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The Apache Commons Codec package contains simple encoder and decoders for various formats such as Base64 and Hexadecimal. In addition to these widely used encoders and decoders, the codec package also maintains a collection of phonetic encoding utilities.
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/* ====================================================================
   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.poi.sl.image;

import java.awt.Dimension;
import java.awt.Rectangle;
import java.io.IOException;
import java.io.OutputStream;

import org.apache.poi.util.Internal;
import org.apache.poi.util.LittleEndian;
import org.apache.poi.util.LittleEndianConsts;
import org.apache.poi.util.POILogFactory;
import org.apache.poi.util.POILogger;
import org.apache.poi.util.Units;

/**
 * Aldus Placeable Metafile header - 22 byte structure before WMF data.
 * 
 *  int Key;               Magic number (always 9AC6CDD7h)
 *  
short  Handle;         Metafile HANDLE number (always 0)
 *  
short Left;            Left coordinate in metafile units
 *  
short Top;             Top coordinate in metafile units
 *  
short Right;           Right coordinate in metafile units
 *  
short Bottom;          Bottom coordinate in metafile units
 *  
short  Inch;           Number of metafile units per inch
 *  
int Reserved;          Reserved (always 0)
 *  
short  Checksum;       Checksum value for previous 10 shorts
 * 
 */
@Internal
public class ImageHeaderWMF {

    public static final int APMHEADER_KEY = 0x9AC6CDD7;
    private static final POILogger LOG = POILogFactory.getLogger(ImageHeaderWMF.class);

    @SuppressWarnings("unused")
    private final int handle;
    private final int left, top, right, bottom;

    /**
     * The number of logical units per inch used to represent the image.
     * This value can be used to scale an image. By convention, an image is
     * considered to be recorded at 1440 logical units (twips) per inch.
     * Thus, a value of 720 specifies that the image SHOULD be rendered at
     * twice its normal size, and a value of 2880 specifies that the image
     * SHOULD be rendered at half its normal size.
     */
    private final int inch;
    @SuppressWarnings("unused")
    private final int reserved;
    private int checksum;

    public ImageHeaderWMF(Rectangle dim) {
        handle = 0;
        left = dim.x;
        top = dim.y;
        right = dim.x + dim.width;
        bottom = dim.y + dim.height;
        inch = Units.POINT_DPI; //default resolution is 72 dpi
        reserved = 0;
    }

    public ImageHeaderWMF(byte[] data, final int off) {
        int offset = off;
        int key = LittleEndian.getInt(data, offset); offset += LittleEndianConsts.INT_SIZE; //header key
        if (key != APMHEADER_KEY) {
            LOG.log(POILogger.WARN, "WMF file doesn't contain a placeable header - ignore parsing");
            handle = 0;
            left = 0;
            top = 0;
            right = 200;
            bottom = 200;
            inch = Units.POINT_DPI; //default resolution is 72 dpi
            reserved = 0;
            return;
        }

        handle = LittleEndian.getUShort(data, offset); offset += LittleEndianConsts.SHORT_SIZE;
        left = LittleEndian.getShort(data, offset); offset += LittleEndianConsts.SHORT_SIZE;
        top = LittleEndian.getShort(data, offset); offset += LittleEndianConsts.SHORT_SIZE;
        right = LittleEndian.getShort(data, offset); offset += LittleEndianConsts.SHORT_SIZE;
        bottom = LittleEndian.getShort(data, offset); offset += LittleEndianConsts.SHORT_SIZE;

        inch = LittleEndian.getUShort(data, offset); offset += LittleEndianConsts.SHORT_SIZE;
        reserved = LittleEndian.getInt(data, offset); offset += LittleEndianConsts.INT_SIZE;

        checksum = LittleEndian.getShort(data, offset); offset += LittleEndianConsts.SHORT_SIZE;
        if (checksum != getChecksum()){
            LOG.log(POILogger.WARN, "WMF checksum does not match the header data");
        }
    }

    /**
     * Returns a checksum value for the previous 10 shorts in the header.
     * The checksum is calculated by XORing each short value to an initial value of 0:
     */
    public int getChecksum(){
        int cs = 0;
        cs ^=  (APMHEADER_KEY & 0x0000FFFF);
        cs ^= ((APMHEADER_KEY & 0xFFFF0000) >> 16);
        cs ^= left;
        cs ^= top;
        cs ^= right;
        cs ^= bottom;
        cs ^= inch;
        return cs;
    }

    public void write(OutputStream out) throws IOException {
        byte[] header = new byte[22];
        int pos = 0;
        LittleEndian.putInt(header, pos, APMHEADER_KEY); pos += LittleEndianConsts.INT_SIZE; //header key
        LittleEndian.putUShort(header, pos, 0); pos += LittleEndianConsts.SHORT_SIZE; //hmf
        LittleEndian.putUShort(header, pos, left); pos += LittleEndianConsts.SHORT_SIZE; //left
        LittleEndian.putUShort(header, pos, top); pos += LittleEndianConsts.SHORT_SIZE; //top
        LittleEndian.putUShort(header, pos, right); pos += LittleEndianConsts.SHORT_SIZE; //right
        LittleEndian.putUShort(header, pos, bottom); pos += LittleEndianConsts.SHORT_SIZE; //bottom
        LittleEndian.putUShort(header, pos, inch); pos += LittleEndianConsts.SHORT_SIZE; //inch
        LittleEndian.putInt(header, pos, 0); pos += LittleEndianConsts.INT_SIZE;  //reserved

        checksum = getChecksum();
        LittleEndian.putUShort(header, pos, checksum);

        out.write(header);
    }

    public Dimension getSize() {
        //coefficient to translate from WMF dpi to 72dpi
        double coeff = ((double)Units.POINT_DPI)/inch;
        return new Dimension((int)Math.round((right-left)*coeff), (int)Math.round((bottom-top)*coeff));
    }

    public Rectangle getBounds() {
        return new Rectangle(left, top, right-left, bottom-top);
    }

    public int getLength(){
        return 22;
    }
}