defmodule Irc.Client do
  @behaviour :gen_statem
  require Logger
  alias Irc.Parser.Line
  alias Irc.Connection
  require Irc.Parser.Numeric
  import Irc.Parser.Numeric

  @moduledoc """
  Fully-featured IRC Client.

  Events emanating from the client are sent to the owner PID, `t:message/0`, and commands can be sent using `command/3`. The response is asynchronous.

  If a command is sent when the client is disconnected, it will be postponed until the client is connected again.

  Known IRC users are cached into `Irc.Client.UserCache`. Depending on the connection capabilities, data returned by the cache may not be up-to-date, and can be retreived with `whois/2`.

  ## Extending

  Most of the commands and capabs are implemented in separate modules. Additional modules can be set in the start options. See `Irc.Client.Capabs`.
  """

  @commands [
    Irc.Client.Command.Join,
    Irc.Client.Command.Who,
    Irc.Client.Command.Names,
    Irc.Client.Command.Away,
    Irc.Client.Command.Chghost,
    Irc.Client.Command.Account,
  ]

  @internal {:next_event, :internal, nil}

  defstruct [:conn, :conn_mon, :module, :modstate, :args, :nick, :modes, :info, :error, :commands, :buffer]

  def callback_mode, do: [:state_enter]

  @type message :: {:irc_client, pid(), event}

  @type event :: event_connected | event_nick | event_modes | event_line | event_down
  | Irc.Client.Command.Join.t
  | Irc.Client.Command.Names.t
  | Irc.Client.Command.Who.t
  | Irc.Client.Command.Away.t
  | Irc.Client.Command.Chghost.t
  | Irc.Client.Command.AccountNotify.t

  @type event_connected :: {:connected, Connection.Info.t}
  @type event_nick :: {:nick, {prev_nick :: String.t, new_nick :: String.t}}
  @type event_modes :: {:modes, {changes :: String.t, prev :: list, modes :: list}}
  @type event_line :: {:line, line :: Irc.Parser.Line.t}
  @type event_down :: {:down, {Connection.error, delay :: integer}}


  @type start_opt :: Connection.start_opt
                  | {:module, module() | Irc.Client}
                  | {:commands, [module()]}
                  | {:conn_statem_opts, [:gen_statem.start_opt]}
  @type start_ret :: {:ok, pid} | {:error, Connection.error} | :gen_statem.start_ret

  @spec start(Connection.nick, Connection.host, [start_opt], [:gen_statem.start_opt]) :: start_ret
  def start(nick, host, opts \\ [], start_opts \\ []) do
    :gen_statem.start(__MODULE__, [nick, host, prepare_args(opts)], start_opts)
  end

  @spec start_link(Connection.nick, Connection.host, [start_opt], [:gen_statem.start_opt]) :: start_ret
  def start_link(nick, host, opts \\ [], start_opts \\ []) do
    :gen_statem.start_link(__MODULE__, [nick, host, prepare_args(opts)], start_opts)
  end

  def command(pid, command, args) do
    ref = make_ref()
    Process.send(pid, {:irc_command, command, ref, args})
    ref
  end

  @doc "Whois an user. Depending on the connection capabilities and cache contents, a `WHOIS` irc command may not be executed; unless `cached: false`."
  @type whois_opt :: {:cached, true | false}
  @spec whois(pid(), String.t, Keyword.t) :: Irc.User.t()
  def whois(pid, nick, opts \\ []) do
  end

  def call_command(pid, command, args, opts \\ []) do
    timeout = Keyword.get(opts, :timeout, 10_000)
    ref = command(pid, command, args)
    receive do
      {:irc_command, command, result} -> result
    after
      timeout -> {:error, :timeout}
    end
  end

  @doc false
  def init([args]) do
    with \
         commands <- init_commands(args),
         capabs <- Enum.uniq(commands.capabs ++ Keyword.get(args, :capabs, [])),
         args <- Keyword.put(args, :capabs, capabs),
         {:ok, conn} <- Connection.start(Keyword.get(args, :nick), Keyword.get(args, :host), args, Keyword.get(args, :conn_statem_opts, [])),
         conn_mon <- Process.monitor(conn)
    do
      Logger.info("Commands registered: #{inspect commands}")
      data = %__MODULE__{
        conn: conn, conn_mon: conn_mon,
        args: args,
        commands: commands
      }
      {:ok, :disconnected, data}
    else
      error -> {:stop, error}
    end
  end

  def handle_event(:enter, :connected, :disconnected, data) do
    Logger.debug "#{inspect data} disconnected: #{inspect data.error}"
    :keep_state_and_data
  end

  def handle_event(:info, msg = {:irc_conn_up, _, info}, :disconnected, data) do
    data = run_handler_event({:connected, info}, data)
    {:next_state, :connected, %__MODULE__{data | nick: info.nick, info: info, modes: info.modes, error: nil}}
  end

