#include <unistd.h>
#include <stdio.h>
#include <sys/types.h>
#include <string.h>
#include <errno.h>
#include <sys/wait.h>

#define LOOPS_PER_CHILD 2000
#define CHILDS 30

#define PIPE_READ 0
#define PIPE_WRITE 1

int main() {
    int pipes[CHILDS][2];
    pid_t childToPipes[CHILDS];

    for (int child = 0; child < CHILDS; child++) {
        if (pipe(pipes[child]) == -1) {
            fprintf(stderr, "Error creating pipe for child %d: %s\n", child, strerror(errno));
            return 2;
        }

        pid_t pid = fork();
        if (pid == -1) {
            fprintf(stderr, "Error forking: %s\n", strerror(errno));
            return 1;
        } else if (pid == 0) {
            // I AM FORK!
            pid_t childPid = getpid();

            // close read of pipe
            close(pipes[child][PIPE_READ]);

            int start = child * LOOPS_PER_CHILD;
            long sum = 0;
            for (int i = start; i < start + LOOPS_PER_CHILD; i++) {
                fprintf(stdout, "%d: %d\n", childPid, i);
                fflush(stdout);
                sum += i;
            }

            printf("Fork %d finished counting from %d. Sum is %d\n", childPid, start, sum);

            if (write(pipes[child][PIPE_WRITE], &sum, sizeof(sum)) == -1) {
                fprintf(stderr, "Error writing pipe for child %d: %s\n", child, strerror(errno));
                return 4;
            }

            close(pipes[child][PIPE_WRITE]);

            return 0;
        } else {
            // close write of pipe
            close(pipes[child][PIPE_WRITE]);
            childToPipes[child] = pid;
            printf("Fork %d successfull\n", pid);
        }
    }

    // wait for all childs to terminate
    pid_t childPid;
    long overallSum = 0;
    while ((childPid = wait(NULL)) != -1) {
        printf("Child %d terminated\n", childPid);
        long sum = -1;
        for (int child = 0; child < CHILDS && sum == -1; child++) {
            if (childToPipes[child] == childPid) {
                read(pipes[child][PIPE_READ], &sum, sizeof(sum));
                close(pipes[child][PIPE_READ]);
            }
        }

        if (sum != -1) {
            overallSum += sum;
        } else {
            fprintf(stderr, "Error reading from pipe\n");
            return 3;
        }
    }

    printf("Overall Sum: %d\n", overallSum);

    return 0;

    fork();
    fork();
    fork();
    printf("Hello World\n");
}