
FC.sourceNormalizers = [];
FC.sourceFetchers = [];

var ajaxDefaults = {
	dataType: 'json',
	cache: false
};

var eventGUID = 1;


function EventManager(options) { // assumed to be a calendar
	var t = this;
	
	
	// exports
	t.isFetchNeeded = isFetchNeeded;
	t.fetchEvents = fetchEvents;
	t.addEventSource = addEventSource;
	t.removeEventSource = removeEventSource;
	t.updateEvent = updateEvent;
	t.renderEvent = renderEvent;
	t.removeEvents = removeEvents;
	t.clientEvents = clientEvents;
	t.mutateEvent = mutateEvent;
	t.normalizeEventDates = normalizeEventDates;
	t.normalizeEventTimes = normalizeEventTimes;
	
	
	// imports
	var reportEvents = t.reportEvents;
	
	
	// locals
	var stickySource = { events: [] };
	var sources = [ stickySource ];
	var rangeStart, rangeEnd;
	var currentFetchID = 0;
	var pendingSourceCnt = 0;
	var cache = []; // holds events that have already been expanded


	$.each(
		(options.events ? [ options.events ] : []).concat(options.eventSources || []),
		function(i, sourceInput) {
			var source = buildEventSource(sourceInput);
			if (source) {
				sources.push(source);
			}
		}
	);
	
	
	
	/* Fetching
	-----------------------------------------------------------------------------*/


	// start and end are assumed to be unzoned
	function isFetchNeeded(start, end) {
		return !rangeStart || // nothing has been fetched yet?
			start < rangeStart || end > rangeEnd; // is part of the new range outside of the old range?
	}
	
	
	function fetchEvents(start, end) {
		rangeStart = start;
		rangeEnd = end;
		cache = [];
		var fetchID = ++currentFetchID;
		var len = sources.length;
		pendingSourceCnt = len;
		for (var i=0; i<len; i++) {
			fetchEventSource(sources[i], fetchID);
		}
	}
	
	
	function fetchEventSource(source, fetchID) {
		_fetchEventSource(source, function(eventInputs) {
			var isArraySource = $.isArray(source.events);
			var i, eventInput;
			var abstractEvent;

			if (fetchID == currentFetchID) {

				if (eventInputs) {
					for (i = 0; i < eventInputs.length; i++) {
						eventInput = eventInputs[i];

						if (isArraySource) { // array sources have already been convert to Event Objects
							abstractEvent = eventInput;
						}
						else {
							abstractEvent = buildEventFromInput(eventInput, source);
						}

						if (abstractEvent) { // not false (an invalid event)
							cache.push.apply(
								cache,
								expandEvent(abstractEvent) // add individual expanded events to the cache
							);
						}
					}
				}

				pendingSourceCnt--;
				if (!pendingSourceCnt) {
					reportEvents(cache);
				}
			}
		});
	}
	
	
	function _fetchEventSource(source, callback) {
		var i;
		var fetchers = FC.sourceFetchers;
		var res;

		for (i=0; i<fetchers.length; i++) {
			res = fetchers[i].call(
				t, // this, the Calendar object
				source,
				rangeStart.clone(),
				rangeEnd.clone(),
				options.timezone,
				callback
			);

			if (res === true) {
				// the fetcher is in charge. made its own async request
				return;
			}
			else if (typeof res == 'object') {
				// the fetcher returned a new source. process it
				_fetchEventSource(res, callback);
				return;
			}
		}

		var events = source.events;
		if (events) {
			if ($.isFunction(events)) {
				t.pushLoading();
				events.call(
					t, // this, the Calendar object
					rangeStart.clone(),
					rangeEnd.clone(),
					options.timezone,
					function(events) {
						callback(events);
						t.popLoading();
					}
				);
			}
			else if ($.isArray(events)) {
				callback(events);
			}
			else {
				callback();
			}
		}else{
			var url = source.url;
			if (url) {
				var success = source.success;
				var error = source.error;
				var complete = source.complete;

