/*
 * See LICENSE file in distribution for copyright and licensing information.
 */
package org.jvyamlb.util;

/**
 * @author <a href="mailto:ola.bini@gmail.com">Ola Bini</a>
 */
public class Base64Coder {
    // Mapping table from 6-bit nibbles to Base64 characters.
    private final static char[] map1 = new char[64];
    static {
        int i=0;
        for(char c='A'; c<='Z'; c++) map1[i++] = c;
        for(char c='a'; c<='z'; c++) map1[i++] = c;
        for(char c='0'; c<='9'; c++) map1[i++] = c;
        map1[i++] = '+'; map1[i++] = '/';
    }
    
    // Mapping table from Base64 characters to 6-bit nibbles.
    private final static byte[] map2 = new byte[128];
    static {
        for(int i=0; i<map2.length; i++) map2[i] = -1;
        for(int i=0; i<64; i++) map2[map1[i]] = (byte)i; 
    }
    
    /**
     * Encodes a string into Base64 format.
     * No blanks or line breaks are inserted.
     * @param s  a String to be encoded.
     * @return   A String with the Base64 encoded data.
     */
    public static String encode(final String s) {
        try {
            return new String(encode(s.getBytes("ISO-8859-1")));
        } catch(Exception e) {
            // Theoritically shouldn't happen
            return null;
        }
    }

    /**
     * Encodes a byte array into Base64 format.
     * No blanks or line breaks are inserted.
     * @param in  an array containing the data bytes to be encoded.
     * @return    A character array with the Base64 encoded data.
     */
    public static char[] encode(final byte[] in) {
        int iLen = in.length;
        int oDataLen = (iLen*4+2)/3;       // output length without padding
        int oLen = ((iLen+2)/3)*4;         // output length including padding
        char[] out = new char[oLen];
        int ip = 0;
        int op = 0;
        while (ip < iLen) {
            int i0 = in[ip++] & 0xff;
            int i1 = ip < iLen ? in[ip++] & 0xff : 0;
            int i2 = ip < iLen ? in[ip++] & 0xff : 0;
            int o0 = i0 >>> 2;
            int o1 = ((i0 &   3) << 4) | (i1 >>> 4);
            int o2 = ((i1 & 0xf) << 2) | (i2 >>> 6);
            int o3 = i2 & 0x3F;
            out[op++] = map1[o0];
            out[op++] = map1[o1];
            out[op] = op < oDataLen ? map1[o2] : '='; op++;
            out[op] = op < oDataLen ? map1[o3] : '='; op++; }
        return out;
    }

    /**
     * Decodes Base64 data.
     * No blanks or line breaks are allowed within the Base64 encoded data.
     * @param in  a character array containing the Base64 encoded data.
     * @return    An array containing the decoded data bytes.
     * @throws    IllegalArgumentException if the input is not valid Base64 encoded data.
     */
    public static byte[] decode(final byte[] in) {
        int iLen = in.length;
        if (iLen%4 != 0) throw new IllegalArgumentException ("Length of Base64 encoded input string is not a multiple of 4.");
        while (iLen > 0 && in[iLen-1] == '=') iLen--;
        int oLen = (iLen*3) / 4;
        byte[] out = new byte[oLen];
        int ip = 0;
        int op = 0;
        while (ip < iLen) {
            int i0 = in[ip++];
            int i1 = in[ip++];
            int i2 = ip < iLen ? in[ip++] : 'A';
            int i3 = ip < iLen ? in[ip++] : 'A';
            if (i0 > 127 || i1 > 127 || i2 > 127 || i3 > 127)
                throw new IllegalArgumentException ("Illegal character in Base64 encoded data.");
            int b0 = map2[i0];
            int b1 = map2[i1];
            int b2 = map2[i2];
            int b3 = map2[i3];
            if (b0 < 0 || b1 < 0 || b2 < 0 || b3 < 0)
                throw new IllegalArgumentException ("Illegal character in Base64 encoded data.");
            int o0 = ( b0       <<2) | (b1>>>4);
            int o1 = ((b1 & 0xf)<<4) | (b2>>>2);
            int o2 = ((b2 &   3)<<6) |  b3;
            out[op++] = (byte)o0;
            if (op<oLen) out[op++] = (byte)o1;
            if (op<oLen) out[op++] = (byte)o2; }
        return out; 
    }
}
