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package org.pdfbox.ttf;

import java.io.EOFException;
import java.io.IOException;

import java.util.Calendar;
import java.util.GregorianCalendar;

import org.pdfbox.pdmodel.common.PDStream;

/**
 * An interface into a data stream.
 * 
 * @author Ben Litchfield (ben@benlitchfield.com)
 * @version $Revision: 1.5 $
 */
public abstract class TTFDataStream 
{

    /**
     * Read a 16.16 fixed value, where the first 16 bits are the decimal and the last
     * 16 bits are the fraction.
     * @return A 32 bit value.
     * @throws IOException If there is an error reading the data.
     */
    public float read32Fixed() throws IOException
    {
        float retval = 0;
        retval = readSignedShort();
        retval += (readUnsignedShort()/65536);
        return retval;
    }
    
    /**
     * Read a fixed length ascii string.
     * @param length The length of the string to read.
     * @return A string of the desired length.
     * @throws IOException If there is an error reading the data.
     */
    public String readString( int length ) throws IOException
    {
        return readString( length, "ISO-8859-1" );
    }
    
    /**
     * Read a fixed length ascii string.
     * @param length The length of the string to read in bytes.
     * @param charset The expected character set of the string.
     * @return A string of the desired length.
     * @throws IOException If there is an error reading the data.
     */
    public String readString( int length, String charset ) throws IOException
    {
        byte[] buffer = read( length );
        return new String(buffer, charset);
    }
    
    /**
     * Read an unsigned byte.
     * @return An unsigned byte.
     * @throws IOException If there is an error reading the data.
     */
    public abstract int read() throws IOException;
    
    /**
     * Read an unsigned byte.
     * @return An unsigned byte.
     * @throws IOException If there is an error reading the data.
     */
    public abstract long readLong() throws IOException;
    
    
    /**
     * Read a signed byte.
     * @return A signed byte.
     * @throws IOException If there is an error reading the data.
     */
    public int readSignedByte() throws IOException
    {
        int signedByte = read();
        return signedByte < 127 ? signedByte : signedByte-256;
    }
    
    /**
     * Read an unsigned integer.
     * @return An unsiged integer.
     * @throws IOException If there is an error reading the data.
     */
    public long readUnsignedInt() throws IOException
    {
        long byte1 = read();
        long byte2 = read();
        long byte3 = read();
        long byte4 = read();
        if( byte4 < 0 )
        {
            throw new EOFException();
        }
        return (byte1 << 24) + (byte2 << 16) + (byte3 << 8) + (byte4 << 0);
    }
    
    /**
     * Read an unsigned short.
     * 
     * @return An unsigned short.
     * @throws IOException If there is an error reading the data.
     */
    public abstract int readUnsignedShort() throws IOException;
    
    /**
     * Read an unsigned short array.
     * 
     * @param length The length of the array to read.
     * @return An unsigned short array.
     * @throws IOException If there is an error reading the data.
     */
    public int[] readUnsignedShortArray( int length ) throws IOException
    {
        int[] array = new int[ length ];
        for( int i=0; i<length; i++ )
        {
            array[i] = readUnsignedShort();
        }
        return array;
    }
    
    /**
     * Read an signed short.
     * 
     * @return An signed short.
     * @throws IOException If there is an error reading the data.
     */
    public abstract short readSignedShort() throws IOException;
    
    /**
     * Read an eight byte international date.
     * 
     * @return An signed short.
     * @throws IOException If there is an error reading the data.
     */
    public Calendar readInternationalDate() throws IOException
    {
        long secondsSince1904 = readLong();
        GregorianCalendar cal = new GregorianCalendar( 1904, 0, 1 );
        long millisFor1904 = cal.getTimeInMillis();
        millisFor1904 += (secondsSince1904*1000);
        cal.setTimeInMillis( millisFor1904 );
        return cal;
    }
    
    /**
     * Close the underlying resources.
     * 
     * @throws IOException If there is an error closing the resources.
     */
    public abstract void close() throws IOException;
    
    /**
     * Seek into the datasource.
     * 
     * @param pos The position to seek to.
     * @throws IOException If there is an error seeking to that position.
     */
    public abstract void seek(long pos) throws IOException;
    
    /**
     * Read a specific number of bytes from the stream.
     * @param numberOfBytes The number of bytes to read.
     * @return The byte buffer.
     * @throws IOException If there is an error while reading.
     */
    public byte[] read( int numberOfBytes ) throws IOException
    {
        byte[] data = new byte[ numberOfBytes ];
        int amountRead = 0;
        int totalAmountRead = 0;
        while( (amountRead = read( data, totalAmountRead, numberOfBytes-totalAmountRead ) ) != -1 && 
               totalAmountRead < numberOfBytes )
        {
            totalAmountRead += amountRead;
            //read at most numberOfBytes bytes from the stream.
        }
        return data;
    }
    
    /**
     * @see java.io.InputStream#read( byte[], int, int )
     * 
     * @param b The buffer to write to.
     * @param off The offset into the buffer.
     * @param len The length into the buffer.
     * 
     * @return The number of bytes read.
     * 
     * @throws IOException If there is an error reading from the stream.
     */
    public abstract int read(byte[] b,
            int off,
            int len)
     throws IOException;
    
    /**
     * Get the current position in the stream.
     * @return The current position in the stream.
     * @throws IOException If an error occurs while reading the stream.
     */
    public abstract long getCurrentPosition() throws IOException;
    
    /**
     * Get a COSStream from this TTFDataStream
     * This permit to pass the data read from an
     * external source to the COSObjects to keep
     * a certain persistence layer between specialized
     * objects like the TTF package and the pdmodel package.
     *
     * Created by Pascal Allain
     * Vertical7 Inc.
     *
     * @return COSStream describing this stream
     */
    public abstract PDStream getPDStream();

}