defmodule Dialup.Layout do
  @moduledoc """
  The behaviour and macro for Dialup layout modules.

  A layout wraps one or more pages with shared chrome (navigation, footer, etc.).
  Layouts are discovered automatically based on the directory hierarchy:

      app/
      ├── layout.ex          # wraps all pages under app/
      └── blog/
          ├── layout.ex      # wraps all pages under app/blog/ (nested)
          └── [slug]/
              └── page.ex

  ## Usage

      defmodule MyApp.App.Layout do
        use Dialup.Layout

        # Called once when the WebSocket connection is established.
        # Use it to set session-scoped data (e.g. the current user).
        def mount(session) do
          user = Repo.get(User, session[:user_id])
          {:ok, Map.put(session, :current_user, user)}
        end

        def render(assigns) do
          ~H\"\"\"
          <nav>{@current_user.name}</nav>
          <main>{raw(@inner_content)}</main>
          \"\"\"
        end
      end

  ## Callbacks

  - `mount/1` — optional; called once when the WebSocket connection is established.
    Receives the current session map (empty `%{}` for the root layout, or whatever the
    parent layout returned). Return `{:ok, new_session}`.
  - `render/1` — renders the layout HTML using HEEx. Use `{raw(@inner_content)}` to
    inject the child content.

  ## Colocation CSS

  Place a `layout.css` file in the same directory as `layout.ex`. The styles are
  automatically scoped and applied to all pages under that directory at compile time.

  ## Nesting

  Layout `mount/1` calls are chained from outermost to innermost. Each layout receives
  the session returned by its parent and may enrich it further.

  ## Navigation actions

  A layout may declare navigation links with `<.dialup_action navigate="/path">`, exactly like a
  page. These render the shared chrome links for humans and are merged into the MCP tool catalog of
  every page wrapped by the layout, so an attached agent gets the same site-wide navigation a human
  sees in the nav bar. Layouts support navigation actions only; event-handling actions
  (`<.dialup_action>` with `desc`/`params`) belong on a page that implements `handle_event/3`.
  """

  @callback render(assigns :: map()) :: Phoenix.LiveView.Rendered.t()

  # session :: 親レイアウトが設定したsession（rootレイアウトは %{} を受け取る）
  @callback mount(session :: map()) :: {:ok, map()}

  @optional_callbacks mount: 1

  defmacro __using__(_opts) do
    quote do
      @behaviour Dialup.Layout

      import Phoenix.Component
      import Phoenix.HTML, only: [raw: 1]

      import Dialup.Page,
        only: [overwrite: 2, set_default: 2, declare_action: 1, dialup_action: 1]

      Module.register_attribute(__MODULE__, :dialup_actions, accumulate: true)

      # デフォルト実装：何もしない（mountを定義しないlayoutはsessionに何も追加しない）
      def mount(session), do: {:ok, session}
      defoverridable mount: 1

      @before_compile Dialup.Layout
    end
  end

  defmacro __before_compile__(env) do
    template_path = env.file |> Path.rootname(".ex") |> Kernel.<>(".html.heex")
    has_render = Module.defines?(env.module, {:render, 1})
    has_template = File.exists?(template_path)

    render_quote =
      cond do
        has_render ->
          quote do
          end

        has_template ->
          source = File.read!(template_path)

          compiled =
            EEx.compile_string(source,
              engine: Phoenix.LiveView.TagEngine,
              line: 1,
              file: template_path,
              caller: __CALLER__,
              source: source,
              tag_handler: Phoenix.LiveView.HTMLEngine
            )

          quote do
            @external_resource unquote(template_path)

            def render(assigns) do
              _ = assigns
              unquote(compiled)
            end
          end

        true ->
          raise CompileError,
            file: env.file,
            line: env.line,
            description:
              "#{inspect(env.module)} must define render/1 or provide #{Path.basename(template_path)}"
      end

    css_path = env.file |> Path.rootname(".ex") |> Kernel.<>(".css")

    css_quote =
      if File.exists?(css_path) do
        css_content = File.read!(css_path)

        scope_class =
          "d-" <>
            (env.module
             |> Atom.to_string()
             |> :erlang.md5()
             |> Base.encode16(case: :lower)
             |> binary_part(0, 7))

        scoped_css = ".#{scope_class} {\n#{css_content}\n}"

        quote do
          @external_resource unquote(css_path)
          def __css__, do: unquote(scoped_css)
          def __css_scope__, do: unquote(scope_class)
        end
      else
        quote do
          def __css__, do: nil
          def __css_scope__, do: nil
        end
      end

    actions = Dialup.Page.actions_from_env(env)
    Dialup.Page.validate_navigation_actions!(env, actions)

    quote do
      unquote(render_quote)
      unquote(css_quote)
      def __dialup_actions__, do: unquote(Macro.escape(actions))
    end
  end
end