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// ///////////////////////////////////////////////////////////////////////////////

// Copyright (C) 2010, Frank Blumenberg

//

// See License.txt for complete licensing and attribution information.

// Permission is hereby granted, free of charge, to any person obtaining a copy

// of this software and associated documentation files (the "Software"), to deal

// in the Software without restriction, including without limitation the rights

// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell

// copies of the Software, and to permit persons to whom the Software is

// furnished to do so, subject to the following conditions:

//

// The above copyright notice and this permission notice shall be included in all

// copies or substantial portions of the Software.

//

// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR

// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,

// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE

// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER

// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,

// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN

// THE SOFTWARE.

//

// ///////////////////////////////////////////////////////////////////////////////

#import "NSData+MKCommandDecode.h"

#define kInvalidMKCommand @"Invalid MK command"

// ///////////////////////////////////////////////////////////////////////////////

#pragma mark Helper funktions

static NSData * decode64(const char * inBuffer, int length)

{

  unsigned char a, b, c, d;

  unsigned char x, y, z;

  int srcIdx = 0;

  int dstIdx = 0;

  NSMutableData * outData = [NSMutableData dataWithLength:length];

  unsigned char * outBuffer = [outData mutableBytes];

  if (inBuffer[srcIdx] != 0)

  {

    while (length != 0)

    {

      a = inBuffer[srcIdx++] - '=';

      b = inBuffer[srcIdx++] - '=';

      c = inBuffer[srcIdx++] - '=';

      d = inBuffer[srcIdx++] - '=';

      x = (a << 2) | (b >> 4);

      y = ((b & 0x0f) << 4) | (c >> 2);

      z = ((c & 0x03) << 6) | d;

      if (length--) outBuffer[dstIdx++] = x; else break;

      if (length--) outBuffer[dstIdx++] = y; else break;

      if (length--) outBuffer[dstIdx++] = z; else break;

    }

  }

  [outData setLength:dstIdx];

  return outData;

}

// ///////////////////////////////////////////////////////////////////////////////

@implementation NSData (MKCommandDecode)

- (NSUInteger) frameLength;

{

  NSUInteger frameLength =  [self length];

  const char * frameBytes = [self bytes];

  if (frameLength > 0 && frameBytes[frameLength - 1] == '\r')

    frameLength--;

  return frameLength;

}

- (BOOL) isMkData

{

  NSUInteger frameLength =  [self frameLength];

  const char * frameBytes = [self bytes];

  if ( frameLength < 5)

  {

    NSLog(@"The frame length is to short %d. Frame is invalid", frameLength);

    return NO;

  }

  if (frameBytes[0] != '#')

  {

    NSLog(@"The frame is no MK frame");

    return NO;

  }

  return YES;

}

- (BOOL) isCrcOk

{

  if (![self isMkData])

    return NO;

  NSUInteger frameLength =  [self frameLength];

  const uint8_t * frameBytes = [self bytes];

  uint8_t crc2 = frameBytes[frameLength - 1];

  uint8_t crc1 = frameBytes[frameLength - 2];

  int crc = 0;

  for (int i = 0; i < frameLength - 2; i++)

  {

    crc += frameBytes[i];

  }

  crc %= 4096;

  if (crc1 == ('=' + (crc / 64)) && crc2 == ('=' + crc % 64))

    return YES;

  return NO;

}

- (MKAddress) address

{

  if (![self isCrcOk])

    [NSException raise:kInvalidMKCommand format:@"cannot get the address from a invalid MK frame"];

  const char * frameBytes = [self bytes];

  return (MKAddress)(frameBytes[1] - 'a');

}

- (MKCommandId) command

{

  if (![self isCrcOk])

    [NSException raise:kInvalidMKCommand format:@"cannot get the address from a invalid MK frame"];

  const char * frameBytes = [self bytes];

  return frameBytes[2];

}

- (NSData *) payload;

{

  NSUInteger frameLength =  [self frameLength];

  const char * frameBytes = [self bytes];

  int startIndex = 3;

  int frameDataLength = frameLength - startIndex - 2;

  return decode64(frameBytes + startIndex, frameDataLength);

}

@end