/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.apache.pdfbox.pdfwriter.compress;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.nio.charset.StandardCharsets;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Map;

import org.apache.pdfbox.cos.COSArray;
import org.apache.pdfbox.cos.COSBase;
import org.apache.pdfbox.cos.COSBoolean;
import org.apache.pdfbox.cos.COSDictionary;
import org.apache.pdfbox.cos.COSFloat;
import org.apache.pdfbox.cos.COSInteger;
import org.apache.pdfbox.cos.COSName;
import org.apache.pdfbox.cos.COSNull;
import org.apache.pdfbox.cos.COSObject;
import org.apache.pdfbox.cos.COSObjectKey;
import org.apache.pdfbox.cos.COSStream;
import org.apache.pdfbox.cos.COSString;
import org.apache.pdfbox.pdfparser.PDFXRefStream;
import org.apache.pdfbox.pdfwriter.COSWriter;


/**
 * An instance of this class represents an object stream, that compresses a number of {@link COSObject}s in a stream. It
 * may be added to the top level container of a written PDF document in place of the compressed objects. The document's
 * {@link PDFXRefStream} must be adapted accordingly.
 *
 * @author Christian Appl
 */
public class COSWriterObjectStream
{
    private final COSWriterCompressionPool compressionPool;
    private final List<COSObjectKey> preparedKeys = new ArrayList<>();
    private final List<COSBase> preparedObjects = new ArrayList<>();

    /**
     * Creates an object stream for compressible objects from the given {@link COSWriterCompressionPool}. The objects
     * must first be prepared for this object stream, by adding them via calling
     * {@link COSWriterObjectStream#prepareStreamObject(COSObjectKey, COSBase)} and will be written to this
     * {@link COSStream}, when {@link COSWriterObjectStream#writeObjectsToStream(COSStream)} is called.
     *
     * @param compressionPool The compression pool an object stream shall be created for.
     */
    public COSWriterObjectStream(COSWriterCompressionPool compressionPool)
    {
        this.compressionPool = compressionPool;
    }

    /**
     * Prepares the given {@link COSObject} to be written to this object stream, using the given {@link COSObjectKey} as
     * it's ID for indirect references.
     *
     * @param key The {@link COSObjectKey}, that shall be used for indirect references to the {@link COSObject}.
     * @param object The {@link COSObject}, that shall be written to this object stream.
     */
    public void prepareStreamObject(COSObjectKey key, COSBase object)
    {
        if (key != null && object != null)
        {
            preparedKeys.add(key);
            preparedObjects
                    .add(object instanceof COSObject ? ((COSObject) object).getObject() : object);
        }
    }

    /**
     * Returns all {@link COSObjectKey}s, that shall be added to the object stream, when
     * {@link COSWriterObjectStream#writeObjectsToStream(COSStream)} is called.
     *
     * @return All {@link COSObjectKey}s, that shall be added to the object stream.
     */
    public List<COSObjectKey> getPreparedKeys()
    {
        return Collections.unmodifiableList(preparedKeys);
    }

    /**
     * Writes all prepared {@link COSObject}s to the given {@link COSStream}.
     *
     * @param stream The stream for the compressed objects.
     * @return The given {@link COSStream} of this object stream.
     * @throws IOException Shall be thrown, if writing the object stream failed.
     */
    public COSStream writeObjectsToStream(COSStream stream) throws IOException
    {
        int objectCount = preparedKeys.size();
        stream.setItem(COSName.TYPE, COSName.OBJ_STM);
        stream.setInt(COSName.N, objectCount);
        // Prepare the compressible objects for writing.
        List<Long> objectNumbers = new ArrayList<>(objectCount);
        List<byte[]> objectsBuffer = new ArrayList<>(objectCount);
        for (int i = 0; i < objectCount; i++)
        {
            try (ByteArrayOutputStream partialOutput = new ByteArrayOutputStream())
            {
                objectNumbers.add(preparedKeys.get(i).getNumber());
                COSBase base = preparedObjects.get(i);
                writeObject(partialOutput, base, true);
                objectsBuffer.add(partialOutput.toByteArray());
            }
        }

