#include <signal.h>
#include <stdio.h>
#include <string.h>

#define MAX_ELEMENTS_PLUS_ONE 4
typedef char item_t[256];

struct ring_buffer {
  item_t data[MAX_ELEMENTS_PLUS_ONE];
  size_t first;
  size_t last;
};

void initBuffer(struct ring_buffer *buffer) {
  memset(buffer, 0, sizeof(*buffer));
}

void put(struct ring_buffer *buffer, const item_t *item) {
  if ((buffer->last + 1) % MAX_ELEMENTS_PLUS_ONE == buffer->first)
    // the buffer is full, now what?
    raise(SIGUSR1);
  memcpy(&buffer->data[buffer->last], item, sizeof(*item));
  buffer->last = (buffer->last + 1) % MAX_ELEMENTS_PLUS_ONE;
}

void get(struct ring_buffer *buffer, item_t *item) {
  if (buffer->last == buffer->first)
    // the buffer is empty, what now?
    raise(SIGUSR2);
  memcpy(item, &buffer->data[buffer->first], sizeof(*item));
  buffer->first = (buffer->first + 1) % MAX_ELEMENTS_PLUS_ONE;
}

int main() {
  struct ring_buffer buffer;
  initBuffer(&buffer);
  printf("g             gets data from buffer\n"
         "ptext...      puts 'text...' to buffer\n");
  while (1) {
    printf("> ");
    fflush(stdout);
    char cmd[2], c;
    item_t item = {0};
    scanf("%1[^\n]%255[^\n]", cmd, item);
    do { // this reads all remaining characters in this line including '\n'
      c = getchar();
      if (c == -1)
        return 0;
    } while (c != '\n');
    switch (cmd[0]) {
    case 'p':
      put(&buffer, &item);
      break;
    case 'g':
      get(&buffer, &item);
      printf("%s\n", item);
      break;
    }
  }
  return 0;
}