, 0, 1) == '1' && substr($mid, 7, 1) == '0') {
                $mid = substr($mid, 0, 7) . substr($mid, 8);
            }
        }
        return $mid;
    }

    /**
     * 将10进制转换成62进制
     *
     * @param    string $str 10进制字符串
     * @return    string
     */
    private static function encodeSegment($str)
    {
        $out = '';
        while ($str > 0) {
            $idx = $str % 62;
            $out = substr(self::$string, $idx, 1) . $out;
            $str = floor($str / 62);
        }
        return $out;
    }

    /**
     * 将62进制转换成10进制
     *
     * @param    string $str 62进制字符串
     * @return    string
     */
    private static function decodeSegment($str)
    {
        $out = 0;
        $base = 1;
        for ($t = strlen($str) - 1; $t >= 0; $t -= 1) {
            $out = $out + $base * strpos(self::$string, substr($str, $t, 1));
            $base *= 62;
        }
        return strval($out);
    }

}