pointers

defmodule Pointers.Util do
  @moduledoc false

  @bad_source "You must provide a binary :source option."
  @bad_otp_app "You must provide a valid atom :otp_app option."

  # maps a tuple flip over a list
  def flip(list) when is_list(list),
    do: Enum.map(list, fn {k, v} -> {v, k} end)

  def add_binaries(list) when is_list(list) do
    Enum.flat_map(list, fn {k, v} when is_atom(k) and is_atom(v) ->
      [{k, v}, {Atom.to_string(k), Atom.to_string(v)}]
    end)
  end

  # renames keys in a map or keyword list
  def rename(map, changes) when is_map(map) do
    Enum.reduce(changes, map, fn {k, l}, map ->
      case map do
        %{^k => v} -> Map.put(Map.delete(map, k), l, v)
        _ -> map
      end
    end)
  end

  def rename(kw, changes) when is_list(kw) do
    Enum.reduce(changes, kw, fn {k, l}, kw ->
      case Keyword.fetch(kw, k) do
        {:ok, v} -> [{l, v} | Keyword.delete(kw, k)]
        _ -> kw
      end
    end)
  end

  # option processing
  def get_source(opts), do: check_source(Keyword.get(opts, :source))

  defp check_source(x) when is_binary(x), do: x
  defp check_source(_), do: raise ArgumentError, message: @bad_source

  def get_otp_app(opts), do: check_otp_app(Keyword.get(opts, :otp_app))

  defp check_otp_app(x) when is_atom(x), do: x
  defp check_otp_app(_), do: raise ArgumentError, message: @bad_otp_app

  # expands to putting the attribute if it does not already exist
  def put_new_attribute(module, attribute, value) do
    if not Module.has_attribute?(module, attribute) do
      quote do
        Module.put_attribute(unquote(module), unquote(attribute), unquote(value))
      end
    end
  end

  # defaults the foreign key type to ULID
  def schema_foreign_key_type(module),
    do: put_new_attribute(module, :foreign_key_type, Pointers.ULID)

  def pointers_clause(arg, value) do
    quote do
      def __pointers__(unquote(arg)), do: unquote(value)
    end
  end

end