				// retrieve any outbound GET/POST $.ajax data from the options
				var customData;
				if ($.isFunction(source.data)) {
					// supplied as a function that returns a key/value object
					customData = source.data();
				}
				else {
					// supplied as a straight key/value object
					customData = source.data;
				}

				// use a copy of the custom data so we can modify the parameters
				// and not affect the passed-in object.
				var data = $.extend({}, customData || {});

				var startParam = firstDefined(source.startParam, options.startParam);
				var endParam = firstDefined(source.endParam, options.endParam);
				var timezoneParam = firstDefined(source.timezoneParam, options.timezoneParam);

				if (startParam) {
					data[startParam] = rangeStart.format();
				}
				if (endParam) {
					data[endParam] = rangeEnd.format();
				}
				if (options.timezone && options.timezone != 'local') {
					data[timezoneParam] = options.timezone;
				}

				t.pushLoading();
				$.ajax($.extend({}, ajaxDefaults, source, {
					data: data,
					success: function(events) {
						events = events || [];
						var res = applyAll(success, this, arguments);
						if ($.isArray(res)) {
							events = res;
						}
						callback(events);
					},
					error: function() {
						applyAll(error, this, arguments);
						callback();
					},
					complete: function() {
						applyAll(complete, this, arguments);
						t.popLoading();
					}
				}));
			}else{
				callback();
			}
		}
	}
	
	
	
	/* Sources
	-----------------------------------------------------------------------------*/
	

	function addEventSource(sourceInput) {
		var source = buildEventSource(sourceInput);
		if (source) {
			sources.push(source);
			pendingSourceCnt++;
			fetchEventSource(source, currentFetchID); // will eventually call reportEvents
		}
	}


	function buildEventSource(sourceInput) { // will return undefined if invalid source
		var normalizers = FC.sourceNormalizers;
		var source;
		var i;

		if ($.isFunction(sourceInput) || $.isArray(sourceInput)) {
			source = { events: sourceInput };
		}
		else if (typeof sourceInput === 'string') {
			source = { url: sourceInput };
		}
		else if (typeof sourceInput === 'object') {
			source = $.extend({}, sourceInput); // shallow copy
		}

		if (source) {

			// TODO: repeat code, same code for event classNames
			if (source.className) {
				if (typeof source.className === 'string') {
					source.className = source.className.split(/\s+/);
				}
				// otherwise, assumed to be an array
			}
			else {
				source.className = [];
			}

			// for array sources, we convert to standard Event Objects up front
			if ($.isArray(source.events)) {
				source.origArray = source.events; // for removeEventSource
				source.events = $.map(source.events, function(eventInput) {
					return buildEventFromInput(eventInput, source);
				});
			}

			for (i=0; i<normalizers.length; i++) {
				normalizers[i].call(t, source);
			}

			return source;
		}
	}


	function removeEventSource(source) {
		sources = $.grep(sources, function(src) {
			return !isSourcesEqual(src, source);
		});
		// remove all client events from that source
		cache = $.grep(cache, function(e) {
			return !isSourcesEqual(e.source, source);
		});
		reportEvents(cache);
	}


	function isSourcesEqual(source1, source2) {
		return source1 && source2 && getSourcePrimitive(source1) == getSourcePrimitive(source2);
	}


	function getSourcePrimitive(source) {
		return (
			(typeof source === 'object') ? // a normalized event source?
				(source.origArray || source.googleCalendarId || source.url || source.events) : // get the primitive
				null
		) ||
		source; // the given argument *is* the primitive
	}
	
	
	
	/* Manipulation
	-----------------------------------------------------------------------------*/


	// Only ever called from the externally-facing API
	function updateEvent(event) {

		// massage start/end values, even if date string values
		event.start = t.moment(event.start);
		if (event.end) {
			event.end = t.moment(event.end);
		}
		else {
			event.end = null;
		}

		mutateEvent(event, getMiscEventProps(event)); // will handle start/end/allDay normalization
		reportEvents(cache); // reports event modifications (so we can redraw)
	}


	// Returns a hash of misc event properties that should be copied over to related events.
	function getMiscEventProps(event) {
		var props = {};

