/*
 * [QuickDNS.java]
 *
 * Summary: hosts file updater.
 *
 * Copyright: (c) 2014-2017 Roedy Green, Canadian Mind Products, http://mindprod.com
 *
 * Licence: This software may be copied and used freely for any purpose but military.
 *          http://mindprod.com/contact/nonmil.html
 *
 * Requires: JDK 1.8+
 *
 * Created with: JetBrains IntelliJ IDEA IDE http://www.jetbrains.com/idea/
 *
 * Version History:
 *  1.0 2014-09-06 original.
 *  1.1 2016-05-31 Add error messages to detect running without administrator privilege, now required in Windows 10.
 */
package com.mindprod.quickdns;

import com.mindprod.common18.EIO;
import com.mindprod.common18.ST;
import com.mindprod.hunkio.HunkIO;

import java.io.BufferedReader;
import java.io.File;
import java.io.IOException;
import java.io.PrintWriter;
import java.net.InetAddress;
import java.util.regex.Pattern;

import static java.lang.System.*;

/**
 * hosts file updater.
 *
 * @author Roedy Green, Canadian Mind Products
 * @version 1.1 2016-05-31 Add error messages to detect running without administrator privilege, now required in Windows 10.
 * @since 2014-09-06
 */
public final class QuickDNS
    {
    private static final int FIRST_COPYRIGHT_YEAR = 2014;

    /**
     * when this version was released
     */
    @SuppressWarnings( { "UnusedDeclaration" } )
    private static final String RELEASE_DATE = "2016-05-31";

    /**
     * embedded version string
     */
    @SuppressWarnings( { "UnusedDeclaration" } )
    private static final String VERSION_STRING = "1.1";

    /**
     * not displayed copyright
     */
    @SuppressWarnings( { "UnusedDeclaration" } )
    private static final String EMBEDDED_COPYRIGHT =
            "Copyright: (c) 2014-2017 Roedy Green, Canadian Mind Products, http://mindprod.com";

    /**
     * true if want extra debugging output
     */
    private static final boolean DEBUGGING = false;

    /**
     * Splits field on spaces/tabs
     */
    private static final Pattern SPLITTER = Pattern.compile( "[ \t]+" );
    // methods

    /**
     * display how many updates we made to the hosts file
     *
     * @param hosts   hosts file
     * @param updates count of updates
     */
    public static void displayUpdates( final File hosts, final int updates )
        {
        // leave hosts.bak in place
        switch ( updates )
            {
            case 0:
                out.print( "no updates" );
                break;
            case 1:
                out.print( "one update" );
                break;
            default:
                out.print( updates + " updates" );
            }
        out.println( " to your " + EIO.getCanOrAbsPath( hosts ) + " file." );
        }

    /**
     * update the hosts file
     */
    public static void main( String[] args ) throws IOException
        {
        final File hosts = new File( "C:/Windows//system32/drivers/etc/hosts." );
        final File backup = new File( "C:/Windows//system32/drivers/etc/hosts.bak" );
        final File updated = new File( "C:/Windows//system32/drivers/etc/hosts.updated" );
        safetyChecks( hosts, backup );
        // we have to rename/hide hosts so its entries will not interfere with lookup
        try
            {
            HunkIO.deleteAndRename( hosts, backup );
            }
        catch ( IOException e )
            {
            err.println( "Rename access to " + EIO.getCanOrAbsPath( hosts ) + " blocked.\nPerhaps missing run-as-administrator." );
            System.exit( 2 );
            }
        final BufferedReader br = EIO.getBufferedReader( backup, 16 * 1024, EIO.UTF8 );
        final PrintWriter pw = EIO.getPrintWriter( updated, 16 * 1024, EIO.UTF8 );
        out.println( "QuickDNS " + VERSION_STRING );
        String originalLine;
        int updates = 0;
        while ( ( originalLine = br.readLine() ) != null )
            {
            int commentPlace = originalLine.indexOf( '#' );
            final String comment;
            final String pair;
            final boolean leave;
            if ( commentPlace < 0 )
                {
                // no comment
                comment = "";
                pair = originalLine.trim();
                leave = false;
                }
            else
                {
                // is comment
                comment = originalLine.substring( commentPlace + 1 ).trim();
                leave = comment.toLowerCase().contains( "leave" );
                pair = originalLine.substring( 0, commentPlace ).trim();
                }
            // handle blank line or pure comment line
            if ( pair.length() == 0 )
                {
                pw.println( "# " + comment );
                }
            else
                {
                updates = standardLine( pw, originalLine, updates, comment, pair, leave );
                }
            }  // end loop
        br.close();
        pw.close();
        try
            {
            HunkIO.deleteAndRename( updated, hosts );
            }
        catch ( IOException e )
            {
            err.println( "Delete access to " + EIO.getCanOrAbsPath( hosts ) + " blocked.\nPerhaps missing run-as-administrator." );
            System.exit( 2 );
            }
        if ( !hosts.exists() )
            {
            err.println( "Lost " + EIO.getCanOrAbsPath( hosts ) + ".\nRestore from backup or hosts.bak." );
            System.exit( 2 );
            }
        displayUpdates( hosts, updates );
        } // /method

