#include <stdint.h>
#include <stdio.h>
#include <string.h>

#define MAX_BUF 1024

uint8_t base64_tbl[] = {
    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, 0x3e, 0xff, 0xff, 0xff, 0x3f,
    0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x3a, 0x3b, 0x3c, 0x3d, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
    0xff, 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e,
    0x0f, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0xff, 0xff, 0xff, 0xff, 0xff,
    0xff, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f, 0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27, 0x28,
    0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f, 0x30, 0x31, 0x32, 0x33, 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, 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, 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, 0xff, 0xff, 0xff, 0xff};

void base64_gen_table() {
  uint8_t tbl[256];
  int i, s;

  memset(tbl, 0xff, 256);

  for (i = 0, s = 'A'; s <= 'Z'; ++i, ++s) {
    tbl[s] = i;
  }

  for (s = 'a'; s <= 'z'; ++i, ++s) {
    tbl[s] = i;
  }

  for (s = '0'; s <= '9'; ++i, ++s) {
    tbl[s] = i;
  }

  tbl['+'] = i++;
  tbl['/'] = i;

  for (i = 0; i < 256; ++i) {
    if (i % 0x10 == 0) {
      printf("\n");
    }
    printf("0x%02x,", tbl[i]);
  }
}

int base64_decode(const uint8_t *src, size_t nsrc, uint8_t *dst, int *err) {
  const uint8_t *p;
  int nsrc_rem, ndst, e;
  uint8_t i0, i1, i2, i3;

  p = src;
  nsrc_rem = nsrc % 4;
  nsrc = nsrc & -4;
  ndst = 0;
  e = 0;

  while (nsrc) {
    i0 = base64_tbl[*p++];
    i1 = base64_tbl[*p++];
    i2 = base64_tbl[*p++];
    i3 = base64_tbl[*p++];
    if ((i0 | i1 | i3 | i3) & 0x80) {
      /* encoded text corruption */
      ++e;
      goto next;
    }

    dst[ndst] = i0 << 2 | i1 >> 4;
    dst[ndst + 1] = i1 << 4 | i2 >> 2;
    dst[ndst + 2] = i2 << 6 | i3;

    ndst += 3;

  next:
    nsrc -= 4;
  }

  if (nsrc_rem == 3) {
    i0 = base64_tbl[*p++];
    i1 = base64_tbl[*p++];
    i2 = base64_tbl[*p++];
    if (!(i0 & i1 & i2 & 0x80)) {
      dst[ndst] = i0 << 2 | i1 >> 4;
      dst[ndst + 1] = i1 << 4 | i2 >> 2;
      dst[ndst + 2] = i2 << 6;
      ndst += 3;
    } else {
      ++e;
    }
  } else if (nsrc_rem == 2) {
    i0 = base64_tbl[*p++];
    i1 = base64_tbl[*p++];
    if (!(i0 & i1 & 0x80)) {
      dst[ndst] = i0 << 2 | i1 >> 4;
      dst[ndst + 1] = i1 << 4;
      ndst += 2;
    } else {
      ++e;
    }
  } else if (nsrc_rem == 1) {
    i0 = base64_tbl[*p++];
    if (!(i0 & 0x80)) {
      dst[ndst] = i0 << 2;
      ndst += 2;
    } else {
      ++e;
    }
  }

  *err = e;
  return ndst;
}

int main(int argc, char **argv) {
  uint8_t buf[MAX_BUF];
  int len, err, i, hex;
  char *in;

  if (argc < 2) {
    return 1;
  }

  if (!strcmp(argv[1], "-g")) {
    base64_gen_table();
    return 0;
  }

  hex = 0;
  in = argv[1];

  if (argc > 2 && !strcmp(argv[1], "-hex")) {
    hex = 1;
    in = argv[2];
  }

  len = base64_decode((uint8_t *)in, strlen(in), buf, &err);

  printf("len: %d, err: %d\n", len, err);

  for (i = 0; i < len; ++i) {
    if (hex) {
      printf("%02x ", buf[i]);
    } else {
      printf("%c", (char)buf[i]);
    }
  }

  return 0;
}