EventTracker: add a module to track mixpanel events

Signed-off-by: Pablo Carranza Velez <pablo@resin.io>

src/event-tracker.coffee

@@ -0,0 +1,55 @@
+Promise = require 'bluebird'
+_ = require 'lodash'
+mixpanel = require 'mixpanel'
+mask = require 'json-mask'
+
+mixpanelMask = [
+	'appId'
+	'delay'
+	'error'
+	'interval'
+	'image'
+	'app(appId,name)'
+	'service(appId,serviceId,serviceName,commit,releaseId,image,labels)'
+	'stateDiff/local(os_version,superisor_version,ip_address,apps/*/services)'
+].join(',')
+
+module.exports = class EventTracker
+	constructor: ->
+		@_client = null
+		@_properties = null
+
+	_logEvent: ->
+		console.log(arguments...)
+
+	track: (ev, properties = {}) =>
+		# Allow passing in an error directly and having it assigned to the error property.
+		if properties instanceof Error
+			properties = error: properties
+
+		# If the properties has an error argument that is an Error object then it treats it nicely,
+		# rather than letting it become `{}`
+		if properties.error instanceof Error
+			properties.error =
+				message: properties.error.message
+				stack: properties.error.stack
+
+		properties = _.cloneDeep(properties)
+
+		# Don't log private env vars (e.g. api keys)
+		if properties?.service?.environment?
+			delete properties.service.environment
+		properties = mask(properties, mixpanelMask)
+		@_logEvent('Event:', ev, JSON.stringify(properties))
+		return if !@_client?
+		# Mutation is bad, and it should feel bad
+		properties = _.assign(properties, @_properties)
+		@_client.track(ev, properties)
+
+	init: ({ offlineMode, mixpanelToken, uuid, mixpanelHost }) ->
+		Promise.try =>
+			@_properties =
+				distinct_id: uuid
+				uuid: uuid
+			return if offlineMode
+			@_client = mixpanel.init(mixpanelToken, { host: mixpanelHost })