#include <stdint.h>
#include "ucore_string.h"

static const uint8_t basecode[128] = 
{
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,   62, 0xff, 0xff, 0xff,   63,
      52,   53,   54,   55,   56,   57,   58,   59,   60,   61, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
    0xff,    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, 0xff, 0xff, 0xff, 0xff, 0xff,
    0xff,   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, 0xff, 0xff, 0xff, 0xff, 0xff
};

#define deccode(c)  ((c > 127) ? 0xff : basecode[(c)])

size_t 
uc_base64_dec(const unsigned char *data, size_t len, unsigned char *result)
{
	size_t	i = 0, j = 0, pad;
	uint8_t  c[4];

	while ((i + 3) < len) {

		pad  = 0;
		c[0] = deccode(data[i  ]); pad += (c[0] == 0xff);
		c[1] = deccode(data[i+1]); pad += (c[1] == 0xff);
		c[2] = deccode(data[i+2]); pad += (c[2] == 0xff);
		c[3] = deccode(data[i+3]); pad += (c[3] == 0xff);
		switch (pad) {
		case 1:
			result[j++] = (c[0] << 2) | ((c[1] & 0x30) >> 4);
			result[j++] = ((c[1] & 0x0f) << 4) | ((c[2] & 0x3c) >> 2);
			result[j]   = (c[2] & 0x03) << 6;
			break;
		case 2:
			result[j++] = (c[0] << 2) | ((c[1] & 0x30) >> 4);
			result[j]   = (c[1] & 0x0f) << 4;
			break;
		default:
			result[j++] = (c[0] << 2) | ((c[1] & 0x30) >> 4);
			result[j++] = ((c[1] & 0x0f) << 4) | ((c[2] & 0x3c) >> 2);
			result[j++] = ((c[2] & 0x03) << 6) | (c[3] & 0x3f);
		}

		i += 4;
	}

	return j;
}