define([
    'backbone',
    'backbone.validation',
    'underscore',
    'gettext'
],
    function(Backbone, BackboneValidation, _, gettext) {
        'use strict';

        var errorClass = 'has-error',
            messageEl = '.field-message',
            messageContent = '.field-message-content';

        // These are the same messages provided by Backbone.Validation,
        // marked for translation.
        // See: http://thedersen.com/projects/backbone-validation/#overriding-the-default-error-messages.
        _.extend(Backbone.Validation.messages, {
            required: gettext('{0} is required'),
            acceptance: gettext('{0} must be accepted'),
            min: gettext('{0} must be greater than or equal to {1}'),
            max: gettext('{0} must be less than or equal to {1}'),
            range: gettext('{0} must be between {1} and {2}'),
            length: gettext('{0} must be {1} characters'),
            minLength: gettext('{0} must be at least {1} characters'),
            maxLength: gettext('{0} must be at most {1} characters'),
            rangeLength: gettext('{0} must be between {1} and {2} characters'),
            oneOf: gettext('{0} must be one of: {1}'),
            equalTo: gettext('{0} must be the same as {1}'),
            digits: gettext('{0} must only contain digits'),
            number: gettext('{0} must be a number'),
            email: gettext('{0} must be a valid email'),
            url: gettext('{0} must be a valid url'),
            inlinePattern: gettext('{0} is invalid')
        });

        _.extend(Backbone.Validation.callbacks, {
            // Gets called when a previously invalid field in the
            // view becomes valid. Removes any error message.
            valid: function(view, attr, selector) {
                var $input = view.$('[' + selector + '~="' + attr + '"]'),
                    $message = $input.siblings(messageEl);

                $input.removeClass(errorClass)
                      .removeAttr('data-error');

                $message.removeClass(errorClass)
                        .find(messageContent)
                        .text('');
            },

            // Gets called when a field in the view becomes invalid.
            // Adds a error message.
            invalid: function(view, attr, error, selector) {
                var $input = view.$('[' + selector + '~="' + attr + '"]'),
                    $message = $input.siblings(messageEl);

                $input.addClass(errorClass)
                      .attr('data-error', error);

                $message.addClass(errorClass)
                        .find(messageContent)
                        .text($input.data('error'));
            }
        });

        Backbone.Validation.configure({
            labelFormatter: 'label'
        });
    }
);