/******************************************************************************
* (C) 2019 ECKELMANN AG INDUSTRIEAUTOMATION, WIESBADEN
*******************************************************************************
*
* Author  schenk, ECKELMANN AG
* Date    20.02.2019
*
******************************************************************************/


#include <sys/types.h>
#include <pwd.h>
#include <shadow.h>
#include <crypt.h>
#include <string.h>
#include <stdio.h>

#define ERR_NO_ERROR 0
#define ERR_PASSWORD_MISMATCH 1
#define ERR_USER_DOES_NOT_EXIST 2
#define ERR_NO_PERMISSION 3
#define ERR_UNKNOWN 4


int system_authentificate_user (const char*username, const char*password)
{
    struct passwd*pw;
    struct spwd*sp;
    char*encrypted, *theGoodHash;
    int result=ERR_UNKNOWN;

    pw = getpwnam (username);
    endpwent();

    if (!pw) return ERR_USER_DOES_NOT_EXIST;

    sp = getspnam (pw->pw_name);
    endspent();
    if (sp)
        theGoodHash = sp->sp_pwdp;
    else
        theGoodHash = pw->pw_passwd;

    if (NULL == theGoodHash){
        return ERR_NO_PERMISSION;
    }

    encrypted = crypt (password, theGoodHash);

    if( 0 == strcmp (encrypted, theGoodHash)){
        result = ERR_NO_ERROR;
    }
    else{
        result = ERR_PASSWORD_MISMATCH;
    }
    return result;
}


int main(int argc, char *argv[])
{
    int result;

    if( argc < 3){
        printf("prog <USER> <PASSWORD>\n");
        return 3;
    }

    const char* user= argv[1];
    const char* pw= argv[2];

    result = system_authentificate_user( user, pw);

    if( result == ERR_NO_ERROR ){
        printf("password for %s ist valid.\n", user);
    }

    if( result == ERR_PASSWORD_MISMATCH){
        printf("password for %s ist invalid.\n", user);
    }

    if( result > ERR_PASSWORD_MISMATCH ){
        printf("Error authentificate user %s.\n", user);
    }

    return result;

}