app.cpp

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// Copyright 2020 Arthur Sonzogni. All rights reserved.
// Use of this source code is governed by the MIT license that can be found in
// the LICENSE file.
#include <algorithm>  // for any_of, copy, max, min
#include <array>      // for array
#include <atomic>
#include <chrono>  // for operator-, milliseconds, operator>=, duration, common_type<>::type, time_point
#include <csignal>  // for signal, SIGTSTP, SIGABRT, SIGWINCH, raise, SIGFPE, SIGILL, SIGINT, SIGSEGV, SIGTERM, __sighandler_t, size_t
#include <cstdint>
#include <cstdio>  // for fileno, stdin
#include <ftxui/component/app.hpp>
#include <ftxui/component/task.hpp>  // for Task, Closure, AnimationTask
#include <ftxui/screen/screen.hpp>  // for Cell, Screen::Cursor, Screen, Screen::Cursor::Hidden
#include <functional>        // for function
#include <initializer_list>  // for initializer_list
#include <iostream>  // for cout, ostream, operator<<, basic_ostream, endl, flush
#include <map>
#include <memory>
#include <stack>  // for stack
#include <string>
#include <string_view>
#include <thread>  // for thread, sleep_for
#include <tuple>   // for _Swallow_assign, ignore
#include <type_traits>
#include <utility>  // for move, swap
#include <variant>  // for visit, variant
#include <vector>   // for vector
 
#include "ftxui/component/animation.hpp"  // for TimePoint, Clock, Duration, Params, RequestAnimationFrame
#include "ftxui/component/captured_mouse.hpp"  // for CapturedMouse, CapturedMouseInterface
#include "ftxui/component/component_base.hpp"  // for ComponentBase
#include "ftxui/component/event.hpp"           // for Event
#include "ftxui/component/loop.hpp"            // for Loop
#include "ftxui/component/multi_receiver_buffer.hpp"
#include "ftxui/component/task_runner.hpp"
#include "ftxui/component/terminal_input_parser.hpp"  // for TerminalInputParser
#include "ftxui/dom/node.hpp"                         // for Node, Render
#include "ftxui/screen/cell.hpp"                      // for Cell
#include "ftxui/screen/terminal.hpp"                  // for Dimensions, Size
#include "ftxui/screen/util.hpp"                      // for util::clamp
#include "ftxui/util/autoreset.hpp"                   // for AutoReset
 
#if defined(_WIN32)
#define DEFINE_CONSOLEV2_PROPERTIES
#define WIN32_LEAN_AND_MEAN
#ifndef NOMINMAX
#define NOMINMAX
#endif
#include <io.h>
#include <windows.h>
#else
#include <fcntl.h>
#include <poll.h>
#include <sys/poll.h>
#include <sys/types.h>
#include <termios.h>  // for tcsetattr, termios, tcgetattr, TCSANOW, cc_t, ECHO, ICANON, VMIN, VTIME
#include <unistd.h>  // for STDIN_FILENO, STDOUT_FILENO, read
#endif
 
#if defined(__EMSCRIPTEN__)
#include <emscripten.h>
#endif
 
namespace ftxui {
 
enum class AppDimension {
  FitComponent,
  Fixed,
  Fullscreen,
  TerminalOutput,
};
 
namespace animation {
void RequestAnimationFrame() {
  auto* screen = App::Active();
  if (screen) {
    screen->RequestAnimationFrame();
  }
}
}  // namespace animation
 
#if defined(__EMSCRIPTEN__)
extern "C" {
EMSCRIPTEN_KEEPALIVE
void ftxui_on_resize(int columns, int rows) {
  Terminal::SetFallbackSize({
      columns,
      rows,
  });
  std::raise(SIGWINCH);
}
}
#endif
 
struct App::Internal {
  App* public_;
 
  App* suspended_screen_ = nullptr;
  const AppDimension dimension_;
  const bool use_alternative_screen_;
 
  bool track_mouse_ = true;
 
  std::string set_cursor_position_;
  std::string reset_cursor_position_;
 
  std::atomic<bool> quit_{false};
  bool installed_ = false;
  bool animation_requested_ = false;
  animation::TimePoint previous_animation_time_;
 
  int cursor_x_ = 1;
  int cursor_y_ = 1;
 
  std::uint64_t frame_count_ = 0;
  bool mouse_captured = false;
  bool previous_frame_resized_ = false;
 
  bool frame_valid_ = false;
 
  bool force_handle_ctrl_c_ = true;
  bool force_handle_ctrl_z_ = true;
 
  int cursor_reset_shape_ = 1;
 
  // Piped input handling state (POSIX only)
  bool handle_piped_input_ = true;
  bool is_stdin_a_tty_ = false;
  bool is_stdout_a_tty_ = false;
  // File descriptor for /dev/tty, used for piped input handling.
  int tty_fd_ = -1;
 
  std::string terminal_name_ = "unknown";
  int terminal_version_ = 0;
 
  std::string terminal_emulator_name_ = "unknown";
  std::string terminal_emulator_version_ = "unknown";
 
  std::vector<int> terminal_capabilities_;
 
  // Selection API:
  CapturedMouse selection_pending_;
  struct SelectionData {
    int start_x = -1;
    int start_y = -1;
    int end_x = -2;
    int end_y = -2;
    bool empty = true;
    bool operator==(const SelectionData& other) const {
      if (empty && other.empty) {
        return true;
      }
      if (empty || other.empty) {
        return false;
      }
      return start_x == other.start_x && start_y == other.start_y &&
             end_x == other.end_x && end_y == other.end_y;
    }
    bool operator!=(const SelectionData& other) const {
      return !(*this == other);
    }
  };
  SelectionData selection_data_;
  SelectionData selection_data_previous_;
  std::unique_ptr<Selection> selection_;
  std::function<void()> selection_on_change_;
 
  Component component_;
 
  // Pre-existing in Internal:
  TerminalInputParser terminal_input_parser;
  task::TaskRunner task_runner;
  std::chrono::time_point<std::chrono::steady_clock> last_char_time =
      std::chrono::steady_clock::now();
  std::string output_buffer;
 
  class ThrottledRequest {
   public:
    ThrottledRequest(App::Internal* internal, std::function<void()> send)
        : internal_(internal), send_(std::move(send)) {}
 
    void Request(bool force = false) {
      if (!internal_->is_stdin_a_tty_) {
        return;
      }
 
      if (force) {
        Send();
        return;
      }
 
      // Allow only one pending request at a time. This is to avoid flooding the
      // terminal with requests.
      if (HasPending()) {
        return;
      }
 
      const auto now = std::chrono::steady_clock::now();
      if (now - last_request_time_ < std::chrono::milliseconds(500)) {
        // Too soon since the last request. Skip it: the request must be sent
        // synchronously from Draw(), right after the cursor is moved to the
        // frame's origin, so that the terminal's reply reflects that
        // position. Draw() calls Request() again on the next frame, so the
        // request isn't lost, only delayed.
        return;
      }
 
