defmodule Ami.UnitLesson do
  use Ecto.Schema

  import Ecto.{
    Query,
    Changeset
  }

  alias Ami.{
    Repo,
    Unit,
    Lesson
  }

  schema "unit_lessons" do
    field(:position, :integer)

    belongs_to(:unit, Unit)
    belongs_to(:lesson, Lesson)
  end

  def changeset(struct, params \\ %{}) do
    struct
    |> cast(params, [:unit_id, :lesson_id, :position])
    |> set_position
  end

  defp set_position(%Ecto.Changeset{params: %{"unit_id" => ""}} = changeset) do
    changeset
  end
  defp set_position(%Ecto.Changeset{params: %{}} = changeset) do
    changeset
  end
  defp set_position(changeset) do
    unit_id = changeset.params["unit_id"]
    last_unit_lesson =
      from(ul in __MODULE__,where: ul.unit_id == ^unit_id)
      |> last(:position)
      |> Repo.one()
    if last_unit_lesson do
      put_change(changeset, :position, last_unit_lesson.position + 1)
    else
      put_change(changeset, :position, 0)
    end
  end

  def update_position(unit_lesson_id, position) do
    Repo.get(__MODULE__, unit_lesson_id)
    |> change(%{position: position})
    |> Repo.update()
  end

end