defmodule CmdcTui do
  @moduledoc """
  CMDC TUI — 基于 ExRatatui 的 AI Agent 终端交互界面。

  ## 快速开始

      # 启动 TUI，连接已有的 CMDC session
      CmdcTui.start(session: session_pid)

      # 或者让外部先创建 Agent，拿到 session 后启动 TUI
      {:ok, session} = CMDC.create_agent(model: "anthropic:claude-sonnet-4-5", ...)
      CmdcTui.start(session: session)
  """

  require Logger

  @doc """
  启动 TUI 应用（阻塞到退出）。

  直接模式：`ExRatatui.run` + 紧凑事件循环。
  `poll_event` 和 `draw` 在同一线程顺序执行，无 DirtyIo scheduler 切换开销，
  与 `debug_input.exs` 一致的零延迟体验。

  ## 选项

  - `:session` — 已有 CMDC session pid
  - `:session_id` — 会话 ID（可选，用于显示）
  - `:model_name` — 模型名称（可选，显示用）
  """
  @spec start(keyword()) :: :ok | {:error, term()}
  def start(opts \\ []) do
    prev_level = Logger.level()
    Logger.configure(level: :none)
    write_tty("\e[>1u")

    result =
      ExRatatui.run(fn terminal ->
        textarea = ExRatatui.textarea_new()
        opts = Keyword.put(opts, :textarea, textarea)
        state = CmdcTui.State.new(opts)

        if state.session, do: CMDC.subscribe(state.session)

        r = loop(terminal, state)

        if state.session, do: CMDC.unsubscribe(state.session)
        r
      end)

    write_tty("\e[<u")
    Logger.configure(level: prev_level)
    result
  end

  # 紧凑事件循环——不在 try 内，保证尾递归优化
  defp loop(terminal, state) do
    draw(terminal, state)

    case ExRatatui.poll_event(50) do
      %ExRatatui.Event.Key{code: "c", modifiers: ["ctrl"]} ->
        :ok

      %ExRatatui.Event.Key{} = key ->
        case handle_key(key, state) do
          {:ok, new_state} ->
            new_state = drain_keys(new_state)
            loop(terminal, new_state)

          :stop ->
            :ok
        end

      _ ->
        state = receive_cmdc_events(state)
        state = tick_throbber(state)
        loop(terminal, state)
    end
  end

  defp handle_key(key, state) do
    case CmdcTui.KeyHandler.handle(key, state) do
      {:noreply, new_state} -> {:ok, new_state}
      {:stop, _} -> :stop
    end
  end

  defp drain_keys(state) do
    case ExRatatui.poll_event(0) do
      %ExRatatui.Event.Key{code: "c", modifiers: ["ctrl"]} ->
        state

      %ExRatatui.Event.Key{} = key ->
        case handle_key(key, state) do
          {:ok, new_state} -> drain_keys(new_state)
          :stop -> state
        end

      _ ->
        state
    end
  end

  defp receive_cmdc_events(state) do
    receive do
      {:cmdc_event, _sid, event} ->
        state = CmdcTui.EventRouter.route(event, state)
        receive_cmdc_events(state)
    after
      0 -> state
    end
  end

  defp tick_throbber(%{agent_status: s} = state) when s in [:streaming, :running] do
    %{state | throbber_step: state.throbber_step + 1}
  end

  defp tick_throbber(state), do: state

  defp draw(terminal, state) do
    {w, h} = ExRatatui.terminal_size()
    frame = %ExRatatui.Frame{width: w, height: h}
    widgets = CmdcTui.App.render(state, frame)
    ExRatatui.draw(terminal, widgets)
  end

  # Kitty keyboard protocol — CSI u
  # flags=1 (DISAMBIGUATE_ESCAPE_CODES): 让终端区分 Enter vs Shift+Enter
  # 在 ExRatatui.run 回调外部（raw mode 之前）写入，避免干扰 crossterm
  defp write_tty(data) do
    case :file.open(~c"/dev/tty", [:write, :raw, :binary]) do
      {:ok, fd} ->
        :file.write(fd, data)
        :file.close(fd)

      _ ->
        :ok
    end
  end
end