core.ts

/*
 * JavaScript tracker core for Snowplow: core.js
 *
 * Copyright (c) 2014-2016 Snowplow Analytics Ltd. All rights reserved.
 *
 * This program is licensed to you under the Apache License Version 2.0,
 * and you may not use this file except in compliance with the Apache License Version 2.0.
 * You may obtain a copy of the Apache License Version 2.0 at http://www.apache.org/licenses/LICENSE-2.0.
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the Apache License Version 2.0 is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the Apache License Version 2.0 for the specific language governing permissions and limitations there under.
 */

import uuid = require('uuid');

import * as payload from './payload';
import {PayloadData} from "./payload";
import {
	contextModule as contextConstructor
} from "./contexts";

/**
 * Interface common for any Self-Describing JSON such as custom context or
 * Self-describing (ex-unstuctured) event
 */
export interface SelfDescribingJson extends Object {
	schema: string
	data: Object
}

/**
 * Algebraic datatype representing possible timestamp type choice
 */
export type Timestamp = TrueTimestamp | DeviceTimestamp | number;
export interface TrueTimestamp { readonly type: "ttm"; readonly value: number }
export interface DeviceTimestamp { readonly type: "dtm"; readonly value: number }

/**
 * Pair of timestamp type ready to be included to payload
 */
type TimestampPayload = TrueTimestamp | DeviceTimestamp

/**
 * Transform optional/old-behavior number timestamp into
 * `TrackerTimestamp` ADT
 *
 * @param tstamp optional number or correct timestamp object
 * @returns {Timestamp} correct timestamp object
 */
function getTimestamp(tstamp?: Timestamp): TimestampPayload {
	if (tstamp == null) {
		return {type: 'dtm', value: new Date().getTime() }
	} else if (typeof tstamp === 'number') {
		return { type: 'dtm', value: tstamp }
	} else if (tstamp.type === 'ttm') {		// We can return tstamp here, but this is safer fallback
		return { type: 'ttm', value: tstamp.value }
	} else {
		return { type: 'dtm', value: (tstamp.value || new Date().getTime()) }
	}
}

/**
 * Create a tracker core object
 *
 * @param base64 Whether to base 64 encode contexts and unstructured event JSONs
 * @param callback Function applied to every payload dictionary object
 * @return Tracker core
 */
export function trackerCore(base64: boolean, callback?: (PayloadData) => void) {

	// base 64 encoding should default to true
	if (typeof base64 === 'undefined') {
		base64 = true;
	}

	// Dictionary of key-value pairs which get added to every payload, e.g. tracker version
	var payloadPairs = {};

	let contextModule = contextConstructor();

	/**
	 * Gets all global contexts to be added to events
	 *
	 * @param event
	 */
	function getAllContexts(event: PayloadData) : Array<SelfDescribingJson> {
		return contextModule.getApplicableContexts(event);
	}

	/**
	 * Set a persistent key-value pair to be added to every payload
	 *
	 * @param key Field name
	 * @param value Field value
	 */
	function addPayloadPair(key: string, value: string) {
		payloadPairs[key] = value;
	}

	/**
	 * Returns a copy of a JSON with undefined and null properties removed
	 *
	 * @param eventJson JSON object to clean
	 * @param exemptFields Set of fields which should not be removed even if empty
	 * @return A cleaned copy of eventJson
	 */
	function removeEmptyProperties(eventJson: Object, exemptFields?: Object) {
		var ret = {};
		exemptFields = exemptFields || {};
		for (var k in eventJson) {
			if (exemptFields[k] || (eventJson[k] !== null && typeof eventJson[k] !== 'undefined')) {
				ret[k] = eventJson[k];
			}
		}
		return ret;
	}

	/**
	 * Wraps an array of custom contexts in a self-describing JSON
	 *
	 * @param contexts Array of custom context self-describing JSONs
	 * @return Outer JSON
	 */
	function completeContexts(contexts?: Array<SelfDescribingJson>): Object | undefined {		// TODO: can return nothing
		if (contexts && contexts.length) {
			return {
				schema: 'iglu:com.snowplowanalytics.snowplow/contexts/jsonschema/1-0-0',
				data: contexts
			};
		}
	}

