// C program to demonstrate use of fork() and pipe()
#include<stdio.h>
#include<stdlib.h>
#include<unistd.h>
#include<sys/types.h>
#include<string.h>
#include<sys/wait.h>

int main(int argc, char **argv)
{
    if (argc < 3) {
        printf("Error: This program requires at least 2 arguments\n");
        exit(0);
    }
    int cNum = atoi(argv[1]);
    int offset = 2;
    int inputLen = argc - offset;
    printf("There are %i children\n", cNum);
    // We use two pipes
    // First pipe to send input string from parent
    // Second pipe to send concatenated string from child
    int pipes[cNum][2];  // Used to store two ends of first pipe

    char fixed_str[] = "forgeeks.org";
    char input_str[100];
    pid_t p;

    for(int i = 0; i < cNum; i++) {
        if (pipe(pipes[i])==-1)
        {
        fprintf(stderr, "Pipe Failed" );
        return 1;
        }
    }

    int final = 0;
    for (int i = 0; i < cNum; i++) {
        p = fork();
        if (p < 0)
        {
            fprintf(stderr, "fork Failed" );
            return 1;
        }

        // Parent process
        else if (p > 0)
        {
            wait(NULL);
            close(pipes[i][1]); // Close writing end of second pipe
            // Read string from child, print it and close
            // reading end.
            char readval[20] = { 0 };
            read(pipes[i][0], readval, 20);
            printf("Read value %s\n", readval);
            final += atoi(readval);
            close(pipes[i][0]);
        }
        // child process
        else
        {
            // Close both reading ends
            close(pipes[i][0]);
            int total = 0;
            for (int j = 0; j < inputLen; j++) {
                if (j % cNum == i){
                    total += atoi(argv[offset + j]);
                }
            }
            printf("Child %i got total %i\n", i, total);
            // Write concatenated string and close writing end
            char str[10] = { 0 };
            sprintf(str, "%i", total);
            printf("Data to write for child %i is %s\n", i, str);
            write(pipes[i][1], str, strlen(str));
            close(pipes[i][1]);
            exit(0);
        }
    }

    printf("Parent calculated %i as total\n", final);
}