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In-memory and distributed caching toolkit for Elixir

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nebulex lib nebulex adapters local metadata.ex
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lib/nebulex/adapters/local/metadata.ex 

defmodule Nebulex.Adapters.Local.Metadata do

  @moduledoc false



  defstruct generations: [], n_generations: 2



  @type t :: %__MODULE__{generations: [atom], n_generations: integer}



  alias Nebulex.Adapters.Local.Metadata



  @spec create(cache :: Nebulex.Cache.t(), initial :: Metadata.t()) :: Metadata.t()

  def create(cache, %Metadata{} = initial \\ %Metadata{}) do

    ^cache = :ets.new(cache, [:named_table, read_concurrency: true])

    true = :ets.insert(cache, metadata: initial)

    initial

  end



  @spec get(cache :: Nebulex.Cache.t()) :: Metadata.t()

  def get(cache) do

    :ets.lookup_element(cache, :metadata, 2)

  end



  @spec update(metadata :: Metadata.t(), cache :: Nebulex.Cache.t()) :: Metadata.t()

  def update(%Metadata{} = metadata, cache) do

    true = :ets.update_element(cache, :metadata, {2, metadata})

    metadata

  end



  @spec new_generation(gen :: atom, cache :: Nebulex.Cache.t()) ::

          {generations :: [atom], dropped_generation :: atom | nil}

  def new_generation(gen, cache) do

    metadata = get(cache)



    if length(metadata.generations) >= metadata.n_generations do

      new_metadata =

        metadata

        |> Map.update!(:generations, &[gen | Enum.drop(&1, -1)])

        |> update(cache)



      {new_metadata.generations, List.last(metadata.generations)}

    else

      new_metadata =

        metadata

        |> Map.update!(:generations, &[gen | &1])

        |> update(cache)



      {new_metadata.generations, nil}

    end

  end

end