/*
 * Copyright 2018 Hippo Seven
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.hippo.ehviewer;

/*
 * Created by Hippo on 2018/3/21.
 */

import androidx.annotation.Nullable;

import java.net.InetAddress;
import java.net.UnknownHostException;

public class Hosts {

    @Nullable
    public static InetAddress toInetAddress(String host, String ip) {
        if (!isValidHost(host)) {
            return null;
        }

        if (ip == null) {
            return null;
        }

        byte[] bytes = parseV4(ip);
        if (bytes == null) {
            bytes = parseV6(ip);
        }
        if (bytes == null) {
            return null;
        }

        try {
            return InetAddress.getByAddress(host, bytes);
        } catch (UnknownHostException e) {
            return null;
        }
    }

    /**
     * Returns true if the host is valid.
     */
    public static boolean isValidHost(String host) {
        if (host == null) {
            return false;
        }

        if (host.length() > 253) {
            return false;
        }

        int labelLength = 0;
        for (int i = 0, n = host.length(); i < n; i++) {
            char ch = host.charAt(i);

            if (ch == '.') {
                if (labelLength < 1 || labelLength > 63) {
                    return false;
                }
                labelLength = 0;
            } else {
                labelLength++;
            }

            if ((ch < 'a' || ch > 'z') && (ch < '0' || ch > '9') && ch != '-' && ch != '.') {
                return false;
            }
        }

        return labelLength >= 1 && labelLength <= 63;
    }

    // org.xbill.DNS.Address.parseV4
    @Nullable
    private static byte[] parseV4(String s) {
        int numDigits;
        int currentOctet;
        byte[] values = new byte[4];
        int currentValue;
        int length = s.length();

        currentOctet = 0;
        currentValue = 0;
        numDigits = 0;
        for (int i = 0; i < length; i++) {
            char c = s.charAt(i);
            if (c >= '0' && c <= '9') {
                /* Can't have more than 3 digits per octet. */
                if (numDigits == 3)
                    return null;
                /* Octets shouldn't start with 0, unless they are 0. */
                if (numDigits > 0 && currentValue == 0)
                    return null;
                numDigits++;
                currentValue *= 10;
                currentValue += (c - '0');
                /* 255 is the maximum value for an octet. */
                if (currentValue > 255)
                    return null;
            } else if (c == '.') {
                /* Can't have more than 3 dots. */
                if (currentOctet == 3)
                    return null;
                /* Two consecutive dots are bad. */
                if (numDigits == 0)
                    return null;
                values[currentOctet++] = (byte) currentValue;
                currentValue = 0;
                numDigits = 0;
            } else
                return null;
        }
        /* Must have 4 octets. */
        if (currentOctet != 3)
            return null;
        /* The fourth octet can't be empty. */
        if (numDigits == 0)
            return null;
        values[currentOctet] = (byte) currentValue;
        return values;
    }

    // org.xbill.DNS.Address.parseV6
    @Nullable
    private static byte[] parseV6(String s) {
        int range = -1;
        byte[] data = new byte[16];

        String[] tokens = s.split(":", -1);

        int first = 0;
        int last = tokens.length - 1;

        if (tokens[0].length() == 0) {
            // If the first two tokens are empty, it means the string
            // started with ::, which is fine.  If only the first is
            // empty, the string started with :, which is bad.
            if (last - first > 0 && tokens[1].length() == 0)
                first++;
            else
                return null;
        }

        if (tokens[last].length() == 0) {
            // If the last two tokens are empty, it means the string
            // ended with ::, which is fine.  If only the last is
            // empty, the string ended with :, which is bad.
            if (last - first > 0 && tokens[last - 1].length() == 0)
                last--;
            else
                return null;
        }

        if (last - first + 1 > 8)
            return null;

        int i, j;
        for (i = first, j = 0; i <= last; i++) {
            if (tokens[i].length() == 0) {
                if (range >= 0)
                    return null;
                range = j;
                continue;
            }

            if (tokens[i].indexOf('.') >= 0) {
                // An IPv4 address must be the last component
                if (i < last)
                    return null;
                // There can't have been more than 6 components.
                if (i > 6)
                    return null;
                byte[] v4addr = parseV4(tokens[i]);
                if (v4addr == null)
                    return null;
                for (int k = 0; k < 4; k++)
                    data[j++] = v4addr[k];
                break;
            }

            try {
                for (int k = 0; k < tokens[i].length(); k++) {
                    char c = tokens[i].charAt(k);
                    if (Character.digit(c, 16) < 0)
                        return null;
                }
                int x = Integer.parseInt(tokens[i], 16);
                if (x > 0xFFFF || x < 0)
                    return null;
                data[j++] = (byte) (x >>> 8);
                data[j++] = (byte) (x & 0xFF);
            } catch (NumberFormatException e) {
                return null;
            }
        }

        if (j < 16 && range < 0)
            return null;

        if (range >= 0) {
            int empty = 16 - j;
            System.arraycopy(data, range, data, range + empty, j - range);
            for (i = range; i < range + empty; i++)
                data[i] = 0;
        }

        return data;
    }
}