defmodule ConfigCat.NullDataSource do
  @moduledoc """
  Don't provide any local flag overrides.

  Used to avoid `is_nil` checks in the rest of the code.

  See `ConfigCat.OverrideDataSource` for more details.
  """
  use TypedStruct

  alias ConfigCat.OverrideDataSource

  typedstruct do
    # No fields
  end

  @doc """
  Create a `ConfigCat.OverrideDataSource` that does nothing.
  """
  @spec new :: t
  def new do
    %__MODULE__{}
  end

  defimpl OverrideDataSource do
    alias ConfigCat.Config
    alias ConfigCat.NullDataSource

    @spec behaviour(NullDataSource.t()) :: OverrideDataSource.behaviour()
    def behaviour(_data_source), do: :local_over_remote

    @spec overrides(NullDataSource.t()) :: Config.t()
    def overrides(_data_source), do: Config.new()
  end
end