/*
 * Copyright (c) 2012-2016 Arne Schwabe
 * Distributed under the GNU GPL v2 with additional terms. For full terms see the file doc/LICENSE.txt
 */

package org.spongycastle.util.encoders;

import java.io.IOException;
import java.io.OutputStream;

public class Base64Encoder
    implements Encoder
{
    protected final byte[] encodingTable =
        {
            (byte)'A', (byte)'B', (byte)'C', (byte)'D', (byte)'E', (byte)'F', (byte)'G',
            (byte)'H', (byte)'I', (byte)'J', (byte)'K', (byte)'L', (byte)'M', (byte)'N',
            (byte)'O', (byte)'P', (byte)'Q', (byte)'R', (byte)'S', (byte)'T', (byte)'U',
            (byte)'V', (byte)'W', (byte)'X', (byte)'Y', (byte)'Z',
            (byte)'a', (byte)'b', (byte)'c', (byte)'d', (byte)'e', (byte)'f', (byte)'g',
            (byte)'h', (byte)'i', (byte)'j', (byte)'k', (byte)'l', (byte)'m', (byte)'n',
            (byte)'o', (byte)'p', (byte)'q', (byte)'r', (byte)'s', (byte)'t', (byte)'u',
            (byte)'v',
            (byte)'w', (byte)'x', (byte)'y', (byte)'z',
            (byte)'0', (byte)'1', (byte)'2', (byte)'3', (byte)'4', (byte)'5', (byte)'6',
            (byte)'7', (byte)'8', (byte)'9',
            (byte)'+', (byte)'/'
        };

    protected byte    padding = (byte)'=';
    
    /*
     * set up the decoding table.
     */
    protected final byte[] decodingTable = new byte[128];

    protected void initialiseDecodingTable()
    {
        for (int i = 0; i < encodingTable.length; i++)
        {
            decodingTable[encodingTable[i]] = (byte)i;
        }
    }
    
    public Base64Encoder()
    {
        initialiseDecodingTable();
    }
    
    /**
     * encode the input data producing a base 64 output stream.
     *
     * @return the number of bytes produced.
     */
    public int encode(
        byte[]                data,
        int                    off,
        int                    length,
        OutputStream    out) 
        throws IOException
    {
        int modulus = length % 3;
        int dataLength = (length - modulus);
        int a1, a2, a3;
        
        for (int i = off; i < off + dataLength; i += 3)
        {
            a1 = data[i] & 0xff;
            a2 = data[i + 1] & 0xff;
            a3 = data[i + 2] & 0xff;

            out.write(encodingTable[(a1 >>> 2) & 0x3f]);
            out.write(encodingTable[((a1 << 4) | (a2 >>> 4)) & 0x3f]);
            out.write(encodingTable[((a2 << 2) | (a3 >>> 6)) & 0x3f]);
            out.write(encodingTable[a3 & 0x3f]);
        }

        /*
         * process the tail end.
         */
        int    b1, b2, b3;
        int    d1, d2;

        switch (modulus)
        {
        case 0:        /* nothing left to do */
            break;
        case 1:
            d1 = data[off + dataLength] & 0xff;
            b1 = (d1 >>> 2) & 0x3f;
            b2 = (d1 << 4) & 0x3f;

            out.write(encodingTable[b1]);
            out.write(encodingTable[b2]);
            out.write(padding);
            out.write(padding);
            break;
        case 2:
            d1 = data[off + dataLength] & 0xff;
            d2 = data[off + dataLength + 1] & 0xff;

            b1 = (d1 >>> 2) & 0x3f;
            b2 = ((d1 << 4) | (d2 >>> 4)) & 0x3f;
            b3 = (d2 << 2) & 0x3f;

            out.write(encodingTable[b1]);
            out.write(encodingTable[b2]);
            out.write(encodingTable[b3]);
            out.write(padding);
            break;
        }

        return (dataLength / 3) * 4 + ((modulus == 0) ? 0 : 4);
    }

    private boolean ignore(
        char    c)
    {
        return (c == '\n' || c =='\r' || c == '\t' || c == ' ');
    }
    