        // Deduce the object stream byte offset map.
        byte[] offsetsMapBuffer;
        long nextObjectOffset = 0;
        try (ByteArrayOutputStream partialOutput = new ByteArrayOutputStream())
        {
            for (int i = 0; i < objectNumbers.size(); i++)
            {
                partialOutput.write(
                        String.valueOf(objectNumbers.get(i)).getBytes(StandardCharsets.ISO_8859_1));
                partialOutput.write(COSWriter.SPACE);
                partialOutput.write(
                        String.valueOf(nextObjectOffset).getBytes(StandardCharsets.ISO_8859_1));
                partialOutput.write(COSWriter.SPACE);
                nextObjectOffset += objectsBuffer.get(i).length;
            }
            offsetsMapBuffer = partialOutput.toByteArray();
        }

        // Write Flate compressed object stream data.
        try (OutputStream output = stream.createOutputStream(COSName.FLATE_DECODE))
        {
            output.write(offsetsMapBuffer);
            stream.setInt(COSName.FIRST, offsetsMapBuffer.length);
            for (byte[] rawObject : objectsBuffer)
            {
                output.write(rawObject);
            }
        }
        return stream;
    }

    /**
     * This method prepares and writes COS data to the object stream by selecting appropriate specialized methods for
     * the content.
     *
     * @param output The stream, that shall be written to.
     * @param object The content, that shall be written.
     * @param topLevel True, if the currently written object is a top level entry of this object stream.
     * @throws IOException Shall be thrown, when an exception occurred for the write operation.
     */
    private void writeObject(OutputStream output, COSBase object, boolean topLevel)
            throws IOException
    {
        if (object == null)
        {
            return;
        }
        if (!(object instanceof COSBase))
        {
            throw new IOException("Error: Unknown type in object stream:" + object);
        }
        COSBase base;
        if (object instanceof COSObject)
        {
            base = ((COSObject) object).getObject();
            if (!topLevel)
            {
                COSObjectKey actualKey = ((COSObject) object).getKey();
                // the object reference can't be dereferenced be lenient and write the reference nevertheless
                // or the object is part of a compressed object stream and shouldn't be written directly
                if (base == null || (actualKey != null && preparedKeys.contains(actualKey)))
                {
                    writeObjectReference(output, actualKey);
                    return;
                }
            }
        }
        else
        {
            base = object;
        }
        if (!topLevel && this.compressionPool.contains(base))
        {
            COSObjectKey key = this.compressionPool.getKey(base);
            if (key == null)
            {
                throw new IOException(
                        "Error: Adding unknown object reference to object stream:" + object);
            }
            writeObjectReference(output, key);
            return;
        }
        if (base instanceof COSString)
        {
            writeCOSString(output, (COSString) base);
        }
        else if (base instanceof COSFloat)
        {
            writeCOSFloat(output, (COSFloat) base);
        }
        else if (base instanceof COSInteger)
        {
            writeCOSInteger(output, (COSInteger) base);
        }
        else if (base instanceof COSBoolean)
        {
            writeCOSBoolean(output, (COSBoolean) base);
        }
        else if (base instanceof COSName)
        {
            writeCOSName(output, (COSName) base);
        }
        else if (base instanceof COSArray)
        {
            writeCOSArray(output, (COSArray) base);
        }
        else if (base instanceof COSDictionary)
        {
            writeCOSDictionary(output, (COSDictionary) base);
        }
        else if (base instanceof COSNull)
        {
            writeCOSNull(output);
        }
        else
        {
            throw new IOException("Error: Unknown type in object stream:" + object);
        }
    }

