neiam /gitgud

defmodule GitGudWeb.Plugs.ApDispatcher do
  @moduledoc """
  Pipeline plug that diverts AP-shaped requests to the
  `GitGudWeb.ApActorController` before the browser router can flip the
  conn into a LiveView.

  Recognised paths:

      GET /orgs/:handle             → org actor
      GET /r/:owner/:name           → repo actor
      GET /@:handle                 → user actor

  Plus the per-actor collections:

      GET /<actor>/outbox|followers|following
      POST /<actor>/inbox

  Only fires when the Accept header asks for AP JSON. For browsers,
  this is a no-op and the LiveView renders the HTML page.
  """

  @behaviour Plug

  import Plug.Conn

  alias GitGudWeb.ApActorController
  alias GitGudWeb.Plugs.ApContentNegotiation

  @impl true
  def init(opts), do: opts

  @impl true
  def call(conn, _opts) do
    cond do
      not ApContentNegotiation.ap_requested?(conn) ->
        conn

      conn.method == "GET" ->
        dispatch_get(conn)

      conn.method == "POST" ->
        dispatch_post(conn)

      true ->
        conn
    end
  end

  # ── GET dispatch ────────────────────────────────────────────────────

  defp dispatch_get(%Plug.Conn{path_info: ["@" <> handle]} = conn),
    do: call_action(conn, :user, %{"handle" => handle})

  defp dispatch_get(%Plug.Conn{path_info: ["@" <> _handle, collection]} = conn)
       when collection in ~w(outbox followers following inbox) do
    call_collection(conn, collection)
  end

  defp dispatch_get(%Plug.Conn{path_info: ["orgs", handle]} = conn),
    do: call_action(conn, :org, %{"handle" => handle})

  defp dispatch_get(%Plug.Conn{path_info: ["orgs", _handle, collection]} = conn)
       when collection in ~w(outbox followers following inbox),
       do: call_collection(conn, collection)

  defp dispatch_get(%Plug.Conn{path_info: ["orgs", handle, "repositories"]} = conn),
    do: call_action(conn, :repositories, %{"handle" => handle})

  defp dispatch_get(%Plug.Conn{path_info: ["r", owner, name]} = conn),
    do: call_action(conn, :repo, %{"owner" => owner, "name" => name})

  defp dispatch_get(%Plug.Conn{path_info: ["r", _owner, _name, collection]} = conn)
       when collection in ~w(outbox followers following inbox),
       do: call_collection(conn, collection)

  defp dispatch_get(conn), do: conn

  # ── POST dispatch ───────────────────────────────────────────────────
  #
  # Inbox writes are routed here so other controllers don't need to
  # know about them.

  defp dispatch_post(%Plug.Conn{path_info: path_info} = conn) do
    if List.last(path_info) == "inbox" do
      call_action(conn, :inbox, %{})
    else
      conn
    end
  end

  defp dispatch_post(conn), do: conn

  # ── invocation ──────────────────────────────────────────────────────

  defp call_action(conn, action, params) do
    conn
    |> Phoenix.Controller.put_view(ApActorController)
    |> Phoenix.Controller.put_format(:json)
    |> then(&apply(ApActorController, action, [&1, Map.merge(&1.params, params)]))
    |> halt()
  end

  defp call_collection(conn, "inbox"), do: call_action(conn, :inbox, %{})
  defp call_collection(conn, "outbox"), do: call_action(conn, :outbox, %{})
  defp call_collection(conn, "followers"), do: call_action(conn, :followers, %{})
  defp call_collection(conn, "following"), do: call_action(conn, :following, %{})
end