      Send();
    }
 
    void OnReply() { pending_request_ = false; }
 
    bool HasPending() const {
      if (!pending_request_) {
        return false;
      }
      const auto now = std::chrono::steady_clock::now();
      return now - last_sent_time_ < std::chrono::seconds(5);
    }
 
   private:
    void Send() {
      last_sent_time_ = std::chrono::steady_clock::now();
      last_request_time_ = last_sent_time_;
      pending_request_ = true;
      send_();
    }
 
    App::Internal* internal_;
    std::function<void()> send_;
    bool pending_request_ = false;
    std::chrono::steady_clock::time_point last_request_time_ =
        std::chrono::steady_clock::now() - std::chrono::hours(1);
    std::chrono::steady_clock::time_point last_sent_time_ =
        std::chrono::steady_clock::now() - std::chrono::hours(1);
  };
 
  ThrottledRequest cursor_position_request;
 
  MultiReceiverBuffer<Event> event_buffer;
  std::unique_ptr<MultiReceiverBuffer<Event>::Receiver> main_loop_receiver;
 
  Internal(App* app, AppDimension dimension, bool use_alternative_screen);
 
  void ExitNow();
  void Install();
  void Uninstall();
  void PreMain();
  void PostMain();
  bool HasQuitted();
  void RunOnce(const Component& component);
  void RunOnceBlocking(Component component);
  void HandleTask(Component component, Task& task);
  bool HandleSelection(bool handled, Event event);
  void Draw(Component component);
  std::string ResetCursorPosition();
  void RequestCursorPosition(bool force = false);
  void TerminalSend(std::string_view);
  void TerminalFlush();
  void InstallPipedInputHandling();
  void InstallTerminalInfo();
  void Signal(int signal);
  size_t FetchTerminalEvents();
  void PostAnimationTask();
};
 
namespace {
 
App* g_active_screen = nullptr;  // NOLINT
 
std::stack<Closure> on_exit_functions;  // NOLINT
 
void OnExit() {
  while (!on_exit_functions.empty()) {
    on_exit_functions.top()();
    on_exit_functions.pop();
  }
}
 
// CSI: Control Sequence Introducer
const std::string CSI = "\x1b[";  // NOLINT
                                  //
// DCS: Device Control String
const std::string DCS = "\x1bP";  // NOLINT
 
// ST: String Terminator
const std::string ST = "\x1b\\";  // NOLINT
 
// DECRQSS: Request Status String
// DECSCUSR: Set Cursor Style
const std::string DECRQSS_DECSCUSR = DCS + "$q q" + ST;  // NOLINT
 
// DEC: Digital Equipment Corporation
enum class DECMode : std::uint16_t {
  kLineWrap = 7,
  kCursor = 25,
 
  kMouseX10 = 9,
  kMouseVt200 = 1000,
  kMouseVt200Highlight = 1001,
 
  kMouseBtnEventMouse = 1002,
  kMouseAnyEvent = 1003,
 
  kMouseUtf8 = 1005,
  kMouseSgrExtMode = 1006,
  kMouseUrxvtMode = 1015,
  kMouseSgrPixelsMode = 1016,
  kAlternateScreen = 1049,
};
 
// Device Status Report (DSR) {
enum class DSRMode : std::uint8_t {
  kCursor = 6,
};
 
std::string Serialize(const std::vector<DECMode>& parameters) {
  bool first = true;
  std::string out;
  for (const DECMode parameter : parameters) {
    if (!first) {
      out += ";";
    }
    out += std::to_string(int(parameter));
    first = false;
  }
  return out;
}
 
// DEC Private Mode Set (DECSET)
std::string Set(const std::vector<DECMode>& parameters) {
  return CSI + "?" + Serialize(parameters) + "h";
}
 
// DEC Private Mode Reset (DECRST)
std::string Reset(const std::vector<DECMode>& parameters) {
  return CSI + "?" + Serialize(parameters) + "l";
}
 
// Device Status Report (DSR)
std::string DeviceStatusReport(DSRMode ps) {
  return CSI + std::to_string(int(ps)) + "n";
}
 
class CapturedMouseImpl : public CapturedMouseInterface {
 public:
  explicit CapturedMouseImpl(std::function<void(void)> callback)
      : callback_(std::move(callback)) {}
  ~CapturedMouseImpl() override { callback_(); }
  CapturedMouseImpl(const CapturedMouseImpl&) = delete;
  CapturedMouseImpl(CapturedMouseImpl&&) = delete;
  CapturedMouseImpl& operator=(const CapturedMouseImpl&) = delete;
  CapturedMouseImpl& operator=(CapturedMouseImpl&&) = delete;
 
 private:
  std::function<void(void)> callback_;
};
 
#if !defined(_WIN32)
std::atomic<int> g_signal_exit_count = 0;    // NOLINT
std::atomic<int> g_signal_stop_count = 0;    // NOLINT
std::atomic<int> g_signal_resize_count = 0;  // NOLINT
#else
std::atomic<int> g_signal_exit_count = 0;  // NOLINT
#endif
 
// Tracks whether the terminal is currently configured in raw mode.
// Used to prevent double-restoration in emergency and normal exits.
std::atomic<bool> g_terminal_is_raw{false};
 
// Stores the last received deferred signal (e.g. SIGINT, SIGTERM) to be
// re-raised during uninstallation/exit.
std::atomic<int> g_last_signal{0};  // NOLINT
 
#if defined(_WIN32)
using SignalHandler = void (*)(int);
// Stores the original signal handlers before FTXUI installed its own.
std::map<int, SignalHandler> g_old_signal_handlers;
 
// Stores the original console modes to restore them during exit.
DWORD g_original_stdout_mode = 0;
DWORD g_original_stdin_mode = 0;
bool g_has_original_console_mode = false;
#else
// Stores the original sigaction structures before FTXUI installed its own.
std::map<int, struct sigaction> g_old_sigactions;
 
// Stores the original termios terminal settings to restore them during exit.
struct termios g_original_termios;
bool g_has_original_termios = false;
int g_tty_fd = -1;
#endif
 
// Restores the original signal handler for the given signal and re-raises it.
// Async-signal-safe function.
void RestoreSignalHandlerAndRaise(int signal) {
#if defined(_WIN32)
  auto it = g_old_signal_handlers.find(signal);
  auto old_handler = (it != g_old_signal_handlers.end()) ? it->second : SIG_DFL;
  std::signal(signal, old_handler);
#else
  auto it = g_old_sigactions.find(signal);
  if (it != g_old_sigactions.end()) {
    sigaction(signal, &it->second, nullptr);
  } else {
    struct sigaction sa;
    sa.sa_handler = SIG_DFL;
    sigemptyset(&sa.sa_mask);
    sa.sa_flags = 0;
    sigaction(signal, &sa, nullptr);
  }
#endif
  std::raise(signal);
}
 
