#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <dirent.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <string.h>
#include <fcntl.h>
#include <sys/wait.h>
#include <err.h>

#define MAX_PATH_LENGTH 1024

int pipefd[2];

void explore_and_execute(const char *dirpath) {
    DIR *dir;
    struct dirent *entry;
    char path[MAX_PATH_LENGTH];
    struct stat statbuf;
    int active_processes = 0;

    if (!(dir = opendir(dirpath)))
        return;

    while ((entry = readdir(dir)) != NULL) {
        if (strcmp(entry->d_name, ".") == 0 || strcmp(entry->d_name, "..") == 0)
            continue;

        sprintf(path, "%s/%s", dirpath, entry->d_name);
        if (stat(path, &statbuf) == -1)
            continue;

        if (S_ISDIR(statbuf.st_mode)) {
            char dummy;
            read(pipefd[0], &dummy, 1);
            pid_t pid = fork();
            if (pid == 0) {
                explore_and_execute(path);
                exit(0);
            } else if (pid > 0) {
                active_processes++;
                write(pipefd[1], &dummy, 1);
            }
        } else if (S_ISREG(statbuf.st_mode) && (statbuf.st_mode & S_IXUSR)) {
            char dummy;
            if (read(pipefd[0], &dummy, 1) != 1) {
                err(1, "read from pipe");
            }
            pid_t pid = fork();
            if (pid < 0) {
                err(1, "fork");
            } else if (pid == 0) {
                execl(path, path, (char *)NULL);
                err(1, "execl");
            }
            wait(NULL);
            if (write(pipefd[1], &dummy, 1) != 1) {
                err(1, "write to pipe");
            }
        }
    }
    while (active_processes > 0) {
        wait(NULL);
        active_processes--;
    }
    closedir(dir);
}

void check_pipe(int limit_) {
    for(int i = 0; i < limit_; i++) if(write(pipefd[1], "1", 1) != 1) err(1, "initialize error");
}

int main(int argc, char *argv[]) {
    int k = atoi(argv[1]);
    pipe(pipefd);
    check_pipe(k);

    explore_and_execute(".");

    close(pipefd[0]);
    close(pipefd[1]);

    return 0;
}