    public static void safetyChecks( final File hosts, final File backup )
        {
        if ( !hosts.exists() )
            {
            err.println( "Missing " + EIO.getCanOrAbsPath( hosts ) + ".\nRestore from backup or hosts.bak." );
            System.exit( 2 );
            }
        if ( !hosts.canWrite() )
            {
            err.println( "Cannot modify " + EIO.getCanOrAbsPath( hosts ) + ".\nPerhaps missing run-as-administrator." );
            System.exit( 2 );
            }
        if ( backup.exists() && !backup.canWrite() )
            {
            err.println( "Cannot create " + EIO.getCanOrAbsPath( backup ) + ".\nPerhaps missing run-as-administrator." );
            System.exit( 2 );
            }
        }

    /**
     * Process one stardand line in hosts.
     *
     * @param pw           printwriter where we compose new hosts.
     * @param originalLine originals line from old hosts.
     * @param updates      count of how many changes we made
     * @param comment      comment on end of line
     * @param pair         dns / ip
     * @param leave        true if should leave this line as is
     *
     * @return new updates count
     */
    public static int standardLine( final PrintWriter pw, final String originalLine, int updates, final String comment, final String pair, final boolean leave )
        {
        String pieces[] = SPLITTER.split( pair );
        switch ( pieces.length )
            {
            case 2:
                String ip = pieces[ 0 ];
                final String domain = pieces[ 1 ];
                if ( !leave )
                    {
                    try
                        {
                        final InetAddress newIP = InetAddress.getByName( domain );
                        if ( newIP == null )
                            {
                            err.println( "Lookup of IP failed on " + ip + " for " + domain + ".\n" +
                                         "Usually this means the site does not exist or is temporarily down." );
                            pw.println( originalLine );
                            break;
                            }
                        final String newIp = newIP.getHostAddress();
                        if ( !newIp.equals( ip ) )
                            {
                            out.println( "updated: " + ip + " to " + newIp + " for " + domain );
                            ip = newIp;
                            updates++;
                            }
                        }
                    catch ( IOException e )
                        {
                        err.println( "Lookup of IP failed on " + ip + " for " + domain + ".\n" +
                                     "Usually this means the site does not exist or is temporarily down.\n" +
                                     "Technically " + e.getMessage() );
                        pw.println( originalLine );
                        break;
                        }
                    }
                pw.println( ST.leftPad( ip, 37, false )
                            + "  "
                            + ST.rightPad( domain, 35, false )
                            + ( comment.length() > 0 ? ( "# " + comment ) : "" ) );
                break;
            default:
                err.println( "Line needs both ip and dns separated by space.\n" + originalLine );
                pw.println( originalLine );
                if ( DEBUGGING )
                    {
                    err.println( "{" + pair + "}" );
                    for ( String piece : pieces )
                        {
                        err.println( "[" + piece + "]" );
                        }
                    }
            }
        return updates;
        }
    // /methods
    }