	/**
	 * Adds all global contexts to a contexts array
	 *
	 * @param sb PayloadData
	 * @param contexts Array<SelfDescribingJson>
	 */
	function attachGlobalContexts(sb: PayloadData,
								  contexts?: Array<SelfDescribingJson>): Array<SelfDescribingJson> {
		let globalContexts : Array<SelfDescribingJson> = getAllContexts(sb);
		let returnedContexts : Array<SelfDescribingJson> = [];
		if (contexts && contexts.length) {
			returnedContexts.push(...contexts);
		}
        if (globalContexts && globalContexts.length) {
			returnedContexts.push(...globalContexts);
		}
		return returnedContexts;
	}

	/**
	 * Gets called by every trackXXX method
	 * Adds context and payloadPairs name-value pairs to the payload
	 * Applies the callback to the built payload
	 *
	 * @param sb Payload
	 * @param context Custom contexts relating to the event
	 * @param tstamp TrackerTimestamp of the event
	 * @return Payload after the callback is applied
	 */
	function track(sb: PayloadData, context?: Array<SelfDescribingJson>, tstamp?: Timestamp): PayloadData {
		sb.addDict(payloadPairs);
		sb.add('eid', uuid.v4());
		var timestamp = getTimestamp(tstamp);
		sb.add(timestamp.type, timestamp.value.toString());
		var allContexts = attachGlobalContexts(sb, context);
		var wrappedContexts = completeContexts(allContexts);
		if (wrappedContexts !== undefined) {
			sb.addJson('cx', 'co', wrappedContexts);
		}

		if (typeof callback === 'function') {
			callback(sb);
		}

		return sb;
	}

	/**
	 * Log an self-describing (previously unstruct) event
	 *
	 * @param properties Contains the properties and schema location for the event
	 * @param context Custom contexts relating to the event
	 * @param tstamp TrackerTimestamp of the event
	 * @return Payload
	 */
	function trackSelfDescribingEvent(properties: Object, context?: Array<SelfDescribingJson>, tstamp?: Timestamp): PayloadData {
		var sb = payload.payloadBuilder(base64);
		var ueJson = {
			schema: 'iglu:com.snowplowanalytics.snowplow/unstruct_event/jsonschema/1-0-0',
			data: properties
		};

		sb.add('e', 'ue');
		sb.addJson('ue_px', 'ue_pr', ueJson);

		return track(sb, context, tstamp);
	}

	return {

		/**
		 * Turn base 64 encoding on or off
		 *
		 * @param encode Whether to encode payload
		 */
		setBase64Encoding: function (encode: boolean) {
			base64 = encode;
		},

		addPayloadPair: addPayloadPair,

		/**
		 * Merges a dictionary into payloadPairs
		 *
		 * @param dict Dictionary to add
		 */
		addPayloadDict: function (dict: Object) {
			for (var key in dict) {
				if (dict.hasOwnProperty(key)) {
					payloadPairs[key] = dict[key];
				}
			}
		},

		/**
		 * Replace payloadPairs with a new dictionary
		 *
		 * @param dict object New dictionary
		 */
		resetPayloadPairs: function (dict: Object) {
			payloadPairs = payload.isJson(dict) ? dict : {};
		},

		/**
		 * Set the tracker version
		 *
		 * @param version string
		 */
		setTrackerVersion: function (version: string) {
			addPayloadPair('tv', version);
		},

		/**
		 * Set the tracker namespace
		 *
		 * @param name string
		 */
		setTrackerNamespace: function (name: string) {
			addPayloadPair('tna', name);
		},

		/**
		 * Set the application ID
		 *
		 * @param appId string
		 */
		setAppId: function (appId: string) {
			addPayloadPair('aid', appId);
		},

		/**
		 * Set the platform
		 *
		 * @param value string
		 */
		setPlatform: function (value: string) {
			addPayloadPair('p', value);
		},

		/**
		 * Set the user ID
		 *
		 * @param userId string
		 */
		setUserId: function (userId: string) {
			addPayloadPair('uid', userId);
		},

		/**
		 * Set the screen resolution
		 *
		 * @param width number
		 * @param height number
		 */
		setScreenResolution: function (width: string, height: string) {
			addPayloadPair('res', width + 'x' + height);
		},

		/**
		 * Set the viewport dimensions
		 *
		 * @param width number
		 * @param height number
		 */
		setViewport: function (width: string, height: string) {
			addPayloadPair('vp', width + 'x' + height);
		},

