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

int main(int argc, char* argv[]){
    int pipe1[2], pipe2[2], sync[2];

    int pid1;
    int pid2;

    if(((pipe(pipe1)) < 0) || ((pipe(pipe2)) <0) || ((pipe(sync)) <0)){
        perror("errore pipe");
        exit(1);
    }

    if((pid1 = fork()) < 0){
        perror("errore fork");
        exit(1);
    }

    if(pid1 == 0){  //primo figlio
        int inputF;
        if((inputF = open(argv[1], O_RDONLY)) < 0){
            perror("errore open input");
            exit(1);
        }

        char buff[2];
        char outBuff1[4];

        close(pipe1[0]);
        close(sync[0]);

        int nread = 0;
        while(read(inputF, buff, 2) == 2){
            if(nread == 4){
                write(sync[1], "S", 1);
                nread = 0;
            }
            else{
                write(sync[1], "N", 1);
                nread += 2;
            }

            write(pipe1[1], buff, 2);

        }

        close(pipe1[1]);
        close(sync[1]);
        close(inputF);
    }

    else{
        if((pid2 = fork()) < 0){
            perror("errore seconda fork");
            exit(1);
        }

        if(pid2 == 0){ //secondo figlio
            close(pipe2[1]);

            char buff_2[4];
            char outBuff[2];
            int outputF;
            if((outputF = open(argv[2], O_RDWR)) < 0){
                perror("errore apertura output");
                exit(1);
            }
            while(read(pipe2[0], buff_2, 4) == 4){
                outBuff[0] = buff_2[0];
                outBuff[1] = buff_2[3];
                write(outputF, outBuff, 2);
            }
            close(pipe2[0]);
            close(outputF);
        }

        else{   //padre
            char buff_padre[4];
            char flag;
            close(pipe1[1]);
            close(pipe2[0]);
            close(sync[1]);

            while(read(sync[0], &flag, 1) == 1){
                if(flag == 'S'){
                    if(read(pipe1[0], buff_padre, 4) == 4){
                        if(buff_padre[0] != buff_padre[3])
                            write(pipe2[1], buff_padre, 4);
                    }
                }
            }

            close(pipe1[0]);
            close(pipe2[1]);
            close(sync[0]);
        }
    }

    return 0;
}