		$.each(event, function(name, val) {
			if (isMiscEventPropName(name)) {
				if (val !== undefined && isAtomic(val)) { // a defined non-object
					props[name] = val;
				}
			}
		});

		return props;
	}

	// non-date-related, non-id-related, non-secret
	function isMiscEventPropName(name) {
		return !/^_|^(id|allDay|start|end)$/.test(name);
	}

	
	// returns the expanded events that were created
	function renderEvent(eventInput, stick) {
		var abstractEvent = buildEventFromInput(eventInput);
		var events;
		var i, event;

		if (abstractEvent) { // not false (a valid input)
			events = expandEvent(abstractEvent);

			for (i = 0; i < events.length; i++) {
				event = events[i];

				if (!event.source) {
					if (stick) {
						stickySource.events.push(event);
						event.source = stickySource;
					}
					cache.push(event);
				}
			}

			reportEvents(cache);

			return events;
		}

		return [];
	}
	
	
	function removeEvents(filter) {
		var eventID;
		var i;

		if (filter == null) { // null or undefined. remove all events
			filter = function() { return true; }; // will always match
		}
		else if (!$.isFunction(filter)) { // an event ID
			eventID = filter + '';
			filter = function(event) {
				return event._id == eventID;
			};
		}

		// Purge event(s) from our local cache
		cache = $.grep(cache, filter, true); // inverse=true

		// Remove events from array sources.
		// This works because they have been converted to official Event Objects up front.
		// (and as a result, event._id has been calculated).
		for (i=0; i<sources.length; i++) {
			if ($.isArray(sources[i].events)) {
				sources[i].events = $.grep(sources[i].events, filter, true);
			}
		}

		reportEvents(cache);
	}
	
	
	function clientEvents(filter) {
		if ($.isFunction(filter)) {
			return $.grep(cache, filter);
		}
		else if (filter != null) { // not null, not undefined. an event ID
			filter += '';
			return $.grep(cache, function(e) {
				return e._id == filter;
			});
		}
		return cache; // else, return all
	}
	
	
	
	/* Event Normalization
	-----------------------------------------------------------------------------*/


	// Given a raw object with key/value properties, returns an "abstract" Event object.
	// An "abstract" event is an event that, if recurring, will not have been expanded yet.
	// Will return `false` when input is invalid.
	// `source` is optional
	function buildEventFromInput(input, source) {
		var out = {};
		var start, end;
		var allDay;

		if (options.eventDataTransform) {
			input = options.eventDataTransform(input);
		}
		if (source && source.eventDataTransform) {
			input = source.eventDataTransform(input);
		}

		// Copy all properties over to the resulting object.
		// The special-case properties will be copied over afterwards.
		$.extend(out, input);

		if (source) {
			out.source = source;
		}

		out._id = input._id || (input.id === undefined ? '_fc' + eventGUID++ : input.id + '');

		if (input.className) {
			if (typeof input.className == 'string') {
				out.className = input.className.split(/\s+/);
			}
			else { // assumed to be an array
				out.className = input.className;
			}
		}
		else {
			out.className = [];
		}

		start = input.start || input.date; // "date" is an alias for "start"
		end = input.end;

		// parse as a time (Duration) if applicable
		if (isTimeString(start)) {
			start = moment.duration(start);
		}
		if (isTimeString(end)) {
			end = moment.duration(end);
		}

		if (input.dow || moment.isDuration(start) || moment.isDuration(end)) {

			// the event is "abstract" (recurring) so don't calculate exact start/end dates just yet
			out.start = start ? moment.duration(start) : null; // will be a Duration or null
			out.end = end ? moment.duration(end) : null; // will be a Duration or null
			out._recurring = true; // our internal marker
		}
		else {

			if (start) {
				start = t.moment(start);
				if (!start.isValid()) {
					return false;
				}
			}

			if (end) {
				end = t.moment(end);
				if (!end.isValid()) {
					end = null; // let defaults take over
				}
			}

