A function to convert some special formatting codes into their equivalents in HTML

StringToHTML.php

<?php

if (!function_exists("StringToHTML")) {
    function StringToHTML($string) { 
        // The following regular expression was originally formed by Diego Perini
        // Take a look at it here: https://gist.github.com/dperini/729294
        $LinkRegex = "<\[url\](?:(?:https?|ftp):\/\/)(?:\S+(?::\S*)?@)?(?:(?!10(?:\.\d{1,3}){3})(?!127(?:\.\d{1,3}){3})(?!169\.254(?:\.\d{1,3}){2})(?!192\.168(?:\.\d{1,3}){2})(?!172\.(?:1[6-9]|2\d|3[0-1])(?:\.\d{1,3}){2})(?:[1-9]\d?|1\d\d|2[01]\d|22[0-3])(?:\.(?:1?\d{1,2}|2[0-4]\d|25[0-5])){2}(?:\.(?:[1-9]\d?|1\d\d|2[0-4]\d|25[0-4]))|(?:(?:[a-z\x{00a1}-\x{ffff}0-9]+-?)*[a-z\x{00a1}-\x{ffff}0-9]+)(?:\.(?:[a-z\x{00a1}-\x{ffff}0-9]+-?)*[a-z\x{00a1}-\x{ffff}0-9]+)*(?:\.(?:[a-z\x{00a1}-\x{ffff}]{2,})))(?::\d{2,5})?(?:\/[^\s]*)?\[\/url\]>u";
        $string = preg_replace_callback($LinkRegex, function($matches) {
            $match = preg_replace("<\[url\]|\[\/url\]>", "", $matches[0]);
            return "<a href='" . $match . "' target='_blank'>" . $match ."</a>";
        }, $string);

        $YoutubeRegex = "<\[youtube\](https?:\/\/(www\.)?youtube\.com\/watch\?([-a-zA-Z0-9()@:%_\+.~#?&//=]+))\[\/youtube\]>u";
        $string = preg_replace_callback($YoutubeRegex, function($matches) {
            $id = "";
            $parameters = explode("?", $matches[0])[1];
            $parameters = preg_replace("<\[\/youtube\]>", "", $parameters);
            $parameters = explode("&", $parameters);
            for ($i = 0; $i < count($parameters); $i++) {
                $keyvalue = explode("=", $parameters[$i]);
                if ($keyvalue[0] === "v") {
                    $id = $keyvalue[1];
                }
            }
            
            $match = preg_replace("<\[youtube\]|\[\/youtube\]>", "", $matches[0]);
            return "<div class='embed-responsive embed-responsive-16by9'><iframe src='https://www.youtube.com/embed/" . $id . "' class='embed-responsive-item border border-0'></iframe></div>";
        }, $string);

        $string = str_ireplace("\n", "<br/>", $string);
        $string = str_ireplace("\r", "<br/>", $string);
        $string = str_ireplace("\r\n", "<br/>", $string);

        $BoldRegex = "/\[bold\](.*?)\[\/bold\]/";
        $string = preg_replace_callback($BoldRegex, function($matches) {
            $temp = preg_replace("/\[bold\]|\[\/bold\]/", "", $matches[0]);
            return "<b>" . $temp . "</b>";
        }, $string);

        $ItalicRegex = "/\[italic\](.*?)\[\/italic\]/";
        $string = preg_replace_callback($ItalicRegex, function($matches) {
            $temp = preg_replace("/\[italic\]|\[\/italic\]/", "", $matches[0]);
            return "<i>" . $temp . "</i>";
        }, $string);

        $UnderlinedRegex = "/\[underlined\](.*?)\[\/underlined\]/";
        $string = preg_replace_callback($UnderlinedRegex, function($matches) {
            $temp = preg_replace("/\[underlined\]|\[\/underlined\]/", "", $matches[0]);
            return "<u>" . $temp . "</u>";
        }, $string);

        $CenterRegex = "/\[center\](.*?)\[\/center\]/";
        $string = preg_replace_callback($CenterRegex, function($matches) {
            $temp = preg_replace("/\[center\]|\[\/center\]/", "", $matches[0]);
            return "<div class='text-center'>" . $temp . "</div>";
        }, $string);       

        $RightRegex = "/\[right\](.*?)\[\/right\]/";
        $string = preg_replace_callback($RightRegex, function($matches) {
            $temp = preg_replace("/\[right\]|\[\/right\]/", "", $matches[0]);
            return "<div class='text-right'>" . $temp . "</div>";
        }, $string);      
        
        $LeftRegex = "/\[left\](.*?)\[\/left\]/";
        $string = preg_replace_callback($LeftRegex, function($matches) {
            $temp = preg_replace("/\[left\]|\[\/left\]/", "", $matches[0]);
            return "<div class='text-left'>" . $temp . "</div>";
        }, $string); 

        $UppercaseRegex = "/\[uppercase\](.*?)\[\/uppercase\]/";
        $string = preg_replace_callback($UppercaseRegex, function($matches) {
            $temp = preg_replace("/\[uppercase\]|\[\/uppercase\]/", "", $matches[0]);
            return "<span class='text-uppercase'>" . $temp . "</span>";
        }, $string); 

        $LowercaseRegex = "/\[lowercase\](.*?)\[\/lowercase\]/";
        $string = preg_replace_callback($LowercaseRegex, function($matches) {
            $temp = preg_replace("/\[lowercase\]|\[\/lowercase\]/", "", $matches[0]);
            return "<span class='text-lowercase'>" . $temp . "</span>";
        }, $string); 

        $CapitalizedRegex = "/\[capitalized\](.*?)\[\/capitalized\]/";
        $string = preg_replace_callback($CapitalizedRegex, function($matches) {
            $temp = preg_replace("/\[capitalized\]|\[\/capitalized\]/", "", $matches[0]);
            return "<span class='text-capitalize'>" . $temp . "</span>";
        }, $string); 

        $ColorRegex = "<\[color\=([0-9A-Fa-f]){1,6}\](.*)?\[\/color\]>";
        $string = preg_replace_callback($ColorRegex, function($matches) {
            $match = $matches[0];
            $temp = preg_replace_callback("<\[color\=([0-9A-Fa-f]){1,6}\]>", function($inner_matches) {
                $element = explode("]", $inner_matches[0])[0];
                $element = explode("[", $element)[1];
                $element = explode("=", $element)[1];
                return "<span style='color:#" . $element . ";'>";
            }, $match);
            $temp = preg_replace("<\[\/color\]>", "</span>", $temp);
            return $temp;
        }, $string);

        $BackgroundRegex = "<\[background\=([0-9A-Fa-f]){1,6}\](.*)?\[\/background\]>";
        $string = preg_replace_callback($BackgroundRegex, function($matches) {
            $match = $matches[0];
            $temp = preg_replace_callback("<\[background\=([0-9A-Fa-f]){1,6}\]>", function($inner_matches) {
                $element = explode("]", $inner_matches[0])[0];
                $element = explode("[", $element)[1];
                $element = explode("=", $element)[1];
                return "<span style='background-color:#" . $element . ";'>";
            }, $match);
            $temp = preg_replace("<\[\/background\]>", "</span>", $temp);
            return $temp;
        }, $string);

        return $string;
    }
}

?>