#include <unistd.h>
#include <fcntl.h> /* Definition of AT_* constants */
#include <sys/stat.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/syscall.h> /* Definition of SYS_* constants */
#include <sys/msg.h>

const char *main_key_file = "/tmp/IPC-SERVER-43412321";

struct Msg_pid
{
    long mtype;
    pid_t pid;
} typedef msg_pid;

struct Msg_data
{
    long mtype;
    double data;
} typedef msg_data;

void handle_error(char *txt)
{
    perror(txt);
    exit(-1);
}

int main()
{
    if (access(main_key_file, F_OK) == 0)
        unlink(main_key_file);

    if (mknod(main_key_file, 0600 | S_IFREG, NULL) != 0)
        handle_error("main file creation");

    key_t main_key;
    if ((main_key = ftok(main_key_file, 0)) == -1)
        handle_error("ftok");

    int m_msg_id;
    if ((m_msg_id = msgget(main_key, 0600 | IPC_CREAT)) == -1)
        handle_error("msgget");
    msg_pid pid_msg;

    while (1)
    {
        if (msgrcv(m_msg_id, (void *)&pid_msg, sizeof(pid_t), 1, 0) == -1)
            handle_error("msgrcv");

        printf("%d\n", pid_msg.pid);

        int pid;
        if ((pid = fork()) == -1)
            handle_error("fork");
        if (pid == 0)
        {
            key_t pid_key;
            if ((pid_key = ftok(main_key_file, pid_msg.pid)) == -1)
                handle_error("ftok data");

            int d_msg_id;
            if ((d_msg_id = msgget(pid_key, 0600)) == -1)
                handle_error("msgget data");

            msg_data data_msg;
            if (msgrcv(d_msg_id, (void *)&data_msg, sizeof(double), 1, 0600) == -1)
                handle_error("msgrcv data");
            printf("Received data %f\n", data_msg.data);
            data_msg.mtype = 2;
            data_msg.data *= data_msg.data;
            if (msgsnd(d_msg_id, (void *)&data_msg, sizeof(double), 0) == -1)
                handle_error("msgsnd data");
        }
    }
    if (msgctl(m_msg_id, IPC_RMID, NULL) == -1)
        handle_error("msgctl RMID");

    return 0;
}