			allDay = input.allDay;
			if (allDay === undefined) { // still undefined? fallback to default
				allDay = firstDefined(
					source ? source.allDayDefault : undefined,
					options.allDayDefault
				);
				// still undefined? normalizeEventDates will calculate it
			}

			assignDatesToEvent(start, end, allDay, out);
		}

		return out;
	}


	// Normalizes and assigns the given dates to the given partially-formed event object.
	// NOTE: mutates the given start/end moments. does not make a copy.
	function assignDatesToEvent(start, end, allDay, event) {
		event.start = start;
		event.end = end;
		event.allDay = allDay;
		normalizeEventDates(event);
		backupEventDates(event);
	}


	// Ensures proper values for allDay/start/end. Accepts an Event object, or a plain object with event-ish properties.
	// NOTE: Will modify the given object.
	function normalizeEventDates(eventProps) {

		normalizeEventTimes(eventProps);

		if (eventProps.end && !eventProps.end.isAfter(eventProps.start)) {
			eventProps.end = null;
		}

		if (!eventProps.end) {
			if (options.forceEventDuration) {
				eventProps.end = t.getDefaultEventEnd(eventProps.allDay, eventProps.start);
			}
			else {
				eventProps.end = null;
			}
		}
	}


	// Ensures the allDay property exists and the timeliness of the start/end dates are consistent
	function normalizeEventTimes(eventProps) {
		if (eventProps.allDay == null) {
			eventProps.allDay = !(eventProps.start.hasTime() || (eventProps.end && eventProps.end.hasTime()));
		}

		if (eventProps.allDay) {
			eventProps.start.stripTime();
			if (eventProps.end) {
				// TODO: consider nextDayThreshold here? If so, will require a lot of testing and adjustment
				eventProps.end.stripTime();
			}
		}
		else {
			if (!eventProps.start.hasTime()) {
				eventProps.start = t.applyTimezone(eventProps.start.time(0)); // will assign a 00:00 time
			}
			if (eventProps.end && !eventProps.end.hasTime()) {
				eventProps.end = t.applyTimezone(eventProps.end.time(0)); // will assign a 00:00 time
			}
		}
	}


	// If the given event is a recurring event, break it down into an array of individual instances.
	// If not a recurring event, return an array with the single original event.
	// If given a falsy input (probably because of a failed buildEventFromInput call), returns an empty array.
	// HACK: can override the recurring window by providing custom rangeStart/rangeEnd (for businessHours).
	function expandEvent(abstractEvent, _rangeStart, _rangeEnd) {
		var events = [];
		var dowHash;
		var dow;
		var i;
		var date;
		var startTime, endTime;
		var start, end;
		var event;

		_rangeStart = _rangeStart || rangeStart;
		_rangeEnd = _rangeEnd || rangeEnd;

		if (abstractEvent) {
			if (abstractEvent._recurring) {

				// make a boolean hash as to whether the event occurs on each day-of-week
				if ((dow = abstractEvent.dow)) {
					dowHash = {};
					for (i = 0; i < dow.length; i++) {
						dowHash[dow[i]] = true;
					}
				}

				// iterate through every day in the current range
				date = _rangeStart.clone().stripTime(); // holds the date of the current day
				while (date.isBefore(_rangeEnd)) {

					if (!dowHash || dowHash[date.day()]) { // if everyday, or this particular day-of-week

						startTime = abstractEvent.start; // the stored start and end properties are times (Durations)
						endTime = abstractEvent.end; // "
						start = date.clone();
						end = null;

						if (startTime) {
							start = start.time(startTime);
						}
						if (endTime) {
							end = date.clone().time(endTime);
						}

						event = $.extend({}, abstractEvent); // make a copy of the original
						assignDatesToEvent(
							start, end,
							!startTime && !endTime, // allDay?
							event
						);
						events.push(event);
					}

					date.add(1, 'days');
				}
			}
			else {
				events.push(abstractEvent); // return the original event. will be a one-item array
			}
		}

		return events;
	}



	/* Event Modification Math
	-----------------------------------------------------------------------------------------*/


