freywaros/src/user/app/terminal/terminal.c

#include "src/lib/memory.h"
#include "src/lib/util.h"
#include "src/user/syscall.h"

#define PROMPT_LENGTH 255

static const char bs[PROMPT_LENGTH + 1];
static const char ws[PROMPT_LENGTH + 1];

static char prompt[PROMPT_LENGTH + 1];
static uint8_t prompt_length = 0;
static uint8_t prompt_offset = 0;

static void on_home_pressed() {
  if (!prompt_offset) {
    return;
  }

  write(STDOUT, bs, prompt_offset);
  prompt_offset = 0;
}

static void on_left_pressed() {
  if (!prompt_offset) {
    return;
  }

  write(STDOUT, bs, 1);
  prompt_offset--;
}

static void on_right_pressed() {
  if (prompt_offset == prompt_length) {
    return;
  }

  write(STDOUT, prompt + prompt_offset, 1);
  prompt_offset++;
}

static void on_end_pressed() {
  if (prompt_offset == prompt_length) {
    return;
  }

  write(STDOUT, prompt + prompt_offset, prompt_length - prompt_offset);
  prompt_offset = prompt_length;
}

static void on_enter_pressed() {
  prompt[prompt_length] = '\n';

  write(3, prompt, prompt_length + 1);

  prompt_length = prompt_offset = 0;
}

static void on_cancel_pressed() {
  OUT_S("^C\n");
  write(3, "^C\n", 3);
  prompt_length = prompt_offset = 0;
}

static void on_disconnect_pressed() {
  OUT_S("^D\n");
  write(3, "^D\n", 3);
  exit(EXIT_CODE_OK);
}

static void on_ctrl_character_pressed(char c) {
  if (c == 'c') {
    on_cancel_pressed();
  } else if (c == 'd') {
    on_disconnect_pressed();
  }
}

static void redraw_from_cursor() {
  uint64_t tail = prompt_length - prompt_offset;
  write(STDOUT, prompt + prompt_offset, tail);
  write(STDOUT, ws, 1);        // erase the character past the end
  write(STDOUT, bs, tail + 1); // move back to cursor position
}

static void on_character_pressed(char c) {
  if (prompt_offset >= PROMPT_LENGTH)
    return;

  if (prompt_offset != prompt_length) {
    memory_move(prompt + prompt_offset, prompt_length - prompt_offset, prompt + prompt_offset + 1);
  }
  prompt[prompt_offset] = c;
  prompt_length++;
  prompt_offset++;

  write(STDOUT, &c, 1); // emit the character itself
  redraw_from_cursor();
}

static void on_backspace_pressed() {
  if (!prompt_offset)
    return;

  if (prompt_offset != prompt_length) {
    memory_move(prompt + prompt_offset, prompt_length - prompt_offset, prompt + prompt_offset - 1);
  }
  prompt_offset--;
  prompt_length--;

  write(STDOUT, bs, 1);
  redraw_from_cursor();
}

static void on_delete_pressed() {
  if (prompt_offset == prompt_length)
    return;

  memory_move(prompt + prompt_offset + 1, prompt_length - prompt_offset - 1, prompt + prompt_offset);
  prompt_length--;

  redraw_from_cursor();
}

typedef enum {
  PARSE_NORMAL,
  PARSE_ESC,
  PARSE_CSI,
} parse_state_t;

static parse_state_t parser_state = PARSE_NORMAL;
static char parser_csi_param[8];
static uint8_t parser_csi_len;

static void on_char_received(char c) {
  switch (parser_state) {
  case PARSE_NORMAL:
    if (c == '\x1B') {
      parser_state = PARSE_ESC;
    } else if (c == '\b' || c == '\x7F') {
      on_backspace_pressed();
    } else if (c == '\n' || c == '\r') {
      on_enter_pressed();
    } else if (c >= '\x01' && c <= '\x1A') {
      on_ctrl_character_pressed(c + 'a' - 1);
    } else if (c >= ' ') {
      on_character_pressed(c);
    }
    break;

  case PARSE_ESC:
    if (c == '[') {
      parser_state = PARSE_CSI;
      parser_csi_len = 0;
    } else {
      parser_state = PARSE_NORMAL;
    }
    break;

  case PARSE_CSI:
    if ((c >= '0' && c <= '9') || c == ';') {
      if (parser_csi_len < sizeof(parser_csi_param) - 1) {
        parser_csi_param[parser_csi_len++] = c;
      }
    } else {
      parser_state = PARSE_NORMAL;
      parser_csi_param[parser_csi_len] = '\0';

      switch (c) {
      case 'C':
        on_right_pressed();
        break;
      case 'D':
        on_left_pressed();
        break;
      case 'H':
        on_home_pressed();
        break;
      case 'F':
        on_end_pressed();
        break;
      case '~':
        if (parser_csi_param[0] == '3') {
          on_delete_pressed();
        }
        break;
      }
    }
    break;
  }
}

uint64_t main() {
  memory_set('\b', PROMPT_LENGTH, (char *)bs);
  memory_set(' ', PROMPT_LENGTH, (char *)ws);

  char c;
  while (read(STDIN, 1, &c)) {
    on_char_received(c);
  }

  return 0;
}