    /**
     * Write the given {@link COSString} to the given stream.
     *
     * @param output The stream, that shall be written to.
     * @param cosString The content, that shall be written.
     */
    private void writeCOSString(OutputStream output, COSString cosString) throws IOException
    {
        COSWriter.writeString(cosString, output);
        output.write(COSWriter.SPACE);
    }

    /**
     * Write the given {@link COSFloat} to the given stream.
     *
     * @param output The stream, that shall be written to.
     * @param cosFloat The content, that shall be written.
     */
    private void writeCOSFloat(OutputStream output, COSFloat cosFloat) throws IOException
    {
        cosFloat.writePDF(output);
        output.write(COSWriter.SPACE);
    }

    /**
     * Write the given {@link COSInteger} to the given stream.
     *
     * @param output The stream, that shall be written to.
     * @param cosInteger The content, that shall be written.
     */
    private void writeCOSInteger(OutputStream output, COSInteger cosInteger) throws IOException
    {
        cosInteger.writePDF(output);
        output.write(COSWriter.SPACE);
    }

    /**
     * Write the given {@link COSBoolean} to the given stream.
     *
     * @param output The stream, that shall be written to.
     * @param cosBoolean The content, that shall be written.
     */
    private void writeCOSBoolean(OutputStream output, COSBoolean cosBoolean) throws IOException
    {
        cosBoolean.writePDF(output);
        output.write(COSWriter.SPACE);
    }

    /**
     * Write the given {@link COSName} to the given stream.
     *
     * @param output The stream, that shall be written to.
     * @param cosName The content, that shall be written.
     */
    private void writeCOSName(OutputStream output, COSName cosName) throws IOException
    {
        cosName.writePDF(output);
        output.write(COSWriter.SPACE);
    }

    /**
     * Write the given {@link COSArray} to the given stream.
     *
     * @param output The stream, that shall be written to.
     * @param cosArray The content, that shall be written.
     */
    private void writeCOSArray(OutputStream output, COSArray cosArray) throws IOException
    {
        output.write(COSWriter.ARRAY_OPEN);
        for (COSBase value : cosArray.toList())
        {
            if (value == null)
            {
                writeCOSNull(output);
            }
            else
            {
                writeObject(output, value, false);
            }
        }
        output.write(COSWriter.ARRAY_CLOSE);
        output.write(COSWriter.SPACE);
    }

    /**
     * Write the given {@link COSDictionary} to the given stream.
     *
     * @param output The stream, that shall be written to.
     * @param cosDictionary The content, that shall be written.
     */
    private void writeCOSDictionary(OutputStream output, COSDictionary cosDictionary)
            throws IOException
    {
        output.write(COSWriter.DICT_OPEN);
        for (Map.Entry<COSName, COSBase> entry : cosDictionary.entrySet())
        {
            if (entry.getValue() != null)
            {
                writeObject(output, entry.getKey(), false);
                writeObject(output, entry.getValue(), false);
            }
        }
        output.write(COSWriter.DICT_CLOSE);
        output.write(COSWriter.SPACE);
    }

    /**
     * Write the given {@link COSObjectKey} to the given stream.
     *
     * @param output The stream, that shall be written to.
     * @param indirectReference The content, that shall be written.
     */
    private void writeObjectReference(OutputStream output, COSObjectKey indirectReference)
            throws IOException
    {
        output.write(String.valueOf(indirectReference.getNumber())
                .getBytes(StandardCharsets.ISO_8859_1));
        output.write(COSWriter.SPACE);
        output.write(String.valueOf(indirectReference.getGeneration())
                .getBytes(StandardCharsets.ISO_8859_1));
        output.write(COSWriter.SPACE);
        output.write(COSWriter.REFERENCE);
        output.write(COSWriter.SPACE);
    }

    /**
     * Write {@link COSNull} to the given stream.
     *
     * @param output The stream, that shall be written to.
     */
    private void writeCOSNull(OutputStream output) throws IOException
    {
        output.write("null".getBytes(StandardCharsets.ISO_8859_1));
        output.write(COSWriter.SPACE);
    }
}