// Emergency terminal state restoration.
// Async-signal-safe function.
void RestoreTerminalEmergency() {
  if (!g_terminal_is_raw.exchange(false)) {
    return;
  }
#if defined(_WIN32)
  if (g_has_original_console_mode) {
    auto stdout_handle = GetStdHandle(STD_OUTPUT_HANDLE);
    auto stdin_handle = GetStdHandle(STD_INPUT_HANDLE);
    SetConsoleMode(stdout_handle, g_original_stdout_mode);
    SetConsoleMode(stdin_handle, g_original_stdin_mode);
  }
#else
  if (g_has_original_termios && g_tty_fd >= 0) {
    const char restore_seq[] =
        "\x1b[?25h"    // Show cursor.
        "\x1b[?1049l"  // Switch to normal screen buffer.
        "\x1b[?1000l"  // Disable normal mouse tracking.
        "\x1b[?1002l"  // Disable button event mouse tracking.
        "\x1b[?1003l"  // Disable all motion mouse tracking.
        "\x1b[?1006l"  // Disable SGR mouse tracking.
        "\x1b[?1015l"  // Disable Urxvt mouse tracking.
        "\x1b[?7h";    // Enable line wrapping.
    std::ignore = write(STDOUT_FILENO, restore_seq, sizeof(restore_seq) - 1);
    tcsetattr(g_tty_fd, TCSANOW, &g_original_termios);
  }
#endif
}
 
// Async signal safe function
void RecordSignal(int signal) {
  switch (signal) {
    // Abnormal termination (e.g. abort() or assertion failure).
    case SIGABRT:
    // Erroneous arithmetic operation (e.g. division by zero).
    case SIGFPE:
    // Illegal instruction.
    case SIGILL:
    // Invalid memory reference (segmentation fault).
    case SIGSEGV:
#if !defined(_WIN32)
    // Bus error (e.g. bad memory access alignment).
    case SIGBUS:
    // Bad system call.
    case SIGSYS:
#endif
    {
      RestoreTerminalEmergency();
      RestoreSignalHandlerAndRaise(signal);
      break;
    }
 
    // Terminal interrupt (e.g. Ctrl-C).
    case SIGINT:
    // Termination request.
    case SIGTERM:
#if !defined(_WIN32)
    // Terminal quit (e.g. Ctrl-\, produces core dump).
    case SIGQUIT:
    // Hangup detected on controlling terminal or death of controlling process.
    case SIGHUP:
#endif
      g_last_signal.store(signal);
      g_signal_exit_count++;
      break;
 
#if !defined(_WIN32)
    // Terminal stop signal (e.g. Ctrl-Z).
    case SIGTSTP:  // NOLINT
      g_signal_stop_count++;
      break;
 
    // Terminal window size change.
    case SIGWINCH:  // NOLINT
      g_signal_resize_count++;
      break;
#endif
 
    default:
      break;
  }
}
 
void ExecuteSignalHandlers() {
  if (g_last_signal.load() != 0) {
    App::Private::Signal(*g_active_screen, SIGABRT);
  }
 
  int signal_exit_count = g_signal_exit_count.exchange(0);
  while (signal_exit_count--) {
    App::Private::Signal(*g_active_screen, SIGABRT);
  }
 
#if !defined(_WIN32)
  int signal_stop_count = g_signal_stop_count.exchange(0);
  while (signal_stop_count--) {
    App::Private::Signal(*g_active_screen, SIGTSTP);
  }
 
  int signal_resize_count = g_signal_resize_count.exchange(0);
  while (signal_resize_count--) {
    App::Private::Signal(*g_active_screen, SIGWINCH);
  }
#endif
}
 
void InstallSignalHandler(int sig) {
#if defined(_WIN32)
  auto old_signal_handler = std::signal(sig, RecordSignal);
  g_old_signal_handlers[sig] = old_signal_handler;
  on_exit_functions.emplace(
      [=] { std::ignore = std::signal(sig, old_signal_handler); });
#else
  struct sigaction sa;
  sa.sa_handler = RecordSignal;
  sigemptyset(&sa.sa_mask);
  sa.sa_flags = SA_RESTART;
  struct sigaction old_sa;
  sigaction(sig, &sa, &old_sa);
  g_old_sigactions[sig] = old_sa;
  on_exit_functions.emplace([=] { sigaction(sig, &old_sa, nullptr); });
#endif
}
 
}  // namespace
 
App::Internal::Internal(App* app,
                        AppDimension dimension,
                        bool use_alternative_screen)
    : public_(app),
      dimension_(dimension),
      use_alternative_screen_(use_alternative_screen),
      terminal_input_parser([&](Event event) {
        event_buffer.Push(std::move(event));
      }),
      cursor_position_request(this, [this] {
        TerminalSend(DeviceStatusReport(DSRMode::kCursor));
      }) {
  main_loop_receiver = event_buffer.CreateReceiver();
}
 
void App::Internal::ExitNow() {
  quit_ = true;
}
 
void App::Internal::Install() {
  frame_valid_ = false;
 
  // Flush the buffer for stdout to ensure whatever the user has printed before
  // is fully applied before we start modifying the terminal configuration. This
  // is important, because we are using two different channels (stdout vs
  // termios/WinAPI) to communicate with the terminal emulator below. See
  // https://github.com/ArthurSonzogni/FTXUI/issues/846
  TerminalFlush();
 
  InstallPipedInputHandling();
 
  // After uninstalling the new configuration, flush it to the terminal to
  // ensure it is fully applied:
  on_exit_functions.emplace([this] { TerminalFlush(); });
 
  // Install signal handlers to restore the terminal state on exit. The default
  // signal handlers are restored on exit.
  for (const int signal : {SIGTERM, SIGSEGV, SIGINT, SIGILL, SIGABRT, SIGFPE}) {
    InstallSignalHandler(signal);
  }
 
// Save the old terminal configuration and restore it on exit.
#if defined(_WIN32)
  // Enable VT processing on stdout and stdin
  auto stdout_handle = GetStdHandle(STD_OUTPUT_HANDLE);
  auto stdin_handle = GetStdHandle(STD_INPUT_HANDLE);
 
  DWORD out_mode = 0;
  DWORD in_mode = 0;
  GetConsoleMode(stdout_handle, &out_mode);
  GetConsoleMode(stdin_handle, &in_mode);
  g_original_stdout_mode = out_mode;
  g_original_stdin_mode = in_mode;
  g_has_original_console_mode = true;
  on_exit_functions.push([=] { SetConsoleMode(stdout_handle, out_mode); });
  on_exit_functions.push([=] { SetConsoleMode(stdin_handle, in_mode); });
 
  // https://docs.microsoft.com/en-us/windows/console/setconsolemode
  const int enable_virtual_terminal_processing = 0x0004;
  const int disable_newline_auto_return = 0x0008;
  out_mode |= enable_virtual_terminal_processing;
  out_mode |= disable_newline_auto_return;
 
