macro.ex

defmodule Post do
  defstruct [:id, :title, :body]
end

defmodule Exseed do
  defmacro seed(model, do: block) do
    quote do
      var!(attributes, Exseed) = %{}

      unquote(Macro.postwalk(block, &postwalk(&1, model)))

      struct(unquote(model), var!(attributes, Exseed))
    end
  end

  defmacro attr(attribute, value) do
    quote do
      var!(attributes, Exseed) = Dict.put(var!(attributes, Exseed), unquote(attribute), unquote(value))
    end
  end

  def postwalk({attribute, _meta, [value]} = ast, {_, _, [model]}) do
    attributes = struct(Module.concat([model]), %{}) |> Map.keys |> Enum.reject(fn key -> key in [:__meta__, :__struct__] end)

    if attribute in attributes do
      quote do
        attr(unquote(attribute), unquote(value))
      end
    else
      ast
    end
  end

  def postwalk(ast, _model) do
    ast
  end
end

defmodule ExseedTest do
  import Exseed

  def test do
    attributes = "hello"

    seed Post do
      id 1

      title "LOL"

      body_1 = "RO"

      body_2 = "FL"

      body body_1 <> body_2

      IO.puts "1234"
    end |> IO.inspect

    IO.inspect attributes
  end
end

ExseedTest.test