src/main/java/de/waldheinz/fs/fat/ShortName.java

/*
 * Copyright (C) 2009,2010 Matthias Treydte <mt@waldheinz.de>
 *
 * This library is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as published
 * by the Free Software Foundation; either version 2.1 of the License, or
 * (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
 * License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this library; If not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */

package de.waldheinz.fs.fat;

import java.math.BigInteger;
import java.util.Arrays;

/**
 * Represents a "short" (8.3) file name as used by DOS.
 * 
 * @author Matthias Treydte &lt;waldheinz at gmail.com&gt;
 */
final class ShortName {

    /**
     * These are taken from the FAT specification.
     */
    private final static byte[] ILLEGAL_CHARS = {
            0x22, 0x2A, 0x2B, 0x2C, 0x2E, 0x2F, 0x3A, 0x3B,
            0x3C, 0x3D, 0x3E, 0x3F, 0x5B, 0x5C, 0x5D, 0x7C
    };

    /**
     * The name of the "current directory" (".") entry of a FAT directory.
     */
    public final static ShortName DOT = new ShortName(".", ""); // NOI18N

    /**
     * The name of the "parent directory" ("..") entry of a FAT directory.
     */
    public final static ShortName DOT_DOT = new ShortName("..", ""); // NOI18N

    private final char[] name;
    private boolean mShortNameOnly;

    private ShortName(String nameExt) {
        if (nameExt.length() > 12)
            throw new IllegalArgumentException("name too long");

        final int i = nameExt.indexOf('.');
        final String nameString, extString;

        if (i < 0) {
            nameString = nameExt.toUpperCase();
            extString = "";
        } else {
            nameString = nameExt.substring(0, i).toUpperCase();
            extString = nameExt.substring(i + 1).toUpperCase();
        }

        this.name = toCharArray(nameString, extString);
        checkValidChars(this.name);
    }

    ShortName(String name, String ext) {
        this.name = toCharArray(name, ext);
    }

    ShortName(char[] name) {
        this.name = name;
    }

    public ShortName(char[] nameArr, char[] extArr) {
        char[] result = new char[11];
        System.arraycopy(nameArr, 0, result, 0, nameArr.length);
        System.arraycopy(extArr, 0, result, 8, extArr.length);
        this.name = result;
    }

    private static char[] toCharArray(String name, String ext) {
        checkValidName(name);
        checkValidExt(ext);

        final char[] result = new char[11];
        Arrays.fill(result, ' ');
        System.arraycopy(name.toCharArray(), 0, result, 0, name.length());
        System.arraycopy(ext.toCharArray(), 0, result, 8, ext.length());

        return result;
    }

    /**
     * Calculates the checksum that is used to test a long file name for it's
     * validity.
     * 
     * @return the {@code ShortName}'s checksum
     */
    public byte checkSum() {
        final byte[] dest = new byte[11];
        for (int i = 0; i < 11; i++)
            dest[i] = (byte) name[i];

        int sum = dest[0];
        for (int i = 1; i < 11; i++) {
            sum = dest[i] + (((sum & 1) << 7) + ((sum & 0xfe) >> 1));
        }

        return (byte) (sum & 0xff);
    }

    /**
     * Parses the specified string into a {@code ShortName}.
     * 
     * @param name the name+extension of the {@code ShortName} to get
     * @return the {@code ShortName} representing the specified name
     * @throws IllegalArgumentException if the specified name can not be parsed
     *             into a {@code ShortName}
     * @see #canConvert(java.lang.String)
     */
    public static ShortName get(String name) throws IllegalArgumentException {
        if (name.equals("."))
            return DOT;
        else if (name.equals(".."))
            return DOT_DOT;
        else
            return new ShortName(name);
    }

    /**
     * Tests if the specified string can be converted to a {@code ShortName}.
     * 
     * @param nameExt the string to test
     * @return if the string can be converted
     * @see #get(java.lang.String)
     */
    public static boolean canConvert(String nameExt) {
        /* TODO: do this without exceptions */
        try {
            ShortName.get(nameExt);
            return true;
        } catch (IllegalArgumentException ex) {
            return false;
        }
    }

    public static ShortName parse(byte[] data) {
        final char[] nameArr = new char[8];

        for (int i = 0; i < nameArr.length; i++) {
            nameArr[i] = (char) LittleEndian.getUInt8(data, i);
        }

        final char[] extArr = new char[3];
        for (int i = 0; i < extArr.length; i++) {
            extArr[i] = (char) LittleEndian.getUInt8(data, 0x08 + i);
        }

        return new ShortName(nameArr, extArr);
    }

    public void write(byte[] dest) {
        for (int i = 0; i < 11; i++) {
            dest[i] = (byte) name[i];
        }
    }

    public String asSimpleString() {
        return new String(this.name).trim();
    }

    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < this.name.length; i++) {
            sb.append(Integer.toHexString(name[i]));
            sb.append(' ');
        }
        return getClass().getSimpleName() +
                " [" +
                asSimpleString() + " -- " +
                sb.toString() + "]"; // NOI18N
    }

    private static void checkValidName(String name) {
        checkString(name, "name", 1, 8);
    }

    private static void checkValidExt(String ext) {
        checkString(ext, "extension", 0, 3);
    }

    private static void checkString(String str, String strType,
            int minLength, int maxLength) {

        if (str == null)
            throw new IllegalArgumentException(strType +
                    " is null");
        if (str.length() < minLength)
            throw new IllegalArgumentException(strType +
                    " must have at least " + minLength +
                    " characters: " + str);
        if (str.length() > maxLength)
            throw new IllegalArgumentException(strType +
                    " has more than " + maxLength +
                    " characters: " + str);
    }

    @Override
    public boolean equals(Object obj) {
        if (!(obj instanceof ShortName)) {
            return false;
        }

        final ShortName other = (ShortName) obj;
        return Arrays.equals(name, other.name);
    }

    @Override
    public int hashCode() {
        return Arrays.hashCode(this.name);
    }

    public void setHasShortNameOnly(boolean hasShortNameOnly) {
        mShortNameOnly = hasShortNameOnly;
    }

    public boolean hasShortNameOnly() {
        return mShortNameOnly;
    }

    /**
     * Checks if the specified char array consists only of "valid" byte values
     * according to the FAT specification.
     * 
     * @param chars the char array to test
     * @throws IllegalArgumentException if invalid chars are contained
     */
    public static void checkValidChars(char[] chars)
            throws IllegalArgumentException {

        if (chars[0] == 0x20)
            throw new IllegalArgumentException(
                    "0x20 can not be the first character");

        for (int i = 0; i < chars.length; i++) {
            if ((chars[i] & 0xff) != chars[i])
                throw new IllegalArgumentException("multi-byte character at " + i);

            final byte toTest = (byte) (chars[i] & 0xff);

            if (toTest < 0x20 && toTest != 0x05)
                throw new IllegalArgumentException("character < 0x20 at" + i);

            for (int j = 0; j < ILLEGAL_CHARS.length; j++) {
                if (toTest == ILLEGAL_CHARS[j])
                    throw new IllegalArgumentException("illegal character " +
                            ILLEGAL_CHARS[j] + " at " + i);
            }
        }
    }
}