#define _GNU_SOURCE

#include <dlfcn.h>
#include <errno.h>
#include <pwd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>

int strlcpy(char *restrict dest, const char *restrict src, size_t bufsize) {
    size_t i;
    for (i = 0; i < bufsize; ++i) {
        dest[i] = src[i];
        if (src[i] == '\0') {
            return 0;
        }
    }
    return ERANGE;
}

char *getlogin(void) {
    return getenv("USER");
}

int getlogin_r(char *buf, size_t bufsize) {
    const char *login = getlogin();
    if (login == NULL) {
        return ENOENT;
    }
    return strlcpy(buf, login, bufsize);
}

struct passwd *getpwuid(uid_t uid) {
    struct passwd *(*getpwuid)(uid_t) = dlsym(RTLD_NEXT, "getpwuid");
    if (getpwuid == NULL) {
        fprintf(stderr, "Unable to find the adress of the getpwuid function: %s\n", dlerror());
        return NULL;
    }
    struct passwd *pass = getpwuid(uid);
    if (pass == NULL) {
        return NULL;
    }
    char *name = getenv("USER");
    if (name == NULL) {
        fprintf(stderr, "Could not find the USER environment variable. Using the real username.\n");
        return pass;
    }
    pass->pw_name = name;
    return pass;
}

int getpwuid_r(uid_t uid, struct passwd *pw, char *buf, size_t size, struct passwd **res) {
    int prev_err = errno;
    *res = NULL;
    struct passwd *pass = getpwuid(uid);
    if (pass == NULL || errno != prev_err) {
        return errno;
    }
    memcpy(pw, pass, sizeof(struct passwd));
    size_t name_len = strlen(pass->pw_name) + 1;
    size_t passwd_len = strlen(pass->pw_passwd) + 1;
    size_t gecos_len = strlen(pass->pw_gecos) + 1;
    size_t dir_len = strlen(pass->pw_dir) + 1;
    size_t shell_len = strlen(pass->pw_shell) + 1;
    if ((name_len + passwd_len + gecos_len + dir_len + shell_len) > size) {
        return ERANGE;
    }
    pw->pw_name = memcpy(buf, pass->pw_name, name_len);
    pw->pw_passwd = memcpy(buf + name_len, pass->pw_passwd, passwd_len);
    pw->pw_gecos = memcpy(buf + name_len + passwd_len, pass->pw_gecos, gecos_len);
    pw->pw_dir = memcpy(buf + name_len + passwd_len + gecos_len, pass->pw_dir, dir_len);
    pw->pw_shell = memcpy(buf + name_len + passwd_len + gecos_len + dir_len, pass->pw_shell, shell_len);
    *res = pw;
    return 0;
}