something-erlang/lib/something_erlang_web/controllers/page_controller.ex

defmodule SomethingErlangWeb.PageController do
  use SomethingErlangWeb, :controller

  def home(conn, params) do
    # The home page is often custom made,
    # so skip the default app layout.
    conn = assign(conn, :params, params)
    render(conn, :home)
  end

  def to_forum_path(conn, %{"forum_path" => path} = _params) do
    with {:ok, thread, page} <- resolve_url(path) do
      redirect(conn, to: ~p"/thread/#{thread}?page=#{page}")
    else
      _ ->
        put_flash(conn, :error, "Could not resolve URL")
        render(conn, :home)
    end
  end

  def to_forum_path(conn, _params) do
    render(conn, :home)
  end

  defp resolve_url(url) do
    threadid =
      case Regex.run(~r{threadid=(\d+)}, url) do
        [_, threadid] -> {:ok, threadid}
        nil -> {:error, :nothreadid}
      end

    page =
      case Regex.run(~r{pagenumber=(\d+)}, url) do
        [_, page] -> {:ok, page}
        nil -> {:ok, 1}
      end

    with {:ok, threadid} <- threadid,
         {:ok, page} <- page do
      {:ok, threadid, page}
    else
      _ ->
        {:error, :cantparseurl}
    end
  end
end