/*
 * 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 java.nio.charset.CodingErrorAction;
import java.nio.charset.StandardCharsets;

import static java.lang.System.Logger.Level.WARNING;
import static java.net.http.WSUtils.EMPTY_BYTE_BUFFER;
import static java.net.http.WSUtils.logger;
import static java.nio.charset.StandardCharsets.UTF_8;

/*
 * A collection of tools for UTF-8 coding.
 */
final class WSCharsetToolkit {

    private WSCharsetToolkit() { }

    static final class Encoder {

        private final CharsetEncoder encoder = UTF_8.newEncoder();

        ByteBuffer encode(CharBuffer in) throws CharacterCodingException {
            return encoder.encode(in);
        }

        // TODO:
        // ByteBuffer[] encode(CharBuffer in) throws CharacterCodingException {
        //     return encoder.encode(in);
        // }
    }

    static CharBuffer decode(ByteBuffer in) throws CharacterCodingException {
        return UTF_8.newDecoder().decode(in);
    }

    static final class Decoder {

        private final CharsetDecoder decoder = StandardCharsets.UTF_8.newDecoder();

        {
            decoder.onMalformedInput(CodingErrorAction.REPORT);
            decoder.onUnmappableCharacter(CodingErrorAction.REPORT);
        }

        private ByteBuffer leftovers = EMPTY_BYTE_BUFFER;

        WSShared<CharBuffer> decode(WSShared<ByteBuffer> in, boolean endOfInput)
                throws CharacterCodingException {
            ByteBuffer b;
            int rem = leftovers.remaining();
            if (rem != 0) {
                // TODO: We won't need this wasteful allocation & copying when
                // JDK-8155222 has been resolved
                b = ByteBuffer.allocate(rem + in.remaining());
                b.put(leftovers).put(in.buffer()).flip();
            } else {
                b = in.buffer();
            }
            CharBuffer out = CharBuffer.allocate(b.remaining());
            CoderResult r = decoder.decode(b, out, endOfInput);
            if (r.isError()) {
                r.throwException();
            }
            if (b.hasRemaining()) {
                leftovers = ByteBuffer.allocate(b.remaining()).put(b).flip();
            } else {
                leftovers = EMPTY_BYTE_BUFFER;
            }
            // Since it's UTF-8, the assumption is leftovers.remaining() < 4
            // (i.e. small). Otherwise a shared buffer should be used
            if (!(leftovers.remaining() < 4)) {
                logger.log(WARNING,
                        "The size of decoding leftovers is greater than expected: {0}",
                        leftovers.remaining());
            }
            b.position(b.limit()); // As if we always read to the end
            in.dispose();
            // Decoder promises that in the case of endOfInput == true:
            // "...any remaining undecoded input will be treated as being
            // malformed"
            assert !(endOfInput && leftovers.hasRemaining()) : endOfInput + ", " + leftovers;
            if (endOfInput) {
                r = decoder.flush(out);
                decoder.reset();
                if (r.isOverflow()) {
                    // FIXME: for now I know flush() does nothing. But the
                    // implementation of UTF8 decoder might change. And if now
                    // flush() is a no-op, it is not guaranteed to remain so in
                    // the future
                    throw new InternalError("Not yet implemented");
                }
            }
            out.flip();
            return WSShared.wrap(out);
        }
    }
}