defmodule Hafnium do
  @external_resource readme = Path.join([__DIR__, "../README.md"])

  @moduledoc readme
             |> File.read!()
             |> String.split("<!-- MDOC -->")
             |> Enum.fetch!(1)

  @moduledoc since: "0.1.0"

  @typedoc """
  * `:ok` — success
  * `:error` — error
  * `:ignored` — like `ok` but won't trace
  * `:fatal` — error and break
  """
  @type state :: :ignored | :error | :ok | :fatal

  @type result :: {state(), any()}

  @type input :: %{required(atom()) => any()}

  @type pipe_result :: t() | pipe_atom_result() | pipe_tuple_result()

  @typep pipe_atom_result :: :ignored | :ok

  @typep pipe_result_code :: :ok | :error | :fatal

  @typep pipe_tuple_result :: {code :: pipe_result_code(), result_or_reason :: any()}

  @version Mix.Project.config()[:version]

  @doc false
  def version, do: @version

  @typedoc "Base struct"
  @type t :: %__MODULE__{
          context: context :: keyword(),
          result: result :: result(),
          pipelines: pipelines :: [Hafnium.Pipeline.t()],
          traces: traces :: [Hafnium.Trace.t()],
          time: now :: integer(),
          input: input(),
          option: temp_input :: any(),
          __module__: current_module :: module()
        }

  @enforce_keys [:__module__, :pipelines]
  defstruct context: [],
            result: {:ok, nil},
            pipelines: [],
            traces: [],
            time: nil,
            input: %{},
            option: nil,
            __module__: nil

  @callback before_invoke(o :: t()) :: pipe_result()
  @callback after_invoke(o :: t()) :: pipe_result()
  @optional_callbacks before_invoke: 1, after_invoke: 1

  defmacro __using__(_opts) do
    quote do
      @behaviour unquote(__MODULE__)
      Module.register_attribute(__MODULE__, :pipelines, accumulate: true)
      @before_compile unquote(__MODULE__)
    end
  end

  defmacro __before_compile__(_env) do
    quote location: :keep, generated: true do
      @meta struct(unquote(__MODULE__), %{__module__: __MODULE__, pipelines: @pipelines})

      @spec __meta__() :: unquote(__MODULE__).t()
      def __meta__, do: @meta
    end
  end

  defmacro pipeline(_opt) do
    quote do
    end
  end
end