PHP function to turn all URLs in clickable links

linkify.php

<?php
    /**
     * Turn all URLs in clickable links.
     * 
     * @param string $value
     * @param array  $protocols  http/https, ftp, mail, twitter
     * @param array  $attributes
     * @param string $mode       normal or all
     * @return string
     */
    public function linkify($value, $protocols = array('http', 'mail'), array $attributes = array())
    {
        // Link attributes
        $attr = '';
        foreach ($attributes as $key => $val) {
            $attr = ' ' . $key . '="' . htmlentities($val) . '"';
            //for multiple attributes use the following code
            $attr .= ' ' . $key . '="' . htmlentities($val) . '"';
        }
        
        $links = array();
        
        // Extract existing links and tags
        $value = preg_replace_callback('~(<a .*?>.*?</a>|<.*?>)~i', function ($match) use (&$links) { return '<' . array_push($links, $match[1]) . '>'; }, $value);
        
        // Extract text links for each protocol
        foreach ((array)$protocols as $protocol) {
            switch ($protocol) {
                case 'http':
                case 'https':   $value = preg_replace_callback('~(?:(https?)://([^\s<]+)|(www\.[^\s<]+?\.[^\s<]+))(?<![\.,:])~i', function ($match) use ($protocol, &$links, $attr) { if ($match[1]) $protocol = $match[1]; $link = $match[2] ?: $match[3]; return '<' . array_push($links, "<a $attr href=\"$protocol://$link\">$link</a>") . '>'; }, $value); break;
                case 'mail':    $value = preg_replace_callback('~([^\s<]+?@[^\s<]+?\.[^\s<]+)(?<![\.,:])~', function ($match) use (&$links, $attr) { return '<' . array_push($links, "<a $attr href=\"mailto:{$match[1]}\">{$match[1]}</a>") . '>'; }, $value); break;
                case 'twitter': $value = preg_replace_callback('~(?<!\w)[@#](\w++)~', function ($match) use (&$links, $attr) { return '<' . array_push($links, "<a $attr href=\"https://twitter.com/" . ($match[0][0] == '@' ? '' : 'search/%23') . $match[1]  . "\">{$match[0]}</a>") . '>'; }, $value); break;
                default:        $value = preg_replace_callback('~' . preg_quote($protocol, '~') . '://([^\s<]+?)(?<![\.,:])~i', function ($match) use ($protocol, &$links, $attr) { return '<' . array_push($links, "<a $attr href=\"$protocol://{$match[1]}\">{$match[1]}</a>") . '>'; }, $value); break;
            }
        }
        
        // Insert all link
        return preg_replace_callback('/<(\d+)>/', function ($match) use (&$links) { return $links[$match[1] - 1]; }, $value);
    }

short version of this function

	/**
	 * Function used to turn tags into links
	 */
	function tags($input,$type,$sep=', ',$class="")
	{
		//Exploding using comma
		$tags = explode(',',$input);
		$count = 1;
		$total = count($tags);
		$new_tags = '';
		foreach($tags as $tag)
		{
			$params = array('name'=>'tag','tag'=>trim($tag),'type'=>$type);
			$new_tags .= '<a href="'.cblink($params).'" class="'.$class.'">'.$tag.'</a>';
			if($count<$total)
				$new_tags .= $sep;
			$count++;
		}
		
		return $new_tags;
	}
	
       /**
	* Function used to assign link
	* @param : { array } { $params } { an array of parameters }
	* @return : { stirng } { buils link }
	*/

	function cblink($params) {
		$name = getArrayValue($params, 'name');
		$ref = getArrayValue($params, 'ref');
		if($name=='tag') {
			return BASEURL.'/search_result.php?query='.urlencode($params['tag']).'&type='.$params['type'];
		}		
		$param_link = "";
		if(!empty($params['extra_params'])) {
			preg_match('/\?/',$link,$matches);
			if(!empty($matches[0])) {
				$param_link = '&'.$params['extra_params'];
			} else {
				$param_link = '?'.$params['extra_params'];
			}
		}
		
		if(isset($params['assign'])) {
			assign($params['assign'],$link.$param_link);
		} else {
			return $link.$param_link;
		}
	}

This version is for image and youtube

Allow display images and youtube video:
CSS class for links .htmllink and images .htmlimg

public function linkify($showimg = 1, $value, $protocols = array('http', 'mail', 'https'), array $attributes = array('target' => '_blank'))
{       
    // Link attributes
    $attr = '';
    foreach ($attributes as $key => $val) {
        $attr = ' ' . $key . '="' . htmlentities($val) . '"';
    }
    
    $links = array();
    
    // Extract existing links and tags
    $value = preg_replace_callback('~(<a .*?>.*?</a>|<.*?>)~i', function ($match) use (&$links) { return '<' . array_push($links, $match[1]) . '>'; }, $value);
    
    // Extract text links for each protocol
    foreach ((array)$protocols as $protocol) {
        switch ($protocol) {
            case 'http':
            case 'https':   $value = preg_replace_callback('~(?:(https?)://([^\s<]+)|(www\.[^\s<]+?\.[^\s<]+))(?<![\.,:])~i', 
                function ($match) use ($protocol, &$links, $attr, $showimg) { 
                    if ($match[1]){
                        $protocol = $match[1]; $link = $match[2] ?: $match[3]; 
                        // Youtube
                        if($showimg == 1){                                  
                            if(strpos($link, 'youtube.com')>0 || strpos($link, 'youtu.be')>0){                                  
                                $link = '<iframe width="100%" height="315" src="https://www.youtube.com/embed/'.end(explode('=', $link)).'?rel=0&showinfo=0&color=orange&iv_load_policy=3" frameborder="0" allowfullscreen></iframe>';
                                return '<' . array_push($links, $link) . '></a>';
                            }
                            if(strpos($link, '.png')>0 || strpos($link, '.jpg')>0 || strpos($link, '.jpeg')>0 || strpos($link, '.gif')>0 || strpos($link, '.bmp')>0){
                                return '<' . array_push($links, "<a $attr href=\"$protocol://$link\" class=\"htmllink\"><img src=\"$protocol://$link\" class=\"htmlimg\">") . '></a>';
                            }
                        }                           
                        return '<' . array_push($links, "<a $attr href=\"$protocol://$link\" class=\"htmllink\">$link</a>") . '>';                          
                    }                           
            }, $value); break;
            case 'mail':    $value = preg_replace_callback('~([^\s<]+?@[^\s<]+?\.[^\s<]+)(?<![\.,:])~', function ($match) use (&$links, $attr) { return '<' . array_push($links, "<a $attr href=\"mailto:{$match[1]}\" class=\"htmllink\">{$match[1]}</a>") . '>'; }, $value); break;
            case 'twitter': $value = preg_replace_callback('~(?<!\w)[@#](\w++)~', function ($match) use (&$links, $attr) { return '<' . array_push($links, "<a $attr href=\"https://twitter.com/" . ($match[0][0] == '@' ? '' : 'search/%23') . $match[1]  . "\" class=\"htmllink\">{$match[0]}</a>") . '>'; }, $value); break;
            default:        $value = preg_replace_callback('~' . preg_quote($protocol, '~') . '://([^\s<]+?)(?<![\.,:])~i', function ($match) use ($protocol, &$links, $attr) { return '<' . array_push($links, "<a $attr href=\"$protocol://{$match[1]}\" class=\"htmllink\">{$match[1]}</a>") . '>'; }, $value); break;
        }
    }
    
    // Insert all link
    return preg_replace_callback('/<(\d+)>/', function ($match) use (&$links) { return $links[$match[1] - 1]; }, $value);
}