	// Modifies an event and all related events by applying the given properties.
	// Special date-diffing logic is used for manipulation of dates.
	// If `props` does not contain start/end dates, the updated values are assumed to be the event's current start/end.
	// All date comparisons are done against the event's pristine _start and _end dates.
	// Returns an object with delta information and a function to undo all operations.
	// For making computations in a granularity greater than day/time, specify largeUnit.
	// NOTE: The given `newProps` might be mutated for normalization purposes.
	function mutateEvent(event, newProps, largeUnit) {
		var miscProps = {};
		var oldProps;
		var clearEnd;
		var startDelta;
		var endDelta;
		var durationDelta;
		var undoFunc;

		// diffs the dates in the appropriate way, returning a duration
		function diffDates(date1, date0) { // date1 - date0
			if (largeUnit) {
				return diffByUnit(date1, date0, largeUnit);
			}
			else if (newProps.allDay) {
				return diffDay(date1, date0);
			}
			else {
				return diffDayTime(date1, date0);
			}
		}

		newProps = newProps || {};

		// normalize new date-related properties
		if (!newProps.start) {
			newProps.start = event.start.clone();
		}
		if (newProps.end === undefined) {
			newProps.end = event.end ? event.end.clone() : null;
		}
		if (newProps.allDay == null) { // is null or undefined?
			newProps.allDay = event.allDay;
		}
		normalizeEventDates(newProps);

		// create normalized versions of the original props to compare against
		// need a real end value, for diffing
		oldProps = {
			start: event._start.clone(),
			end: event._end ? event._end.clone() : t.getDefaultEventEnd(event._allDay, event._start),
			allDay: newProps.allDay // normalize the dates in the same regard as the new properties
		};
		normalizeEventDates(oldProps);

		// need to clear the end date if explicitly changed to null
		clearEnd = event._end !== null && newProps.end === null;

		// compute the delta for moving the start date
		startDelta = diffDates(newProps.start, oldProps.start);

		// compute the delta for moving the end date
		if (newProps.end) {
			endDelta = diffDates(newProps.end, oldProps.end);
			durationDelta = endDelta.subtract(startDelta);
		}
		else {
			durationDelta = null;
		}

		// gather all non-date-related properties
		$.each(newProps, function(name, val) {
			if (isMiscEventPropName(name)) {
				if (val !== undefined) {
					miscProps[name] = val;
				}
			}
		});

		// apply the operations to the event and all related events
		undoFunc = mutateEvents(
			clientEvents(event._id), // get events with this ID
			clearEnd,
			newProps.allDay,
			startDelta,
			durationDelta,
			miscProps
		);

		return {
			dateDelta: startDelta,
			durationDelta: durationDelta,
			undo: undoFunc
		};
	}


	// Modifies an array of events in the following ways (operations are in order):
	// - clear the event's `end`
	// - convert the event to allDay
	// - add `dateDelta` to the start and end
	// - add `durationDelta` to the event's duration
	// - assign `miscProps` to the event
	//
	// Returns a function that can be called to undo all the operations.
	//
	// TODO: don't use so many closures. possible memory issues when lots of events with same ID.
	//
	function mutateEvents(events, clearEnd, allDay, dateDelta, durationDelta, miscProps) {
		var isAmbigTimezone = t.getIsAmbigTimezone();
		var undoFunctions = [];

		// normalize zero-length deltas to be null
		if (dateDelta && !dateDelta.valueOf()) { dateDelta = null; }
		if (durationDelta && !durationDelta.valueOf()) { durationDelta = null; }

		$.each(events, function(i, event) {
			var oldProps;
			var newProps;

			// build an object holding all the old values, both date-related and misc.
			// for the undo function.
			oldProps = {
				start: event.start.clone(),
				end: event.end ? event.end.clone() : null,
				allDay: event.allDay
			};
			$.each(miscProps, function(name) {
				oldProps[name] = event[name];
			});

			// new date-related properties. work off the original date snapshot.
			// ok to use references because they will be thrown away when backupEventDates is called.
			newProps = {
				start: event._start,
				end: event._end,
				allDay: allDay // normalize the dates in the same regard as the new properties
			};
			normalizeEventDates(newProps); // massages start/end/allDay

