SquirrelJME/SquirrelJME

// -*- Mode: Java; indent-tabs-mode: t; tab-width: 4 -*-
// ---------------------------------------------------------------------------
// SquirrelJME
//     Copyright (C) Stephanie Gawroriski <xer@multiphasicapps.net>
// ---------------------------------------------------------------------------
// SquirrelJME is under the Mozilla Public License Version 2.0.
// See license.mkd for licensing and copyright information.
// ---------------------------------------------------------------------------

package net.multiphasicapps.io;

import java.io.IOException;
import java.io.InputStream;
import java.io.Reader;

/**
 * This encodes binary data to a base64 representation of that data.
 *
 * @since 2021/05/22
 */
public final class Base64Encoder
    extends Reader
{
    /** Character mask. */
    private static final int _CHAR_MASK =
        0b111_111;
    
    /** Character shift. */
    private static final int _BIT_COUNT =
        6;
    
    /** The stream to read from. */
    protected final InputStream in;
    
    /** The alphabet. */
    private final char[] _alphabet;
    
    /** The current bit stream that is left over. */
    int _bitStream;
    
    /** The number of bits in the stream. */
    byte _count;
    
    /** Was EOF hit? */
    boolean _hitEof;
    
    /** Padding that is left to output, when EOF. */
    byte _paddingLeft =
        -1;
    
    /** Bytes converted. */
    int _totalBytes =
        0;
    
    /**
     * Initializes the base64 encoder, using the basic alphabet.
     * 
     * @param __in The stream to read from.
     * @throws NullPointerException On null arguments.
     * @since 2021/05/22
     */
    public Base64Encoder(InputStream __in)
        throws NullPointerException
    {
        this(__in, Base64Alphabet.BASIC);
    }
    
    /**
     * Initializes the base64 encoder.
     * 
     * @param __in The stream to read from.
     * @param __alphabet The alphabet to encode/decode from.
     * @throws NullPointerException On null arguments.
     * @since 2021/05/22
     */
    public Base64Encoder(InputStream __in, Base64Alphabet __alphabet)
        throws NullPointerException
    {
        if (__in == null || __alphabet == null)
            throw new NullPointerException("NARG");
        
        this.in = __in;
        this._alphabet = __alphabet._alphabet;
    }
    
    /**
     * {@inheritDoc}
     * @since 2021/05/22
     */
    @Override
    public void close()
        throws IOException
    {
        this.in.close();
    }
    
    /**
     * {@inheritDoc}
     * @since 2021/05/22
     */
    @Override
    public int read(char[] __c, int __o, int __l)
        throws IndexOutOfBoundsException, IOException, NullPointerException
    {
        if (__c == null)
            throw new NullPointerException("NARG");
        if (__o < 0 || __l < 0 || (__o + __l) < 0 || (__o + __l) > __c.length)
            throw new IndexOutOfBoundsException("IOOB");
            
        InputStream in = this.in;
        char[] alphabet = this._alphabet;
        
        int bitStream = this._bitStream;
        int count = this._count;
        boolean hitEof = this._hitEof;
        int paddingLeft = this._paddingLeft;
        int totalBytes = this._totalBytes;
        
        // We want to restore the data fields back when we are done reading
        try
        {
            int converted = 0;
            while (converted < __l)
            {
                // Determine the character to output
                if (count >= Base64Encoder._BIT_COUNT ||
                    (hitEof && count > 0))
                {
                    // We want the upper bits!
                    int downShift = Math.max(0,
                        count - Base64Encoder._BIT_COUNT);
                    
                    // Read in value, if it is too short then shift it up
                    // and add zero padding accordingly
                    int value = (bitStream >>> downShift) &
                        Base64Encoder._CHAR_MASK;
                    if (hitEof && count < Base64Encoder._BIT_COUNT)
                        value <<= Base64Encoder._BIT_COUNT - count;
                    
                    // Output encoded character
                    __c[__o + (converted++)] = alphabet[value];
                    
                    // Eat up the bit stream
                    count = Math.max(0, count - Base64Encoder._BIT_COUNT);
                    bitStream &= ~(-1 << downShift);
                }
                
                // No padding left to read, we stop
                else if (paddingLeft == 0)
                    break;
                
                // Is there padding left to put in
                else if (paddingLeft > 0)
                {
                    __c[__o + (converted++)] = '=';
                    
                    // We took this padding
                    paddingLeft--;
                    continue;
                }
                
                // We could overflow our own storage, so try again
                if (count + 8 > 24 || hitEof)
                    continue;
                
                // If EOF hit, then we will pad
                int read = in.read();
                if (read < 0)
                {
                    hitEof = true;
                    
                    // How much padding to place in?
                    switch (totalBytes % 3)
                    {
                        case 0: paddingLeft = 0; break;
                        case 1: paddingLeft = 2; break;
                        case 2: paddingLeft = 1; break;
                    }
                }
                
                // When adding bytes push below
                else
                {
                    bitStream <<= 8;
                    bitStream |= (read & 0xFF);
                    count += 8;
                    
                    totalBytes++;
                }
            }
            
            return (hitEof && paddingLeft == 0 && converted == 0 ? -1 :
                converted);
        }
        
        // Always store the fields back when done
        finally
        {
            this._bitStream = bitStream;
            this._count = (byte)count;
            this._hitEof = hitEof;
            this._paddingLeft = (byte)paddingLeft;
            this._totalBytes = totalBytes;
        }
    }
}