// License: GPL. For details, see LICENSE file.
package org.openstreetmap.josm.tools;

import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.text.ParseException;
import java.util.Locale;

/**
 * Represents a Windows shortcut (typically visible to Java only as a '.lnk' file).
 *
 * Retrieved 2011-09-23 from http://stackoverflow.com/questions/309495/windows-shortcut-lnk-parser-in-java/672775#672775
 *
 * Written by: (the stack overflow users, obviously!)
 *   Apache Commons VFS dependency removed by crysxd (why were we using that!?) https://github.com/crysxd
 *   Headerified, refactored and commented by Code Bling http://stackoverflow.com/users/675721/code-bling
 *   Network file support added by Stefan Cordes http://stackoverflow.com/users/81330/stefan-cordes
 *   Adapted by Sam Brightman http://stackoverflow.com/users/2492/sam-brightman
 *   Based on information in 'The Windows Shortcut File Format' by Jesse Hager <jessehager@iname.com>
 *   And somewhat based on code from the book 'Swing Hacks: Tips and Tools for Killer GUIs'
 *     by Joshua Marinacci and Chris Adamson
 *     ISBN: 0-596-00907-0
 *     http://www.oreilly.com/catalog/swinghks/
 * @since 13692
 */
public class WindowsShortcut {
    private boolean isDirectory;
    private boolean isLocal;
    private String realFile;

    /**
     * Provides a quick test to see if this could be a valid link !
     * If you try to instantiate a new WindowShortcut and the link is not valid,
     * Exceptions may be thrown and Exceptions are extremely slow to generate,
     * therefore any code needing to loop through several files should first check this.
     *
     * @param file the potential link
     * @return true if may be a link, false otherwise
     * @throws IOException if an IOException is thrown while reading from the file
     */
    public static boolean isPotentialValidLink(File file) throws IOException {
        final int minimumLength = 0x64;
        boolean isPotentiallyValid = false;
        try (InputStream fis = Files.newInputStream(file.toPath())) {
            isPotentiallyValid = file.isFile()
                && file.getName().toLowerCase(Locale.ENGLISH).endsWith(".lnk")
                && fis.available() >= minimumLength
                && isMagicPresent(getBytes(fis, 32));
        }
        return isPotentiallyValid;
    }

    /**
     * Constructs a new {@code WindowsShortcut}
     * @param file file
     * @throws IOException if an I/O error occurs
     * @throws ParseException if a parsing error occurs
     */
    public WindowsShortcut(File file) throws IOException, ParseException {
        try (InputStream in = Files.newInputStream(file.toPath())) {
            parseLink(getBytes(in));
        }
    }

    /**
     * @return the name of the filesystem object pointed to by this shortcut
     */
    public String getRealFilename() {
        return realFile;
    }

    /**
     * Tests if the shortcut points to a local resource.
     * @return true if the 'local' bit is set in this shortcut, false otherwise
     */
    public boolean isLocal() {
        return isLocal;
    }

    /**
     * Tests if the shortcut points to a directory.
     * @return true if the 'directory' bit is set in this shortcut, false otherwise
     */
    public boolean isDirectory() {
        return isDirectory;
    }

    /**
     * Gets all the bytes from an InputStream
     * @param in the InputStream from which to read bytes
     * @return array of all the bytes contained in 'in'
     * @throws IOException if an IOException is encountered while reading the data from the InputStream
     */
    private static byte[] getBytes(InputStream in) throws IOException {
        return getBytes(in, null);
    }

    /**
     * Gets up to max bytes from an InputStream
     * @param in the InputStream from which to read bytes
     * @param max maximum number of bytes to read
     * @return array of all the bytes contained in 'in'
     * @throws IOException if an IOException is encountered while reading the data from the InputStream
     */
    private static byte[] getBytes(InputStream in, Integer max) throws IOException {
        // read the entire file into a byte buffer
        ByteArrayOutputStream bout = new ByteArrayOutputStream();
        byte[] buff = new byte[256];
        while (max == null || max > 0) {
            int n = in.read(buff);
            if (n == -1) {
                break;
            }
            bout.write(buff, 0, n);
            if (max != null)
                max -= n;
        }
        in.close();
        return bout.toByteArray();
    }

    private static boolean isMagicPresent(byte[] link) {
        final int magic = 0x0000004C;
        final int magicOffset = 0x00;
        return link.length >= 32 && bytesToDword(link, magicOffset) == magic;
    }

    /**
     * Gobbles up link data by parsing it and storing info in member fields
     * @param link all the bytes from the .lnk file
     * @throws ParseException if a parsing error occurs
     */
    private void parseLink(byte[] link) throws ParseException {
        try {
            if (!isMagicPresent(link))
                throw new ParseException("Invalid shortcut; magic is missing", 0);

            // get the flags byte
            byte flags = link[0x14];

            // get the file attributes byte
            final int fileAttsOffset = 0x18;
            byte fileAtts = link[fileAttsOffset];
            byte isDirMask = (byte) 0x10;
            if ((fileAtts & isDirMask) != 0) {
                isDirectory = true;
            } else {
                isDirectory = false;
            }

            // if the shell settings are present, skip them
            final int shellOffset = 0x4c;
            final byte hasShellMask = (byte) 0x01;
            int shellLen = 0;
            if ((flags & hasShellMask) != 0) {
                // the plus 2 accounts for the length marker itself
                shellLen = bytesToWord(link, shellOffset) + 2;
            }

            // get to the file settings
            int fileStart = 0x4c + shellLen;

            final int fileLocationInfoFlagOffsetOffset = 0x08;
            int fileLocationInfoFlag = link[fileStart + fileLocationInfoFlagOffsetOffset];
            isLocal = (fileLocationInfoFlag & 2) == 0;
            // get the local volume and local system values
            final int basenameOffsetOffset = 0x10;
            final int networkVolumeTableOffsetOffset = 0x14;
            final int finalnameOffsetOffset = 0x18;
            int finalnameOffset = link[fileStart + finalnameOffsetOffset] + fileStart;
            String finalname = getNullDelimitedString(link, finalnameOffset);
            if (isLocal) {
                int basenameOffset = link[fileStart + basenameOffsetOffset] + fileStart;
                String basename = getNullDelimitedString(link, basenameOffset);
                realFile = basename + finalname;
            } else {
                int networkVolumeTableOffset = link[fileStart + networkVolumeTableOffsetOffset] + fileStart;
                int shareNameOffsetOffset = 0x08;
                int shareNameOffset = link[networkVolumeTableOffset + shareNameOffsetOffset]
                    + networkVolumeTableOffset;
                String shareName = getNullDelimitedString(link, shareNameOffset);
                realFile = shareName + "\\" + finalname;
            }
        } catch (ArrayIndexOutOfBoundsException e) {
            ParseException ex = new ParseException("Could not be parsed, probably not a valid WindowsShortcut", 0);
            ex.initCause(e);
            throw ex;
        }
    }

    private static String getNullDelimitedString(byte[] bytes, int off) {
        int len = 0;
        // count bytes until the null character (0)
        while (true) {
            if (bytes[off + len] == 0) {
                break;
            }
            len++;
        }
        return new String(bytes, off, len, StandardCharsets.UTF_8);
    }

    /*
     * convert two bytes into a short note, this is little endian because it's for an Intel only OS.
     */
    private static int bytesToWord(byte[] bytes, int off) {
        return ((bytes[off + 1] & 0xff) << 8) | (bytes[off] & 0xff);
    }

    private static int bytesToDword(byte[] bytes, int off) {
        return (bytesToWord(bytes, off + 2) << 16) | bytesToWord(bytes, off);
    }
}