defmodule MessageServer.MessageHandler do
  require Logger

  alias MessageServer.{
    MessageRequest,
    RemoteClient,
    ServerRegistry,
    Storage
  }

  @spec handle_message(MessageRequest.t()) :: :ok | {:error, String.t()}
  def handle_message(%MessageRequest{from: from, to: to, message: message}) do
    with {:ok, from_server} <- extract_server_id(from),
         {:ok, to_server} <- extract_server_id(to),
         :ok <- validate_sender_ownership(from_server),
         :ok <- route_message(to_server, from, to, message) do
      Logger.info("Message routed successfully from #{from} to #{to}")
      :ok
    else
      {:error, reason} = error ->
        Logger.warning("Message routing failed: #{reason}")
        error
    end
  end

  @spec extract_server_id(String.t()) :: {:ok, String.t()} | {:error, String.t()}
  defp extract_server_id(user_id) do
    case String.split(user_id, "-", parts: 2) do
      [server_id, _user_part] -> {:ok, server_id}
      _ -> {:error, "Invalid user ID format: #{user_id}"}
    end
  end

  @spec validate_sender_ownership(String.t()) :: :ok | {:error, String.t()}
  defp validate_sender_ownership(sender_server) do
    local_server = ServerRegistry.get_server_id()

    if sender_server == local_server do
      :ok
    else
      {:error, "Cannot send messages on behalf of users from other servers"}
    end
  end

  @spec route_message(String.t(), String.t(), String.t(), String.t()) ::
          :ok | {:error, String.t()}
  defp route_message(to_server, from, to, message) do
    local_server = ServerRegistry.get_server_id()

    if to_server == local_server do
      handle_local_message(from, to, message)
    else
      handle_remote_message(to_server, from, to, message)
    end
  end

  @spec handle_local_message(String.t(), String.t(), String.t()) :: :ok | {:error, String.t()}
  defp handle_local_message(from, to, message) do
    Storage.append_message(to, from, message)
  end

  @spec handle_remote_message(String.t(), String.t(), String.t(), String.t()) ::
          :ok | {:error, String.t()}
  defp handle_remote_message(to_server, from, to, message) do
    payload = %MessageRequest{from: from, to: to, message: message}
    RemoteClient.send_message_to_server(to_server, payload)
  end
end