define(['jquery', 'date', 'js/utils/change_on_enter', 'jquery.ui', 'jquery.timepicker'],
    function($, date, TriggerChangeEventOnEnter) {
        'use strict';

        function getDate(datepickerInput, timepickerInput) {
        // given a pair of inputs (datepicker and timepicker), return a JS Date
        // object that corresponds to the datetime.js that they represent. Assume
        // UTC timezone, NOT the timezone of the user's browser.
            var selectedDate = null,
                selectedTime = null;
            if (datepickerInput.length > 0) {
                selectedDate = $(datepickerInput).datepicker('getDate');
            }
            if (timepickerInput.length > 0) {
                selectedTime = $(timepickerInput).timepicker('getTime');
            }
            if (selectedDate && selectedTime) {
                return new Date(Date.UTC(
                    selectedDate.getFullYear(), selectedDate.getMonth(), selectedDate.getDate(),
                    selectedTime.getHours(), selectedTime.getMinutes()
                ));
            } else if (selectedDate) {
                return new Date(Date.UTC(
                    selectedDate.getFullYear(), selectedDate.getMonth(), selectedDate.getDate()));
            } else {
                return null;
            }
        }

        function setDate(datepickerInput, timepickerInput, datetime) {
        // given a pair of inputs (datepicker and timepicker) and the date as an
        // ISO-formatted date string.
            var parsedDatetime = Date.parse(datetime);
            if (parsedDatetime) {
                $(datepickerInput).datepicker('setDate', parsedDatetime);
                if (timepickerInput.length > 0) {
                    $(timepickerInput).timepicker('setTime', parsedDatetime);
                }
            }
        }

        function renderDate(dateArg) {
        // Render a localized date from an argument that can be passed to
        // the Date constructor (e.g. another Date or an ISO 8601 string)
            var dateObj = new Date(dateArg);
            return dateObj.toLocaleString(
                [],
                {timeZone: 'UTC', timeZoneName: 'short'}
            );
        }

        function parseDateFromString(stringDate) {
            if (stringDate && typeof stringDate === 'string') {
                return new Date(stringDate);
            } else {
                return stringDate;
            }
        }

        function convertDateStringsToObjects(obj, dateFields) {
            var i;
            for (i = 0; i < dateFields.length; i++) {
                if (obj[dateFields[i]]) {
                    obj[dateFields[i]] = parseDateFromString(obj[dateFields[i]]);
                }
            }
            return obj;
        }

        function setupDatePicker(fieldName, view, index) {
            var cacheModel;
            var div;
            var datefield;
            var timefield;
            var cacheview;
            var setfield;
            var currentDate;
            if (typeof index !== 'undefined' && view.hasOwnProperty('collection')) {
                cacheModel = view.collection.models[index];
                div = view.$el.find('#' + view.collectionSelector(cacheModel.cid));
            } else {
                cacheModel = view.model;
                div = view.$el.find('#' + view.fieldToSelectorMap[fieldName]);
            }
            datefield = $(div).find('input.date');
            timefield = $(div).find('input.time');
            cacheview = view;
            setfield = function(event) {
                var newVal = getDate(datefield, timefield);

                // Setting to null clears the time as well, as date and time are linked.
                // Note also that the validation logic prevents us from clearing the start date
                // (start date is required by the back end).
                cacheview.clearValidationErrors();
                cacheview.setAndValidate(fieldName, (newVal || null), event);
            };

            // instrument as date and time pickers
            timefield.timepicker({timeFormat: 'H:i'});
            datefield.datepicker();

            // Using the change event causes setfield to be triggered twice, but it is necessary
            // to pick up when the date is typed directly in the field.
            datefield.change(setfield).keyup(TriggerChangeEventOnEnter);
            timefield.on('changeTime', setfield);
            timefield.on('input', setfield);

            currentDate = null;
            if (cacheModel) {
                currentDate = cacheModel.get(fieldName);
            }
            // timepicker doesn't let us set null, so check that we have a time
            if (currentDate) {
                setDate(datefield, timefield, currentDate);
            } else {
                // but reset fields either way
                timefield.val('');
                datefield.val('');
            }
        }

        return {
            getDate: getDate,
            setDate: setDate,
            renderDate: renderDate,
            convertDateStringsToObjects: convertDateStringsToObjects,
            parseDateFromString: parseDateFromString,
            setupDatePicker: setupDatePicker
        };
    });