/*
 * Copyright 2015-2016 the original author or authors
 *
 * This software is licensed under the Apache License, Version 2.0,
 * the GNU Lesser General Public License version 2 or later ("LGPL")
 * and the WTFPL.
 * You may choose either license to govern your use of this software only
 * upon the condition that you accept all of the terms of either
 * the Apache License 2.0, the LGPL 2.1+ or the WTFPL.
 */

package de.pixart.messenger.utils;

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.LineNumberReader;
import java.net.InetAddress;
import java.util.HashSet;
import java.util.logging.Level;

import de.measite.minidns.dnsserverlookup.AbstractDNSServerLookupMechanism;
import de.measite.minidns.dnsserverlookup.AndroidUsingReflection;
import de.measite.minidns.dnsserverlookup.DNSServerLookupMechanism;
import de.measite.minidns.util.PlatformDetection;

/**
 * Try to retrieve the list of DNS server by executing getprop.
 */
public class AndroidUsingExecLowPriority extends AbstractDNSServerLookupMechanism {

    public static final DNSServerLookupMechanism INSTANCE = new AndroidUsingExecLowPriority();
    public static final int PRIORITY = AndroidUsingReflection.PRIORITY + 1;

    private AndroidUsingExecLowPriority() {
        super(AndroidUsingExecLowPriority.class.getSimpleName(), PRIORITY);
    }

    @Override
    public String[] getDnsServerAddresses() {
        try {
            Process process = Runtime.getRuntime().exec("getprop");
            InputStream inputStream = process.getInputStream();
            LineNumberReader lnr = new LineNumberReader(
                    new InputStreamReader(inputStream));
            String line;
            HashSet<String> server = new HashSet<>(6);
            while ((line = lnr.readLine()) != null) {
                int split = line.indexOf("]: [");
                if (split == -1) {
                    continue;
                }
                String property = line.substring(1, split);
                String value = line.substring(split + 4, line.length() - 1);

                if (value.isEmpty()) {
                    continue;
                }

                if (property.endsWith(".dns") || property.endsWith(".dns1") ||
                        property.endsWith(".dns2") || property.endsWith(".dns3") ||
                        property.endsWith(".dns4")) {

                    // normalize the address

                    InetAddress ip = InetAddress.getByName(value);

                    if (ip == null) continue;

                    value = ip.getHostAddress();

                    if (value == null) continue;
                    if (value.length() == 0) continue;

                    server.add(value);
                }
            }
            if (server.size() > 0) {
                return server.toArray(new String[server.size()]);
            }
        } catch (IOException e) {
            LOGGER.log(Level.WARNING, "Exception in findDNSByExec", e);
        }
        return null;
    }

    @Override
    public boolean isAvailable() {
        return PlatformDetection.isAndroid();
    }

}