Advanced NSObject additions to handle commands

AGCommand.h

@interface AGCommand : NSObject
 
@property(nonatomic, weak) UIResponder *firingObject;
@property(nonatomic, readonly) SEL action;
 
+ (instancetype)command;
 
@end

AGCommand.m

 
@implementation AGCommand
 
+ (instancetype)command {
    return [[self alloc] init];    
}
 
- (SEL)action {
    return @selector(performGenericCommand:);
}
 
@end

NSObject+AGCommands.h

@interface NSObject (AGCommands)

@property (nonatomic, assign) NSObject *nextCommandResponder;

- (BOOL)canPerformCommand:(AGCommand *)command;
- (NSObject *)targetForCommand:(AGCommand *)command;
- (BOOL)sendCommand:(AGCommand *)command;
@end

NSObject+AGCommands.m

#import "NSObject+AGCommands.h"
#import <objc/runtime.h>

@implementation NSObject (AGCommands)

#pragma mark - Public API

- (BOOL)canPerformCommand:(AGCommand *)command {
    return [self respondsToSelector:command.action];
}

- (NSObject *)targetForCommand:(AGCommand *)command {
    NSObject *implementor = self;
    while (implementor) {
        if ([implementor canPerformCommand:command] == YES) {
            return implementor;
        }
        implementor = [implementor nextCommandResponder];
    }
    return nil;
}

- (BOOL)sendCommand:(AGCommand *)command {
    if (!command) return NO;
    if (command.firingObject == nil) {
        command.firingObject = self;
    }
    
    NSObject *target = [self targetForCommand:command];
    if (target) {
        [self performCommand:command onResponder:target];
        return YES;
    }
    return NO;
}

#pragma mark - Properties

static void *const kNextCommandResponderKey = (void *)&kNextCommandResponderKey;
- (NSObject *)nextCommandResponder {
    NSObject *responder = objc_getAssociatedObject(self, kNextCommandResponderKey);
    if (responder) return responder;
    if ([self respondsToSelector:@selector(nextResponder)]) {
        return [self performSelector:@selector(nextResponder)];
    }
    return nil;
}

- (void)setNextCommandResponder:(NSObject *)object {
    objc_setAssociatedObject(self, kNextCommandResponderKey, object, OBJC_ASSOCIATION_ASSIGN);
}

#pragma mark - Helpers

- (void)performCommand:(AGCommand *)command onResponder:(NSObject *)responder {
    NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:[[responder class] instanceMethodSignatureForSelector:command.action]];
    [invocation setSelector:command.action];
    [invocation setTarget:responder];
    [invocation setArgument:&command atIndex:2];
    [invocation invoke];
}

@end