		/**
		 * Set the color depth
		 *
		 * @param depth number
		 */
		setColorDepth: function (depth: string) {
			addPayloadPair('cd', depth);
		},

		/**
		 * Set the timezone
		 *
		 * @param timezone string
		 */
		setTimezone: function (timezone: string) {
			addPayloadPair('tz', timezone);
		},

		/**
		 * Set the language
		 *
		 * @param lang string
		 */
		setLang: function (lang: string) {
			addPayloadPair('lang', lang);
		},

		/**
		 * Set the IP address
		 *
		 * @param ip string
		 */
		setIpAddress: function (ip: string) {
			addPayloadPair('ip', ip);
		},

		trackUnstructEvent: trackSelfDescribingEvent,

		trackSelfDescribingEvent: trackSelfDescribingEvent,

		/**
		 * Log the page view / visit
		 *
		 * @param pageUrl Current page URL
		 * @param pageTitle The user-defined page title to attach to this page view
		 * @param referrer URL users came from
		 * @param context Custom contexts relating to the event
		 * @param tstamp TrackerTimestamp of the event
		 * @return Payload
		 */
		trackPageView: function (
			pageUrl: string,
			pageTitle: string,
			referrer: string,
			context?: Array<SelfDescribingJson>,
			tstamp?: Timestamp): PayloadData {

			var sb = payload.payloadBuilder(base64);
			sb.add('e', 'pv'); // 'pv' for Page View
			sb.add('url', pageUrl);
			sb.add('page', pageTitle);
			sb.add('refr', referrer);

			return track(sb, context, tstamp);
		},
		/**
		 * Log that a user is still viewing a given page
		 * by sending a page ping
		 *
		 * @param pageUrl Current page URL
		 * @param pageTitle The page title to attach to this page ping
		 * @param referrer URL users came from
		 * @param minXOffset Minimum page x offset seen in the last ping period
		 * @param maxXOffset Maximum page x offset seen in the last ping period
		 * @param minYOffset Minimum page y offset seen in the last ping period
		 * @param maxYOffset Maximum page y offset seen in the last ping period
		 * @param context Custom contexts relating to the event
		 * @param tstamp TrackerTimestamp of the event
		 * @return object Payload
		 */
		trackPagePing: function (
			pageUrl: string,
			pageTitle: string,
			referrer: string,
			minXOffset: number,
			maxXOffset: number,
			minYOffset: number,
			maxYOffset: number,
			context?: Array<SelfDescribingJson>,
			tstamp?: Timestamp): PayloadData {

			var sb = payload.payloadBuilder(base64);
			sb.add('e', 'pp'); // 'pp' for Page Ping
			sb.add('url', pageUrl);
			sb.add('page', pageTitle);
			sb.add('refr', referrer);
			sb.add('pp_mix', minXOffset.toString());
			sb.add('pp_max', maxXOffset.toString());
			sb.add('pp_miy', minYOffset.toString());
			sb.add('pp_may', maxYOffset.toString());

			return track(sb, context, tstamp);
		},
		/**
		 * Track a structured event
		 *
		 * @param category The name you supply for the group of objects you want to track
		 * @param action A string that is uniquely paired with each category, and commonly used to define the type of user interaction for the web object
		 * @param label (optional) An optional string to provide additional dimensions to the event data
		 * @param property (optional) Describes the object or the action performed on it, e.g. quantity of item added to basket
		 * @param value (optional) An integer that you can use to provide numerical data about the user event
		 * @param context Custom contexts relating to the event
		 * @param tstamp TrackerTimestamp of the event
		 * @return Payload
		 */
		trackStructEvent: function (
			category: string,
			action: string,
			label: string,
			property: string,
			value?: number,
			context?: Array<SelfDescribingJson>,
			tstamp?: Timestamp): PayloadData {

			var sb = payload.payloadBuilder(base64);
			sb.add('e', 'se'); // 'se' for Structured Event
			sb.add('se_ca', category);
			sb.add('se_ac', action);
			sb.add('se_la', label);
			sb.add('se_pr', property);
			sb.add('se_va', (value == null ? undefined : value.toString()));

