Detect URLs in plain text and active them as HTML links

activate-links.js

// Detect URLs in plain text and active them as HTML links
// created by Mindon <mindon@gmail.com>
// from <http://mindon.github.io>
//
// usage example:
// document.write( activateLinks("mindon@gmail.com from mindon.github.io") );
// document.write(activateLinks('skip <a href="http://mindon.github.io">Mindon.IDEA</a>'))


(function(){

// URL parser ( http, https, ftp, ftps
var axp = /(((http[s]?:\/\/|ftps?:\/\/)|((?:([\s\xA0,\?:;\"\'!，。；：！？“”‘’]|[^\x00-\xFF]|^))))(((([a-z0-9]+|[a-z0-9][\w\-]+[a-z0-9])\.)+((com|net|org|edu|gov|tel|info|biz|mobi|name)|(((com|net|org|edu|gov|tel|info|biz|mobi|name)\.)?(a[defgilmnoqrstuwz]|b[abdefghijmnorstvwyz]|c[acfghiklmnoqruvxyz]|d[ejkmoz]|e[ceghstv]|f[ijkmor]|g[abdefhilmnprstuwy]|h[kmnrtu]|i[delnoqrst]|j[mop]|k[eghimnprwyz]|l[abcikrstuvy]|m[acedghlmnopqrstvwxyz]|n[acefgiloprtuz]|om|p[aefghklmnrtwy]|qa|r[eouw]|s[abcdeghijklmnortuyz]|t[cdfghjklmnoprtvwz]|u[agksy]|v[acegnu]|w[fs]|y[eu]|z[amrw])))|\d+(\.\d+){3})(:\d+)?((?:([\s\xA0,:;\"\'!，。；：！？“”‘’]|[^\x00-\xFF]))|$|[\/\?][^\s]*)))|([\w\.-]+@([\w-]+\.)+\w+)/ig
	, txp = /([^\s]+)(([\s\xA0]+.*)|([>\)\]\}\"\'].*))$/i
	, tarr = [ '&nbsp', '&gt' ], ttxp = /([,\.\u001e]|%1e)$/i;

var hxp = /^([\s\xA0,\?:;\"\'!，。；：！？“”‘’]|[^\x00-\xFF])/;

function fnlink(s) {
	var h = '', t = '', i = s.indexOf('@'), j = s.indexOf('?');
	if (i < 0 || (j > 0 && i > j)) { // url
		txp.lastIndex = 0;
		var m = s.match(txp);
		if (m) {
			s = m[1];
			t = m[2];
		}
		if (tarr && tarr.length > 0) {
			for ( var k = tarr.length - 1; k > -1; k--) {
				var n = s.toLowerCase().indexOf(tarr[k]);
				if (n > 0) {
					t = s.substr(n) + t;
					s = s.substr(0, n);
				}
			}
		}
		ttxp.lastIndex = 0;
		while (m = s.match(ttxp)) {
			t = m[1] + t;
			s = s.substr(0, s.length - m[1].length);
		}
		h = s.substr(0, 1);
		hxp.lastIndex = 0;
		if (!hxp.test(h))
			h = '';
		else
			s = s.substr(1);
		
		t = [ h, ' <a href="' + (s.indexOf('://') < 0 ? 'http://' : ''),
		      decodeURI(s).replace(/\"/g, '%22'), '">', (s), '</a> ', t ]
				.join("");
	} else { // mail
		t = [ h, ' <a href="mailto:', s, '">', (s), '</a> ', t ]
				.join("");
	}
	return t;
}

var hasLink = /[\.@]|(:\/\/)/;
function makeLinks(c) {
	hasLink.lastIndex = 0;
	if (!hasLink.test(c))
		return c;
	return c.replace(axp, fnlink);
}

window.activateLinks = function(c){
	var tagA = "<a", tagAt = '</a>';

  var lc = c.toLowerCase(); // allow case insensitive
	var n = lc.indexOf(tagA);
	if( n < 0 || lc.indexOf(tagAt) < 0 ) {
		return makeLinks(c); // parse links
	}
	// filter <a*>...</a>
	var d = [];
	do {
		var v = c.substr(0, n), n2 = lc.indexOf(tagAt, n+2);
    if( n2 == -1 ) {
      d.push(makeLinks(c));
      break;
    }
		d.push(makeLinks(v) + c.substring(n, n2 +4));
		c = c.substr(n2 +4);

    lc = lc.substr(n2 +4); // 
		n = lc.indexOf(tagA);
		if( n == -1) {
			d.push(makeLinks(c));
		}
	} while( n > -1);
	if(d.length > 0) {
		c = d.join("");
	}
  return c;
};
})();