SRGLoadableViewModel

SRGLoadableViewModel.h

@class RACSignal;

@interface SRGLoadableViewModel : NSObject

@property (nonatomic) BOOL loading;
@property (nonatomic) NSError *lastError;

@property (nonatomic) id result;
@property (nonatomic) RACSignal *computationSignal;

@end

SRGLoadableViewModel.m

#import "SRGLoadableViewModel.h"
#import <ReactiveCocoa/ReactiveCocoa.h>


@implementation SRGLoadableViewModel

- (instancetype)init {
	self = [super init];
	if (self) {

		RACSignal *loadableSignal = [[RACObserve(self, computationSignal)
		                              map: ^id (RACSignal *signal) {
		    return signal ?: RACSignal.empty;
		}] map: ^id (RACSignal *loadingSignal) {
		    return loadingSignal.replayLazily;
		}].replayLast;
		
		RAC(self, lastError) = [loadableSignal map:^id(RACSignal *signal) {
			return [[signal.ignoreValues.materialize filter:^BOOL(RACEvent *event) {
				return event.eventType == RACEventTypeError;
			}] map:^id(RACEvent *event) {
				return event.error;
			}];
		}].switchToLatest;
		
		RAC(self, result) = [loadableSignal map:^id(RACSignal *signal) {
			return [signal catchTo:[RACSignal return:nil]];
		}].switchToLatest;
		
		RAC(self, loading) = [loadableSignal map:^id(RACSignal *signal) {
			return [RACSignal concat:@[
									   [RACSignal return:@YES],
									   [signal.ignoreValues catchTo:RACSignal.empty],
									   [RACSignal return:@NO]
									   ]];
		}].switchToLatest;

	}
	return self;
}