/*
cencoder.c - c source to a base64 encoding algorithm implementation

This is part of the libb64 project, and has been placed in the public domain.
For details, see http://sourceforge.net/projects/libb64
*/

#include "cencode.h"

void base64_init_encodestate(base64_encodestate *state_in) {
  state_in->step = step_A;
  state_in->result = 0;
}

char base64_encode_value(char value_in) {
  static const char *encoding = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
  if (value_in > 63) {
    return '=';
  }
  return encoding[(int)value_in];
}

int base64_encode_block(const char *plaintext_in, int length_in, char *code_out, base64_encodestate *state_in) {
  const char *plainchar = plaintext_in;
  const char *const plaintextend = plaintext_in + length_in;
  char *codechar = code_out;
  char result;
  char fragment;

  result = state_in->result;

  switch (state_in->step) {
    while (1) {
      case step_A:
        if (plainchar == plaintextend) {
          state_in->result = result;
          state_in->step = step_A;
          return codechar - code_out;
        }
        fragment = *plainchar++;
        result = (fragment & 0x0fc) >> 2;
        *codechar++ = base64_encode_value(result);
        result = (fragment & 0x003) << 4;
        // fall through
      case step_B:
        if (plainchar == plaintextend) {
          state_in->result = result;
          state_in->step = step_B;
          return codechar - code_out;
        }
        fragment = *plainchar++;
        result |= (fragment & 0x0f0) >> 4;
        *codechar++ = base64_encode_value(result);
        result = (fragment & 0x00f) << 2;
        // fall through
      case step_C:
        if (plainchar == plaintextend) {
          state_in->result = result;
          state_in->step = step_C;
          return codechar - code_out;
        }
        fragment = *plainchar++;
        result |= (fragment & 0x0c0) >> 6;
        *codechar++ = base64_encode_value(result);
        result = (fragment & 0x03f) >> 0;
        *codechar++ = base64_encode_value(result);
    }
  }
  /* control should not reach here */
  return codechar - code_out;
}

int base64_encode_blockend(char *code_out, base64_encodestate *state_in) {
  char *codechar = code_out;

  switch (state_in->step) {
    case step_B:
      *codechar++ = base64_encode_value(state_in->result);
      *codechar++ = '=';
      *codechar++ = '=';
      break;
    case step_C:
      *codechar++ = base64_encode_value(state_in->result);
      *codechar++ = '=';
      break;
    case step_A: break;
  }
  *codechar = 0x00;

  return codechar - code_out;
}

int base64_encode_chars(const char *plaintext_in, int length_in, char *code_out) {
  base64_encodestate _state;
  base64_init_encodestate(&_state);
  int len = base64_encode_block(plaintext_in, length_in, code_out, &_state);
  return len + base64_encode_blockend((code_out + len), &_state);
}
