/**
 *
 * Copyright © 2015-2024 Florian Schmaus
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.jxmpp.xml.splitter;

import java.io.IOException;
import java.io.OutputStream;
import java.nio.ByteBuffer;
import java.util.Arrays;
import java.util.Collection;

/**
 * Extended version of {@link XmppXmlSplitter} allowing input to be bytes or
 * {@link ByteBuffer} representing a UTF-8 encoded XML string for XMPP. Just as
 * they come from a network socket.
 * <p>
 * This class respects the byte order mark (BOM )requirement of RFC 6120 11.6
 * and treats the BOM as zero width no-break space, and not as byte order mark.
 * </p>
 * 
 * @author Florian Schmaus
 *
 */
public class Utf8ByteXmppXmlSplitter extends OutputStream {

        private final XmppXmlSplitter xmppXmlSplitter;

        /**
         * Create a new splitter with the given callback.
         *
         * @param xmppElementCallback the callback invoked once a complete element has been processed.
         */
        public Utf8ByteXmppXmlSplitter(XmppElementCallback xmppElementCallback) {
                this(new XmppXmlSplitter(xmppElementCallback));
        }

        /**
         * Create a new UTF-8 splitter with the given XMPP XML splitter.
         *
         * @param xmppXmlSplitter the used XMPP XML splitter.
         */
        public Utf8ByteXmppXmlSplitter(XmppXmlSplitter xmppXmlSplitter) {
                this.xmppXmlSplitter = xmppXmlSplitter;
        }

        private final byte[] buffer = new byte[6];

        private char[] writeBuffer = new char[1024];
        private int writeBufferPos;
        private byte count;
        private byte expectedLength;

        @Override
        public void write(int b) throws IOException {
                write((byte) (b & 0xff));
        }

        /**
         * Write a single byte. The byte must be part of a UTF-8 String.
         *
         * @param b the byte to write.
         * @throws IOException if an error occurs.
         */
        public void write(byte b) throws IOException {
                process(b);
                afterInputProcessed();
        }

        /**
         * Write the given array of byte buffers.
         *
         * @param byteBuffers the array of byte buffers.
         * @throws IOException if an error occurs.
         */
        public void write(ByteBuffer[] byteBuffers) throws IOException {
                write(Arrays.asList(byteBuffers));
        }

        /**
         * Write the given collection of byte buffers.
         *
         * @param byteBuffers the collection of byte buffers.
         * @throws IOException if an error occurs.
         */
        public void write(Collection<? extends ByteBuffer> byteBuffers) throws IOException {
                int requiredNewCapacity = 0;
                for (ByteBuffer byteBuffer : byteBuffers) {
                        requiredNewCapacity += byteBuffer.remaining();
                }

                ensureWriteBufferHasCapacityFor(requiredNewCapacity);

                for (ByteBuffer byteBuffer : byteBuffers) {
                        writeByteBufferInternal(byteBuffer);
                }

                afterInputProcessed();
        }

        /**
         * Write the given byte buffer.
         *
         * @param byteBuffer the byte buffer.
         * @throws IOException if an error occurs.
         */
        public void write(ByteBuffer byteBuffer) throws IOException {
                final int remaining = byteBuffer.remaining();
                ensureWriteBufferHasCapacityFor(remaining);

                writeByteBufferInternal(byteBuffer);

                afterInputProcessed();
        }

        private void writeByteBufferInternal(ByteBuffer byteBuffer) throws IOException {
                final int remaining = byteBuffer.remaining();

                if (byteBuffer.hasArray()) {
                        writeInternal(byteBuffer.array(), byteBuffer.arrayOffset(), remaining);
                } else {
                        int initialPosition = byteBuffer.position();
                        for (int i = 0; i < remaining; i++) {
                                process(byteBuffer.get(initialPosition + i));
                        }
                }