			return track(sb, context, tstamp);
		},

		/**
		 * Track an ecommerce transaction
		 *
		 * @param orderId Required. Internal unique order id number for this transaction.
		 * @param affiliation Optional. Partner or store affiliation.
		 * @param totalValue Required. Total amount of the transaction.
		 * @param taxValue Optional. Tax amount of the transaction.
		 * @param shipping Optional. Shipping charge for the transaction.
		 * @param city Optional. City to associate with transaction.
		 * @param state Optional. State to associate with transaction.
		 * @param country Optional. Country to associate with transaction.
		 * @param currency Optional. Currency to associate with this transaction.
		 * @param context Optional. Context relating to the event.
		 * @param tstamp Optional. TrackerTimestamp of the event
		 * @return Payload
		 */
		trackEcommerceTransaction: function (
			orderId: string,
			affiliation: string,
			totalValue: string,
			taxValue?: string,
			shipping?: string,
			city?: string,
			state?: string,
			country?: string,
			currency?: string,
			context?: Array<SelfDescribingJson>,
			tstamp?: Timestamp): PayloadData {

			var sb = payload.payloadBuilder(base64);
			sb.add('e', 'tr'); // 'tr' for Transaction
			sb.add("tr_id", orderId);
			sb.add("tr_af", affiliation);
			sb.add("tr_tt", totalValue);
			sb.add("tr_tx", taxValue);
			sb.add("tr_sh", shipping);
			sb.add("tr_ci", city);
			sb.add("tr_st", state);
			sb.add("tr_co", country);
			sb.add("tr_cu", currency);

			return track(sb, context, tstamp);
		},

		/**
		 * Track an ecommerce transaction item
		 *
		 * @param orderId Required Order ID of the transaction to associate with item.
		 * @param sku Required. Item's SKU code.
		 * @param name Optional. Product name.
		 * @param category Optional. Product category.
		 * @param price Required. Product price.
		 * @param quantity Required. Purchase quantity.
		 * @param currency Optional. Product price currency.
		 * @param context Optional. Context relating to the event.
		 * @param tstamp Optional. TrackerTimestamp of the event
		 * @return object Payload
		 */
		trackEcommerceTransactionItem: function (
			orderId: string,
			sku: string,
			name: string,
			category: string,
			price: string,
			quantity: string,
			currency?: string,
			context?: Array<SelfDescribingJson>,
			tstamp?: Timestamp): PayloadData {

			var sb = payload.payloadBuilder(base64);
			sb.add("e", "ti"); // 'tr' for Transaction Item
			sb.add("ti_id", orderId);
			sb.add("ti_sk", sku);
			sb.add("ti_nm", name);
			sb.add("ti_ca", category);
			sb.add("ti_pr", price);
			sb.add("ti_qu", quantity);
			sb.add("ti_cu", currency);

			return track(sb, context, tstamp);
		},

		/**
		 * Track a screen view unstructured event
		 *
		 * @param name The name of the screen
		 * @param id The ID of the screen
		 * @param context Optional. Contexts relating to the event
		 * @param tstamp TrackerTimestamp of the event
		 * @return Payload
		 */
		trackScreenView: function (
			name: string,
			id: string,
			context?: Array<SelfDescribingJson>,
			tstamp?: Timestamp): PayloadData {

			return trackSelfDescribingEvent({
				schema: 'iglu:com.snowplowanalytics.snowplow/screen_view/jsonschema/1-0-0',
				data: removeEmptyProperties({
					name: name,
					id: id
				})
			}, context, tstamp);
		},

		/**
		 * Log the link or click with the server
		 *
		 * @param targetUrl
		 * @param elementId
		 * @param elementClasses
		 * @param elementTarget
		 * @param elementContent innerHTML of the link
		 * @param context Custom contexts relating to the event
		 * @param tstamp TrackerTimestamp of the event
		 * @return Payload
		 */
		trackLinkClick: function (
			targetUrl: string,
			elementId: string,
			elementClasses: Array<string>,
			elementTarget: string,
			elementContent: string,
			context?: Array<SelfDescribingJson>,
			tstamp?: Timestamp) {

			var eventJson = {
				schema: 'iglu:com.snowplowanalytics.snowplow/link_click/jsonschema/1-0-1',
				data: removeEmptyProperties({
					targetUrl: targetUrl,
					elementId: elementId,
					elementClasses: elementClasses,
					elementTarget: elementTarget,
					elementContent: elementContent
				})
			};

