Windows ANSI line editor

line.cpp

#include <Windows.h>

class ModeRestore {
  HANDLE in, out;
  DWORD inmode, outmode;
public:
  ModeRestore(HANDLE in, DWORD inmode, HANDLE out, DWORD outmode) : in(in), out(out) {
    DWORD written;
    if (GetConsoleMode(in, &this->inmode)) {
      SetConsoleMode(in, inmode);
    } else {
      this->inmode = 0;
    }
    if (GetConsoleMode(out, &this->outmode)) {
      SetConsoleMode(out, outmode);
    } else {
      this->outmode = 0;
    }
  }
  ~ModeRestore() {
    if (inmode) {
      SetConsoleMode(in, inmode);
    }
    if (outmode) {
      SetConsoleMode(out, outmode);
    }
  }
};

int main() {
  DWORD written;
  auto out = CreateFileW(L"CONOUT$", GENERIC_READ | GENERIC_WRITE, 3, 0, 3, 0, 0);
  if (out == INVALID_HANDLE_VALUE) {
    return 1;
  }
  auto in = CreateFileW(L"CONIN$", GENERIC_READ | GENERIC_WRITE, 3, 0, 3, 0, 0);
  if (in == INVALID_HANDLE_VALUE) {
    WriteFile(out, "no input\n", 9, &written, nullptr);
    return 1;
  }

  ModeRestore moderestore(in, 0x204, out, 0xF);
  SetConsoleCtrlHandler(nullptr, TRUE);

  char esc[16];
  int esc_idx = 0;
  int cursor;
  auto handle_esc = [&]() -> bool {
    if (esc_idx == 1) {
      return true;
    }
    if (esc[1] != '[') {
      return false;
    }
    if (esc_idx == 2) {
      return true;
    }
    if (esc[2] == 'C' || esc[2] == 'D') {
      // ^[[C, ^[[D = right/left
      if (esc[2] == 'C') {
        ++cursor;
      } else {
        if (--cursor < 0) { cursor = 0; }
      }
      char m[] = { '\x1b', '[', 0, 0, 'G' };
      m[2] = '0' + cursor / 10;
      m[3] = '0' + cursor % 10;
      WriteFile(out, m, 5, &written, nullptr);
    } else if (esc[2] == 'A') {
      // ^[[A = up
      WriteFile(out, "\x1b[S", 3, &written, nullptr);
    } else if (esc[2] == 'B') {
      // ^[[B = down
      WriteFile(out, "\x1b[T", 3, &written, nullptr);
    }
    esc_idx = 0;
    return true;
  };

  int line = 0;
  auto handle_char = [&](char c) {
    if (esc_idx > 0) {
      // Continue escape sequence
      esc[esc_idx++] = c;
      if (handle_esc()) {
        return;
      }
    } else if (c == 0x1b) {
      // Begin escape sequence
      esc[0] = 0x1b;
      esc_idx = 1;
    } else if (c == 8 || c == 0x7f) {
      // Backspace
      char m[] = { '\x1b', '[', 0, 0, 'G', ' ', '\x1b', '[', 0, 0, 'G' };
      if (--cursor < 0) { cursor = 0; }
      m[2] = '0' + cursor / 10;
      m[3] = '0' + cursor % 10;
      m[8] = '0' + cursor / 10;
      m[9] = '0' + cursor % 10;
      WriteFile(out, m, 11, &written, nullptr);
    } else if (c == 11) { // ^K
      // Clear the screen
      WriteFile(out, "\x1b[2J\x1b[1;0H> \x1b[3G", 16, &written, nullptr);
      cursor = 3;
      line = 1;
    } else if (c >= 0 && c < 0x20) {
      // Echo the control sequence
      char m[2] = { '^', 0 };
      char *s = "@ABCDEFGHI\0KL\0NOPQRSTUVWXYZ[\\]^_";
      if ((m[1] = s[c]) == 0) {
        return;
      }
      cursor += 2;
      WriteFile(out, m, 2, &written, nullptr);
    } else {
      // Echo the character
      ++cursor;
      WriteFile(out, &c, 1, &written, nullptr);
    }
  };

  auto next_line = [&]() {
    // Query cursor position
    WriteFile(out, "\x1b[6n", 4, &written, nullptr);
    int stage = 0;
    int nl = 0, nc = 0;
    while (true) {
      char c;
      DWORD read;
      ReadFile(in, &c, 1, &read, nullptr);
      if (stage == 0 && c == 0x1b) {
        stage = 1;
        continue;
      }
      if (stage == 1 && c == '[') {
        stage = 2;
        continue;
      }
      if (stage == 2) {
        if (c >= '0' && c <= '9') {
          nl = nl * 10 + (c - '0');
        } else if (c == ';') {
          stage = 3;
        } else {
          break;
        }
        continue;
      }
      if (stage == 3) {
        if (c >= '0' && c <= '9') {
          nc = nc * 10 + (c - '0');
          continue;
        } else if (c == 'R') {
          line = nl + 1;
        }
      }
      break;
    }
    cursor = 3;
    char m[] = { '\x1b', '[', 0, 0, ';', '0', 'H', '>', ' ', '\x1b', '[', '3', 'G' };
    m[2] = '0' + line / 10;
    m[3] = '0' + line % 10;
    WriteFile(out, m, 13, &written, nullptr);
  };

  WriteFile(out, "> ", 2, &written, nullptr);
  cursor = 3;
  while (true) {
    char c;
    DWORD read;
    while (true) {
      ReadFile(in, &c, 1, &read, nullptr);
      if (read == 0) { return 2; }
      handle_char(c);
      if (c == 4) { return 0; }
      if (c == 0xA || c == 0xD) {
        next_line();
        break;
      }
    }
  }
}