objc-xml-gen.m

#import <Foundation/Foundation.h>
#import <objc/runtime.h>

@interface HTMLNode : NSObject

@property (nonatomic, copy) NSString *tag;
@property (nonatomic, strong) NSMutableDictionary<NSString *, NSString *> *attributes;
@property (nonatomic, strong) NSMutableArray *children;

+ (instancetype)element: (NSString *)tag;
- (NSString *)description;

@end


@implementation HTMLNode

+ (instancetype)element:(NSString *)tag {
    HTMLNode *node = [[HTMLNode alloc] init];
    node.tag       = tag;
    node.attributes = [NSMutableDictionary dictionary];
    node.children   = [NSMutableArray array];
    return node;
}

- (NSMethodSignature *)methodSignatureForSelector:(SEL)sel {
    NSString *selString = NSStringFromSelector(sel);
    NSUInteger colonCount = 0;
    for (NSUInteger i = 0; i < selString.length; i++) {
        if ([selString characterAtIndex:i] == ':') colonCount++;
    }
    
    NSMutableString *types = [NSMutableString stringWithString:@"@@:"];
    for (NSUInteger i = 0; i < colonCount; i++) {
        [types appendString:@"@"];
    }
    return [NSMethodSignature signatureWithObjCTypes:types.UTF8String];
}

- (void)forwardInvocation:(NSInvocation *)invocation {
    NSString *selString = NSStringFromSelector(invocation.selector);
    
    if ([selString hasSuffix:@":"]) {
        selString = [selString substringToIndex:selString.length - 1];
    }
    
    NSArray *parts = [selString componentsSeparatedByString:@":"];

    for (NSUInteger i = 0; i < parts.count; i++) {
        __unsafe_unretained id value;
        [invocation getArgument:&value atIndex:(i + 2)];
        NSString *key = parts[i];
        if ([key isEqualToString:@"children"]) {
            if ([value isKindOfClass:[NSArray class]]) {
                [self.children addObjectsFromArray:value];
            } else {
                [self.children addObject:value];
            }
        } else {
            self.attributes[key] = value;
        }
    }
    HTMLNode *result = self;
    [invocation setReturnValue:&result];
}

- (NSString *)description {
    NSMutableString *html = [NSMutableString stringWithFormat:@"<%@", self.tag];
    for (NSString *key in self.attributes) {
        [html appendFormat:@" %@=\"%@\"", key, self.attributes[key]];
    }
    [html appendString:@">"];
    for (id child in self.children) {
        [html appendString:[child description]];
    }
    [html appendFormat:@"</%@>", self.tag];
    return html;
}

@end


#define $node(...) [HTMLNode element: @#__VA_ARGS__]
#define html $node(html)
#define head $node(head)
#define body $node(body)
#define h1 $node(h1)
#define p $node(p)

int main()
{
#pragma clang diagnostic ignored "-Wobjc-method-access"
    HTMLNode *doc = [html children: @[
        [body children: @[
            [h1 class: @"header" children: @"Hello!"],
            [p class: @"para" id: @"main" children: @"this is a paragraph"]
        ]]
    ]];

    NSLog(@"%@", doc);
}