gistfile1.scala

package edu.gatech.dt87.scalaverse

package object planner {
    /**
     * An ActionElement is either an Event or a Goal.
     *
     * @tparam S a state type
     */
    sealed trait ActionElement[S]

    /**
     * An Action is a sequence of ActionElements.
     *
     * @param actionElementSequence a sequence of ActionElements.
     * @tparam S a state type
     */
    case class Action[S](actionElementSequence: ActionElement[S]*)

    /**
     * An Event is a transition from a state to either Some state or no state.
     *
     * @param transition a transition
     * @tparam S a state type
     */
    case class Event[S](transition: S => Option[S]) extends ActionElement[S]

    /**
     * A Goal is a set of Actions, any one of which may satisfy the Goal.
     *
     * @param actionSet a set of Actions, any one of which may satisfy the Goal.
     * @tparam S a state.
     */
    case class Goal[S](actionSet: Action[S]*) extends ActionElement[S]

    /**
     * A Planner
     *
     * @param goalSet
     * @tparam S
     */
    case class Planner[S](goalSet: Goal[S]*) {
        def satisfiableGoalSet(state : S): Set[Goal[S]] = {
            Set[Goal[S]]()
        }

        def satisfyGoal(state : S, goal : Goal[S]): Option[S] = {
            scala.util.Random.shuffle(goal.actionSet.toSet).foldLeft(None : Option[S])((next : Option[S], action : Action[S]) => {
                next match {
                    case Some(_) => next
                    case None => satisfyAction(state, action)
                }
            })
        }
        
        def satisfyAction(state : S, action : Action[S]): Option[S] = {
            action.actionElementSequence.foldLeft(Some(state) : Option[S])((state : Option[S], actionElement : ActionElement[S]) =>  {
                (state, actionElement) match {
                    case (Some(previous), event : Event[S]) => satisfyEvent(previous, event)
                    case (Some(previous), goal : Goal[S]) => satisfyGoal(previous, goal)
                    case (None, actionElement) => None
                }
            })
        }

        def satisfyEvent(previous : S, event : Event[S]): Option[S] = {
            event.transition(previous)
        }
    }
}