    /**
     * decode the base 64 encoded byte data writing it to the given output stream,
     * whitespace characters will be ignored.
     *
     * @return the number of bytes produced.
     */
    public int decode(
        byte[]          data,
        int             off,
        int             length,
        OutputStream    out)
        throws IOException
    {
        byte    b1, b2, b3, b4;
        int     outLen = 0;
        
        int     end = off + length;
        
        while (end > off)
        {
            if (!ignore((char)data[end - 1]))
            {
                break;
            }
            
            end--;
        }
        
        int  i = off;
        int  finish = end - 4;
        
        i = nextI(data, i, finish);

        while (i < finish)
        {
            b1 = decodingTable[data[i++]];
            
            i = nextI(data, i, finish);
            
            b2 = decodingTable[data[i++]];
            
            i = nextI(data, i, finish);
            
            b3 = decodingTable[data[i++]];
            
            i = nextI(data, i, finish);
            
            b4 = decodingTable[data[i++]];

            out.write((b1 << 2) | (b2 >> 4));
            out.write((b2 << 4) | (b3 >> 2));
            out.write((b3 << 6) | b4);
            
            outLen += 3;
            
            i = nextI(data, i, finish);
        }

        outLen += decodeLastBlock(out, (char)data[end - 4], (char)data[end - 3], (char)data[end - 2], (char)data[end - 1]);
        
        return outLen;
    }

    private int nextI(byte[] data, int i, int finish)
    {
        while ((i < finish) && ignore((char)data[i]))
        {
            i++;
        }
        return i;
    }
    
    /**
     * decode the base 64 encoded String data writing it to the given output stream,
     * whitespace characters will be ignored.
     *
     * @return the number of bytes produced.
     */
    public int decode(
        String          data,
        OutputStream    out)
        throws IOException
    {
        byte    b1, b2, b3, b4;
        int     length = 0;
        
        int     end = data.length();
        
        while (end > 0)
        {
            if (!ignore(data.charAt(end - 1)))
            {
                break;
            }
            
            end--;
        }
        
        int  i = 0;
        int  finish = end - 4;
        
        i = nextI(data, i, finish);
        
        while (i < finish)
        {
            b1 = decodingTable[data.charAt(i++)];
            
            i = nextI(data, i, finish);
            
            b2 = decodingTable[data.charAt(i++)];
            
            i = nextI(data, i, finish);
            
            b3 = decodingTable[data.charAt(i++)];
            
            i = nextI(data, i, finish);
            
            b4 = decodingTable[data.charAt(i++)];

            out.write((b1 << 2) | (b2 >> 4));
            out.write((b2 << 4) | (b3 >> 2));
            out.write((b3 << 6) | b4);
            
            length += 3;
            
            i = nextI(data, i, finish);
        }

        length += decodeLastBlock(out, data.charAt(end - 4), data.charAt(end - 3), data.charAt(end - 2), data.charAt(end - 1));

        return length;
    }

    private int decodeLastBlock(OutputStream out, char c1, char c2, char c3, char c4) 
        throws IOException
    {
        byte    b1, b2, b3, b4;
        
        if (c3 == padding)
        {
            b1 = decodingTable[c1];
            b2 = decodingTable[c2];

            out.write((b1 << 2) | (b2 >> 4));
            
            return 1;
        }
        else if (c4 == padding)
        {
            b1 = decodingTable[c1];
            b2 = decodingTable[c2];
            b3 = decodingTable[c3];

            out.write((b1 << 2) | (b2 >> 4));
            out.write((b2 << 4) | (b3 >> 2));
            
            return 2;
        }
        else
        {
            b1 = decodingTable[c1];
            b2 = decodingTable[c2];
            b3 = decodingTable[c3];
            b4 = decodingTable[c4];

            out.write((b1 << 2) | (b2 >> 4));
            out.write((b2 << 4) | (b3 >> 2));
            out.write((b3 << 6) | b4);
            
            return 3;
        } 
    }

    private int nextI(String data, int i, int finish)
    {
        while ((i < finish) && ignore(data.charAt(i)))
        {
            i++;
        }
        return i;
    }
}