  // https://docs.microsoft.com/en-us/windows/console/setconsolemode
  const int enable_line_input = 0x0002;
  const int enable_echo_input = 0x0004;
  const int enable_virtual_terminal_input = 0x0200;
  const int enable_window_input = 0x0008;
  in_mode &= ~enable_echo_input;
  in_mode &= ~enable_line_input;
  in_mode |= enable_virtual_terminal_input;
  in_mode |= enable_window_input;
 
  SetConsoleMode(stdin_handle, in_mode);
  SetConsoleMode(stdout_handle, out_mode);
#else  // POSIX (Linux & Mac)
  for (const int signal :
       {SIGWINCH, SIGTSTP, SIGBUS, SIGSYS, SIGQUIT, SIGHUP}) {
    InstallSignalHandler(signal);
  }
 
  struct termios terminal;  // NOLINT
  tcgetattr(tty_fd_, &terminal);
  g_original_termios = terminal;
  g_tty_fd = tty_fd_;
  g_has_original_termios = true;
  on_exit_functions.emplace([terminal = terminal, tty_fd_ = tty_fd_] {
    tcsetattr(tty_fd_, TCSANOW, &terminal);
  });
 
  // Enabling raw terminal input mode
  terminal.c_iflag &= ~IGNBRK;  // Disable ignoring break condition
  terminal.c_iflag &= ~BRKINT;  // Disable break causing input and output to be
                                // flushed
  terminal.c_iflag &= ~PARMRK;  // Disable marking parity errors.
  terminal.c_iflag &= ~ISTRIP;  // Disable stripping 8th bit off characters.
  terminal.c_iflag &= ~INLCR;   // Disable mapping NL to CR.
  terminal.c_iflag &= ~IGNCR;   // Disable ignoring CR.
  terminal.c_iflag &= ~ICRNL;   // Disable mapping CR to NL.
  terminal.c_iflag &= ~IXON;    // Disable XON/XOFF flow control on output
 
  terminal.c_lflag &= ~ECHO;    // Disable echoing input characters.
  terminal.c_lflag &= ~ECHONL;  // Disable echoing new line characters.
  terminal.c_lflag &= ~ICANON;  // Disable Canonical mode.
  terminal.c_lflag &= ~ISIG;    // Disable sending signal when hitting:
                                // -     => DSUSP
                                // - C-Z => SUSP
                                // - C-C => INTR
                                // - C-d => QUIT
  terminal.c_lflag &= ~IEXTEN;  // Disable extended input processing
  terminal.c_cflag |= CS8;      // 8 bits per byte
 
  terminal.c_cc[VMIN] = 0;   // Minimum number of characters for non-canonical
                             // read.
  terminal.c_cc[VTIME] = 0;  // Timeout in deciseconds for non-canonical read.
 
  tcsetattr(tty_fd_, TCSANOW, &terminal);
 
#endif
 
  auto enable = [&](const std::vector<DECMode>& parameters) {
    TerminalSend(Set(parameters));
    on_exit_functions.emplace(
        [this, parameters] { TerminalSend(Reset(parameters)); });
  };
 
  auto disable = [&](const std::vector<DECMode>& parameters) {
    TerminalSend(Reset(parameters));
    on_exit_functions.emplace(
        [this, parameters] { TerminalSend(Set(parameters)); });
  };
 
  if (use_alternative_screen_) {
    enable({
        DECMode::kAlternateScreen,
    });
  }
 
  disable({
      DECMode::kLineWrap,
  });
 
  if (track_mouse_) {
    enable({DECMode::kMouseVt200});
    enable({DECMode::kMouseAnyEvent});
    enable({DECMode::kMouseUrxvtMode});
    enable({DECMode::kMouseSgrExtMode});
  }
 
  // After installing the new configuration, flush it to the terminal to
  // ensure it is fully applied:
  TerminalFlush();
 
  InstallTerminalInfo();
 
  quit_ = false;
 
  PostAnimationTask();
 
  installed_ = true;
  g_terminal_is_raw = true;
}
 
void App::Internal::Uninstall() {
  g_terminal_is_raw = false;
  installed_ = false;
 
  // During shutdown, wait for all of the replies.
  if (is_stdin_a_tty_ && is_stdout_a_tty_) {
    auto closing_receiver =
        event_buffer.CreateReceiverAt(main_loop_receiver->index());
    auto start = std::chrono::steady_clock::now();
    while (cursor_position_request.HasPending()) {
      FetchTerminalEvents();
 
      while (closing_receiver->Has()) {
        const auto event = closing_receiver->Pop();
        if (event.is_cursor_position()) {
          cursor_x_ = event.cursor_x();
          cursor_y_ = event.cursor_y();
          cursor_position_request.OnReply();
        }
      }
 
      task_runner.RunUntilIdle();
 
      if (std::chrono::steady_clock::now() - start >
          std::chrono::milliseconds(400)) {
        break;
      }
      std::this_thread::sleep_for(std::chrono::milliseconds(10));
    }
  }
 
  OnExit();
}
 
void App::Internal::PreMain() {
  // Suspend previously active screen:
  if (g_active_screen) {
    std::swap(suspended_screen_, g_active_screen);
    // Reset cursor position to the top of the screen and clear the screen.
    suspended_screen_->internal_->TerminalSend(
        suspended_screen_->internal_->ResetCursorPosition());
    suspended_screen_->ResetPosition(
        suspended_screen_->internal_->output_buffer,
        /*clear=*/true);
    suspended_screen_->dimx_ = 0;
    suspended_screen_->dimy_ = 0;
 
    // Reset dimensions to force drawing the screen again next time:
    suspended_screen_->internal_->Uninstall();
  }
 
  // This screen is now active:
  g_active_screen = public_;
  g_active_screen->internal_->Install();
 
  previous_animation_time_ = animation::Clock::now();
}
 
void App::Internal::PostMain() {
  // Put cursor position at the end of the drawing.
  TerminalSend(ResetCursorPosition());
 
  g_active_screen = nullptr;
 
  // Restore suspended screen.
  if (suspended_screen_) {
    // Clear screen, and put the cursor at the beginning of the drawing.
    public_->ResetPosition(output_buffer, /*clear=*/true);
    public_->dimx_ = 0;
    public_->dimy_ = 0;
    Uninstall();
    std::swap(g_active_screen, suspended_screen_);
    g_active_screen->internal_->Install();
  } else {
    Uninstall();
 
    std::cout << "\r";
    // On final exit, keep the current drawing and reset cursor position one
    // line after it.
    if (!use_alternative_screen_) {
      std::cout << "\n";
    }
    std::cout << std::flush;
  }
 
  int sig = g_last_signal.exchange(0);
  if (sig != 0) {
    RestoreSignalHandlerAndRaise(sig);
  }
}
 
bool App::Internal::HasQuitted() {
  return quit_;
}
 
void App::Internal::RunOnce(const Component& component) {
  const AutoReset set_component(&component_, component);
  ExecuteSignalHandlers();
  FetchTerminalEvents();
 
  while (!quit_ && main_loop_receiver->Has()) {
    public_->Post(main_loop_receiver->Pop());
  }
 
