Random Permutation Picker Device

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• using { /Fortnite.com/Devices }
  using { /Verse.org/Random }
  using { /Verse.org/Simulation }
  using { /UnrealEngine.com/Temporary/Diagnostics }
  
  # The random_permutation_picker device generates a random permutation of
  # its Choices and then picks them one at a time, without item repetition, with Pick.
  # When the last choice has been picked, a new permutation is generated.
  random_permutation_picker_device := class(creative_device):
      @editable
      PickButton:button_device = button_device{}
      # The Choices array is the set of elements to be picked.
      @editable
      var<private> Choices:[]switch_device = array{}
     
      var<private> PickStartIndex<private>:int=0
     
      # Pick one of the Choices, without repetition.
      # The algorithm uses a form of the Fisher-Yates shuffle to generate a random permutation.
      # See https://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle
      # for a description of the Fisher-Yates shuffle algorithm.
      Pick<public>()<transacts><decides>:switch_device=
          # Imagine a hat with all the Choices in it.
          # The hat is full at the start of the permutation.
          # PickStartIndex is the index of the first element in the hat.
          # We pick an element from the hat, remove it from the hat, and return it.
          # When the hat is empty, we refill it and start a new permutation.