import java.sql.*;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Random;

public class QuestionManager {

    private String DBDriver;
    private String DBHost;
    private String DBUser;
    private String DBPassword;

    private ArrayList<Question> questions;
    private ArrayList<Question> final_questions;

    public QuestionManager(String DB_Driver, String DB_Host, String DB_User, String DB_Password){
        DBDriver = DB_Driver;
        DBHost = DB_Host;
        DBUser = DB_User;
        DBPassword = DB_Password;
        questions = new ArrayList<>();
        final_questions = new ArrayList<>();
        refresh_questions();
    }

    public void refresh_questions(){
        Connection con = null;
        try {
            Class.forName(DBDriver);
        } catch (ClassNotFoundException exc) {
            System.out.println("Exception in QuestionManager constructor (driver)" + exc);
        }
        try {
            con = DriverManager.getConnection(DBHost, DBUser, DBPassword);

            Statement st = con.createStatement();
            ResultSet quest = st.executeQuery("select * from questions");
            while (quest.next()) {
                Question result = new Question();
                result.id = quest.getInt(1);
                result.quest = quest.getString(2);
                for (int j = 3; j <= quest.getMetaData().getColumnCount(); j++) {

                    if (result.answers.size() == j - 3) {
                        result.answers.add("");
                    }
                    result.answers.set(j - 3, quest.getString(j));
                }
                result.correct = 0;
                questions.add(result);
            }                                           //взяли и распарсили обычные вопросы

            st = con.createStatement();
            quest = st.executeQuery("select * from final");
            while (quest.next()) {
                Question result = new Question();
                result.id = quest.getInt(1);
                result.quest = quest.getString(2);
                for (int j = 3; j <= quest.getMetaData().getColumnCount(); j++) {
                    if (result.answers.size() == j - 3) {
                        result.answers.add("");
                    }
                    result.answers.set(j - 3, quest.getString(j));
                }
                result.correct = 0;
                final_questions.add(result);
            }
                                                         //взяли и распарсили финальные вопросы
        } catch(Exception exc){
            System.out.println("Exception in QuestionManager constructor (connection)" + exc);
        }
        try {
            if (con != null)
                con.close();
        } catch (SQLException exc) {
            System.out.println("Exception in QuestionManager close connection" + exc);
        }
    }


    public ArrayList<Question> get_questions(int number){
        ArrayList<Question> result = new ArrayList<>();
        while(number > 0){
            ArrayList<Integer> order = new ArrayList<>();
            for (int j = 0; j < questions.size(); j++) {            //order = [1,2,3..n]
                order.add(j);
            }
            long seed = System.nanoTime();
            Collections.shuffle(order, new Random(seed));           //order теперь случайная перестановка
            for(int i = 0; i < Math.min(number, order.size()); i++){
                result.add(shuffle_answers(questions.get(order.get(i))));      // заполнили result вопросами в порядке из order
            }
            order.clear();
            number -= questions.size();
        }
        return result;
    }

    public ArrayList<Question> get_final_questions(int number){
        ArrayList<Question> result = new ArrayList<>();
        while(number > 0){
            ArrayList<Integer> order = new ArrayList<>();
            for (int j = 0; j < final_questions.size(); j++) {
                order.add(j);
            }
            long seed = System.nanoTime();
            Collections.shuffle(order, new Random(seed));
            for(int i = 0; i < Math.min(number, order.size()); i++){
                result.add(shuffle_answers(final_questions.get(order.get(i))));
            }
            order.clear();
            number -= final_questions.size();
        }
        return result;
    }

    public Question shuffle_answers(Question quest){        //перемешивание ответов в вопросе

        ArrayList<Integer> order = new ArrayList<Integer>();
        for (int j = 0; j < quest.answers.size(); j++) {
            order.add(j);
        }
        long seed = System.nanoTime();
        Collections.shuffle(order, new Random(seed));
        Collections.shuffle(quest.answers, new Random(seed));
        quest.correct = order.indexOf(quest.correct);
        order.clear();

        return quest;
    }

}