knit

defmodule Knit.Model do
  @moduledoc """

  Sets up schemas.

  """
  @callback schema() :: any

  defmacro __using__(_) do
    quote do
      @behaviour Knit.Model
      import Knit.Model, only: [schema: 1]
    end
  end

  @doc """

  Register a schema for the module.

  """
  defmacro schema(do: block) do
    quote do
      fields = unquote(block)
      struct_keys = Map.keys(fields)

      @doc """

      Returns the schema map.

      """
      def schema do
        unquote(block)
      end

      # Add a struct to the calling module.

      Module.eval_quoted __ENV__, [
        Knit.Model.__defstruct__(struct_keys)
      ]
    end
  end

  @doc false
  def __defstruct__(struct_keys) do
    quote do
      defstruct unquote(Macro.escape(struct_keys))
    end
  end
end