squid

defmodule SquidWeb.Router do
  @moduledoc """
  Router helper to forward request to tentacle.

  ## Configurations

      # tentacle/config/config.exs

      config :squid,
        scopes:
          admin:
            prefix: "/admin"
          prefixed_tentacle:
            prefix: "/{{tentacle_name}}/api"

  `{{tentacle_name}}` is a reserved keyword that will be replace with your
  tentacle name (also know as the otp app). The app's name will be formated
  to kebab case.

  Using the previous example, an app `my_app` with a `prefixed_tentacle`
  squid's scope  will generate a phoenix scope prefiexed by `/my-app/api`.

  You could also add specified configuration by env

      # tentacles/config/prod.exs
      config :squid,
        scopes:
          dev:
            disable: true

  ## Examples

      defmodule MyTentacleWeb.Router do
        use SquidWeb.Router, otp_app: :my_tentacle

        squid_scope "/resources" do
          get "/action", MyTentacleWeb.MyResourceController, :index
        end

        squid_scope "/resources", as: :admin do
          get "/action", MyTentacleWeb.MyResourceAdminController, :index
        end

        squid_scope "/resources/dev", as: :dev do
          get "/action", MyTentacleWeb.MyResourceController, :debug
        end
      end

  With the configuration define in the previous chapter, this will generate
  followings path:

  - `/resources/action`
  - `/admin/resources/action`
  - `/resources/dev/action`

  Those path could be generate by your router's helper (as phoenix does)

      iex> MyTentacleWeb.Router.Helpers.custom_path(conn, :index)
      "/resources/action"

      iex> MyTentacleWeb.Router.Helpers.admin_custom_path(conn, :index)
      "/admin/resources/action"

  """

  @type tentacle_app :: atom()
  @type ast() :: any()

  @spec create_dynamic_router([tentacle_app()]) :: ast()
  def create_dynamic_router(tentacles) do
    quote do
      use Phoenix.Router

      import Plug.Conn
      import Phoenix.Controller
      import Phoenix.LiveView.Router

      unquote(squid_pipelines(tentacles))
      unquote(squid_scopes(tentacles))
    end
    |> tap(fn _ -> Code.compiler_options(ignore_module_conflict: true) end)
    |> then(&Module.create(SquidWeb.HeadRouter, &1, Macro.Env.location(__ENV__)))
    |> tap(fn _ -> Code.compiler_options(ignore_module_conflict: false) end)
  end

  defp squid_scopes(tentacles) do
    scopes = Application.get_env(:squid, :scopes)

    SquidWeb.registered_routers()
    |> Enum.filter(fn {tentacle, _} -> tentacle in tentacles end)
    |> Enum.flat_map(fn {tentacle, router} ->
      [otp_app] = router.__info__(:attributes)[:otp_app]

      if tentacle != otp_app do
        raise "Squid: tentacle #{tentacle} have router #{router} with invalid otp_app registered (#{otp_app})"
      end

      router.squid_scopes()
      |> Enum.map(fn {scope, block} -> {tentacle, scope, block} end)
    end)
    |> Enum.reject(fn {_tentacle, scope, _} -> scopes[scope][:disable] end)
    |> Enum.map(fn {tentacle, scope, do_block} ->
      prefix = build_tentacle_prefix(tentacle, scopes[scope][:prefix])

      quote do
        scope unquote(prefix), as: unquote(tentacle) do
          unquote(do_block)
        end
      end
    end)
  end

  defp squid_pipelines(tentacles) do
    SquidWeb.registered_routers()
    |> Enum.filter(fn {tentacle, _} -> tentacle in tentacles end)
    |> Enum.flat_map(fn {_tentacle, router} -> router.squid_pipelines() end)
  end

  @doc """
  Helper to create a tentacle router.

  ## Example

      use SquidWeb.Router, otp_app: :my_tentacle

      squid_scope "/my-tentacle-prefix" do
        get "/page", MyTentacleWeb.PageController, :index
      end

  > See `squid_scope/3` for more informations.

