defmodule Frontier do
  @moduledoc """
  Smart boundary enforcement for Elixir projects.

  Frontier enforces architectural boundaries using convention-based defaults.
  Context roots are public, schemas are auto-exported, and internal modules are private.
  You only configure exceptions.

  ## Usage

      # Project root — global config
      defmodule MyApp do
        use Frontier,
          globals: [Result, Mailer],
          ignore: [SomeLegacyThing]
      end

      # Context root — zero config
      defmodule MyApp.Accounts do
        use Frontier
      end

      # Context root — with restrictions
      defmodule MyApp.Billing do
        use Frontier,
          reaches: [MyApp.Accounts],
          externals: [:stripe],
          exports: [InvoiceGenerator]
      end
  """

  defmacro __using__(opts) do
    # Expand aliases at compile time so we store fully qualified module names.
    # We do this in a clean env to avoid creating compile-time dependencies.
    expanded_opts =
      opts
      |> Macro.prewalk(fn term ->
        with {:__aliases__, _, _} <- term do
          Macro.expand(term, %{__CALLER__ | function: {:frontier, 1}, lexical_tracker: nil})
        end
      end)

    quote bind_quoted: [opts: expanded_opts] do
      @after_compile {Frontier, :__after_compile__}
      Module.put_attribute(__MODULE__, :frontier_opts, opts)
    end
  end

  def __after_compile__(%{module: module}, _bytecode) do
    Frontier.Config.init()
    opts = Module.get_attribute(module, :frontier_opts) || []

    case Frontier.Definition.parse_opts(module, opts) do
      {:root, config} ->
        Frontier.Config.register_root(module, config)

        for ignored_module <- config.ignore do
          Frontier.Config.register_ignored(ignored_module)
        end

      {:context, config} ->
        Frontier.Config.register_context(module, config)

      {:ignored, mod} ->
        Frontier.Config.register_ignored(mod)

      {:reclassified, target} ->
        Frontier.Config.register_reclassified(module, target)
    end
  end
end