package com.noname;

import java.util.*;

public class UserUtils {

    public static List<User> findDuplicates(Collection<User> collA, Collection<User> collB) {
        if (collA == null || collB == null) {
            return Collections.emptyList();
        }

        Set<UserWrapper> wrapperSetB = new HashSet<>(collB.size());
        for (User userB : collB) {
            wrapperSetB.add(new UserWrapper(userB));
        }

        Set<UserWrapper> wrapperDuplicates = new HashSet<>();

        for (User userA : collA) {
            UserWrapper sample = new UserWrapper(userA);
            if (wrapperSetB.contains(sample)) {
                wrapperDuplicates.add(sample);
            }
        }

        List<User> duplicates = new ArrayList<>(wrapperDuplicates.size());
        for (UserWrapper wrapper : wrapperDuplicates) {
            duplicates.add(wrapper.user);
        }

        return duplicates;
    }

    private static class UserWrapper {

        final User user;

        UserWrapper(User user) {
            this.user = user;
        }

        @Override
        public int hashCode() {
            return hashCode(user.getUsername()) * 633910099
                    + hashCode(user.getEmail()) * 160481183
                    + Arrays.hashCode(user.getPasswordHash());
        }

        @Override
        public boolean equals(Object obj) {
            if (!(obj instanceof UserWrapper)) {
                return false;
            }
            User u = ((UserWrapper) obj).user;
            return equal(user.getUsername(), u.getUsername()) && equal(user.getEmail(), u.getEmail())
                    && Arrays.equals(user.getPasswordHash(), u.getPasswordHash());
        }

        static boolean equal(Object o1, Object o2) {
            return o1 == o2 || (o1 != null && o1.equals(o2));
        }

        static int hashCode(Object o) {
            return o == null ? 961748941 : o.hashCode();
        }
    }

    private static final int NUMBER_OF_USERS = 100000;
    private static Random RANDOM = new Random();

    public static void main(String[] args) {
        List<User> listA = new ArrayList<>(NUMBER_OF_USERS);
        List<User> listB = new ArrayList<>(NUMBER_OF_USERS);

        for (int i = 0; i < NUMBER_OF_USERS; i++) {
            User userA = newUser();
            listA.add(userA);

            listB.add(newUser());

            if (i % 1000 == 0) {
                // Добавим дубликат.
                User userB = new User();
                userB.setUsername(userA.getUsername());
                userB.setEmail(userA.getEmail());
                userB.setPasswordHash(Arrays.copyOf(userA.getPasswordHash(), userA.getPasswordHash().length));
                listB.add(userB);
            }
        }

        long stamp = System.currentTimeMillis();

        List<User> dups = findDuplicates(listA, listB);

        System.out.println(dups.size() + " " + (System.currentTimeMillis() - stamp) / 1000d);
    }

    private static User newUser() {
        User user = new User();

        user.setUsername(Math.random() + "");
        user.setEmail(Math.random() + "");

        byte[] bytes = new byte[32];
        RANDOM.nextBytes(bytes);
        user.setPasswordHash(bytes);

        return user;
    }
}