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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

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 * This code is free software; you can redistribute it and/or modify it

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 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code 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 General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

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 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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package sun.nio.cs.ext;

import java.nio.ByteBuffer;

import java.nio.CharBuffer;

import java.nio.charset.Charset;

import java.nio.charset.CharsetDecoder;

import java.nio.charset.CharsetEncoder;

import java.nio.charset.CoderResult;

import java.nio.charset.CharacterCodingException;

import java.nio.charset.MalformedInputException;

import sun.nio.cs.DelegatableDecoder;

import sun.nio.cs.HistoricallyNamedCharset;

import java.security.AccessController;

import java.security.PrivilegedAction;

import sun.nio.cs.*;

import static java.lang.Character.UnicodeBlock;

public class JISAutoDetect

    extends Charset

    implements HistoricallyNamedCharset

{

    private static final int EUCJP_MASK       = 0x01;

    private static final int SJIS2B_MASK      = 0x02;

    private static final int SJIS1B_MASK      = 0x04;

    private static final int EUCJP_KANA1_MASK = 0x08;

    private static final int EUCJP_KANA2_MASK = 0x10;

    public JISAutoDetect() {

        super("x-JISAutoDetect", ExtendedCharsets.aliasesFor("x-JISAutoDetect"));

    }

    public boolean contains(Charset cs) {

        return ((cs.name().equals("US-ASCII"))

                || (cs instanceof SJIS)

                || (cs instanceof EUC_JP)

                || (cs instanceof ISO2022_JP));

    }

    public boolean canEncode() {

        return false;

    }

    public CharsetDecoder newDecoder() {

        return new Decoder(this);

    }

    public String historicalName() {

        return "JISAutoDetect";

    }

    public CharsetEncoder newEncoder() {

        throw new UnsupportedOperationException();

    }

    // A heuristic algorithm for guessing if EUC-decoded text really

    // might be Japanese text.  Better heuristics are possible...

    private static boolean looksLikeJapanese(CharBuffer cb) {

        int hiragana = 0;       // Fullwidth Hiragana

        int katakana = 0;       // Halfwidth Katakana

        while (cb.hasRemaining()) {

            char c = cb.get();

            if (0x3040 <= c && c <= 0x309f && ++hiragana > 1) return true;

            if (0xff65 <= c && c <= 0xff9f && ++katakana > 1) return true;

        }

        return false;

    }

    private static class Decoder extends CharsetDecoder {

        @SuppressWarnings("removal")

        private static final String osName = AccessController.doPrivileged(

            (PrivilegedAction<String>) () -> System.getProperty("os.name"));

        private static final String SJISName = getSJISName();

        private static final String EUCJPName = "EUC_JP";

        private DelegatableDecoder detectedDecoder = null;

        public Decoder(Charset cs) {

            super(cs, 0.5f, 1.0f);

        }

        private static boolean isPlainASCII(byte b) {

            return b >= 0 && b != 0x1b;

        }

        private static void copyLeadingASCII(ByteBuffer src, CharBuffer dst) {

            int start = src.position();

            int limit = start + Math.min(src.remaining(), dst.remaining());

            int p;

            byte b;

            for (p = start; p < limit && isPlainASCII(b = src.get(p)); p++)

                dst.put((char)(b & 0xff));

            src.position(p);

        }

        private CoderResult decodeLoop(DelegatableDecoder decoder,

                                       ByteBuffer src, CharBuffer dst) {

            ((CharsetDecoder)decoder).reset();

            detectedDecoder = decoder;

            return detectedDecoder.decodeLoop(src, dst);

        }

        protected CoderResult decodeLoop(ByteBuffer src, CharBuffer dst) {

            if (detectedDecoder == null) {

                copyLeadingASCII(src, dst);

                // All ASCII?

                if (! src.hasRemaining())

                    return CoderResult.UNDERFLOW;

                // Overflow only if there is still ascii but no out buffer.

                if (!dst.hasRemaining() &&

                    isPlainASCII(src.get(src.position())))

                    return CoderResult.OVERFLOW;

                // We need to perform double, not float, arithmetic; otherwise

                // we lose low order bits when src is larger than 2**24.

                int cbufsiz = (int)(src.limit() * (double)maxCharsPerByte());

                CharBuffer sandbox = CharBuffer.allocate(cbufsiz);

                // First try ISO-2022-JP, since there is no ambiguity

                Charset cs2022 = Charset.forName("ISO-2022-JP");

                DelegatableDecoder dd2022

                    = (DelegatableDecoder) cs2022.newDecoder();

                ByteBuffer src2022 = src.asReadOnlyBuffer();

                CoderResult res2022 = dd2022.decodeLoop(src2022, sandbox);

                if (! res2022.isError())

                    return decodeLoop(dd2022, src, dst);

                // We must choose between EUC and SJIS

                Charset csEUCJ = Charset.forName(EUCJPName);

                Charset csSJIS = Charset.forName(SJISName);

                DelegatableDecoder ddEUCJ

                    = (DelegatableDecoder) csEUCJ.newDecoder();

                DelegatableDecoder ddSJIS

                    = (DelegatableDecoder) csSJIS.newDecoder();

                ByteBuffer srcEUCJ = src.asReadOnlyBuffer();

                sandbox.clear();

                CoderResult resEUCJ = ddEUCJ.decodeLoop(srcEUCJ, sandbox);

                // If EUC decoding fails, must be SJIS

                if (resEUCJ.isError())

                    return decodeLoop(ddSJIS, src, dst);

                ByteBuffer srcSJIS = src.asReadOnlyBuffer();

                CharBuffer sandboxSJIS = CharBuffer.allocate(cbufsiz);

                CoderResult resSJIS = ddSJIS.decodeLoop(srcSJIS, sandboxSJIS);

                // If SJIS decoding fails, must be EUC

                if (resSJIS.isError())

                    return decodeLoop(ddEUCJ, src, dst);

                // From here on, we have some ambiguity, and must guess.

                // We prefer input that does not appear to end mid-character.

                if (srcEUCJ.position() > srcSJIS.position())

                    return decodeLoop(ddEUCJ, src, dst);

                if (srcEUCJ.position() < srcSJIS.position())

                    return decodeLoop(ddSJIS, src, dst);

                // end-of-input is after the first byte of the first char?

                if (src.position() == srcEUCJ.position())

                    return CoderResult.UNDERFLOW;

                // Use heuristic knowledge of typical Japanese text

                sandbox.flip();

                return decodeLoop(looksLikeJapanese(sandbox) ? ddEUCJ : ddSJIS,

                                  src, dst);

            }

            return detectedDecoder.decodeLoop(src, dst);

        }

        protected void implReset() {

            detectedDecoder = null;

        }

        protected CoderResult implFlush(CharBuffer out) {

            if (detectedDecoder != null)

                return detectedDecoder.implFlush(out);

            else

                return super.implFlush(out);

        }

        public boolean isAutoDetecting() {

            return true;

        }

        public boolean isCharsetDetected() {

            return detectedDecoder != null;

        }

        public Charset detectedCharset() {

            if (detectedDecoder == null)

                throw new IllegalStateException("charset not yet detected");

            return ((CharsetDecoder) detectedDecoder).charset();

        }

        /**

         * Returned Shift_JIS Charset name is OS dependent

         */

        private static String getSJISName() {

            if (osName.startsWith("Windows"))

                return("windows-31J");

            else

                return("Shift_JIS");

        }

    }

}