decojs/Source/deco/spa/whenContext.js

Scalable frontend architecture

define([
  
], function(
  
){

  function unsubscribe(event, reaction){
    event.dont(reaction);
  }

  function subscribe(event, reaction){
    event(reaction);
    return event.dont.bind(null, reaction);
  }

  function whenSomething(){
    if(this.destroyed) throw new Error("This context has been destroyed!");

    if(arguments.length == 0){
      var childContext = createContext();
      this.childContexts.push(childContext);
      return childContext.when;
    }else if(arguments.length == 1 && typeof arguments[0] === "function"){
      return {
        dont: unsubscribe.bind(null, arguments[0])
      }
    }else if(arguments.length == 2 && typeof arguments[1] === "function"){
      this.eventSubscribers.push(subscribe(arguments[0], arguments[1]));
    }
  }

  function thisIsDestroyed(reaction){
    this.onDestroyListeners.push(reaction);
  }

  function destroyChildContexts(){
    var context;
    while(context = this.childContexts.pop())
      context.destroyContext();
  }

  function destroyContext(){
    var subscriber, listener, context;
    while(subscriber = this.eventSubscribers.pop())
      subscriber();
    while(listener = this.onDestroyListeners.pop())
      listener();
    while(context = this.childContexts.pop())
      context.destroyContext();
    this.destroyed = true;
  }

  function createContext(){
    var context = {
      destroyed: false,
      onDestroyListeners: [],
      childContexts: [],
      eventSubscribers: []
    };

    var when = whenSomething.bind(context);

    when.thisIsDestroyed = thisIsDestroyed.bind(context);

    when.destroyChildContexts = destroyChildContexts.bind(context);

    return {
      when: when,
      destroyContext: destroyContext.bind(context)
    };
  }

  return createContext().when;
});