//::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
/** @author  John Miller
 *  @version 2.0
 *  @date    Sun Sep 26 15:00:24 EDT 2021
 *  @see     LICENSE (MIT style license file).
 *
 *  @note    Example Model: Poisson for Event Scheduling Simulation
 */

package scalation
package simulation
package event
package example_1

import scalation.mathstat.Statistic
import scalation.random.Exponential

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/** The `runPoisson` function is used to launch the `PoissonModel` class.
 *  > runMain scalation.simulation.event.example_1.runPoisson
 */
@main def runPoisson (): Unit =  new PoissonModel ()

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/** The `PoissonModel` models the detection of particles (e.g., gamma rays)
 *  from the decay of radioactive atoms as a Poisson Process.
 *  @see http://stuff.mit.edu/afs/sipb/user/biyeun/Public/8.13/poisson/poisson_statistics_biyeun.pdf
 *  @param name    the name of the simulation model
 *  @param reps    the number of independent replications to run
 *  @param nStop   the number arrivals before stopping
 *  @param stream  the base random number stream (0 to 999)
 */
class PoissonModel (name: String = "Poisson", reps: Int = 1, nStop: Int = 100, stream: Int = 0)
      extends Model (name, reps):

    //--------------------------------------------------
    // Initialize Model Constants

    val lambda = 1.0                                  // customer arrival rate (per hr)

    //--------------------------------------------------
    // Create Random Variables (RVs)

    val iArrivalRV = Exponential (1.0 / lambda, stream)

    //--------------------------------------------------
    // Create State Variables

    var nArr = 0.0                                    // number of particles detected

    val t_ia_stat = new Statistic ("t_ia")            // time between Arrivals statistics
    addStats (t_ia_stat)

    //--------------------------------------------------
    // Specify Logic for each Type of Simulation Event

    //::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
    /** `Arrival` is a subclass of `Event` for handling arrival events.
     *  @param call   the entity that arrives, in this case a phone call
     *  @param delay  the time delay for this event's occurrence
     */
    case class Arrival (call: Entity, delay: Double)
         extends Event (call, this, delay, t_ia_stat):

        def occur (): Unit =
            if nArr < nStop - 1 then
                val toArrive = Entity (iArrivalRV.gen, 0.0, PoissonModel.this)
                schedule (Arrival (toArrive, toArrive.iArrivalT))
            end if
            nArr += 1                                      // update the current state
        end occur

    end Arrival

    //--------------------------------------------------
    // Start the simulation after scheduling the first priming event

    val firstArrival = Entity (iArrivalRV.gen, 0.0, this)
    schedule (Arrival (firstArrival, firstArrival.iArrivalT))     // first priming event
    simulate ()                                                   // start simulating

    report (("nArr", nArr))
    reportStats ()

end PoissonModel