RACCommand category for tracking completion

RACCommand+ARLCompletedSignal.h

#import "RACCommand.h"

@interface RACCommand (ARLCompletedSignal)

@property (nonatomic, readonly) RACSignal *completed;

@end

RACCommand+ARLCompletedSignal.m

#import <ReactiveCocoa/ReactiveCocoa.h>
#import "RACCommand+ARLCompletedSignal.h"

@implementation RACCommand (ARLCompletedSignal)

- (RACSignal *)completed
{
    RACSignal *executing = self.executing;
    RACSignal *signals = self.executionSignals;
    RACSignal *errors = self.errors;
    
    RACSignal *startingExecution = [RACSignal combineLatest:@[executing, [signals take:1]]
                                                     reduce:^id(NSNumber *executing, id _){ return executing; }];
    
    return [[[startingExecution
       ignore:@NO]
       flattenMap:^RACStream *(id value) {
           RACSignal *comletedOrFailed = [[[executing ignore:@YES] subscribeOn:[RACScheduler scheduler]]
                                          map:^id(id value) { return @YES; }];
           RACSignal *failed = [[errors subscribeOn:[RACScheduler scheduler]]
                                map:^id(id value) { return @NO; }];
           
           return [[RACSignal merge:@[comletedOrFailed, failed]] take:1];
       }] replayLast];
}

@end