  // Execute the pending tasks from the queue.
  const size_t executed_task = task_runner.ExecutedTasks();
  task_runner.RunUntilIdle();
  // If no executed task, we can return early without redrawing the screen.
  if (executed_task == task_runner.ExecutedTasks()) {
    return;
  }
 
  ExecuteSignalHandlers();
  Draw(component);
 
  if (selection_data_previous_ != selection_data_) {
    selection_data_previous_ = selection_data_;
    if (selection_on_change_) {
      selection_on_change_();
      public_->Post(Event::Custom);
    }
  }
}
 
void App::Internal::RunOnceBlocking(Component component) {
  // Set FPS to 60 at most.
  const auto time_per_frame = std::chrono::microseconds(16666);  // 1s / 60fps
 
  auto time = std::chrono::steady_clock::now();
  const size_t executed_task = task_runner.ExecutedTasks();
 
  // Wait for at least one task to execute.
  while (executed_task == task_runner.ExecutedTasks() && !HasQuitted()) {
    RunOnce(component);
 
    const auto now = std::chrono::steady_clock::now();
    const auto delta = now - time;
    time = now;
 
    if (delta < time_per_frame) {
      const auto sleep_duration = time_per_frame - delta;
      std::this_thread::sleep_for(sleep_duration);
    }
  }
}
 
void App::Internal::HandleTask(Component component, Task& task) {
  std::visit(
      [&](auto&& arg) {
        using T = std::decay_t<decltype(arg)>;
        // clang-format off
 
    // Handle Event.
    if constexpr (std::is_same_v<T, Event>) {
 
      if (arg.is_cursor_position()) {
        cursor_x_ = arg.cursor_x();
        cursor_y_ = arg.cursor_y();
        cursor_position_request.OnReply();
        return;
      }
 
      if (arg.is_cursor_shape()) {
        cursor_reset_shape_ = arg.cursor_shape();
        return;
      }
 
      if (arg.IsTerminalCapabilities()) {
        terminal_capabilities_ = arg.TerminalCapabilities();
        return;
      }
 
      if (arg.IsTerminalNameVersion()) {
        terminal_name_ = arg.TerminalName();
        terminal_version_ = arg.TerminalVersion();
        return;
      }
 
      if (arg.IsTerminalEmulator()) {
        terminal_emulator_name_ = arg.TerminalEmulatorName();
        terminal_emulator_version_ = arg.TerminalEmulatorVersion();
        return;
      }
 
      if (arg.is_mouse()) {
        arg.mouse().x -= cursor_x_;
        arg.mouse().y -= cursor_y_;
      }
 
      arg.screen_ = public_;
 
      bool handled = component->OnEvent(arg);
      handled = HandleSelection(handled, arg);
 
      if (arg == Event::CtrlC && (!handled || force_handle_ctrl_c_)) {
        RecordSignal(SIGINT);
      }
 
#if !defined(_WIN32)
      if (arg == Event::CtrlZ && (!handled || force_handle_ctrl_z_)) {
        RecordSignal(SIGTSTP);
      }
#endif
      
      frame_valid_ = false;
      return;
    }
 
    // Handle callback
    if constexpr (std::is_same_v<T, Closure>) {
      arg();
      return;
    }
 
    // Handle Animation
    if constexpr (std::is_same_v<T, AnimationTask>) {
      if (!animation_requested_) {
        return;
      }
 
      animation_requested_ = false;
      const animation::TimePoint now = animation::Clock::now();
      const animation::Duration delta = now - previous_animation_time_;
      previous_animation_time_ = now;
 
      animation::Params params(delta);
      component->OnAnimation(params);
      frame_valid_ = false;
      return;
    }
  },
  task);
  // clang-format on
}
 
bool App::Internal::HandleSelection(bool handled, Event event) {
  if (handled) {
    selection_pending_ = nullptr;
    selection_data_.empty = true;
    selection_ = nullptr;
    return true;
  }
 
  if (!event.is_mouse()) {
    return false;
  }
 
  auto& mouse = event.mouse();
  if (mouse.button != Mouse::Left) {
    return false;
  }
 
  if (mouse.motion == Mouse::Pressed) {
    selection_pending_ = public_->CaptureMouse();
    selection_data_.start_x = mouse.x;
    selection_data_.start_y = mouse.y;
    selection_data_.end_x = mouse.x;
    selection_data_.end_y = mouse.y;
    return false;
  }
 
  if (!selection_pending_) {
    return false;
  }
 
  if (mouse.motion == Mouse::Moved) {
    if ((mouse.x != selection_data_.end_x) ||
        (mouse.y != selection_data_.end_y)) {
      selection_data_.end_x = mouse.x;
      selection_data_.end_y = mouse.y;
      selection_data_.empty = false;
    }
 
    return true;
  }
 
  if (mouse.motion == Mouse::Released) {
    selection_pending_ = nullptr;
    selection_data_.end_x = mouse.x;
    selection_data_.end_y = mouse.y;
    selection_data_.empty = false;
    return true;
  }
 
  return false;
}
 
void App::Internal::Draw(Component component) {
  if (frame_valid_) {
    return;
  }
  auto document = component->Render();
  int dimx = 0;
  int dimy = 0;
  auto terminal = Terminal::Size();
  document->ComputeRequirement();
  switch (dimension_) {
    case AppDimension::Fixed:
      dimx = public_->dimx_;
      dimy = public_->dimy_;
      break;
    case AppDimension::TerminalOutput:
      dimx = terminal.dimx;
      dimy = util::clamp(document->requirement().min_y, 0, terminal.dimy);
      break;
    case AppDimension::Fullscreen:
      dimx = terminal.dimx;
      dimy = terminal.dimy;
      break;
    case AppDimension::FitComponent:
      dimx = util::clamp(document->requirement().min_x, 0, terminal.dimx);
      dimy = util::clamp(document->requirement().min_y, 0, terminal.dimy);
      break;
  }
 
  // Hide cursor to prevent flickering during reset.
  TerminalSend("\033[?25l");
 
  const bool resized =
      frame_count_ == 0 || (dimx != public_->dimx_) || (dimy != public_->dimy_);
  TerminalSend(ResetCursorPosition());
 
  if (frame_count_ != 0) {
    // Reset the cursor position to the lower left corner to start drawing the
    // new frame.
    public_->ResetPosition(output_buffer, resized);
 
    // If the terminal width decrease, the terminal emulator will start wrapping
    // lines and make the display dirty. We should clear it completely.
    if ((dimx < public_->dimx_) && !use_alternative_screen_) {
      TerminalSend("\033[J");  // clear terminal output
      TerminalSend("\033[H");  // move cursor to home position
    }
  }
 
  // Resize the screen if needed.
  if (resized) {
    public_->dimx_ = dimx;
    public_->dimy_ = dimy;
    public_->cells_ = std::vector<Cell>(static_cast<size_t>(dimx) *
                                        static_cast<size_t>(dimy));
    Cursor cursor = public_->cursor_;
    cursor.x = dimx - 1;
    cursor.y = dimy - 1;
    public_->SetCursor(cursor);
  }
 
