package prometheus.server;

/*
 * Author: Sajid Anwar
 * Program: Prometheus
 * Date: 3/28/2012
 * School: Ironwood High School
 */

import java.io.*;

import prometheus.util.Md5Util;

public class AuthenticationDatabase {

    private static RandomAccessFile _database;

    private static String FILE_PATH;
    private static final int SIZE_USERNAME = 36;
    private static final int SIZE_PASSWORDHASH = 16;
    private static final int SIZE_RECORD = SIZE_USERNAME + SIZE_PASSWORDHASH;

    /*
     *      username = {36 bytes}
     *      password = {16 bytes}
     *      record = [username][password]
     *
     * The file is basically a list of [record]s. So, 36 bytes and 16 bytes for the
     * the first user's username and password, and then another 36+16 bytes for the
     * next user, and so on.
     */

    public static void initialize() throws IOException {

        FILE_PATH = new File(System.getProperty("user.home"), "prometheus-auth.db").getPath();

        if (!new File(FILE_PATH).exists())
        {
            _database = new RandomAccessFile(FILE_PATH, "rw");
            _database.writeInt(0);
            _database.seek(0);
        }
        else
        {
            _database = new RandomAccessFile(FILE_PATH, "rw");
        }
    }

    public static boolean checkUser(String username, String password) throws Exception
    {
        // Seek to the beginning of the file.
        _database.seek(0);

        // Check if we have any users.
        int users = _database.readInt();
        if (users < 1)
            return false;

        for (int i = 0; i < users; i++)
        {
            // Read SIZE_USERNAME bytes (username) for this user.
            byte[] unBuffer = new byte[SIZE_USERNAME];
            _database.read(unBuffer);
            String un = new String(unBuffer).replace("\0", "");;

            // If the names do not match, skip this user.
            if (!un.equals(username))
            {
                _database.skipBytes(SIZE_PASSWORDHASH);
                continue;
            }

            // Read SIZE_PASSWORDHASH byte (password hash) for this user.
            byte[] pwBuffer = new byte[SIZE_PASSWORDHASH];
            _database.read(pwBuffer);

            // Return whether the password hashes match.
            return AuthenticationDatabase.bytesEqual(pwBuffer, Md5Util.computeHash(password));
        }

        // Couldn't find the user.
        return false;
    }

    public static boolean addUser(String username, String password) throws Exception {
        // Seek to the beginning of the file.
        _database.seek(0);

        // Check if we have any users.
        int users = _database.readInt();

        for (int i = 0; i < users; i++)
        {
            // Read SIZE_USERNAME bytes (username) for this user.
            byte[] unBuffer = new byte[SIZE_USERNAME];
            _database.read(unBuffer);
            String un = new String(unBuffer).replace("\0", "");

            // If the names do match, abort the operation.
            if (un.equals(username))
            {
                return false;
            }

            // Skip the password hash.
            _database.skipBytes(SIZE_PASSWORDHASH);
        }

        // Write the user to the end of our files.
        if (username.length() > SIZE_USERNAME)
            _database.writeBytes(username.substring(0, SIZE_USERNAME));
        else
        {
            _database.writeBytes(username);

            for (int i = 0; i < SIZE_USERNAME - username.length(); i++)
                _database.writeByte(0);
        }


        // Write the password to file.
        _database.write(Md5Util.computeHash(password));

        // Increase the number of users.
        _database.seek(0);
        _database.writeInt(users + 1);

        return true;
    }

    public static boolean deleteUser(String username) throws Exception {
        // Seek to the beginning of the file.
        _database.seek(0);

        // Check if we have any users.
        int users = _database.readInt();
        if (users < 1)
            return false;

        for (int i = 0; i < users; i++)
        {
            // Read SIZE_USERNAME bytes (username) for this user.
            byte[] unBuffer = new byte[SIZE_USERNAME];
            _database.read(unBuffer);
            String un = new String(unBuffer).replace("\0", "");

            // If the names do not match, skip this user.
            if (!un.equals(username))
            {
                _database.skipBytes(SIZE_PASSWORDHASH);
                continue;
            }

            // Skip back SIZE_USERNAME bytes to the beginning of the entry, and clear it.
            _database.seek(_database.getFilePointer() - SIZE_USERNAME);
            for (int j = 0; j < SIZE_RECORD; j++)
                _database.writeByte(0);
            _database.seek(_database.getFilePointer() - SIZE_RECORD);

            // Save the current position, and then read the last entry of the file.
            long insertIndex = _database.getFilePointer();
            byte[] lastEntry = new byte[SIZE_RECORD];
            _database.seek(_database.length() - SIZE_RECORD);
            _database.read(lastEntry);

            // Rewrite the last entry into the space of the deleted entry.
            _database.seek(insertIndex);
            _database.write(lastEntry);
            _database.setLength(_database.length() - SIZE_RECORD);

            // Decrease the number of users.
            _database.seek(0);
            _database.writeInt(users - 1);

            return true;
        }

        // Couldn't find the user.
        return false;
    }

    public static boolean editUser(String username, String newPassword) throws Exception {
        // Seek to the beginning of the file.
        _database.seek(0);

        // Check if we have any users.
        int users = _database.readInt();
        if (users < 1)
            return false;

        for (int i = 0; i < users; i++)
        {
            // Read SIZE_USERNAME bytes (username) for this user.
            byte[] unBuffer = new byte[SIZE_USERNAME];
            _database.read(unBuffer);
            String un = new String(unBuffer).replace("\0", "");;

            // If the names do not match, skip this user.
            if (!un.equals(username))
            {
                _database.skipBytes(SIZE_PASSWORDHASH);
                continue;
            }

            // Write the SIZE_PASSWORDHASH byte (password hash) for this user.
            _database.write(Md5Util.computeHash(newPassword));

            return true;
        }

        // Couldn't find the user.
        return false;
    }

    public static String[] getUsers() throws Exception {
        // Seek to the beginning of the file.
        _database.seek(0);

        // Check if we have any users.
        int users = _database.readInt();
        if (users < 1)
            return new String[0];

        String[] usersArr = new String[users];

        for (int i = 0; i < users; i++)
        {
            // Read SIZE_USERNAME bytes (username) for this user.
            byte[] unBuffer = new byte[SIZE_USERNAME];
            _database.read(unBuffer);
            String un = new String(unBuffer).replace("\0", "");;
            usersArr[i] = un;

            _database.skipBytes(SIZE_PASSWORDHASH);
        }

        // Couldn't find the user.
        return usersArr;
    }

    private static boolean bytesEqual(byte[] b1, byte[] b2) {
        if (b1.length != b2.length)
            return false;

        for (int i = 0; i < b1.length; i++)
            if (b1[i] != b2[i])
                return false;

        return true;
    }

}