PHP : writing a simple removeEmoji function

if(preg_match('/xEE[x80-xBF][x80-xBF]|xEF[x81-x83][x80-xBF]/', $value) 

You really want to match Unicode at a character level, rather than trying to keep track of UTF-8 byte sequences. Use the u modifier to treat your UTF-8 string on a character basis.

The emoji are encoded in the block U+1F300–U+1F5FF. However:

• many characters from Japanese carriers' ‘emoji’ sets are actually mapped to existing Unicode symbols, eg the card suits, zodiac signs and some arrows. Do you count these symbols as ‘emoji’ now?

• there are still systems which don't use the newly-standardised Unicode emoji code points, instead using ad-hoc ranges in the Private Use Area. Each carrier had their own encodings. iOS 4 used the Softbank set. More info. You may wish to block the entire Private Use Area.

eg:

function unichr($i) {
    return iconv('UCS-4LE', 'UTF-8', pack('V', $i));
}

if (preg_match('/['.
    unichr(0x1F300).'-'.unichr(0x1F5FF).
    unichr(0xE000).'-'.unichr(0xF8FF).
']/u'), $value) {
    ...
}

Here's my "basic" version that works and does the job. It's "half" recursive (a loop that may call the function or not) and the improvements I'm planning to do (handle "+" separator to "add" returns of two functions, and handle "=" to set variables to make short aliases of the value of a return function) seem quite easy to implement in the _compute() function... maybe because I wrote the code myself, and maybe because, like Paul Crovella said, I'm not using PCRE, because it can very easily become an unmaintainable mess...

NB: this code can be easily optimized, and it's not perfect (there are some cases it doesnt work like (a()+b()))... but if someone is willing to finish it he/she's welcome!

class Parser
{
    private $ref = array(
        'a'         => array( 'type' => 'fn',  'val' => '_a'),
        'b'         => array( 'type' => 'fn',  'val' => '_b'),
        'c'         => array( 'type' => 'fn',  'val' => '_c'),
        'd'         => array( 'type' => 'fn',  'val' => '_d'),
        'e'         => array( 'type' => 'fn',  'val' => '_e'),
        'f'         => array( 'type' => 'fn',  'val' => '_f'),
        'intro'         => array( 'type' => 'fn',  'val' => '_getIntro'),
        'insist'        => array( 'type' => 'fn',  'val' => '_insist'),
        'summoner_name' => array( 'type' => 'fn',  'val' => '_getSummonerName'),
        'type'          => array( 'type' => 'fn',  'val' => '_getEtat'),
        ' '             => array( 'type' => 'str', 'val' => ' ')
    );
    private function _a($p)        { return 'valfnA'; }
    private function _b($p)        { return 'valfnB'; }
    private function _c($p)        { return 'valfnC'; }
    private function _d($p)        { return 'valfnD'; }
    private function _e($p)        { return 'valfnE'; }
    private function _f($p)        { return 'valfnF'; }
    private function _getIntro($p)        { return 'valGetIntro'; }
    private function _insist($p)          { return 'valInsist'; }
    private function _getSummonerName($p) { return 'valGetSqmmonerName'; }
    private function _getEtat($p)         { return 'valGetEtat'; }

    private function _convertKey($key, $params=false)
    {
        $retour = 'indéfini';
        if (isset($this->ref[$key])) {
            $val = $this->ref[$key];
            switch ($val['type']) {
                case 'fn':
                    $val=$val['val'];
                    if (method_exists($this, $val)) {
                        $retour = $this->$val($params);
                    }
                    break;

                default:
                    if (isset($this->val['val'])) {
                        $retour = $this->val['val'];
                    }
                    break;
            }
        }
        return $retour;
    }
    private function _compute($str)
    {
        $p=strpos($str, '?');
        if ($p===false) {
            $p=strpos($str, '=');
            if ($p===false) {
                return $str;
            }
        } else {
            $or=strpos($str, '|');
            if ($or===false) {
                return false;
            }
            $s=substr($str,0,$p);
            if (empty($s) || (strtolower($s)=='false')) {
                return substr($str, $or+1);
            }
            return substr($str, $p+1, ($or-$p)-1);
        }
        return $str;
    }
    private function _getTexte($str, $i, $level)
    {
        if (empty($str)) {
            return $str;
        }
        $level++;
        $f   = (strlen($str)-$i);
        $val = substr($str, $i);
        do {
            $d = $i;
            do {
                $p=$d;
                $d=strpos($str, '(', $p+1);
                if (($p==$i) && ($d===false)) {
                    $retour = $this->_compute($str);
                    return $retour;
                } elseif (($d===false) && ($p>$i)) {
                    $f=strpos($str, ')', $p+1);
                    if ($f===false) {
                        return false;
                    }
                    $d=$p;
                    while((--$d)>=$i) {
                        if (($str[$d]!=' ')
                            && ($str[$d]!='_')
                            && (!ctype_alnum($str[$d]))
                        ) {
                            break;
                        }
                    }
                    if ($d>=$i) {
                        $d++;
                    } else {
                        $d=$i;
                    }
                    $val=substr($str, $d, ($f-$d)+1);
                    $fn=substr($str, $d, $p-$d);
                    $param=$this->_getTexte(
                        substr($str, $p+1, ($f-$p)-1), 0, $level+1
                    );
                    if (!empty($fn)) {
                        $val = $this->_convertKey($fn, $param);
                    } else {
                        $val = $this->_compute($param);
                    }
                    $str = substr($str, 0, $d).$val.substr($str, $f+1);
                    break;
                } elseif ($d===false) {
                    break;
                }
            } while (true);
        } while (true);
    }
    public function parse($str)
    {
        $retour=preg_replace('/{*[^.{]+*}/', '', $str); //}
        $retour=str_replace("n", "", $retour);
        $retour=str_replace("r", "", $retour);
        while (strpos($retour, '  ')!==false) {
            $retour=str_replace("  ", " ", $retour);
        }
        return trim($this->_getTexte($retour, 0, 0));
    }
}

$p=new Parser();
$tests = [
    "a",
    "a()",
    "a(b)",
    "(a?b|c)",
    "(a()?(b()?d|e)|(c()?f|g))",
    "(a()?(b()?d|e)|(c()?f()|g))",
    "((h() ? a | i) ? (b() ? d | e) | (c() ? f | g))",
    "(a(d(f))?b(e(f))|c)",
    '(intro(intro(type(insist(poou))))?toutou|tutu)',
    'type()intro(intro(type(insist(poou))))?type()|tutu'
];
foreach ($tests as $test) {
    $res=$p->parse($test);
    echo $test.' = '.var_export($res,true)."n";
}