			// strip or ensure the end date
			if (clearEnd) {
				newProps.end = null;
			}
			else if (durationDelta && !newProps.end) { // the duration translation requires an end date
				newProps.end = t.getDefaultEventEnd(newProps.allDay, newProps.start);
			}

			if (dateDelta) {
				newProps.start.add(dateDelta);
				if (newProps.end) {
					newProps.end.add(dateDelta);
				}
			}

			if (durationDelta) {
				newProps.end.add(durationDelta); // end already ensured above
			}

			// if the dates have changed, and we know it is impossible to recompute the
			// timezone offsets, strip the zone.
			if (
				isAmbigTimezone &&
				!newProps.allDay &&
				(dateDelta || durationDelta)
			) {
				newProps.start.stripZone();
				if (newProps.end) {
					newProps.end.stripZone();
				}
			}

			$.extend(event, miscProps, newProps); // copy over misc props, then date-related props
			backupEventDates(event); // regenerate internal _start/_end/_allDay

			undoFunctions.push(function() {
				$.extend(event, oldProps);
				backupEventDates(event); // regenerate internal _start/_end/_allDay
			});
		});

		return function() {
			for (var i = 0; i < undoFunctions.length; i++) {
				undoFunctions[i]();
			}
		};
	}


	/* Business Hours
	-----------------------------------------------------------------------------------------*/

	t.getBusinessHoursEvents = getBusinessHoursEvents;


	// Returns an array of events as to when the business hours occur in the given view.
	// Abuse of our event system :(
	function getBusinessHoursEvents(wholeDay) {
		var optionVal = options.businessHours;
		var defaultVal = {
			className: 'fc-nonbusiness',
			start: '09:00',
			end: '17:00',
			dow: [ 1, 2, 3, 4, 5 ], // monday - friday
			rendering: 'inverse-background'
		};
		var view = t.getView();
		var eventInput;

		if (optionVal) { // `true` (which means "use the defaults") or an override object
			eventInput = $.extend(
				{}, // copy to a new object in either case
				defaultVal,
				typeof optionVal === 'object' ? optionVal : {} // override the defaults
			);
		}

		if (eventInput) {

			// if a whole-day series is requested, clear the start/end times
			if (wholeDay) {
				eventInput.start = null;
				eventInput.end = null;
			}

			return expandEvent(
				buildEventFromInput(eventInput),
				view.start,
				view.end
			);
		}

		return [];
	}


	/* Overlapping / Constraining
	-----------------------------------------------------------------------------------------*/

	t.isEventSpanAllowed = isEventSpanAllowed;
	t.isExternalSpanAllowed = isExternalSpanAllowed;
	t.isSelectionSpanAllowed = isSelectionSpanAllowed;


	// Determines if the given event can be relocated to the given span (unzoned start/end with other misc data)
	function isEventSpanAllowed(span, event) {
		var source = event.source || {};
		var constraint = firstDefined(
			event.constraint,
			source.constraint,
			options.eventConstraint
		);
		var overlap = firstDefined(
			event.overlap,
			source.overlap,
			options.eventOverlap
		);
		return isSpanAllowed(span, constraint, overlap, event);
	}


	// Determines if an external event can be relocated to the given span (unzoned start/end with other misc data)
	function isExternalSpanAllowed(eventSpan, eventLocation, eventProps) {
		var eventInput;
		var event;

		// note: very similar logic is in View's reportExternalDrop
		if (eventProps) {
			eventInput = $.extend({}, eventProps, eventLocation);
			event = expandEvent(buildEventFromInput(eventInput))[0];
		}

		if (event) {
			return isEventSpanAllowed(eventSpan, event);
		}
		else { // treat it as a selection

			return isSelectionSpanAllowed(eventSpan);
		}
	}


	// Determines the given span (unzoned start/end with other misc data) can be selected.
	function isSelectionSpanAllowed(span) {
		return isSpanAllowed(span, options.selectConstraint, options.selectOverlap);
	}


