defmodule Pointers.Pointer do
  @moduledoc """
  A Pointer is a kind of global foreign key that can point to any of
  the tables participating in the abstraction.
  """

  use Ecto.Schema
  alias Ecto.Changeset
  alias Pointers.Config
  alias Pointers.Pointer
  alias Pointers.Table
  alias Pointers.Tables

  @primary_key {:id, Pointers.ULID, autogenerate: false}
  @foreign_key_type Pointers.ULID
  schema(Config.pointer_table()) do
    belongs_to :table, Table
    field :pointed, :any, virtual: true
  end

  def create(id \\ Ecto.ULID.generate(), table) do
    table_id = Tables.id!(table)
    Changeset.cast(%Pointer{}, %{id: id, table_id: table_id}, [:id, :table_id])
  end

  def repoint(%Pointer{}=pointer, table) do
    table_id = Tables.id!(table)
    Changeset.cast(pointer, %{table_id: table_id}, [:table_id])
  end

end