var shiftingTweet = false;

function nextTweet() {
	if (!shiftingTweet) {
		var tweetHolder = $("tweetHolder");
		tweetHolder.set("morph",{
			onComplete:function(e){
				shiftingTweet = false;
			}
		});
		shiftingTweet = true;
		var tweetHolderTop = tweetHolder.offsetTop;
		var allTweets = $$(".tweet");
		
		var tweetCombinedHeight=0;
	
		var curTweetPos = 0;
		while ((-tweetCombinedHeight) != tweetHolderTop) {
			if (curTweetPos < allTweets.length) {
				curTweet = allTweets[curTweetPos];
				tweetCombinedHeight += curTweet.getHeight();
				curTweetPos++;
			} else { break; }
		}
		if ((curTweetPos+1) < allTweets.length) {
			var curTweetHeight = allTweets[curTweetPos].getHeight();
			tweetHolder.morph({'top':tweetHolderTop-curTweetHeight});
		}
	
		var remainingTweetsHeight=0;
		for (var i=curTweetPos+1; i<allTweets.length; i++) { remainingTweetsHeight += allTweets[i].getHeight();}
	
		if (remainingTweetsHeight < $(tweetHolder.parentNode).getHeight()) {
			$("nextTweet").set("class","bb_navInactive");
			$("nextTweet").onclick = "";
			$("prevTweet").set("class","bb_navActive");
			$("prevTweet").onclick = function() { prevTweet(); }
			$("firstTweet").set("class","bb_navActive");
		} else if (curTweetPos >= 0) {
			$("prevTweet").set("class","bb_navActive");
			$("prevTweet").onclick = function() { prevTweet(); }
			$("firstTweet").set("class","bb_navActive");
		}
	}
}

function prevTweet() {

	if (!shiftingTweet) {
		var tweetHolder = $("tweetHolder");
		tweetHolder.set("morph",{
			onComplete:function(e){
				shiftingTweet = false;
			}
		});
		shiftingTweet = true;
		var tweetHolderTop = tweetHolder.offsetTop;
		var allTweets = $$(".tweet");
	
		var tweetCombinedHeight = 0;
		for (var i=(allTweets.length-1); i>=0; i--) { tweetCombinedHeight += allTweets[i].getHeight(); }
	
		var curTweetPos = allTweets.length-1;
		while ((-tweetCombinedHeight) != tweetHolderTop) {
			if (curTweetPos >= 0) {
				curTweet = allTweets[curTweetPos];
				tweetCombinedHeight -= curTweet.getHeight();
				curTweetPos--;
			} else { break; }
		}
	
		if (curTweetPos >= 0) {
			var curTweetHeight = allTweets[curTweetPos].getHeight();
			tweetHolder.morph({'top':tweetHolderTop+curTweetHeight});
		}
	
		var remainingTweetsHeight=0;
		for (var i=curTweetPos; i<allTweets.length; i++) { remainingTweetsHeight += allTweets[i].getHeight();}
	
		if (remainingTweetsHeight >= ($(tweetHolder.parentNode).getHeight()-10)) {
			$("nextTweet").set("class","bb_navActive");
			$("nextTweet").onclick = function() { nextTweet(); }
			
			if (curTweetPos > 0) {
				$("prevTweet").set("class","bb_navActive");
				$("prevTweet").onclick = function() { prevTweet(); }
				$("firstTweet").set("class","bb_navActive");
			} else {
				$("prevTweet").set("class","bb_navInactive");
				$("prevTweet").onclick = "";
				$("firstTweet").set("class","bb_navInactive");
			}
		}
	}
}

function firstTweet() {
	var tweetHolder = $("tweetHolder");
	tweetHolder.morph({'top':'0px'});
	$("prevTweet").set("class","bb_navInactive");
	$("prevTweet").onclick = "";
	$("nextTweet").set("class","bb_navActive");
	$("nextTweet").onclick = function() { nextTweet(); }
	$("firstTweet").set("class","bb_navInactive");
}