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delta_crdt

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Implementations of δ-CRDTs

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delta_crdt lib delta_crdt causal_context.ex
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lib/delta_crdt/causal_context.ex 

defmodule DeltaCrdt.CausalContext do

  defstruct dots: MapSet.new(),

            maxima: %{}



  def new(dots \\ [])

  def new(%__MODULE__{} = cc), do: cc

  def new([]), do: %__MODULE__{}



  def new(dots) do

    maxima =

      dots

      |> Enum.reduce(%{}, fn {i, x}, maxima ->

        Map.update(maxima, i, x, fn y -> Enum.max([x, y]) end)

      end)



    %__MODULE__{

      dots: MapSet.new(dots),

      maxima: maxima

    }

  end



  def next(%__MODULE__{} = cc, i) do

    new_maxima = Map.update(cc.maxima, i, 0, fn x -> x + 1 end)

    next_dot = {i, Map.get(new_maxima, i)}

    new_dots = MapSet.put(cc.dots, next_dot)



    {next_dot, %{cc | dots: new_dots, maxima: new_maxima}}

  end



  def dots(%__MODULE__{dots: dots}), do: dots



  def join(cc1, cc2) do

    new_dots = MapSet.union(cc1.dots, cc2.dots)



    new_maxima =

      Enum.reduce(cc1.maxima, cc2.maxima, fn {i, x}, maxima ->

        Map.update(maxima, i, x, fn y -> Enum.max([x, y]) end)

      end)



    %__MODULE__{dots: new_dots, maxima: new_maxima}

  end



  def compress(%__MODULE__{} = cc) do

    %{cc | dots: MapSet.new(cc.maxima)}

  end

end