function documentReady()
{
	initJSSupport();
	initDocumentInput();
	initReferenceInput();
}

function initJSSupport()
{
	$('.js-support').attr('value', 'true');
}

function initDocumentInput()
{
	$('#form-submit-document').attr('disabled', 'disabled');
	$('#edit-document').change(enableDocumentContinue)
}

function initReferenceInput()
{
	$('#form-submit-reference').attr('disabled', 'disabled');
	
	// enable autoadvance on the form:
	// focus will be transfered to the next control when the maximum number of characters are entered 
	$('#input-reference').autoAdvance();
	
	// check the state each time a key a pressed
	$('#guid-1').keyup(checkValidness);
	$('#guid-2').keyup(checkValidness);
	$('#guid-3').keyup(checkValidness);
	$('#guid-4').keyup(checkValidness);
	
	// do an initial check (values could be prefilled by the browser)
	checkValidness();
}

// the divider of the checksum
var divider = 1021;

// the mapping of characters to their numerical value
var chars = ['2','3','4','5','6','7','8','9','a','b','c','d','e','f','g','h','i','j','k','m','n','p','q','r','s','t','u','v','w','x','y','z'];
var charset = new Array();
for (i = 0; i < chars.length; ++i)
{
  charset[chars[i]] = i;
}

/**
 * Checks if the current input is a valid reference.
 */
function checkValidness()
{
	var valid = 0;
	var guid = new Array();
	guid[0] = $('#guid-1').val();
	guid[1] = $('#guid-2').val();
	guid[2] = $('#guid-3').val();
	guid[3] = $('#guid-4').val();
	if (guid[0].length == 6 && guid[1].length == 6 && guid[2].length == 6 && guid[3].length == 2)
	{
		// all fields are filled
		
		// calculate the checksum
		var val = 0;
		for (var i = 0; i < 3; ++i)
		{
			for (var j = 0; j < 6; ++j)
			{
				val = val * 32 + charset[guid[i].charAt(j)];
				if (val > divider)
				{
					val = val % divider;
				}
			}
		}
		var remainder = charset[guid[3].charAt(0)] * 32 + charset[guid[3].charAt(1)];
		if (val === remainder)
		{
			// the reference is valid
			if (valid !== 1)
			{
				$('#guid-empty').hide();
				$('#guid-valid').show();
				$('#guid-invalid').hide();
				// enable the continue button and give it focus
				$('#form-submit-reference').removeAttr("disabled").focus();
				valid = 1;
			}
		}
		else
		{
			// the reference is invalid
			if (valid !== -1)
			{
				$('#guid-empty').hide();
				$('#guid-valid').hide();
				$('#guid-invalid').show();
				$('#form-submit-reference').attr('disabled', 'disabled');
				valid = -1;
			}
		}
	}
	else
	{
		// the reference is not complete
		$('#guid-empty').show();
		$('#guid-valid').hide();
		$('#guid-invalid').hide();
		$('#form-submit-reference').attr('disabled', 'disabled');
		valid = 0;
	}
}

function enableDocumentContinue()
{
	var file = $('#edit-document').val();
	if (file !== null && file.length > 0)
	{
		$('#form-submit-document').removeAttr("disabled").focus();
	}
	else
	{
		$('#form-submit-document').attr('disabled', 'disabled');
	}
}