#include <map>
#include <fstream>
#include <sstream>
#include <vector>
#include <string>
#include <iostream>
#include <openssl/md5.h>
#include <unistd.h>
using namespace std;

vector<string> split(string &s, char delim) {
    vector<string> elems;
    stringstream ss(s);
    string item;
    while(getline(ss,item,delim))
        elems.push_back(item);
    return elems;
}

void load_hashes(map<string, pair<string,string> > &active, string &fileName) {
    ifstream file(fileName);
    string str;
    while(getline(file,str)) {
        vector<string> elems = split(str,' ');
        active[elems[0]] = {elems[1],elems[2]};
    }
}

bool check_username_exists(map<string, pair<string,string> > &active, string username) {
    if(active.find(username)!=active.end())
        return true;
    return false;
}

char *md5_conversion(const char *str) {
    MD5_CTX c;
    MD5_Init(&c);
    MD5_Update(&c, str, 30);
    unsigned char digest[16];
    MD5_Final(digest, &c);
    char* md5string = (char*) malloc(sizeof(char)*33);
    for(int i = 0; i < 16; ++i)
        sprintf(&md5string[i*2], "%02x", (unsigned int)digest[i]);
    return md5string;
}

string password_and_salt_hash(const char* password, string& salt) {
    char password_plus_salt[50];
    int i = 0;
    while(password[i]!=0) {
        password_plus_salt[i] = password[i];
        i++;
    }
    for(int j=0;j<salt.length();j++,i++)
        password_plus_salt[i] = salt[j];
    password_plus_salt[i] = 0;
    const char* str = password_plus_salt;
    char* md5_value = md5_conversion(password_plus_salt);
    string return_value(md5_value);
    delete[] md5_value;
    return return_value;
}

/* Complete this function or use third party libraries */
string generate_random_salt() {
    return "asdfadfadcasdcaf";
}

bool new_entry(map<string, pair<string,string> > &active, string& username, const char* password) {
    if(check_username_exists(active,username)) {
        cout << "The username already exists." << endl;
        return 0;
    }
    string salt = generate_random_salt();
    string hash = password_and_salt_hash(password,salt);
    active[username] = {salt,hash};
    cout << "Username successfully added." << endl;
    return 1;
}

bool check_entry(map<string, pair<string,string> > &active, string& username, const char* password) {
    if(!check_username_exists(active,username)) {
        cout << "Username does not exist." << endl;
        return 0;
    }
    string salt = active[username].first;
    string hash = password_and_salt_hash(password,salt);
    string stored_hash = active[username].second;
    if(hash==stored_hash) {
        cout << "Correct Username and Password." << endl;
        return 1;
    }
    else cout << "Wrong Password." << endl;
    return 0;
}

bool change_entry(map<string, pair<string,string> > &active, string& username, const char* password) {
    if(!check_username_exists(active,username)) {
        cout << "Username does not exist." << endl;
        return 0;
    }
    string salt = generate_random_salt();
    string hash = password_and_salt_hash(password,salt);
    active[username] = {salt,hash};
    cout << "Password successfully changed." << endl;
    return 1;
}

/* This function is just for debugging purpose during development. */
void print_map(map<string, pair<string,string> > &active) {
    for(auto elem : active)
        cout << elem.first << " " << elem.second.first << " " << elem.second.second << endl;
}

void store_hashes(map<string, pair<string,string> > &active,string &fileName) {
    ofstream file(fileName);
    for(auto elems: active)
        file << elems.first << " " << elems.second.first << " " << elems.second.second << "n";
}

void test() {
    // You can also use Boost Library for serialization stuff or else use a database
    map<string, pair<string,string> > active;
    string fileName = "secret.txt";
    load_hashes(active,fileName);
    print_map(active);
    string username = "shubham";
    // Limit the length of password , You can add additional constraints (Capital Letters, Numbers, Special characters)
    const char* password = "darkknight";
    new_entry(active, username, password);
    print_map(active);
    check_entry(active,username, password);
    const char* wrong_password = "fastestmanalive";
    check_entry(active,username, wrong_password);
    const char* change_password = "darkknightrises";
    change_entry(active,username, change_password);
    print_map(active);
    store_hashes(active,fileName);
}

int main() {
    test();
    return 0;
}

g++ password.cpp -std=c++11 -lcrypto