cnake.c

#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/select.h>
#include <termios.h>
#include <unistd.h>

#define COLS (60)
#define ROWS (20)
#define MAX_SNAKE_LENGTH (COLS * ROWS)

/* ANSI escape sequences */
/* @see https://gist.github.com/ConnerWill/d4b6c776b509add763e17f9f113fd25b */
#define AES_ESCAPE "\x1B["
#define AES_ERASE AES_ESCAPE "0J"
#define AES_CURSOR_HIDE AES_ESCAPE "?25l"
#define AES_CURSOR_SHOW AES_ESCAPE "?25h"
#define AES_CURSOR_UP AES_ESCAPE "%dA"
#define AES_CURSOR_DOWN AES_ESCAPE "%dB"
#define AES_CURSOR_RIGHT AES_ESCAPE "%dC"
#define AES_CURSOR_LEFT AES_ESCAPE "%dD"
#define AES_TEXT_COLOR_RED AES_ESCAPE "0;31m"
#define AES_TEXT_COLOR_GREEN AES_ESCAPE "0;32m"
#define AES_TEXT_RESET AES_ESCAPE "0m"
#define AES_TEXT_BLINK AES_ESCAPE "5m"
#define AES_CURSOR_UP_BOL AES_ESCAPE "%dF"

enum TextStyle {
  TEXT_DEFAULT,
  TEXT_RED,
  TEXT_GREEN,
  TEXT_BLINK,
};

const char *TEXT_GAME_OVER = "Game Over!";
const char *text_styles[] = {
    AES_TEXT_RESET,
    AES_TEXT_COLOR_RED,
    AES_TEXT_COLOR_GREEN,
    AES_TEXT_BLINK,
};
struct termios term_initial;

void print_table(void) {
  printf("┌");
  for (unsigned c = 0; c < COLS; c++) {
    printf("─");
  }
  printf("┐\n");

  for (unsigned r = 0; r < ROWS; r++) {
    printf("│");
    for (unsigned c = 0; c < COLS; c++) {
      printf(" ");
    }
    printf("│\n");
  }

  printf("└");
  for (unsigned c = 0; c < COLS; c++) {
    printf("─");
  }
  printf("┘\n");

  // Cursor now at final (ROWS+2, 0)
  // Move it back to BOL of starting position
  printf(AES_CURSOR_UP, ROWS + 2);
}

void print_at(const char *str, const int row, const int col,
              const enum TextStyle style) {
  printf(AES_CURSOR_DOWN, row);
  printf(AES_CURSOR_RIGHT, col);
  printf("%s", text_styles[style]);
  printf("%s", str);
  printf(AES_TEXT_RESET);
  printf(AES_CURSOR_UP_BOL, row);
}

void play_sound(void) { printf("\a"); }

void exit_handler(void) {
  printf(AES_CURSOR_SHOW);
  printf(AES_ERASE);
  tcsetattr(STDIN_FILENO, TCSANOW, &term_initial);
}

/* Ensure our exit handler runs when Ctrl+C is pressed */
void sigint_handle(int _unused) {
  (void)_unused; // ignore unused attr warning
  exit_handler();
  exit(1);
}

/* Sleeps for the given amount in miliseconds */
/* Like sleep or usleep, but with ms precision (and not a GNU extension) */
void wait(unsigned int ms) {
  struct timeval tv = {0L, ms * 1000L};
  fd_set fds;
  FD_ZERO(&fds);
  FD_SET(STDERR_FILENO, &fds);
  select(STDERR_FILENO, &fds, NULL, NULL, &tv);
}

/* Checks if there is any input waiting to be read in stdin */
int kbhit(void) {
  struct timeval tv = {0L, 0L};
  fd_set fds;
  FD_ZERO(&fds);
  FD_SET(STDIN_FILENO, &fds);
  select(STDOUT_FILENO, &fds, NULL, NULL, &tv);
  return FD_ISSET(0, &fds);
}

/* Normalizes key presses to WASD */
int getch(void) {
  if (!kbhit()) {
    return 0;
  }

  int ch = 0;
  read(STDIN_FILENO, &ch, 1);
  if (ch != 27) {
    return ch;
  }

  /* ANSI escape sequence was pressed */
  /* If nothing follows, ESC was pressed */
  if (!kbhit()) {
    return ch;
  }

