//
// Written for Computer Networks and Systems lab classes
// AUTHOR : Sergiusz Warga

#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <time.h>
#include <unistd.h>

#define N_OF_ELEMENTS 1e6
#define N_OF_CHILDREN 10
#define SPAN (int)(N_OF_ELEMENTS/N_OF_CHILDREN)

union floaty {
        float number;
        char bytes[sizeof(float)];
};

int child_task(float * array, int start) {
    union floaty sum;
    for (int i = start; i < start + SPAN; ++i ) {
        sum.number += array[i];
    }

    char filename[16];
    snprintf(filename, 16, "sum%d.txt", getpid());
    int file = open(filename, O_CREAT | O_WRONLY);
    write(file, sum.bytes, sizeof(sum));
    close(file);

    return 0;
}

float avg(float * array) {
    float sum = 0;
    for (int i = 0; i < N_OF_CHILDREN; ++i) {
        sum += array[i];
    }
    return sum/N_OF_ELEMENTS;
}

int main() {
    srandom(time(NULL));
    int status[N_OF_CHILDREN];
    float sums[N_OF_CHILDREN] = {0};
    int children_pids[N_OF_CHILDREN];
    float * array = malloc(N_OF_ELEMENTS * sizeof(float));

    for (int i = 0; i < N_OF_ELEMENTS; ++i) {
        array[i] = 2*(float)random()/RAND_MAX - 1;  // Nasty
    }

    pid_t pid;

    for (int i = 0; i < N_OF_CHILDREN; ++i) {
        pid = fork();
        if (pid == -1) {    // If something went wrong.
            perror("Fork: ");
            exit(EXIT_FAILURE);
        }
        if (pid == 0){      // If this is a child process.
            child_task(array, (int)(i*SPAN));
            exit(EXIT_SUCCESS);
        }
        children_pids[i] = pid;
    }

    for (int i = 0; i < N_OF_CHILDREN; ++i) {
        waitpid(children_pids[i], &status[i], 0);
    }
        
    char filename[16];
    union floaty sum;

    for (int i = 0; i < N_OF_CHILDREN; ++i) {
        sum.number = 0;
        snprintf(filename, 16, "sum%d.txt", children_pids[i]);
        int file = open(filename, O_RDONLY);
        read(file, sum.bytes, sizeof(sum));    
        sums[i] = sum.number;
        close(file);
    }

    printf("avg = %f\n", avg(sums));

    return 0;
}