defmodule SNet.Manager do
  @moduledoc"""
  Maintains a table `:connections` of currently connected peers, which is a list of:

      { peer_info, pid, nil | %SNet.Auth{my_pk: my_pk, his_pk: his_pk} }
  """

  use GenServer

  require Logger

  def start_link(_) do
    GenServer.start_link(__MODULE__, nil, name: __MODULE__)
  end

  def init(_) do
    Process.flag(:trap_exit, true)

    :ets.new(:connections, [:bag, :protected, :named_table])

    {:ok, nil} 
  end

  def handle_call({:add_peer, peer_info, auth, callback}, _from, state) do
    pid = add_peer_internal(peer_info, auth)
    if callback != nil do
      GenServer.cast(pid, {:callback, callback})
    end
    {:reply, pid, state}
  end

  def handle_call({:accept, client}, _from, state) do
    my_port = Application.get_env(:shard, :port)
    {:ok, pid} = SNet.TCPConn.start_link(%{socket: client, my_port: my_port})
    {:reply, pid, state}
  end

  def handle_call({:peer_up, pid, peer_info, auth}, _from, state) do
    case :ets.match(:connections,  {peer_info, :'$1', (if auth != nil do auth else :_ end), :_}) do
      [[pid2]|_] when pid2 != pid ->
        {:reply, :redundant, state}
      _ ->
        :ets.match_delete(:connections, {peer_info, pid, :_, :_})
        :ets.insert(:connections, {peer_info, pid, auth, :established})

        if auth != nil do
          for [pid3] <- :ets.match(:connections, {peer_info, :'$1', nil, :_}) do
            GenServer.cast(pid3, :close)
          end
        end

        # Send interested message for all our shards
        id_list = (for {id, _, _} <- Shard.Manager.list_shards(), do: id)
        GenServer.cast(pid, {:send_msg, {:interested, id_list}})

        {:reply, :ok, state}
    end
  end

  def handle_cast({:connect_and_send, peer_info, auth, msg}, state) do
    pid = add_peer_internal(peer_info, auth)
    GenServer.cast(pid, {:send_msg, msg})
    {:noreply, state}
  end

  def handle_info({:EXIT, pid, _reason}, state) do
    :ets.match_delete(:connections, {:_, pid, :_, :_})
    {:noreply, state}
  end

  defp add_peer_internal(peer_info, auth) do
    if SNet.Addr.is_local? peer_info do
      nil
    else
      case :ets.match(:connections, {peer_info, :'$1', (if auth != nil do auth else :_ end), :_}) do
        [[pid]|_] -> pid
        [] -> 
          my_port = Application.get_env(:shard, :port)
          {:ok, pid} = SNet.TCPConn.start_link(%{connect_to: peer_info, my_port: my_port, auth: auth})
          :ets.insert(:connections, {peer_info, pid, auth, :establishing})
          pid
      end
    end
  end

  # =========
  # INTERFACE
  # =========

  @doc"""
  Connect to a peer specified by ip address and port

      peer_info := {:inet, ip, port}
  """
  def add_peer(peer_info, opts \\ []) do
    GenServer.call(__MODULE__, {:add_peer, peer_info, opts[:auth], opts[:callback]})
  end

  @doc"""
  Return the list of all connected peers
  """
  def list_connections() do
    :ets.tab2list(:connections)
  end

  @doc"""
  Return the list of connections to a given peer, possibly with different auth
  """
  def get_connections_to(peer_info) do
    for {^peer_info, pid, auth, _} <- :ets.lookup(:connections, peer_info), do: {pid, auth}
  end

  @doc"""
  Return the list of connections to a given peer that match a given auth spec
  """
  def get_auth_connections_to(peer_info, my_auth, his_auth) do
    for {^peer_info, pid, %SNet.Auth{my_pk: my_pk, his_pk: his_pk}, _} <- :ets.lookup(:connections, peer_info),
      my_pk == my_auth or my_pk in my_auth,
      his_pk == his_auth or his_pk in his_auth,
    do: pid
  end

  @doc"""
  Send message to a peer specified by peer info.
  Opens a connection if necessary.
  """
  def send(peer_info, msg) do
    case :ets.lookup(:connections, peer_info) do
      [{^peer_info, pid, _auth, _}|_] ->
        GenServer.cast(pid, {:send_msg, msg})
      [] ->
        GenServer.cast(__MODULE__, {:connect_and_send, peer_info, nil, msg})
    end
  end

  @doc"""
  Send message to a peer specified by peer info over authenticated channel.
  `auth` is a `SNet.Auth` struct describing the required authentication.
  Opens a connection if necessary.
  """
  def send_auth(peer_info, auth, msg) do
    case :ets.match(:connections, {peer_info, :'$1', auth, :_}) do
      [[pid]|_] ->
        GenServer.cast(pid, {:send_msg, msg})
      [] ->
        GenServer.cast(__MODULE__, {:connect_and_send, peer_info, auth, msg})
    end
  end

  @doc"""
  Send message to a peer specified by peer id
  """
  def send_pid(pid, msg) do
    GenServer.cast(pid, {:send_msg, msg})
  end
end