			return trackSelfDescribingEvent(eventJson, context, tstamp);
		},

		/**
		 * Track an ad being served
		 *
		 * @param impressionId Identifier for a particular ad impression
		 * @param costModel The cost model. 'cpa', 'cpc', or 'cpm'
		 * @param cost Cost
		 * @param targetUrl URL ad pointing to
		 * @param bannerId Identifier for the ad banner displayed
		 * @param zoneId Identifier for the ad zone
		 * @param advertiserId Identifier for the advertiser
		 * @param campaignId Identifier for the campaign which the banner belongs to
		 * @param context Custom contexts relating to the event
		 * @param tstamp TrackerTimestamp of the event
		 * @return object Payload
		 */
		trackAdImpression: function (
			impressionId: string,
			costModel: string,
			cost: number,
			targetUrl: string,
			bannerId: string,
			zoneId: string,
			advertiserId: string,
			campaignId: string,
			context?: Array<SelfDescribingJson>,
			tstamp?: Timestamp): PayloadData {

			var eventJson = {
				schema: 'iglu:com.snowplowanalytics.snowplow/ad_impression/jsonschema/1-0-0',
				data: removeEmptyProperties({
					impressionId: impressionId,
					costModel: costModel,
					cost: cost,
					targetUrl: targetUrl,
					bannerId: bannerId,
					zoneId: zoneId,
					advertiserId: advertiserId,
					campaignId: campaignId
				})
			};

			return trackSelfDescribingEvent(eventJson, context, tstamp);
		},

		/**
		 * Track an ad being clicked
		 *
		 * @param targetUrl (required) The link's target URL
		 * @param clickId Identifier for the ad click
		 * @param costModel The cost model. 'cpa', 'cpc', or 'cpm'
		 * @param cost Cost
		 * @param bannerId Identifier for the ad banner displayed
		 * @param zoneId Identifier for the ad zone
		 * @param impressionId Identifier for a particular ad impression
		 * @param advertiserId Identifier for the advertiser
		 * @param campaignId Identifier for the campaign which the banner belongs to
		 * @param context Custom contexts relating to the event
		 * @param tstamp TrackerTimestamp of the event
		 * @return object Payload
		 */
		trackAdClick: function (
			targetUrl: string,
			clickId: string,
			costModel: string,
			cost: number,
			bannerId: string,
			zoneId: string,
			impressionId: string,
			advertiserId: string,
			campaignId: string,
			context?: Array<SelfDescribingJson>,
			tstamp?: Timestamp): PayloadData {

			var eventJson = {
				schema: 'iglu:com.snowplowanalytics.snowplow/ad_click/jsonschema/1-0-0',
				data: removeEmptyProperties({
					targetUrl: targetUrl,
					clickId: clickId,
					costModel: costModel,
					cost: cost,
					bannerId: bannerId,
					zoneId: zoneId,
					impressionId: impressionId,
					advertiserId: advertiserId,
					campaignId: campaignId
				})
			};

			return trackSelfDescribingEvent(eventJson, context, tstamp);
		},

		/**
		 * Track an ad conversion event
		 *
		 * @param conversionId Identifier for the ad conversion event
		 * @param costModel The cost model. 'cpa', 'cpc', or 'cpm'
		 * @param cost Cost
		 * @param category The name you supply for the group of objects you want to track
		 * @param action A string that is uniquely paired with each category
		 * @param property Describes the object of the conversion or the action performed on it
		 * @param initialValue Revenue attributable to the conversion at time of conversion
		 * @param advertiserId Identifier for the advertiser
		 * @param campaignId Identifier for the campaign which the banner belongs to
		 * @param context Custom contexts relating to the event
		 * @param tstamp TrackerTimestamp of the event
		 * @return object Payload
		 *
		 * @todo make costModel enum
		 */
		trackAdConversion: function (
			conversionId: string,
			costModel: string,
			cost: number,
			category: string,
			action: string,
			property: string,
			initialValue: number,
			advertiserId: string,
			campaignId: string,
			context?: Array<SelfDescribingJson>,
			tstamp?: Timestamp): PayloadData {

			var eventJson = {
				schema: 'iglu:com.snowplowanalytics.snowplow/ad_conversion/jsonschema/1-0-0',
				data: removeEmptyProperties({
					conversionId: conversionId,
					costModel: costModel,
					cost: cost,
					category: category,
					action: action,
					property: property,
					initialValue: initialValue,
					advertiserId: advertiserId,
					campaignId: campaignId
				})
			};