  /* If next byte is 91, an arrow key was pressed */
  int a = 0;
  read(STDIN_FILENO, &a, 1);
  if (a != 91) {
    return ch;
  }

  if (!kbhit()) {
    return ch;
  }
  int b = 0;
  read(STDIN_FILENO, &b, 1);

  switch (b) {
  case 65:
    return 'w';
    break;
  case 66:
    return 's';
    break;
  case 67:
    return 'd';
    break;
  case 68:
    return 'a';
    break;
  default:
    return ch;
    break;
  }

  return ch;
}

void term_init(void) {
  /* Initialize terminal */
  printf(AES_CURSOR_HIDE);
  struct termios term_cfg;
  tcgetattr(STDIN_FILENO, &term_initial);
  term_cfg = term_initial;

  /* Like cfmakeraw() but without the output flags */
  term_cfg.c_lflag &= (tcflag_t) ~(ECHO | ECHONL | ICANON | ISIG | IEXTEN);
  term_cfg.c_cflag &= (tcflag_t) ~(CSIZE | PARENB);
  term_cfg.c_iflag &= (tcflag_t) ~(IGNBRK | BRKINT | PARMRK | ISTRIP | INLCR |
                                   IGNCR | ICRNL | IXON);
  tcsetattr(STDIN_FILENO, TCSANOW, &term_cfg);
  signal(SIGINT, &sigint_handle);
  atexit(&exit_handler);
}

int main(void) {
  term_init();
  int x[MAX_SNAKE_LENGTH];
  int y[MAX_SNAKE_LENGTH];

  while (1) {
    print_table();

    unsigned int head = 0;
    unsigned int tail = 0;
    unsigned int speed = 20;
    x[head] = COLS / 2;
    y[head] = ROWS / 2;

    char game_over = 0;
    int dx = 1;
    int dy = 0;
    int food_x = -1;
    int food_y;

    while (!game_over) {
      /* maybe place new food */
      if (food_x < 0) {
        food_x = rand() % COLS;
        food_y = rand() % ROWS;

        /* check for instant collission */
        for (unsigned int i = tail; i != head; i = (i + 1) % MAX_SNAKE_LENGTH) {
          if (x[i] == food_x && y[i] == food_y) {
            food_x = -1;
            break;
          }
        }

        if (food_x >= 0) {
          print_at("❤", food_y + 1, food_x + 1, TEXT_RED);
        }
      }

      /* Draw over tail */
      print_at(" ", y[tail] + 1, x[tail] + 1, TEXT_DEFAULT);

      /* Check if head collided with food */
      if (x[head] == food_x && y[head] == food_y) {
        food_x = -1;
        play_sound();
      } else {
        tail = (tail + 1) % MAX_SNAKE_LENGTH;
      }

      /* Calculate position for new head */
      unsigned int newhead = (head + 1) % MAX_SNAKE_LENGTH;
      x[newhead] = (x[head] + dx + COLS) % COLS;
      y[newhead] = (y[head] + dy + ROWS) % ROWS;
      head = newhead;

      /* Check if new head collides with any part of snake body */
      for (unsigned int i = tail; i != head; i = (i + 1) % MAX_SNAKE_LENGTH) {
        if (x[i] == x[head] && y[i] == y[head]) {
          game_over = 1;
          break;
        }
      }

      /* Draw head */
      print_at("█", y[head] + 1, x[head] + 1, TEXT_GREEN);
      fflush(stdout);
      wait(1000 / speed);

      int ch = getch();
      if (ch) {
        if (ch == 27) {
          return EXIT_SUCCESS;
        } else if (ch == 'w' && dy != 1) {
          dx = 0;
          dy = -1;
        } else if (ch == 'a' && dx != 1) {
          dx = -1;
          dy = 0;
        } else if (ch == 's' && dy != -1) {
          dx = 0;
          dy = 1;
        } else if (ch == 'd' && dx != -1) {
          dx = 1;
          dy = 0;
        } else if (ch == '+' && speed < 40) {
          speed += 4;
        } else if (ch == '-' && speed > 4) {
          speed -= 4;
        }
      }
    }

    if (game_over) {
      print_at(TEXT_GAME_OVER, ROWS / 2,
               COLS / 2 - ((int)strlen(TEXT_GAME_OVER) / 2), TEXT_BLINK);
      fflush(stdout);
      wait(1000);
      getchar();
    }
  }

  return EXIT_SUCCESS;
}