  // Periodically request the terminal emulator the frame position relative to
  // the screen. This is useful for converting mouse position reported in
  // screen's coordinates to frame's coordinates.
  if (!use_alternative_screen_ && is_stdout_a_tty_) {
    RequestCursorPosition(previous_frame_resized_);
  }
  previous_frame_resized_ = resized;
 
  selection_ = selection_data_.empty
                   ? std::make_unique<Selection>()
                   : std::make_unique<Selection>(
                         selection_data_.start_x, selection_data_.start_y,  //
                         selection_data_.end_x, selection_data_.end_y);
  Render(*public_, document.get(), *selection_);
 
  // Set cursor position for user using tools to insert CJK characters.
  {
    const int dx = public_->dimx_ - 1 - public_->cursor_.x +
                   int(public_->dimx_ != terminal.dimx);
    const int dy = public_->dimy_ - 1 - public_->cursor_.y;
 
    set_cursor_position_.clear();
    reset_cursor_position_.clear();
 
    if (dy != 0) {
      set_cursor_position_ += "\x1B[" + std::to_string(dy) + "A";
      reset_cursor_position_ += "\x1B[" + std::to_string(dy) + "B";
    }
 
    if (dx != 0) {
      set_cursor_position_ += "\x1B[" + std::to_string(dx) + "D";
      reset_cursor_position_ += "\x1B[" + std::to_string(dx) + "C";
    }
 
    if (public_->cursor_.shape != Screen::Cursor::Hidden) {
      set_cursor_position_ += "\033[?25h";
      set_cursor_position_ +=
          "\033[" + std::to_string(int(public_->cursor_.shape)) + " q";
    }
  }
 
  public_->ToString(output_buffer);
  TerminalSend(set_cursor_position_);
  TerminalFlush();
 
  public_->Clear();
  frame_valid_ = true;
  frame_count_++;
}
 
std::string App::Internal::ResetCursorPosition() {
  std::string result = std::move(reset_cursor_position_);
  reset_cursor_position_ = "";
  return result;
}
 
void App::Internal::RequestCursorPosition(bool force) {
  cursor_position_request.Request(force);
}
 
void App::Internal::TerminalSend(std::string_view s) {
  output_buffer += s;
}
 
void App::Internal::TerminalFlush() {
  // Emscripten doesn't implement flush. We interpret zero as flush.
  output_buffer += '\0';
  std::cout << output_buffer << std::flush;
  output_buffer.clear();
}
 
void App::Internal::InstallPipedInputHandling() {
  is_stdin_a_tty_ = false;
  is_stdout_a_tty_ = false;
#if defined(__EMSCRIPTEN__)
  is_stdin_a_tty_ = true;
  is_stdout_a_tty_ = true;
#elif defined(_WIN32)
  is_stdin_a_tty_ = _isatty(_fileno(stdin));
  is_stdout_a_tty_ = _isatty(_fileno(stdout));
#else
  tty_fd_ = STDIN_FILENO;
  is_stdout_a_tty_ = isatty(STDOUT_FILENO);
  // Handle piped input redirection if explicitly enabled by the application.
  // This allows applications to read data from stdin while still receiving
  // keyboard input from the terminal for interactive use.
  if (!handle_piped_input_) {
    is_stdin_a_tty_ = isatty(STDIN_FILENO);
  } else if (isatty(STDIN_FILENO)) {
    is_stdin_a_tty_ = true;
  } else {
    // Open /dev/tty for keyboard input.
    tty_fd_ = open("/dev/tty", O_RDONLY);  // NOLINT
    if (tty_fd_ < 0) {
      // Failed to open /dev/tty (containers, headless systems, etc.)
      tty_fd_ = STDIN_FILENO;  // Fallback to stdin.
      is_stdin_a_tty_ = isatty(STDIN_FILENO);
    } else {
      is_stdin_a_tty_ = true;
      // Close the /dev/tty file descriptor on exit.
      on_exit_functions.emplace([this] {
        close(tty_fd_);
        tty_fd_ = -1;
      });
    }
  }
#endif
}
 
void App::Internal::InstallTerminalInfo() {
  // Request the terminal to report the current cursor shape. We will restore it
  // on exit.
  if (is_stdout_a_tty_) {
    TerminalSend(DECRQSS_DECSCUSR);
    TerminalSend("\033[>q");  // XTVERSION
    TerminalSend("\033[>c");  // DA2
    TerminalSend("\033[c");   // DA1
    TerminalFlush();
  }
 
  // Wait for the cursor shape reply using the setup head.
  if (is_stdin_a_tty_ && is_stdout_a_tty_) {
    // A receiver scoped to the setup: keeping one alive after setup would pin
    // every subsequent event in the buffer, growing it for the whole app
    // lifetime.
    auto setup_receiver = event_buffer.CreateReceiver();
    auto start = std::chrono::steady_clock::now();
    bool terminal_capabilities_received = false;
    // Wait for the cursor shape reply using the setup head.
    while (true) {
      FetchTerminalEvents();
      while (setup_receiver->Has()) {
        const auto event = setup_receiver->Pop();
        if (event.is_cursor_shape()) {
          cursor_reset_shape_ = event.cursor_shape();
        }
 
        if (event.IsTerminalCapabilities()) {
          terminal_capabilities_ = event.TerminalCapabilities();
          terminal_capabilities_received = true;
        }
 
        if (event.IsTerminalNameVersion()) {
          terminal_name_ = event.TerminalName();
          terminal_version_ = event.TerminalVersion();
        }
 
        if (event.IsTerminalEmulator()) {
          terminal_emulator_name_ = event.TerminalEmulatorName();
          terminal_emulator_version_ = event.TerminalEmulatorVersion();
        }
      }
 
      // Response are expected to be received in order, so we can break when
      // the last one (XTVERSION) is received. We also set a timeout to prevent
      // waiting forever in case the terminal doesn't support these queries.
      if (terminal_capabilities_received) {
        break;
      }
 
      if (std::chrono::steady_clock::now() - start >
          std::chrono::milliseconds(500)) {
        break;
      }
      std::this_thread::sleep_for(std::chrono::milliseconds(10));
    }
  }
 
  // Set quirks and color support based on terminal identification.
  Terminal::Quirks quirks = Terminal::GetQuirks();
 
  auto color_support = Terminal::ComputeColorSupport(
      util::GetEnv("TERM"), util::GetEnv("COLORTERM"),
      util::GetEnv("TERM_PROGRAM"), terminal_name_, terminal_emulator_name_,
      terminal_capabilities_);
 
  quirks.SetColorSupport(color_support);
 
  const bool is_modern_emulator = (terminal_emulator_name_ != "unknown");
  const bool is_vt220_plus =
      (terminal_name_ != "vt100" && terminal_name_ != "unknown");
  bool reports_utf8 = false;
  for (const int x : terminal_capabilities_) {
    if (x == 52) {
      reports_utf8 = true;
      break;
    }
  }
 