			return trackSelfDescribingEvent(eventJson, context, tstamp);
		},

		/**
		 * Track a social event
		 *
		 * @param action Social action performed
		 * @param network Social network
		 * @param target Object of the social action e.g. the video liked, the tweet retweeted
		 * @param context Custom contexts relating to the event
		 * @param tstamp TrackerTimestamp of the event
		 * @return Payload
		 */
		trackSocialInteraction: function (
			action: string,
			network: string,
			target: string,
			context?: Array<SelfDescribingJson>,
			tstamp?: Timestamp): PayloadData {

			var eventJson = {
				schema: 'iglu:com.snowplowanalytics.snowplow/social_interaction/jsonschema/1-0-0',
				data: removeEmptyProperties({
					action: action,
					network: network,
					target: target
				})
			};

			return trackSelfDescribingEvent(eventJson, context, tstamp);
		},

		/**
		 * Track an add-to-cart event
		 *
		 * @param sku Required. Item's SKU code.
		 * @param name Optional. Product name.
		 * @param category Optional. Product category.
		 * @param unitPrice Optional. Product price.
		 * @param quantity Required. Quantity added.
		 * @param currency Optional. Product price currency.
		 * @param context Optional. Context relating to the event.
		 * @param tstamp Optional. TrackerTimestamp of the event
		 * @return Payload
		 */
		trackAddToCart: function (
			sku: string,
			name: string,
			category: string,
			unitPrice: string,
			quantity: string,
			currency?: string,
			context?: Array<SelfDescribingJson>,
			tstamp?: Timestamp): PayloadData {

			return trackSelfDescribingEvent({
				schema: 'iglu:com.snowplowanalytics.snowplow/add_to_cart/jsonschema/1-0-0',
				data: removeEmptyProperties({
					sku: sku,
					name: name,
					category: category,
					unitPrice: unitPrice,
					quantity: quantity,
					currency: currency
				})
			}, context, tstamp);
		},

		/**
		 * Track a remove-from-cart event
		 *
		 * @param sku Required. Item's SKU code.
		 * @param name Optional. Product name.
		 * @param category Optional. Product category.
		 * @param unitPrice Optional. Product price.
		 * @param quantity Required. Quantity removed.
		 * @param currency Optional. Product price currency.
		 * @param context Optional. Context relating to the event.
		 * @param tstamp Optional. TrackerTimestamp of the event
		 * @return Payload
		 */
		trackRemoveFromCart: function (
			sku: string,
			name: string,
			category: string,
			unitPrice: string,
			quantity: string,
			currency?: string,
			context?: Array<SelfDescribingJson>,
			tstamp?: Timestamp): PayloadData {

			return trackSelfDescribingEvent({
				schema: 'iglu:com.snowplowanalytics.snowplow/remove_from_cart/jsonschema/1-0-0',
				data: removeEmptyProperties({
					sku: sku,
					name: name,
					category: category,
					unitPrice: unitPrice,
					quantity: quantity,
					currency: currency
				})
			}, context, tstamp);
		},

		/**
		 * Track the value of a form field changing
		 *
		 * @param formId The parent form ID
		 * @param elementId ID of the changed element
		 * @param nodeName "INPUT", "TEXTAREA", or "SELECT"
		 * @param type Type of the changed element if its type is "INPUT"
		 * @param elementClasses List of classes of the changed element
		 * @param value The new value of the changed element
		 * @param context Optional. Context relating to the event.
		 * @param tstamp Optional. TrackerTimestamp of the event
		 * @return Payload
		 *
		 * @todo make `nodeName` enum
		 */
		trackFormChange: function (
			formId: string,
			elementId: string,
			nodeName: string,
			type: string,
			elementClasses: Array<string>,
			value: string,
			context?: Array<SelfDescribingJson>,
			tstamp?: Timestamp): PayloadData {

			return trackSelfDescribingEvent({
				schema: 'iglu:com.snowplowanalytics.snowplow/change_form/jsonschema/1-0-0',
				data: removeEmptyProperties({
					formId: formId,
					elementId: elementId,
					nodeName: nodeName,
					type: type,
					elementClasses: elementClasses,
					value: value
				}, {value: true})
			}, context, tstamp);
		},

