package plan9.lib;

// from styx-n-9p.googlecode.com (MIT licence)
public class Base64 implements Encoding {

	public final String enc(byte[] a){
		int n = a.length;
		if(n == 0)
			return "";
		char[] out = new char[4*n/3+4];
		int j = 0;
		for(int i = 0; i < n;) {
			int x = ((int)a[i++]&255) << 16;
			if(i < n)
				x |= ((int)a[i++]&255) << 8;
			if(i < n)
				x |= ((int)a[i++]&255);
			out[j++] = c64(x>>18);
			out[j++] = c64(x>>12);
			out[j++] = c64(x>> 6);
			out[j++] = c64(x);
		}
		int nmod3 = n % 3;
		if(nmod3 != 0) {
			out[j-1] = '=';
			if(nmod3 == 1)
				out[j-2] = '=';
		}
		return new String(out, 0, j);
	}

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

	private static char c64(int c)
	{
		return cmap[c&63];
	}

	private static final short INVAL = 255;

	private static final short[] t64d = {
	   INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,
	   INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,
	   INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,   62,INVAL,INVAL,INVAL,   63,
	      52,   53,   54,   55,   56,   57,   58,   59,   60,   61,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,
	   INVAL,    0,    1,    2,    3,    4,    5,    6,    7,    8,    9,   10,   11,   12,   13,   14,
	      15,   16,   17,   18,   19,   20,   21,   22,   23,   24,   25,INVAL,INVAL,INVAL,INVAL,INVAL,
	   INVAL,   26,   27,   28,   29,   30,   31,   32,   33,   34,   35,   36,   37,   38,   39,   40,
	      41,   42,   43,   44,   45,   46,   47,   48,   49,   50,   51,INVAL,INVAL,INVAL,INVAL,INVAL,
	   INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,
	   INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,
	   INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,
	   INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,
	   INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,
	   INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,
	   INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,
	   INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL,INVAL
	};

	public final byte[] dec(String s){
		int b24 = 0;
		int i = 0;
		int l = s.length();
		byte[] out = new byte[(3*l+3)/4];	// upper bound, especially if s contains white space
		int o = 0;
		for(int n = 0; n < l; n++){
			int c;
			if((c = s.charAt(n)) > 0xFF || (c = t64d[c]) == INVAL)
				continue;
			switch(i++){
			case 0:
				b24 = c<<18;
				break;
			case 1:
				b24 |= c<<12;
				break;
			case 2:
				b24 |= c<<6;
				break;
			case 3:
				b24 |= c;
				out[o++] = (byte) (b24>>16);
				out[o++] = (byte) (b24>>8);
				out[o++] = (byte) b24;
				i = 0;
				break;
			default:
				// impossible; sop to findbugs
				break;
			}
		}
		switch(i){
		case 2:
			out[o++] = (byte) (b24>>16);
			break;
		case 3:
			out[o++] = (byte) (b24>>16);
			out[o++] = (byte) (b24>>8);
			break;
		}
		if(o != out.length){
			byte[] trimmed = new byte[o];
			System.arraycopy(out, 0, trimmed, 0, o);
			out = trimmed;
		}
		return out;
	}
}