/*
Title:		Preview Your Links with Unobtrusive JavaScript
Author: 	Chris Campbell
URL:		http://particletree.com/features/preview-your-links
Description:	Inspired by the TargetAlert Firefox extension that “provides visual cues for the destinations of hyperlinks” and Christian Heilmann’s Image previews with DOM JavaScript, we wrote a simple set of unobtrusive JavaScript functions to find links on a page that go to amazon product pages, pdfs, word documents or whatever destination that might slow down the browsing process and adds an icon next to them to let you know what you might expect to find behind a link.
Created: 	7/24/2005
Modified: 	7/27/2005
*/

// code enters here
addEvent(window, 'load', linkPreview);

// Summary:	Attaches an event to the object passed in (Script written by Christian Heilmann at http://www.onlinetools.org/articles/unobtrusivejavascript/chapter4.html)
// Parameters: 	Object to attach event to | type of event to attach | function call
// Return:	Boolean indicating success or failure

function addEvent(obj, evType, fn){ 
	if (obj.addEventListener){ 
		obj.addEventListener(evType, fn, false); 
		return true; 
	} 
	else if (obj.attachEvent){ 
		var r = obj.attachEvent("on"+evType, fn); 
		return r; 
	}
	else { 
		return false; 
	} 
}

// Summary: Grabs all non-image links from the page and calls checkLinks() if amazon.com is not located in the link 
function linkPreview(){
	var links = document.getElementsByTagName("a");

	for (i=0; i<links.length; i++){
		var currentLink = links[i];
		var	images = currentLink.getElementsByTagName("img");
		
	 	// Check if the link is an image. We don't want icons next to images.
		if (images.length == 0){
			var linkHref = currentLink.href;
			
			// Find all links directed to amazon.com 
			if (linkHref.match(/amazon.com/)){
				append(currentLink, "amazon");
			}
			else{
				checkLinks(linkHref, currentLink)
			}
		}
	}
}

// Summary: Checks if the link goes to an external file (ie. .doc, .pdf) and calls append()
// Parameters: The href of the link | the <a> object 
function checkLinks(linkHref, currentLink){
	var linkHrefParts = linkHref.split(".");
	
	// extension is the last element in the LinkSplit array
	var extension = linkHrefParts[linkHrefParts.length - 1];
	
	// In some browsers there is a "/" placed after the link. removes the "/"
	extension = extension.replace("/","");
	
	if( extension in { doc:1, pdf:1, ppt:1, txt:1, xls:1, zip:1 } ){
		append(currentLink, extension );
	}
}

// Summary: Creates a span after the object passed in and sets the class to the link type
// Parameters: <a> object | external link type
function append(currentLink, extension){
	var span = document.createElement('span');
	span.innerHTML = "&nbsp;";
	currentLink.parentNode.insertBefore(span,currentLink.nextSibling);
	span.className = extension;
}