  #
  # --- Connected
  #

  def handle_event(:enter, _, :connected, data) do
    Logger.debug "#{inspect data} UP"
    :keep_state_and_data
  end

  def handle_event(:info, msg = {:irc_conn_nick, _, prev_nick, new_nick}, :connected, data) do
    data = run_handler_event({:nick, prev_nick, new_nick}, data)
    {:keep_state, %__MODULE__{data | nick: new_nick}}
  end

  def handle_event(:info, msg = {:irc_conn_modes, _, changes, prev, modes}, :connected, data) do
    data = run_handler_event({:modes, changes, prev, modes}, data)
    {:keep_state, %__MODULE__{data | modes: modes}}
  end

  def handle_event(:info, {:irc_conn_down, _, reason, delay}, :connected, data) do
    data = run_handler_event({:down, reason, delay}, data)
    {:next_state, :disconnected, %__MODULE__{data | error: reason}}
  end

  def handle_event(:info, {:irc_command, command, args}, :connected, data) do
    if module = get_in(data, [:commands, :user, command]) do
      {next, actions} = case module.handle_command(command, args, data.info) do
        {next, next_arg} -> {{next, next_arg}, []}
        {next, next_arg, actions} -> {{next, next_arg}, List.wrap(actions)}
        next when is_atom(next) -> {{next, nil}, []}
      end

      data = handle_actions(actions, data)

      case next do
        {:buffer, acc} -> {:next_state, {:buffer, module}, %__MODULE__{data | buffer: acc}}
      end
    else
      data = run_handler_event({:irc_command, command, {:error, :unsupported_command, command}}, data) # MEH?
      {:keep_state, data}
    end
  end

  # DOES NOT HANDLE ERROR (actions can just return data now)
  defp handle_actions([{:send, line} | rest], data) do
    case Connection.sendline(data.conn, line) do
      :ok -> handle_actions(rest, data)
      error -> {:next_state, :disconnected, %__MODULE__{data | error: error}}
    end
    data
  end
  defp handle_actions([{:event, event} | rest], data) do
    run_handler_event(event, data)
  end
  defp handle_actions([], data), do: data

  # TODO: REMOVE?
  def handle_event(:info, {:irc_conn_line, _, line}, :connected, data) do
    data = run_handler_event({:line, line}, data)
    :keep_state_and_data
  end

  #
  # --- Buffer
  #

  def handle_event(:info, {:irc_conn_line, _, line}, {:buffer, module}, data) do
    {next, actions} = case module.handle_buffer(line, data.buffer, data.info) do
      {next, next_arg} -> {{next, next_arg}, []}
      {next, next_arg, actions} -> {{next, next_arg}, List.wrap(actions)}
      next when is_atom(next) -> {{next, nil}, []}
    end

    data = handle_actions(actions, data)

    case next do
      {:finish, _} -> {:next_state, :connected, %__MODULE__{data | buffer: nil}}
      {:buffer, acc} -> {:keep_state, %__MODULE__{data | buffer: acc}}
    end
  end

  # TODO: Callback stop?
  def handle_event(:internal, reason, :error, data) do
    Logger.error "#{inspect data}: #{inspect reason}"
    data.module.stop(reason, data.modstate)
    {:stop, :normal}
  end

  def handle_event(:info, {:irc_conn_error, _, reason}, _, data) do
    {:next_state, :error, data, {:next_event, :internal, reason}}
  end

  def handle_event(:enter, _, _, _) do
    :keep_state_and_data
  end

  def terminate(reason, state, data) do
    Logger.error("#{inspect(data)} terminating in #{inspect(state)}: #{inspect reason}")
  end

  def code_change(_old_vsn, old_state, old_data, _extra) do
    {:ok, old_state, old_data}
  end

  defp prepare_args(args) do
    args
  end

  defp run_handler_event(event, data) do
    case data.module.handle_event(event, data.modstate) do
      {:ok, modstate} -> %__MODULE__{data | modstate: modstate}
      :ok -> data
    end
  end

  defp init_commands(args) do
    commands = @commands ++ Keyword.get(args, :commands, [])
    Enum.reduce(commands, %{server: %{}, user: %{}, capabs: []}, fn(module, acc) ->
      {server_commands, user_commands, capabs} = module.init()

      get_value = fn(option) ->
        case option do
          str when is_binary(str) -> [str]
          nil -> []
          list when is_list(list) -> list
        end
      end

      reduce_fun = fn(command, acc) -> Map.put(acc, command, module) end

      server = Enum.reduce(List.wrap(server_commands), acc.server, reduce_fun)
      user = Enum.reduce(List.wrap(user_commands), acc.user, reduce_fun)
      capabs = List.concat(acc.capabs, List.wrap(capabs))
      %{server: server, user: user, capabs: capabs}
    end)
  end

  defimpl Inspect, for: __MODULE__ do
    import Inspect.Algebra
    def inspect(struct, _opts) do
      concat(["#Irc.Client<", inspect(self()), ">"])
    end
  end


end