// A utility function that returns true if a string contains only 
// whitespace characters.
function isblank(s)
{
    for(var i = 0; i < s.length; i++) {
        var c = s.charAt(i);
        if ((c != ' ') && (c != '\n') && (c != '\t')) return false;
    }
    return true;
}

// This is the function that performs form verification. It will be invoked
// from the onSubmit() event handler. The handler should return whatever
// value this function returns.
function verify(f)
{
    var msg;
    var empty_fields = "";
    var errors = "";

    // Loop through the elements of the form, looking for all 
    // text and textarea elements that don't have an "optional" property
    // defined. Then, check for fields that are empty and make a list of them.
    // Also, if any of these elements have a "min" or a "max" property defined,
    // then verify that they are numbers and that they are in the right range.
    // Put together error messages for fields that are wrong.
    for(var i = 0; i < f.length; i++) {
        var e = f.elements[i];
        if (((e.type == "text") || (e.type == "textarea")) && e.required) {
            // first check if the field is empty
            if ((e.value == null) || (e.value == "") || isblank(e.value)) {
            	n=e.visiblename;
                empty_fields += "\n          " + n;
                continue;
            }

        }
                    // Now check for fields that are supposed to be numeric.
	            if (e.numeric || (e.min != null) || (e.max != null)) { 
	                var v = parseFloat(e.value);
	                if (isNaN(v) || 
	                    ((e.min != null) && (v < e.min)) || 
	                    ((e.max != null) && (v > e.max))) {
	                    errors += "- Il campo " + e.name + " deve essere un numero";
	                    if (e.min != null) 
	                        errors += " maggiore di " + e.min;
	                    if (e.max != null && e.min != null) 
	                        errors += " e minore di " + e.max;
	                    else if (e.max != null)
	                        errors += " minore di " + e.max;
	                    errors += ".\n";
	                }
	            }

    }

    // Now, if there were any errors, display the messages, and
    // return false to prevent the form from being submitted. 
    // Otherwise return true.
    if (!empty_fields && !errors) return true;

    msg  = "______________________________________________________\n\n"
    msg += "                            Ci sono alcuni errori nei dati.\n";
    msg += "                            Correggili e invia nuovamente.\n";
    msg += "______________________________________________________\n\n"

    if (empty_fields) {
        msg += "- I seguenti campi non possono essere vuoti:" 
                + empty_fields + "\n";
        if (errors) msg += "\n";
    }
    msg += errors;
    alert(msg);
    return false;
}