#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <unistd.h>

#define CHECK(result, textOnFail)                                              \
  if (((long int)result) == -1) {                                              \
    perror(textOnFail);                                                        \
    exit(1);                                                                   \
  }

struct myData {
  int version;
  char text[1020];
};

int main() {
  int fd = shm_open("/os_cp", O_RDWR | O_CREAT, 0600);
  CHECK(fd, "shm_open failed");
  int r = ftruncate(fd, sizeof(struct myData));
  CHECK(r, "ftruncate failed");
  struct myData *data = mmap(NULL, sizeof(struct myData),
                             PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
  CHECK(data, "mmap failed");
  close(fd);

  printf("commands:\n"
         "  r           - reads the text\n"
         "  w <text>    - writes new text\n"
         "  q           - quits\n");

  while (1) {
    printf("> ");
    fflush(stdout);

    char c, text[1022] = {0};
    scanf("%1021[^\n]", text);
    do { // this reads all remaining characters in this line including '\n'
      c = getchar();
      CHECK(c, "getchar EOF'ed");
    } while (c != '\n');

    if (!strlen(text)) // empty line
      continue;

    switch (text[0]) {
    case 'r':
      printf("version: %d\n   text: %s\n", data->version, data->text);
      break;
    case 'w':
      data->version++;
      strcpy(data->text, text + 2);
      break;
    case 'q':
      munmap(data, sizeof(struct myData));
      exit(0);
      break;
    }
  }
}