#Traffic lights control simulator

Project proposed and implemented during Scala Hackaton in Berlin

##Backlog

##Requirements:

• models behaviour of traffic lights
• works in real-time
• can optimise throughput using different kinds of detectors
• street layout is configurable

##Technologies:

• Scala
• Akka (main logic flow)
• Spray (http service)
• Html5 + AngularJs (frontend)
• ScalaTest (tests)
• Akka TestKit (tests)
• SBT (build)

##Design:

• all main components are Actors:

  • traffic lights TrafficLight models single traffic lights box with red, orange and green colours,
  • lights groups LightsGroupWithOnlyOneIsGreenStrategy groups traffic lights and governs them with "Only one may be green at the same time" strategy,
  • detectors TrafficDetector provides size of the queue on the lane
  • route directors TrafficDirector analyzes traffic and initializes lights change,
  • demo traffic system DemoTrafficSystem models simple crossroad with 4 directions,
  • http service HttpServiceActor provides /status resource with current traffic system state and index page with crossroad visualization.

• all kinds of logic are implemented via messages flow (commands,querries,events)

##How to run demo app?

run command: $sbt re-start

open url in browser

##Description

Traffic control app uses message passing between asynchronous actors as a tool to model real-time traffic lights system. Few commands, querries and events forms control and supervision protocol. Demo implemented at hackaton represents simple crossroad but we took approach that allows design systems of a larger scale.

The innermost primitive component of a traffic system is a TrafficLight actor simulating red/orange/green signals using finite state machine. TrafficLight processes ChangeToRed, ChangeToGreen and GetStatusQuery. Light switching with orange blink phase is handled internally with scheduler. Externally are exposed ACK events: ChangedToRedEvent and ChangedToGreenEvent. StatusEvent is used by MonitoringActor to report system state via http service. TrafficLights are intended to be grouped by outer components like groups, managers, directors, etc.