defmodule Frajtano.BackingAgent do
  alias Frajtano.Proto
  require Logger
  use GenServer, restart: :temporary

  defmodule Spawner do
    use Supervisor, restart: :permanent

    def start_link(spec) do
      Supervisor.start_link(__MODULE__, spec, [])
    end

    @impl true
    def init({executable, args}) do
      Temp.track!()
      path = Path.join(Temp.mkdir!(), "agent.sock")

      children = [
        Supervisor.child_spec({MuonTrap.Daemon, [executable, args ++ [path]]}, restart: :temporary, significant: true),
        Supervisor.child_spec({Frajtano.BackingAgent, {path, :spawned, {executable, args}}}, restart: :permanent)
      ]

      Supervisor.init(children, strategy: :one_for_all, auto_shutdown: :any_significant)
    end
  end

  def start({:socket, path}) do
    DynamicSupervisor.start_child(Frajtano.BackingAgentSupervisor, {__MODULE__, {path}})
  end

  def start({:spawn, spec}) do
    Logger.info("Spawning #{inspect spec}")
    DynamicSupervisor.start_child(Frajtano.BackingAgentSupervisor, {Spawner, spec})
  end

  def start_link({path}) do
    GenServer.start_link(__MODULE__, {path}, name: {:via, Registry, {Frajtano.BackingAgents, path}})
  end
  def start_link({_, _, _} = spec) do
    GenServer.start_link(__MODULE__, spec, name: {:via, Registry, {Frajtano.BackingAgents, spec}})
  end

  @impl true
  def init({path}) do
    {:ok, conn} = :gen_tcp.connect({:local, path}, 0, [:binary, active: :once])
    {:ok, %{conn: conn, clients: :queue.new(), buffer: <<>>}}
  end

  @impl true
  def init({path, :spawned, spec}) do
    if File.exists?(path) do
      {:ok, conn} = :gen_tcp.connect({:local, path}, 0, [:binary, active: :once])
      Logger.info("Connected to #{inspect spec}")
      {:ok, %{conn: conn, clients: :queue.new(), buffer: <<>>}}
    else
      Process.sleep(100)
      init({path, :spawned, spec})
    end
  end

  def reply({client, ref}, msg) do
    send(client, {ref, msg})
  end

  defp handle_messages(%{clients: clients, buffer: buffer} = state) do
    case Proto.decode(buffer) do
      {nil, buffer} ->
        {:noreply, %{state | buffer: buffer}}

      {msg, buffer} ->
        {{:value, client}, clients} = :queue.out(clients)
        reply(client, {:ok, msg})
        handle_messages(%{state | clients: clients, buffer: buffer})
    end
  end

  @impl true
  def handle_info({:send, packet, from}, %{conn: conn, clients: clients} = state) do
    case :gen_tcp.send(conn, Proto.encode(packet)) do
      :ok ->
        {:noreply, %{state | clients: :queue.in(from, clients)}}

      {:error, e} ->
        {:noreply, state, {:continue, {:error, e}}}
    end
  end

  @impl true
  def handle_info({:tcp, conn, msg}, %{conn: conn, buffer: buffer} = state) do
    :inet.setopts(conn, active: :once)
    buffer = buffer <> msg

    handle_messages(%{state | buffer: buffer})
  end

  @impl true
  def handle_info({:tcp_closed, _}, state) do
    {:noreply, state, {:continue, {:error, :closed}}}
  end

  @impl true
  def handle_info(:timeout, state) do
    {:noreply, state, {:continue, {:error, :closed}}}
  end

  @impl true
  def handle_continue({:error, e}, %{clients: clients}) do
    clients
    |> :queue.to_list()
    |> Enum.each(&reply(&1, {:error, e}))

    {:stop, {:error, e}, %{}}
  end

  def identities(backing_agent) do
    ref = make_ref()
    send(backing_agent, {:send, {:agentc_request_identities, nil}, {self(), ref}})
    # Needs to be less than the timeout in Frajtano.Agent.identities on the Task.async_stream call
    # That's 5000 by default
    timer = Process.send_after(backing_agent, :timeout, 4500)

    receive do
      {^ref, msg} ->
        Process.cancel_timer(timer)
        msg
    end
    |> case do
      {:ok, {:agent_identities_answer, identities}} -> {:ok, identities}
      {:ok, {:agent_failure, nil}} -> {:error, :agent_failure}
      {:ok, msg} -> raise("Unexpected message #{inspect(msg)}")
      {:error, e} -> {:error, e}
    end
  end

  def sign(backing_agent, request) do
    # Signing may take some time, as a password may need to be entered or similar
    # There is therefore no timeout
    # If something requests identities afterwards, it will timeout, which also kills this signature request
    # The SSH agent protocol strict ordering leaves fun problems with timeouts, as it turns out
    ref = make_ref()
    send(backing_agent, {:send, {:agentc_sign_request, request}, {self(), ref}})

    receive do
      {^ref, msg} -> msg
    end
    |> case do
      {:ok, {:agent_sign_response, signature}} -> {:ok, signature}
      {:ok, {:agent_failure, nil}} -> {:error, :agent_failure}
      {:ok, msg} -> raise("Unexpected message #{inspect(msg)}")
      {:error, e} -> {:error, e}
    end
  end
end