defmodule Ark.StructAccess do
  def __ark__(:doc) do
    """
    This module provides a simple way to implement the Access behaviour for any struct.

    #### Example

    ```elixir
    defmodule MyStruct do
      defstruct [:k]
      use Ark.StructAccess
    end

    s = %MyStruct{k: 1}
    put_in(s.k, 2)

    # => %MyStruct{k: 2}
    ```
    """
  end

  @doc ~S"""
  Using this module will allow to use the access macros and functions
  (`Kernel.get_in/2`, `Kernel.put_in/2`, _etc._) with a struct.
  """
  defmacro __using__(_) do
    quote do
      @behaviour Access
      @doc false
      defdelegate fetch(term, key), to: Map
      @doc false
      defdelegate get(term, key, default), to: Map
      @doc false
      defdelegate get_and_update(term, key, fun), to: Map

      def pop(_, key) do
        raise RuntimeError, message: "cannot pop key #{key} from struct %#{__MODULE__}{}"
      end
    end
  end
end