// function to hide column(s) in array (number) with empty header
// remaining columns are stretched to original total width
// "table.questions-list" is default to find the input table -- may be this can be defined more accurate?
//
function hideEmptyColumns(tableIdentifyer = "table.questions-list") {
	
	$(tableIdentifyer).each(function(){
		var basetable=$(this);
		var i = 0;
		var p = 0;
		var hiddenPos = [];
		var remainPos = [];
		var oldWidth = [];
		var oldWidthPercentages = [];
		var sumRemainWidth = 0;
		var sumOldWidth = 0;
		var stretchFactor = 0;
		var dummy = "";

		// works with thead in LS 3.18 former version worked with col (why?)
		$(this).find("thead tr.ls-heading th").each(function(){
			
			// save the index of those cols that are to hide and those who remain visible => how to do with valudation?
			if($.trim($(this).html())===""){
				hiddenPos.push(i);
			} else {
				remainPos.push(i);
			}
			
			oldWidth.push($(this).width());			
			i = i + 1;			
		});

		// calculate the sum with of all cols as they are without shrink
		sumOldWidth  = oldWidth.reduce(function(a,b){ return a + b; });
		
		// recalculate the old *percentages* of all columns
		oldWidth.forEach(function(w){
		    oldWidthPercentages.push(w/sumOldWidth*100);
		});
		
		// calculate the sum width of only the remaining cols
		for (p of remainPos) {
			sumRemainWidth += oldWidth[p -1];
		}
		
		// calculate the stretch factor
		stretchFactor = sumOldWidth/sumRemainWidth;		
		
		// hide all columns with empty header but not col 1 
		for (p of hiddenPos) {
			i= p+1;   
			
			$(tableIdentifyer + " th:nth-child("+ i + ")").hide();
			$(tableIdentifyer + " td:nth-child("+ i + ")").hide();			
		}

		// refresh the column css width attributes, but let first column as it was
		dummy = "'" + oldWidthPercentages[0] + "%" + "'";
		$(tableIdentifyer + ' col:nth-child(0)').css({ 'width': dummy });
		
		// set hidden cols to 0%
		p = remainPos.length + 2; 
		for (i of hiddenPos) {
			
			$(tableIdentifyer + " col:nth-child(" + p + ")").css({ 'width': '0%' });		
			p = p + 1;			
		}
		
		// stretch visible cols, line title with original width first
		p = 0;
		i = 1;
		dummy = oldWidthPercentages[p]  + "%" ;
		$(tableIdentifyer + " col:nth-child(" + i + ")").css({ 'width': dummy });
		
		// now answer columns
		p = 2;
		for(i of remainPos) {
			
			dummy = oldWidthPercentages[i] * stretchFactor + "%";
			$(tableIdentifyer + " col:nth-child(" + p + ")").css({ 'width': dummy });
			
			p = p + 1;
		}

	});
}