	// Returns true if the given span (caused by an event drop/resize or a selection) is allowed to exist
	// according to the constraint/overlap settings.
	// `event` is not required if checking a selection.
	function isSpanAllowed(span, constraint, overlap, event) {
		var constraintEvents;
		var anyContainment;
		var peerEvents;
		var i, peerEvent;
		var peerOverlap;

		// the range must be fully contained by at least one of produced constraint events
		if (constraint != null) {

			// not treated as an event! intermediate data structure
			// TODO: use ranges in the future
			constraintEvents = constraintToEvents(constraint);

			anyContainment = false;
			for (i = 0; i < constraintEvents.length; i++) {
				if (eventContainsRange(constraintEvents[i], span)) {
					anyContainment = true;
					break;
				}
			}

			if (!anyContainment) {
				return false;
			}
		}

		peerEvents = t.getPeerEvents(span, event);

		for (i = 0; i < peerEvents.length; i++)  {
			peerEvent = peerEvents[i];

			// there needs to be an actual intersection before disallowing anything
			if (eventIntersectsRange(peerEvent, span)) {

				// evaluate overlap for the given range and short-circuit if necessary
				if (overlap === false) {
					return false;
				}
				// if the event's overlap is a test function, pass the peer event in question as the first param
				else if (typeof overlap === 'function' && !overlap(peerEvent, event)) {
					return false;
				}

				// if we are computing if the given range is allowable for an event, consider the other event's
				// EventObject-specific or Source-specific `overlap` property
				if (event) {
					peerOverlap = firstDefined(
						peerEvent.overlap,
						(peerEvent.source || {}).overlap
						// we already considered the global `eventOverlap`
					);
					if (peerOverlap === false) {
						return false;
					}
					// if the peer event's overlap is a test function, pass the subject event as the first param
					if (typeof peerOverlap === 'function' && !peerOverlap(event, peerEvent)) {
						return false;
					}
				}
			}
		}

		return true;
	}


	// Given an event input from the API, produces an array of event objects. Possible event inputs:
	// 'businessHours'
	// An event ID (number or string)
	// An object with specific start/end dates or a recurring event (like what businessHours accepts)
	function constraintToEvents(constraintInput) {

		if (constraintInput === 'businessHours') {
			return getBusinessHoursEvents();
		}

		if (typeof constraintInput === 'object') {
			return expandEvent(buildEventFromInput(constraintInput));
		}

		return clientEvents(constraintInput); // probably an ID
	}


	// Does the event's date range fully contain the given range?
	// start/end already assumed to have stripped zones :(
	function eventContainsRange(event, range) {
		var eventStart = event.start.clone().stripZone();
		var eventEnd = t.getEventEnd(event).stripZone();

		return range.start >= eventStart && range.end <= eventEnd;
	}


	// Does the event's date range intersect with the given range?
	// start/end already assumed to have stripped zones :(
	function eventIntersectsRange(event, range) {
		var eventStart = event.start.clone().stripZone();
		var eventEnd = t.getEventEnd(event).stripZone();

		return range.start < eventEnd && range.end > eventStart;
	}


	t.getEventCache = function() {
		return cache;
	};

}


// Returns a list of events that the given event should be compared against when being considered for a move to
// the specified span. Attached to the Calendar's prototype because EventManager is a mixin for a Calendar.
Calendar.prototype.getPeerEvents = function(span, event) {
	var cache = this.getEventCache();
	var peerEvents = [];
	var i, otherEvent;

	for (i = 0; i < cache.length; i++) {
		otherEvent = cache[i];
		if (
			!event ||
			event._id !== otherEvent._id // don't compare the event to itself or other related [repeating] events
		) {
			peerEvents.push(otherEvent);
		}
	}

	return peerEvents;
};


// updates the "backup" properties, which are preserved in order to compute diffs later on.
function backupEventDates(event) {
	event._allDay = event.allDay;
	event._start = event.start.clone();
	event._end = event.end ? event.end.clone() : null;
}
