function nextTweet() {
	var tweetHolder = $("tweetHolder");
	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() {
	var tweetHolder = $("tweetHolder");
	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");
}