		/**
		 * Track a form submission event
		 *
		 * @param formId ID of the form
		 * @param formClasses Classes of the form
		 * @param elements Mutable elements within the form
		 * @param context Optional. Context relating to the event.
		 * @param tstamp Optional. TrackerTimestamp of the event
		 * @return Payload
		 */
		trackFormSubmission: function(
			formId: string,
			formClasses: Array<string>,
			elements: Array<string>,
			context?: Array<SelfDescribingJson>,
			tstamp?: Timestamp): PayloadData {

			return trackSelfDescribingEvent({
				schema: 'iglu:com.snowplowanalytics.snowplow/submit_form/jsonschema/1-0-0',
				data: removeEmptyProperties({
					formId: formId,
					formClasses: formClasses,
					elements: elements
				})
			}, context, tstamp);
		},

		/**
		 * Track an internal search event
		 *
		 * @param terms Search terms
		 * @param filters Search filters
		 * @param totalResults Number of results
		 * @param pageResults Number of results displayed on page
		 * @param context Optional. Context relating to the event.
		 * @param tstamp Optional. TrackerTimestamp of the event
		 * @return Payload
		 */
		trackSiteSearch: function(
			terms: Array<string>,
			filters: Object,
			totalResults: number,
			pageResults: number,
			context?: Array<SelfDescribingJson>,
			tstamp?: Timestamp): PayloadData {

			return trackSelfDescribingEvent({
				schema: 'iglu:com.snowplowanalytics.snowplow/site_search/jsonschema/1-0-0',
				data: removeEmptyProperties({
					terms: terms,
					filters: filters,
					totalResults: totalResults,
					pageResults: pageResults
				})
			}, context, tstamp);
		},

		/**
		 * Track a consent withdrawn event
		 *
		 * @param {boolean} all - Indicates user withdraws consent for all documents.
		 * @param {string} [id] - ID number associated with document.
		 * @param {string} [version] - Version number of document.
		 * @param {string} [name] - Name of document.
		 * @param {string} [description] - Description of document.
		 * @param {Array<SelfDescribingJson>} [context] - Context relating to the event.
		 * @param {Timestamp} [tstamp] - TrackerTimestamp of the event.
		 * @return Payload
		 */
		trackConsentWithdrawn: function(
			all: boolean,
			id?: string,
			version?: string,
			name?: string,
			description?: string,
			context?: Array<SelfDescribingJson>,
			tstamp?: Timestamp): PayloadData {

			let documentJson = {
				schema: 'iglu:com.snowplowanalytics.snowplow/consent_document/jsonschema/1-0-0',
				data: removeEmptyProperties({
					id: id,
					version: version,
					name: name,
					description: description
				})
			};

			return trackSelfDescribingEvent({
				schema: 'iglu:com.snowplowanalytics.snowplow/consent_withdrawn/jsonschema/1-0-0',
				data: removeEmptyProperties({
					all: all
				})
			}, documentJson.data && context ? context.concat([documentJson]) : context, tstamp);
		},

		/**
		 * Track a consent granted event
		 *
		 * @param {string} id - ID number associated with document.
		 * @param {string} version - Version number of document.
		 * @param {string} [name] - Name of document.
		 * @param {string} [description] - Description of document.
		 * @param {string} [expiry] - Date-time when consent expires.
		 * @param {Array<SelfDescribingJson>} [context] - Context relating to the event.
		 * @param {Timestamp} [tstamp] - TrackerTimestamp of the event.
		 * @return Payload
		 */
		trackConsentGranted: function(
			id: string,
			version: string,
			name?: string,
			description?: string,
			expiry?: string,
			context?: Array<SelfDescribingJson>,
			tstamp?: Timestamp): PayloadData {

			let documentJson = {
				schema: 'iglu:com.snowplowanalytics.snowplow/consent_document/jsonschema/1-0-0',
				data: removeEmptyProperties({
					id: id,
					version: version,
					name: name,
					description: description,
				})
			};

			return trackSelfDescribingEvent({
				schema: 'iglu:com.snowplowanalytics.snowplow/consent_granted/jsonschema/1-0-0',
				data: removeEmptyProperties({
					expiry: expiry,
				})
			}, context ? context.concat([documentJson]) : [documentJson], tstamp);
		},

		addGlobalContexts: function(contexts: Array<Object>) {
			contextModule.addGlobalContexts(contexts);
		},

		clearGlobalContexts: function() {
			contextModule.clearGlobalContexts();
		},

		removeGlobalContexts: function(contexts: Array<Object>) {
			contextModule.removeGlobalContexts(contexts);
		}
	};
}