Przetwarzanie tekstu -> wyłuskiwanie fragmentów

abc[math]x^2 + 4 > 0[/math],
[math][b]Kasia[/b] 2 * 2 * 2 = 8[/math]

<?php
    function getOpenPos($txt)
    {
        $temp = [];
        $pos = strpos($txt, "[math]", 0);
        
        while ($pos)
        {
            array_push($temp, $pos);
            $pos = strpos($txt, "[math]", $pos + 1);
        }
        
        return $temp;
    }
    
    function getClosPos($txt)
    {
        $temp = [];
        $pos = strpos($txt, "[/math]", 0);
        
        while ($pos)
        {
            array_push($temp, $pos);
            $pos = strpos($txt, "[/math]", $pos + 1);
        }
        
        return $temp;
    }
    
    function checkPossProgress($arr)
    {
        $cnt = count($arr);
        
        for ($i = 0; $i < $cnt; $i++)
            if ($arr[$i][0] > $arr[$i][1])
                return false;
        
        return true;
    }
    
    function removeTags(&$arr)
    {
        $cnt = count($arr);
        
        for ($i = 0; $i < $cnt; $i++)
            $arr[$i][0] += 6;
    }
    
    function combinePos($txt)
    {
        $opened = getOpenPos($txt);
        $closed = getClosPos($txt);
        $combined = [];
        
        if ((count($opened) == count($closed)) and (count($opened) > 0))
        {
            $cnt = count($opened);
            
            for ($i = 0; $i < $cnt; $i++)
                array_push($combined, [$opened[$i], $closed[$i]]);
        }
        
        if (checkPossProgress($combined) == false)
            return ["error"];
        
        removeTags($combined);
        
        return $combined;
    }
    
    function checkForOtherTags($arr)
    {
        $tags   = ["[b]", "[i]", "[u]", "[quote", "[code]", "[list]", "[list=", "[img]", "[url]", "[url=", "[flash=", "[size=", "[color=",
                   "[/b]", "[/i]", "[/u]", "[/quote", "[/code]", "[/list]", "[/img]", "[/url]", "[/flash]", "[/size]", "[/color]"];
        $cnt    = count($arr);
        $cnt2   = count($tags);
        
        for ($i = 0; $i < $cnt; $i++)
            for ($j = 0; $j < $cnt2; $j++)
                if ((strpos($arr[$i], $tags[$j]) !== FALSE) or (strpos($arr[$i], $tags[$j]) !== FALSE))
                    return true;
        
        return false;
    }
    
    function extractContent($txt)
    {
        $poss = combinePos($txt);
        $arr = [];
        $cnt = count($poss);
        
        for ($i = 0; $i < $cnt; $i++)
            array_push($arr, substr($txt, $poss[$i][0], $poss[$i][1] - $poss[$i][0]));
        
        if (checkForOtherTags($arr) == true)
            return ["error"];
        
        return $arr;
    }
    
    $text = "abc[math][b]x^2+4[/math][math]2*4=8[/math]";
    
    echo json_encode(extractContent($text));
?>