  """
  defmacro __using__(opts) do
    otp_app =
      opts[:otp_app] || raise ":otp_app option is required by squid router (#{__CALLER__.module})"

    Module.register_attribute(__CALLER__.module, :squid_scopes, accumulate: true)
    Module.register_attribute(__CALLER__.module, :squid_pipelines, accumulate: true)
    Module.register_attribute(__CALLER__.module, :otp_app, persist: true)
    Module.put_attribute(__CALLER__.module, :otp_app, otp_app)

    quote do
      use Phoenix.Router
      import SquidWeb.Router

      import Plug.Conn
      import Phoenix.Controller
      import Phoenix.LiveView.Router

      @before_compile SquidWeb.Router
    end
  end

  defmacro __before_compile__(_env) do
    quote do
      def squid_scopes, do: @squid_scopes
      def squid_pipelines, do: @squid_pipelines
    end
  end

  @doc """
  Helper to create a tentacle router.

  ## Examples

      use SquidWeb.Router, otp_app: :my_tentacle

      squid_scope "/my-tentacle-prefix" do
        get "/page", MyTentacleWeb.PageController, :index
      end

  This will register following helpers:

  - `SquidWeb.HeadRouter.Helpers.tentacle_app_page_path/2` and
  - `MyTentacleWeb.Router.Helpers.page_path/2`

  You could also create routes under a scope such as `admin`.

      squid_scope "/my-tentacle-prefix", scope: :admin do
        get "/users", MyTentacleWeb.UserController, :index
      end

  ## Options

  - `scope` define the scope of the router such as `api`, `web`, `admin`. (default: `:default`)

  """
  defmacro squid_scope(path, opts \\ [], do_block) do
    scopes = Application.get_env(:squid, :scopes)
    curr_scope = Keyword.get(opts, :as, :default)

    otp_app = Module.get_attribute(__CALLER__.module, :otp_app)
    prefix = build_tentacle_prefix(otp_app, scopes[curr_scope][:prefix])

    do_squid_internal_scope(path, opts, do_block)
    |> Macro.prewalk(&expand_alias(&1, __CALLER__))
    |> tap(&Module.put_attribute(__CALLER__.module, :squid_scopes, {curr_scope, &1}))
    |> then(&quote(do: scope(unquote(prefix), do: unquote(&1))))
  end

  @doc """
  Helper to create a tentacle pipeline.

  ## Examples

      use SquidWeb.Router, otp_app: :my_tentacle

      squid_scope "/my-tentacle" do
        pipe_through :my_tentacle_api

        # your actions, phoenix scopes ...
      end

      squid_pipeline :my_tentacle_api do
        plug :your_function
      end

      def your_function(conn, _opts) do
        # Do what ever you want

        conn
      end

  ## Limitations

  Currently we don't fully support plug pipe_through. If you want to
  pipe_through a function, you should write an explicit function name
  as you can see in the next example. Otherwise, if multiples tentacles
  router defined the same function name, you'll have a compiled error.


      use SquidWeb.Router, otp_app: :my_tentacle

      squid_scope "/my-tentacle" do
        scope "/" do
          pipe_through :my_tentacle_function_name
          # your actions, phoenix scopes ...
        end

        def my_tentacle_function_name(conn, _opts) do
          # Do what ever you want
          conn
        end
      end

  """
  defmacro squid_pipeline(plug, do: block) do
    caller_module = __CALLER__.module

    quote do
      Phoenix.Router.pipeline unquote(plug) do
        import unquote(caller_module)
        unquote(block)
      end
    end
    |> then(&Module.put_attribute(__CALLER__.module, :squid_pipelines, &1))

    quote do
      Phoenix.Router.pipeline(unquote(plug), do: unquote(block))
    end
  end

  defp expand_alias({:__aliases__, _, _} = alias, env),
    do: Macro.expand(alias, %{env | function: {:init, 1}})

  defp expand_alias(other, _env), do: other

  defp do_squid_internal_scope(path, opts, do_block) do
    quote do
      scope unquote(path), unquote(Macro.escape(opts)) do
        unquote(do_block)
      end
    end
  end

  defp build_tentacle_prefix(_tentacle, nil = _prefix), do: "/"

  defp build_tentacle_prefix(tentacle, prefix) do
    tentacle_name = String.replace("#{tentacle}", "_", "-")
    String.replace(prefix, "{{tentacle_name}}", tentacle_name)
  end
end