NSAttributedString from NSAttributedString format

NSAttributedString+AttributedFormat.h

//
//  NSAttributedString+AttributedFormat.h
//  AttributedFormat
//
//  Created by rintaro on 11/28/14.
//  Copyright (c) 2014 rintaro. All rights reserved.
//

#import <Foundation/Foundation.h>

@interface NSAttributedString (AttributedFormat)
- (instancetype)initWithFormat:(NSAttributedString *)attrFormat, ...;
- (instancetype)initWithFormat:(NSAttributedString *)attrFormat arguments:(va_list)arguments;
@end

NSAttributedString+AttributedFormat.m

//
//  NSAttributedString+AttributedFormat.m
//  AttributedFormat
//
//  Created by rintaro on 11/28/14.
//  Copyright (c) 2014 rintaro. All rights reserved.
//

#import "NSAttributedString+AttributedFormat.h"

@implementation NSAttributedString (AttributedFormat)

- (instancetype)initWithFormat:(NSAttributedString *)attrFormat, ... {
    va_list args;
    va_start(args, attrFormat);
    self = [self initWithFormat:attrFormat arguments:args];
    va_end(args);
    return self;
}

- (instancetype)initWithFormat:(NSAttributedString *)attrFormat arguments:(va_list)arguments {
    NSRegularExpression *regex;
    regex = [[NSRegularExpression alloc] initWithPattern: @"(%.*?[@%dDuUxXoOfeEgGccsSpaAF])"
                                                 options: 0
                                                   error: nil];
    NSString *format = attrFormat.string;
    format = [regex stringByReplacingMatchesInString: format
                                             options: 0
                                               range: NSMakeRange(0, format.length)
                                        withTemplate: @"\0$1\0"];
    NSLog(@"%@", format);
    //va_list args;
    //va_copy(args, arguments);
    NSString *result = [[NSString alloc] initWithFormat:format arguments:arguments];
    //va_end(args);
    NSMutableArray *f_comps = [format componentsSeparatedByString:@"\0"].mutableCopy;
    NSMutableArray *r_comps = [result componentsSeparatedByString:@"\0"].mutableCopy;
    
    NSMutableAttributedString *output = [[NSMutableAttributedString alloc] init];
    __block int consumed_length = 0;
    
    [attrFormat enumerateAttributesInRange:NSMakeRange(0, attrFormat.length) options:0 usingBlock:^(NSDictionary *attrs, NSRange range, BOOL *stop) {
        NSMutableString *substr = [NSMutableString string];
        while(f_comps.count > 0 && NSMaxRange(range) >= consumed_length + [(NSString *)f_comps[0] length]){
            NSString *f_str = f_comps[0];
            NSString *r_str = r_comps[0];
            [substr appendString:r_str];
            [f_comps removeObjectAtIndex:0];
            [r_comps removeObjectAtIndex:0];
            consumed_length += f_str.length;
        }

        NSUInteger idx = NSMaxRange(range) - consumed_length;
        if(f_comps.count > 0 && idx > 0) {
            NSString *f_str = f_comps[0];
            
            NSString *leading = [f_str substringToIndex:idx];
            [substr appendString:leading];
            
            NSString *trailing = [f_str substringFromIndex:idx];
            [f_comps replaceObjectAtIndex:0 withObject:trailing];
            [r_comps replaceObjectAtIndex:0 withObject:trailing];
            consumed_length += idx;
        }
        [output appendAttributedString:[[NSAttributedString alloc] initWithString:substr attributes:attrs]];
    }];
    
    return [self initWithAttributedString:output];
}
@end

Usage.m

@interface ViewController ()
@property (weak, nonatomic) IBOutlet UILabel *formatLabel;
@property (weak, nonatomic) IBOutlet UILabel *resultLabel;
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    NSMutableAttributedString *fmt = [[NSMutableAttributedString alloc] initWithString:@"test: "];
    [fmt appendAttributedString: [[NSAttributedString alloc] initWithString: @"Some%%string"
                                                                 attributes: @{
                                                                               NSFontAttributeName: [UIFont systemFontOfSize:17]
                                                                               }]];
    [fmt appendAttributedString: [[NSAttributedString alloc] initWithString: @"bold %@ template %.3f %d"
                                                                 attributes: @{
                                                                               NSFontAttributeName: [UIFont boldSystemFontOfSize:20],
                                                                               NSForegroundColorAttributeName: [UIColor redColor]
                                                                               }]];
    [fmt appendAttributedString: [[NSAttributedString alloc] initWithString: @"%@ blah blah blah"
                                                                 attributes: @{
                                                                               NSFontAttributeName: [UIFont systemFontOfSize:16],
                                                                               NSForegroundColorAttributeName: [UIColor blueColor]
                                                                               }]];
    
    NSAttributedString *result = [[NSAttributedString alloc] initWithFormat:fmt, @"[foo]", 1.23, 56, @"[[bar]]"];
    self.formatLabel.attributedText = fmt;
    self.resultLabel.attributedText = result;
}

@end