/**
 * Validates form defined by form name.
 *
 * @access public
 * @param  string
 */
function validate(formName)
{
    switch (formName) {
    case 'letter':
        conditions = [
            ['attention', 'empty', 'Attention field must be empty.'],
            ['letter_subject', 'not_empty', 'Subject is required.'],
            ['letter_body', 'not_empty', 'Please enter a letter to send.'],
            ['letter_sincerely', 'not_empty', 'Sincerely is a required field.'],
            ['sender_first_name', 'not_empty', 'First Name is a required field.'],
            ['sender_last_name', 'not_empty', 'Last Name is a required field.'],
            ['sender_address', 'not_empty', 'Address is a required field.'],
            ['sender_city', 'not_empty', 'City is a required field.'],
            ['sender_state', 'not_empty', 'State is a required field.'],
            ['sender_zip', 'not_empty', 'Zip is a required field.'],
            ['sender_email', 'not_empty', 'Email is a required field.'],
            ['sender_email', 'email', 'Please input correct e-mail address.']
        ];
        break;
    default:
        alert('Error! Incorrect form name');
        return false;
    }

    return checkSelection() && check(conditions, formName);
}

/**
 * Checks form using given conditions.
 *
 * @access public
 * @param  string
 */
function check(conditions, formName)
{
    form = document.forms[formName];
    elems = form.elements;

    for (i = 0; i<conditions.length; i++) {
        field = conditions[i][0];
        type = conditions[i][1];
        message = conditions[i][2];

        for (j = 0; j < elems.length; j++) {
            if (elems[j].name == field) {
                elem = elems[j];
                value = elem.value;
                switch (type) {
                case 'empty':
                    if (value != '') {
                        fail(message, formName, elem);
                        return false;
                    }
                    break;
                case 'not_empty':
                    if (value == '') {
                        fail(message, formName, elem);
                        return false;
                    }
                    break;
                case 'email':
                    if (!value.match(/.+@.+\..+/)) {
                        fail(message, formName, elem);
                        return false;
                    }
                    break;
                case 'url':
                    if (!(
                        value == 'http://www.' ||
                        value == '' ||
                        value.match(/^https?:\/\/([\w-]+\.)+[\w-]+(\/.*|)$/)
                    )) {
                        fail(message, formName, elem);
                        return false;
                    }
                    break;
                case 'positive':
                    value = Number(value);
                    if (value <= 0) {
                        fail(message, formName, elem);
                        return false;
                    }
                    break;
                case 'regexp':
                    param = conditions[i][3];
                    if (!value.match(param)) {
                        fail(message, formName, elem);
                        return false;
                    }
                    break;
                case 'not_equal':
                    param = conditions[i][3];
                    if (value == param) {
                        fail(message, formName, elem);
                        return false;
                    }
                    break;
                case 'exp':
                    parts = value.split('/');
                    if (!(
                        parts.length == 2 &&
                        parts[0] > 0 &&
                        parts[0] <= 12 &&
                        parts[1] >= 2000
                    )) {
                        fail(message, formName, elem);
                        return false;
                    }
                    break;
                case 'integer':
                    if (!value.match(/^\d+$/)) {
                        fail(message, formName, elem);
                        return false;
                    }
                    break;
                case 'date':
                    if (value != '' && !isCorrectDate(value)) {
                        fail(message, formName, elem);
                        return false;
                    }
                    break;
                case 'currency':
                    if (value != '' && !isCorrectCurrency(value)) {
                        fail(message, formName, elem);
                        return false;
                    }
                    break;
                case 'currency/date':
                    if (value != '') {
                        parts = value.split('/');
                        if (parts.length != 4) {
                            fail(message, formName, elem);
                            return false;
                        }
                        price = parts[0];
                        date = parts[1] + '/' + parts[2] + '/' + parts[3];

                        if (!(
                            isCorrectCurrency(price) &&
                            isCorrectDate(date)
                        )) {
                            fail(message, formName, elem);
                            return false;
                        }
                    }
                    break;
                case 'zip':
                    if (value != '' && !value.match(/^\d{5,}$/)) {
                        fail(message, formName, elem);
                        return false;
                    }
                    break;
                case 'phone':
                    if (value != '' && !value.match(/^[0-9 \+\-\(\)]+$/)) {
                        fail(message, formName, elem);
                        return false;
                    }
                    break;
                }
            }
        }
    }

    return true;
}

/**
 * Checks if given string is a correct date in format mm/dd/yyyy.
 *
 * @param  string
 * @return bool
 */
function isCorrectDate(str)
{
    parts = str.split('/');
    if (parts.length != 3) {
        return false;
    }
    date = new Date(parts[2], parts[0] - 1, parts[1]);

    if(
        (Number(date.getDate()) == Number(parts[1])) &&
        (Number(date.getMonth()) + 1 == Number(parts[0])) &&
        (Number(date.getFullYear()) == Number(parts[2]))
    ) {
        return true;
    } else {
        return false;
    }
}

/**
 * Checks if given string is a correct currency with thouthands and decimals separators.
 *
 * @param  string
 * @return bool
 */
function isCorrectCurrency(value)
{
    return value.match(/^\d+(,\d{3})*(\.\d+)?$/);
}

/**
 * Fails form field one condition check.
 *
 * @param string
 * @param string
 * @param object element
 */
function fail(message, formName, field)
{
    alert(message);
    focus(field);
}

/**
 * Sets focus to given element.
 *
 * @access public
 * @param  object element
 */
function focus(element)
{
    element.focus();
}

/**
 * Sets focus to given element of given form.
 *
 * @access public
 * @param  string
 * @param  string
 */
function focusElement(formName, elementName)
{
    focus(document.forms[formName].elements[elementName]);
}

/**
 * Checks if an official or newspaper selected
 *
 * @access public
 * @return bool
 */
function somethingSelected()
{
    var form = document.forms['letter'];
    var officials = form.elements['officials[]'];
    var newspapers = form.elements['newspapers[]'];

    for (var i = 0; i < officials.length; i++) {
        if (officials[i].checked) {
            return true;
        }
    }
    for (var i = 0; i < newspapers.length; i++) {
        if (newspapers[i].checked) {
            return true;
        }
    }
    return false;
}

function checkSelection()
{
    if (somethingSelected()) {
        return true;
    } else {
        var form = document.forms['letter'];
        var officials = form.elements['officials[]'];
        var message = 'Please select at least one official or newspaper';
        fail(message, '', officials[0]);
        return false;
    }
}