/*

 * Copyright (c) 2016, Oracle and/or its affiliates. All rights reserved.

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

 *

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

 * under the terms of the GNU General Public License version 2 only, as

 * 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,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

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

 * or visit www.oracle.com if you need additional information or have any

 */

package java.net.http;

import java.nio.ByteBuffer;

import java.nio.CharBuffer;

import java.nio.charset.CharacterCodingException;

import java.nio.charset.CharsetDecoder;

import java.nio.charset.CharsetEncoder;

import java.nio.charset.CoderResult;

import static java.nio.charset.StandardCharsets.UTF_8;

// The purpose of this class is to separate charset-related tasks from the main

// WebSocket logic, simplifying where possible.

//

//     * Coders hide the differences between coding and flushing stages on the

//       API level

//     * Verifier abstracts the way the verification is performed

//       (spoiler: it's a decoding into a throw-away buffer)

//

// Coding methods throw exceptions instead of returning coding result denoting

// errors, since any kind of handling and recovery is not expected.

final class CharsetToolkit {

    private CharsetToolkit() { }

    static final class Verifier {

        private final CharsetDecoder decoder = UTF_8.newDecoder();

        // A buffer used to check validity of UTF-8 byte stream by decoding it.

        // The contents of this buffer are never used.

        // The size is arbitrary, though it should probably be chosen from the

        // performance perspective since it affects the total number of calls to

        // decoder.decode() and amount of work in each of these calls

        private final CharBuffer blackHole = CharBuffer.allocate(1024);

        void verify(ByteBuffer in, boolean endOfInput)

                throws CharacterCodingException {

            while (true) {

                // Since decoder.flush() cannot produce an error, it's not

                // helpful for verification. Therefore this step is skipped.

                CoderResult r = decoder.decode(in, blackHole, endOfInput);

                if (r.isOverflow()) {

                    blackHole.clear();

                } else if (r.isUnderflow()) {

                    break;

                } else if (r.isError()) {

                    r.throwException();

                } else {

                    // Should not happen

                    throw new InternalError();

                }

            }

        }

        Verifier reset() {

            decoder.reset();

            return this;

        }

    }

    static final class Encoder {

        private final CharsetEncoder encoder = UTF_8.newEncoder();

        private boolean coding = true;

        CoderResult encode(CharBuffer in, ByteBuffer out, boolean endOfInput)

                throws CharacterCodingException {

            if (coding) {

                CoderResult r = encoder.encode(in, out, endOfInput);

                if (r.isOverflow()) {

                    return r;

                } else if (r.isUnderflow()) {

                    if (endOfInput) {

                        coding = false;

                    } else {

                        return r;

                    }

                } else if (r.isError()) {

                    r.throwException();

                } else {

                    // Should not happen

                    throw new InternalError();

                }

            }

            assert !coding;

            return encoder.flush(out);

        }

        Encoder reset() {

            coding = true;

            encoder.reset();

            return this;

        }

    }

    static CharBuffer decode(ByteBuffer in) throws CharacterCodingException {

        return UTF_8.newDecoder().decode(in);

    }

    static final class Decoder {

        private final CharsetDecoder decoder = UTF_8.newDecoder();

        private boolean coding = true; // Either coding or flushing

        CoderResult decode(ByteBuffer in, CharBuffer out, boolean endOfInput)

                throws CharacterCodingException {

            if (coding) {

                CoderResult r = decoder.decode(in, out, endOfInput);

                if (r.isOverflow()) {

                    return r;

                } else if (r.isUnderflow()) {

                    if (endOfInput) {

                        coding = false;

                    } else {

                        return r;

                    }

                } else if (r.isError()) {

                    r.throwException();

                } else {

                    // Should not happen

                    throw new InternalError();

                }

            }

            assert !coding;

            return decoder.flush(out);

        }

        Decoder reset() {

            coding = true;

            decoder.reset();

            return this;

        }

    }

}