First progress on making a modern EAN13 Barcode generator ...

BCKEAN13Code.m

//
//  BCKEAN13Code.m
//  BarCodeKit
//
//  Created by Oliver Drobnik on 8/9/13.
//  Copyright (c) 2013 Oliver Drobnik. All rights reserved.
//

#import "BCKEAN13Code.h"

typedef NS_ENUM(NSUInteger, CodeVariant)
{
	CodeVariant_L = 0,
	CodeVariant_G = 1,
	CodeVariant_R = 2
};

// source: https://en.wikipedia.org/wiki/European_Article_Number

// the encoding variants for each digits, L/G/R
static char *digit_encodings[10][3] = {{"0001101", "0100111", "1110010"},  // 0
                                       {"0011001", "0110011", "1100110"},  // 1
                                       {"0010011", "0011011", "1101100"},  // 2
                                       {"0111101", "0100001", "1000010"},  // 3
                                       {"0100011", "0011101", "1011100"},  // 4
                                       {"0110001", "0111001", "1001110"},  // 5
                                       {"0101111", "0000101", "1010000"},  // 6
                                       {"0111011", "0010001", "1000100"},  // 7
                                       {"0110111", "0001001", "1001000"},  // 8
                                       {"0001011", "0010111", "1110100"}   // 9
                                      };

// the variant pattern to use based on the first digit
static char *variant_patterns[10] = {"LLLLLLRRRRRR",  // 0
                                     "LLGLGGRRRRRR",  // 1
                                     "LLGGLGRRRRRR",  // 2
                                     "LLGGGLRRRRRR",  // 3
                                     "LGLLGGRRRRRR",  // 4
                                     "LGGLLGRRRRRR",  // 5
                                     "LGGGLLRRRRRR",  // 6
                                     "LGLGLGRRRRRR",  // 7
                                     "LGLGGLRRRRRR",  // 8
                                     "LGGLGLRRRRRR"   // 9
                                    };

// the marker to use at the left and right ends
static char *outside_marker = "101";

// the marker to use in the center
static char *middle_marker = "01010";


@implementation BCKEAN13Code

- (NSUInteger)_digitAtIndex:(NSUInteger)index
{
	NSString *digitStr = [self.content substringWithRange:NSMakeRange(index, 1)];
	return [digitStr integerValue];
}

- (NSUInteger)_codeVariantIndexForDigitAtIndex:(NSUInteger)index withVariantPattern:(char *)variantPattern
{
	NSAssert(index>0 && index<13, @"Index must be from 1 to 12");
	
	char variantForDigit = variantPattern[index-1];
	NSUInteger variantIndex = CodeVariant_L;
	
	if (variantForDigit == 'G')
	{
		variantIndex = CodeVariant_G;
	}
	else if (variantForDigit == 'R')
	{
		variantIndex = CodeVariant_R;
	}
	
	return variantIndex;
}

- (NSString *)description
{
	NSMutableString *tmpString = [NSMutableString string];
	
	NSUInteger firstDigit = [self _digitAtIndex:0];
	char *variant_pattern = variant_patterns[firstDigit];
	
	// add left end marker
	[tmpString appendString:[NSString stringWithUTF8String:outside_marker]];
	
	for (NSUInteger i=1; i<[self.content length]; i++)
	{
		NSUInteger digit = [self _digitAtIndex:i];
		
		NSUInteger variantIndex = [self _codeVariantIndexForDigitAtIndex:i withVariantPattern:variant_pattern];
		
		NSString *encoding = [NSString stringWithUTF8String:digit_encodings[digit][variantIndex]];
		[tmpString appendString:encoding];
		
		if (i==6)
		{
			// add middle marker
			[tmpString appendString:[NSString stringWithUTF8String:middle_marker]];
		}
	}
	
	// add right end marker
	[tmpString appendString:[NSString stringWithUTF8String:outside_marker]];
	
	return tmpString;
}

@end