  // Heuristic: If the terminal emulator is modern, or it reports supporting
  // UTF-8 or color, we can assume it supports block characters and cursor
  // hiding, which are essential for a good experience. This is a heuristic, but
  // it allows us to work around some older terminal emulators that don't
  // support these features, while still providing a good experience on modern
  // terminal emulators that do support these features.
  bool modern = is_modern_emulator || is_vt220_plus || reports_utf8;
  if (modern) {
    quirks.SetBlockCharacters(true);
    quirks.SetCursorHiding(true);
    quirks.SetComponentAscii(false);
  }
 
  Terminal::SetQuirks(quirks);
 
  on_exit_functions.emplace([this] {
    TerminalSend("\033[?25h");  // Enable cursor.
    if (is_stdout_a_tty_) {
      TerminalSend("\033[" + std::to_string(cursor_reset_shape_) + " q");
    }
  });
}
 
void App::Internal::Signal(int signal) {
  if (signal == SIGABRT) {
    public_->Exit();
    return;
  }
 
// Windows do no support SIGTSTP / SIGWINCH
#if !defined(_WIN32)
  if (signal == SIGTSTP) {
    public_->Post([&] {
      TerminalSend(ResetCursorPosition());
      public_->ResetPosition(output_buffer, /*clear*/ true);
      Uninstall();
      public_->dimx_ = 0;
      public_->dimy_ = 0;
      (void)std::raise(SIGTSTP);
      Install();
    });
    return;
  }
 
  if (signal == SIGWINCH) {
    public_->Post(Event::Special({0}));
    return;
  }
#endif
}
 
size_t App::Internal::FetchTerminalEvents() {
#if defined(_WIN32)
  auto get_input_records = [&]() -> std::vector<INPUT_RECORD> {
    // Check if there is input in the console.
    auto console = GetStdHandle(STD_INPUT_HANDLE);
    DWORD number_of_events = 0;
    if (!GetNumberOfConsoleInputEvents(console, &number_of_events)) {
      return std::vector<INPUT_RECORD>();
    }
    if (number_of_events <= 0) {
      // No input, return.
      return std::vector<INPUT_RECORD>();
    }
    // Read the input events.
    std::vector<INPUT_RECORD> records(number_of_events);
    DWORD number_of_events_read = 0;
    if (!ReadConsoleInput(console, records.data(), (DWORD)records.size(),
                          &number_of_events_read)) {
      return std::vector<INPUT_RECORD>();
    }
    records.resize(number_of_events_read);
    return records;
  };
 
  auto records = get_input_records();
  if (records.size() == 0) {
    const auto timeout = std::chrono::steady_clock::now() - last_char_time;
    const size_t timeout_microseconds =
        std::chrono::duration_cast<std::chrono::microseconds>(timeout).count();
    terminal_input_parser.Timeout(timeout_microseconds);
    return 0;
  }
  last_char_time = std::chrono::steady_clock::now();
 
  // Convert the input events to FTXUI events.
  // For each event, we call the terminal input parser to convert it to
  // Event.
  std::wstring wstring;
  for (const auto& r : records) {
    switch (r.EventType) {
      case KEY_EVENT: {
        auto key_event = r.Event.KeyEvent;
        // ignore UP key events
        if (key_event.bKeyDown == FALSE) {
          continue;
        }
        const wchar_t wc = key_event.uChar.UnicodeChar;
        wstring += wc;
        if (wc >= 0xd800 && wc <= 0xdbff) {
          // Wait for the Low Surrogate to arrive in the next record.
          continue;
        }
        for (auto it : to_string(wstring)) {
          terminal_input_parser.Add(it);
        }
        wstring.clear();
      } break;
      case WINDOW_BUFFER_SIZE_EVENT:
        public_->Post(Event::Special({0}));
        break;
      case MENU_EVENT:
      case FOCUS_EVENT:
      case MOUSE_EVENT:
        // TODO(mauve): Implement later.
        break;
    }
  }
  return records.size();
#elif defined(__EMSCRIPTEN__)
  // Read chars from the terminal.
  // We configured it to be non blocking.
  std::array<char, 4096> out{};
  const ssize_t l = read(STDIN_FILENO, out.data(), out.size());
  if (l <= 0) {
    const auto timeout = std::chrono::steady_clock::now() - last_char_time;
    const size_t timeout_microseconds =
        std::chrono::duration_cast<std::chrono::microseconds>(timeout).count();
    terminal_input_parser.Timeout(timeout_microseconds);
    return 0;
  }
  last_char_time = std::chrono::steady_clock::now();
 
  // Convert the chars to events.
  for (ssize_t i = 0; i < l; ++i) {
    terminal_input_parser.Add(out.at(static_cast<size_t>(i)));
  }
  return (size_t)l;
#else  // POSIX (Linux & Mac)
  struct pollfd pfd = {tty_fd_, POLLIN, 0};
  const int poll_result = poll(&pfd, 1, 0);
  if (poll_result <= 0) {
    const auto timeout = std::chrono::steady_clock::now() - last_char_time;
    const size_t timeout_ms =
        std::chrono::duration_cast<std::chrono::milliseconds>(timeout).count();
    terminal_input_parser.Timeout(static_cast<int>(timeout_ms));
    return 0;
  }
  last_char_time = std::chrono::steady_clock::now();
 
  // Drain the available input, so that bursts (e.g. fast mouse wheel
  // scrolling) do not accumulate across frames. The total is bounded to keep
  // the frame responsive under a continuous input flood. See #1348.
  constexpr size_t kMaxBytesPerFetch = 64 * 1024;
  std::array<char, 4096> out{};
  size_t total = 0;
  while (total < kMaxBytesPerFetch) {
    const ssize_t l = read(tty_fd_, out.data(), out.size());
    if (l <= 0) {
      break;
    }
 
    // Convert the chars to events.
    for (ssize_t i = 0; i < l; ++i) {
      terminal_input_parser.Add(out.at(static_cast<size_t>(i)));
    }
    total += static_cast<size_t>(l);
 
    pfd.revents = 0;
    if (poll(&pfd, 1, 0) <= 0) {
      break;
    }
  }
  return total;
#endif
}
 
void App::Internal::PostAnimationTask() {
  public_->Post(AnimationTask());
 
  // Repeat the animation task every 15ms. This correspond to a frame rate
  // of around 66fps.
  task_runner.PostDelayedTask([this] { PostAnimationTask(); },
                              std::chrono::milliseconds(15));
}
 
App::App(std::unique_ptr<Internal> internal, int dimx, int dimy)
    : Screen(dimx, dimy), internal_(std::move(internal)) {
  internal_->public_ = this;
}
 
App::App(App&& other) noexcept : Screen(std::move(other)) {
  internal_ = std::move(other.internal_);
  if (internal_) {
    internal_->public_ = this;
  }
}
 
App& App::operator=(App&& other) noexcept {
  Screen::operator=(std::move(other));
  internal_ = std::move(other.internal_);
  if (internal_) {
    internal_->public_ = this;
  }
  return *this;
}
 
