NudgeModel.h

//
//  NudgeModel.h
//  NudgeFoundation
//
//  Created by Jeremy Tregunna on 10/7/2013.
//  Copyright (c) 2013 Jeremy Tregunna. All rights reserved.
//

#import <Foundation/Foundation.h>

#define weakify(o) try {} @finally {} \
    __weak typeof(o) nf_weak_ ## o = o

#define strongify(o) try {} @finally {} \
    _Pragma("clang diagnostic push") \
    _Pragma("clang diagnostic ignored \"-Wshadow\"") \
    typeof(nf_weak_ ## o) o = nf_weak_ ## o \
    _Pragma("clang diagnostic pop")

@interface NudgeModel : NSObject <NSSecureCoding, NSCopying, NSFastEnumeration>

- (instancetype)initWithAttributes:(NSDictionary*)attributes;

// Override this method and return a dictionary whose keys are the
// property name you define, and whose values are their key path to
// some external dictionary supplied during initialization.
- (NSDictionary*)keyPathsByPropertyKey;

@end

NudgeModel.m

//
//  NudgeModel.m
//  NudgeFoundation
//
//  Created by Jeremy Tregunna on 10/7/2013.
//  Copyright (c) 2013 Jeremy Tregunna. All rights reserved.
//

#import "NudgeModel.h"
#import <objc/runtime.h>

@implementation NudgeModel

- (instancetype)initWithAttributes:(NSDictionary*)attributes
{
    if((self = [super init]))
    {
        @weakify(self);
        [[self keyPathsByPropertyKey] enumerateKeysAndObjectsUsingBlock:^(id key, NSString* keyPath, BOOL *stop) {
            @strongify(self);
            id object = [attributes valueForKeyPath:keyPath];
            if(object != nil)
                [self setValue:object forKey:key];
        }];
    }
    return self;
}

#pragma mark - NSCoding

+ (BOOL)supportsSecureCoding
{
    return YES;
}

- (id)initWithCoder:(NSCoder*)decoder
{
    if((self = [super init]))
    {
        [[self keyPathsByPropertyKey] enumerateKeysAndObjectsUsingBlock:^(id key, id obj, BOOL *stop) {
            id object = [decoder decodeObjectForKey:key];
            [self setValue:object forKey:key];
        }];
    }
    return self;
}

- (void)encodeWithCoder:(NSCoder*)coder
{
    [[self keyPathsByPropertyKey] enumerateKeysAndObjectsUsingBlock:^(id key, id obj, BOOL *stop) {
        id object = [self valueForKey:key];
        if(object != nil)
            [coder encodeObject:object forKey:key];
    }];
}

#pragma mark - NSCopying

- (id)copyWithZone:(NSZone*)zone
{
    typeof(self) obj = [[[self class] alloc] init];
    @weakify(self);
    [[self keyPathsByPropertyKey] enumerateKeysAndObjectsUsingBlock:^(id key, NSString* keyPath, BOOL *stop) {
        @strongify(self);
        id o = [self valueForKey:key];
        [obj setValue:o forKey:key];
    }];

    return obj;
}

#pragma mark - NSFastEnumeration

- (NSUInteger)countByEnumeratingWithState:(NSFastEnumerationState*)state objects:(__unsafe_unretained id[])buffer count:(NSUInteger)len
{
    return [[[self keyPathsByPropertyKey] allKeys] countByEnumeratingWithState:state objects:buffer count:len];
}

#pragma mark - NSObject

- (BOOL)isEqual:(NudgeModel*)model
{
    if(self == model)
        return YES;

    if(![model isMemberOfClass:[self class]])
        return NO;

    __block BOOL result = YES;
    @weakify(self);
    [[self keyPathsByPropertyKey] enumerateKeysAndObjectsUsingBlock:^(id key, id obj, BOOL *stop) {
        @strongify(self);
        id o1 = [self valueForKey:key];
        id o2 = [model valueForKey:key];

        result = ((o1 == nil && o2 == nil) || [o1 isEqual:o2]);
        if(!result)
            *stop = YES;
    }];

    return result;
}

- (NSUInteger)hash
{
    __block NSUInteger hash = 0;
    @weakify(self);
    [[self keyPathsByPropertyKey] enumerateKeysAndObjectsUsingBlock:^(id key, id obj, BOOL *stop) {
        @strongify(self);
        hash ^= [[self valueForKey:key] hash];
    }];
    return hash;
}

#pragma mark - Key paths

- (NSDictionary*)keyPathsByPropertyKey
{
    @throw [NSException exceptionWithName:NSInternalInconsistencyException reason:[NSString stringWithFormat:@"You must override %@ in a subclass", NSStringFromSelector(_cmd)] userInfo:nil];
}

@end