                ((java.nio.Buffer) byteBuffer).flip();
        }

        @Override
        public void write(byte[] b, int offset, int length) throws IOException {
                ensureWriteBufferHasCapacityFor(length);

                writeInternal(b, offset, length);

                afterInputProcessed();
        }

        private void writeInternal(byte[] b, int offset, int length) throws IOException {
                for (int i = 0; i < length; i++ ) {
                        process(b[offset + i]);
                }
        }

        /**
         * Reset the write buffer to the given size.
         *
         * @param size the new write buffer size.
         */
        public void resetWriteBuffer(int size) {
                writeBuffer = new char[size];
                writeBufferPos = 0;
        }

        private void process(byte b) throws IOException {
                buffer[count] = b;

                if (count == 0) {
                        int firstByte = buffer[0] & 0xff;
                        if (firstByte < 0x80) {
                                expectedLength = 1;
                        } else if (firstByte < 0xe0) {
                                expectedLength = 2;
                        } else if (firstByte < 0xf0) {
                                expectedLength = 3;
                        } else if (firstByte < 0xf8) {
                                expectedLength = 4;
                        } else {
                                throw new IOException("Invalid first UTF-8 byte: " + firstByte);
                        }
                }

                if (++count == expectedLength) {
                        int codepoint;
                        if (expectedLength == 1) {
                                codepoint = buffer[0] & 0x7f;
                        } else {
                                // The following switch-case could also be omitted. Note sure
                                // how it would affect performance. Using switch-case means that
                                // the bitsToMask does not need to be calculated, but the code
                                // would be shorter if the switch-code was not here and maybe
                                // this affects JIT'ed performance (maybe even positive).
                                switch (expectedLength) {
                                case 2:
                                        codepoint = buffer[0] & 0x1f;
                                        codepoint <<= 6 * 1;
                                        break;
                                case 3:
                                        codepoint = buffer[0] & 0xf;
                                        codepoint <<= 6 * 2;
                                        break;
                                case 4:
                                        codepoint = buffer[0] & 0x6;
                                        codepoint <<= 6 * 3;
                                        break;
                                default:
                                        throw new IllegalStateException();
                                }

                                for (int i = 1; i < expectedLength; i++) {
                                        // Get the lower 6 bits.
                                        int bits = buffer[i] & 0x3f;
                                        // Shift the bits to the right position.
                                        bits <<= 6 * (expectedLength - 1 - i);
                                        codepoint |= bits;
                                }
                        }

                        ensureWriteBufferHasCapacityFor(2);

                        if (codepoint < 0x10000) {
                                appendToWriteBuffer((char) codepoint);
                        } else {
                                // We have to convert the codepoint into a surrogate pair.
                                // high surrogate: top ten bits added to 0xd800 give the first 16-bit code unit.
                                appendToWriteBuffer((char) (0xd800 + (codepoint & 0xffa00000)));
                                // low surrogate: low ten bits added to 0xdc00 give the second 16-bit code unit.
                                appendToWriteBuffer((char) (0xdc00 + (codepoint & 0x3ff)));
                        }

                        // Reset count since we are done handling this UTF-8 codepoint.
                        count = 0;
                }
        }

        private void afterInputProcessed() throws IOException {
                xmppXmlSplitter.write(writeBuffer, 0, writeBufferPos);
                writeBufferPos = 0;
        }

        private void appendToWriteBuffer(char c) {
                writeBuffer[writeBufferPos++] = c;
        }

        private void ensureWriteBufferHasCapacityFor(int additionalCapacity) {
                final int requiredCapacity = writeBufferPos + additionalCapacity;
                if (requiredCapacity <= writeBuffer.length) {
                        return;
                }

                // Simple resize logic of write buffer.
                char[] newWriteBuffer = new char[requiredCapacity];
                System.arraycopy(writeBuffer, 0, newWriteBuffer, 0, writeBufferPos);
                writeBuffer = newWriteBuffer;
        }
}