App::~App() = default;
 
// static
App App::FixedSize(int dimx, int dimy) {
  auto internal =
      std::make_unique<Internal>(nullptr, AppDimension::Fixed, false);
  return App(std::move(internal), dimx, dimy);
}
 
// static
App App::Fullscreen() {
  return FullscreenAlternateScreen();
}
 
// static
App App::FullscreenPrimaryScreen() {
  auto terminal = Terminal::Size();
  auto internal =
      std::make_unique<Internal>(nullptr, AppDimension::Fullscreen, false);
  return App(std::move(internal), terminal.dimx, terminal.dimy);
}
 
// static
App App::FullscreenAlternateScreen() {
  auto terminal = Terminal::Size();
  auto internal =
      std::make_unique<Internal>(nullptr, AppDimension::Fullscreen, true);
  return App(std::move(internal), terminal.dimx, terminal.dimy);
}
 
// static
App App::FitComponent() {
  auto terminal = Terminal::Size();
  auto internal =
      std::make_unique<Internal>(nullptr, AppDimension::FitComponent, false);
  return App(std::move(internal), terminal.dimx, terminal.dimy);
}
 
// static
App App::TerminalOutput() {
  auto terminal = Terminal::Size();
  auto internal =
      std::make_unique<Internal>(nullptr, AppDimension::TerminalOutput, false);
  return App(std::move(internal), terminal.dimx, terminal.dimy);
}
 
void App::TrackMouse(bool enable) {
  internal_->track_mouse_ = enable;
}
 
void App::HandlePipedInput(bool enable) {
  internal_->handle_piped_input_ = enable;
}
 
// static
App* App::Active() {
  return g_active_screen;
}
 
void App::Loop(Component component) {
  class Loop loop(this, std::move(component));
  loop.Run();
}
 
void App::Exit() {
  Post([this] { internal_->ExitNow(); });
}
 
Closure App::ExitLoopClosure() {
  return [this] { Exit(); };
}
 
void App::Post(Task task) {
  internal_->task_runner.PostTask([this, task = std::move(task)]() mutable {
    if (internal_->component_) {
      internal_->HandleTask(internal_->component_, task);
      return;
    }
 
    // If there is no component, we can still execute closures.
    if (std::holds_alternative<Closure>(task)) {
      std::get<Closure>(task)();
    }
  });
}
 
void App::PostEvent(Event event) {
  // PostEvent is documented as thread safe: go through the mutex-protected
  // task queue. The event_buffer is only safe to use from the main thread.
  Post(Task(std::move(event)));
}
 
// static
void App::PostEventOrExecute(Closure closure) {
  if (!closure) {
    return;
  }
  if (auto* app = App::Active()) {
    app->Post(std::move(closure));
  } else {
    closure();
  }
}
 
void App::RequestAnimationFrame() {
  if (internal_->animation_requested_) {
    return;
  }
  internal_->animation_requested_ = true;
  auto now = animation::Clock::now();
  const auto time_histeresis = std::chrono::milliseconds(33);
  if (now - internal_->previous_animation_time_ >= time_histeresis) {
    internal_->previous_animation_time_ = now;
  }
}
 
CapturedMouse App::CaptureMouse() {
  if (internal_->mouse_captured) {
    return nullptr;
  }
  internal_->mouse_captured = true;
  return std::make_unique<CapturedMouseImpl>(
      [this] { internal_->mouse_captured = false; });
}
 
Closure App::WithRestoredIO(Closure fn) {
  return [this, fn] {
    internal_->Uninstall();
    fn();
    internal_->Install();
  };
}
 
void App::ForceHandleCtrlC(bool force) {
  internal_->force_handle_ctrl_c_ = force;
}
 
void App::ForceHandleCtrlZ(bool force) {
  internal_->force_handle_ctrl_z_ = force;
}
 
std::string App::GetSelection() {
  if (!internal_->selection_) {
    return "";
  }
  return internal_->selection_->GetParts();
}
 
void App::SelectionChange(std::function<void()> callback) {
  internal_->selection_on_change_ = std::move(callback);
}
 
const std::string& App::TerminalName() const {
  return internal_->terminal_name_;
}
 
int App::TerminalVersion() const {
  return internal_->terminal_version_;
}
 
const std::string& App::TerminalEmulatorName() const {
  return internal_->terminal_emulator_name_;
}
 
const std::string& App::TerminalEmulatorVersion() const {
  return internal_->terminal_emulator_version_;
}
 
const std::vector<int>& App::TerminalCapabilities() const {
  return internal_->terminal_capabilities_;
}
 
std::vector<std::string> App::TerminalCapabilityNames() const {
  return Event::TerminalCapabilities("", internal_->terminal_capabilities_)
      .TerminalCapabilityNames();
}
 
// Loop calls these:
 
void App::ExitNow() {
  internal_->ExitNow();
}
void App::Install() {
  internal_->Install();
}
void App::Uninstall() {
  internal_->Uninstall();
}
void App::PreMain() {
  internal_->PreMain();
}
void App::PostMain() {
  internal_->PostMain();
}
bool App::HasQuitted() {
  return internal_->HasQuitted();
}
void App::RunOnce(const Component& component) {
  internal_->RunOnce(component);
}
void App::RunOnceBlocking(Component component) {
  internal_->RunOnceBlocking(component);
}
void App::HandleTask(Component component, Task& task) {
  internal_->HandleTask(component, task);
}
bool App::HandleSelection(bool handled, Event event) {
  return internal_->HandleSelection(handled, event);
}
void App::Draw(Component component) {
  internal_->Draw(component);
}
std::string App::ResetCursorPosition() {
  return internal_->ResetCursorPosition();
}
void App::RequestCursorPosition(bool force) {
  internal_->RequestCursorPosition(force);
}
void App::TerminalSend(std::string_view s) {
  internal_->TerminalSend(s);
}
void App::TerminalFlush() {
  internal_->TerminalFlush();
}
void App::InstallPipedInputHandling() {
  internal_->InstallPipedInputHandling();
}
void App::InstallTerminalInfo() {
  internal_->InstallTerminalInfo();
}
void App::Signal(int signal) {
  internal_->Signal(signal);
}
size_t App::FetchTerminalEvents() {
  return internal_->FetchTerminalEvents();
}
void App::PostAnimationTask() {
  internal_->PostAnimationTask();
}
 
Loop::Loop(App* screen, Component component)
    : screen_(screen), component_(std::move(component)) {
  screen_->PreMain();
}
 
Loop::~Loop() {
  screen_->PostMain();
}
 
bool Loop::HasQuitted() {
  return screen_->HasQuitted();
}
 
void Loop::RunOnce() {
  screen_->RunOnce(component_);
}
 
void Loop::RunOnceBlocking() {
  screen_->RunOnceBlocking(component_);
}
 
void Loop::Run() {
  while (!HasQuitted()) {
    RunOnceBlocking();
  }
}
 
}  // namespace ftxui