/*

     File: HexString.m

 Abstract: An NSData-backed string that displays its bytes as pairs of hex digits, separated by spaces.

  Version: 1.2

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 */

#import "HexString.h"

@implementation HexString

- (id)initWithData:(NSData *)obj {

    if (self = [super init]) {

        data = [obj copy];

    }

    return self;

}

- (id)init {

    return [self initWithData:[NSData data]];

}

- (void)dealloc {

    [data release];

    [super dealloc];

}

- (NSData *)data {

    return data;

}

#pragma mark -

/* Returns the length of the string in Unicode characters; each byte results in three characters in the string (e.g. "3a ").

 */

- (NSUInteger)length {

    return [data length] * 3;

}

/* Returns the character at the given index, taking a shortcut if we know beforehand it's a space, and using a format string otherwise.

 */

- (unichar)characterAtIndex:(NSUInteger)index {

    unsigned char which = index % 3;

    if (which == 2) {

        return ' '; // every third character is a space

    } else {

        const unsigned char *bytes = [data bytes];

        NSString *byteString = [[NSString alloc] initWithFormat:@"%02hhx", bytes[index / 3]];

        unichar result = [byteString characterAtIndex:which];

        [byteString release];

        return result;

    }

}

/* Converts bytes in the given range into printable characters and stores them in the given buffer. Each byte is appended to a mutable string using a format string, then its characters are transferred to the buffer. There are special cases for when the range overlaps part of a "byte" on either end.

 */

- (void)getCharacters:(unichar *)buffer range:(NSRange)range {

    if (NSMaxRange(range) > [self length]) {

        @throw [NSException exceptionWithName:NSRangeException reason:[NSString stringWithFormat:@"*** -[%@ %@]: Range %@ is out of bounds", NSStringFromClass([self class]), NSStringFromSelector(_cmd), NSStringFromRange(range)] userInfo:nil];

    }

    NSMutableString *byteString = [[NSMutableString alloc] initWithCapacity:2];

    const unsigned char *bytes = [data bytes];

    NSUInteger firstByte = range.location / 3;

    NSUInteger offset = 3 - (range.location % 3); // how much of the first byte we need to handle separately

    // handle the first byte specially (note that it's the *last* 1, 2, or 3 characters of the first byte)

    if (offset == 1) {

        buffer[0] = ' ';

    } else if (offset == 2) {

        [byteString appendFormat:@"%02hhx", bytes[firstByte]];

        buffer[0] = [byteString characterAtIndex:1];

        buffer[1] = ' ';

        [byteString setString:@""];

    } else {

        [byteString appendFormat:@"%02hhx", bytes[firstByte]];

        buffer[0] = [byteString characterAtIndex:0];

        buffer[1] = [byteString characterAtIndex:1];

        buffer[2] = ' ';

        [byteString setString:@""];

    }

    firstByte += 1;

    // each byte has three characters, for example "3a "

    NSUInteger byteCount = (range.length - offset) / 3;

    NSUInteger i;

    for (i = 0; i < byteCount; i++) {

        [byteString appendFormat:@"%02hhx", bytes[i + firstByte]];

        buffer[(3 * i) + offset] = [byteString characterAtIndex:0];

        buffer[(3 * i) + offset + 1] = [byteString characterAtIndex:1];

        buffer[(3 * i) + offset + 2] = ' ';

        [byteString setString:@""];

    }

    // if the range has part of the next byte, the integer divison for byteCount would have left it out

    // so we handle it here

    NSUInteger charCountSoFar = ((3 * i) + offset);

    if (charCountSoFar <= (range.length - 1)) {

        [byteString appendFormat:@"%02hhx", bytes[i + firstByte]];

        buffer[charCountSoFar] = [byteString characterAtIndex:0];

        if (charCountSoFar == (range.length - 2)) {

            buffer[charCountSoFar + 1] = [byteString characterAtIndex:1];

        }

    }

    [byteString release];

}

@end