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

void make_fifo_if_not_exists(char *fifo_name) {
    struct stat s;
    // stat is a function that returns information about a file (if it exists) -> see man 2 stat
    // we will check the owner and file type from here
    // if we don't own the file -> abort
    // if file is not a FIFO -> abort
    // if it is a FIFO and we own it -> try to unlink and remake FIFO to ensure that it is empty.
    if(0 > stat(fifo_name, &s)) {
        // ENOENT -> file doesn't exist
        // We can try to create a FIFO with that name
        if(ENOENT == errno) {
            printf("No file with the name %s exists, we're good to go.\n", fifo_name);
            if(0 > mkfifo(fifo_name, 0600)) {
                perror("Error on creating fifo: ");
                exit(1);
            }
        } else {
            // other error encountered
            // best to abort here
            perror("Error encountered while trying to get info about the filename: ");
            exit(1);
        }
    } else {
        // we found a file with the given name, let's check who owns it and what type of file it is
        if (s.st_uid == getuid()) {
            // if we are the owner of the file
            // S_ISFIFO is a macro described in the manual page of stat (man 2 stat)
            // it uses the st_mode field of the stat structure to identify the type
            if(S_ISFIFO(s.st_mode)) {
                printf("FIFO %s already exists. Trying to unlink and remake.\n", fifo_name);
                // file is a FIFO and we own it
                // let's remake it to clean it up
                if(0 > unlink(fifo_name)) {
                    perror("Unable to remove fifo: ");
                    exit(1);
                }
                if(0 > mkfifo(fifo_name, 0600)) {
                    perror("Error on creating fifo: ");
                    exit(1);
                }
            } else {
                // if not a FIFO, leave it alone and abort
                printf("File %s exists and is not a FIFO.\n", fifo_name);
            }
        } else {
            // we are not the owner of the file, it's best to leave it alone
            printf("The file %s belongs to somebody else.", fifo_name);
            exit(1);
        }
    }
}

int main(int argc, char *argv[]) {
    make_fifo_if_not_exists("./myfifo");
    return 0;
}