Calculator = {
	
	formElement: null,

	initialize: function ( formElement ) {
		
		Calculator.formElement = formElement;
		
		var inputElements = Calculator.formElement.getElementsByTagName('input');
		for ( var i = 0; i < inputElements.length; i++ ) {
			
			var inputElement = inputElements[i];
			if ( inputElement.disabled != "disabled" ) {
				
				inputElement.onchange = function (  ) { Calculator.update(); }
				
			} // if
			
		} // for inputElement
		
		Calculator.update();
		
	},
	
	update: function (  ) {
		
		var documentPattern = new RegExp("documents\\[[0-9]+\\]", "i");
		var inputElements = Calculator.formElement.getElementsByTagName('input');
		
		var documentsCount = 0;
		var workersCount = 0;
		var documentsCountElement = null;
		var estimatedPriceElement = null;
		
		// validate and collect form data and elements
		for ( var i = 0; i < inputElements.length; i++ ) {
			
			var inputElement = inputElements[i];
			if ( documentPattern.test(inputElement.name) ) {
				
				inputElement.value = parseInt(inputElement.value, 10);
				if ( isNaN(parseInt(inputElement.value, 10)) || (parseInt(inputElement.value, 10) <= 0) ) { inputElement.value = 0; }
				documentsCount += parseInt(inputElement.value, 10);
				
			} else if ( inputElement.name == 'workersCount' ) {
				
				inputElement.value = parseInt(inputElement.value, 10);
				if ( parseInt(inputElement.value, 10) <= 1 ) { inputElement.value = 1; }
				workersCount = parseInt(inputElement.value, 10);
				
			} else if ( inputElement.name == 'documentsCount' ) {
				
				documentsCountElement = inputElement;
				
			} else if ( inputElement.name == 'estimatedPrice' ) {
				
				estimatedPriceElement = inputElement;
				
			} // else
			
		} // for i
		
		// output documents' count
		if ( documentsCountElement != null ) {
			
			documentsCountElement.value = documentsCount;
			
		} // if
		
		// calculate and output estimated price
		if ( estimatedPriceElement != null ) {
			
			var documentsCountValuation = [ // entries should be sorted ascendingly by upperBound field
				{upperBound:20,  price:700},
				{upperBound:40,  price:1000},
				{upperBound:60,  price:1300},
				{upperBound:80,  price:1500},
				{upperBound:100, price:1800},
				{upperBound:130, price:2300},
				{upperBound:160, price:2600},
				{upperBound:190, price:2900},
				{upperBound:230, price:3200},
				{upperBound:260, price:3500},
				{upperBound:290, price:3800},
				{upperBound:330, price:4100},
				{upperBound:360, price:4400}
			];
			
			var workersCountValuation = 50;
			
			// check if special offer should be applied
			if ( documentsCount <= documentsCountValuation[documentsCountValuation.length-1].upperBound ) {
				
				// hide special offer
				document.getElementById("special-offer").style.display = "none";
				
				// search for valuation in table
				var documentsPrice = 0;
				for ( var i = 0; i < documentsCountValuation.length; i++ ) {
					
					var tableEntry = documentsCountValuation[i];
					if ( documentsCount <= tableEntry.upperBound ) {
						
						documentsPrice = tableEntry.price;
						break;
						
					} // if
					
				} // for i
				
				var workersPrice = workersCount*workersCountValuation;
				estimatedPriceElement.value = Math.ceil((documentsPrice + workersPrice)*100)/100;
				
			} else { // documents' count not listed in table - special offer
				
				// show special offer
				document.getElementById("special-offer").style.display = "block";
				
				estimatedPriceElement.value = "-";
				
			} // else
			
		} // if
		
	}
	
}