$(document).ready(function(){

	/* next/previous impression */
    var currentImpressionsIndex = 0;                  // holds index of current impression
	var impressionsLength = $(".container").length;

    $("#nextImpression").click(function(event){
    	event.preventDefault();
       	nextImpressionsIndex = (currentImpressionsIndex + 1) % impressionsLength;
        switchImpression(currentImpressionsIndex, nextImpressionsIndex);
		currentImpressionsIndex = nextImpressionsIndex;
		updateIndex(nextImpressionsIndex, impressionsLength);
    });
    $("#previousImpression").click(function(event){
        event.preventDefault();
        previousImpressionsIndex = (impressionsLength + currentImpressionsIndex - 1) % impressionsLength;
       	switchImpression(currentImpressionsIndex, previousImpressionsIndex);
		currentImpressionsIndex = previousImpressionsIndex;
		updateIndex(previousImpressionsIndex, impressionsLength);
    });

    /* change impression */
    function switchImpression(current, next)
    {
				
		$("#container_" + current).css({opacity: 1.0}).animate({opacity: 0.0}, 500, function(){
			$("#container_" + next).css({opacity: 0.0}).show().animate({opacity: 1.0}, 500);
		});

    }

	/* update index-numbers */
    function updateIndex(current, length) {
		
		current = current + 1;
		
		$("#currentIndex").html(current);
		$("#indexLength").html(length);
	
	}
	
	updateIndex(currentImpressionsIndex, impressionsLength);


});