Reactive Search Table View Model

MMReactiveSearchTableViewModel.m

@interface MMBaseReactiveSearchTableViewModel()

// Most of these will actually be public/header file
@property (copy, nonatomic) NSArray *searchResults;
@property (copy, nonatomic) NSString *searchTerm;
@property (strong, nonatomic) NSError *error;
@property (assign, nonatomic) BOOL isLoading;
@property (strong, nonatomic) RACSubject *forceRestartServerRequestSubject;

@end

@implementation MMBaseReactiveSearchTableViewModel

- (instancetype)init {
    if (self = [super init]) {
        self.forceRestartServerRequestSubject = RACSubject.new;
        RAC(self, searchResults) = [self.searchResultsSignal distinctUntilChanged];
    }

    return self;
}

- (RACSignal *)searchResultsSignal {
    @weakify(self)
    RACSignal *latestSearchTerm = [[RACObserve(self, searchTerm) map:^id(NSString *searchTerm) {
        @strongify(self)
        if (searchTerm.length == 0) {
            self.isLoading = NO;
            return [RACSignal return:nil]; // so we immediately get an empty results table
        }

        return [[[RACSignal empty] delay:0.3] concat:[RACSignal return:searchTerm]];
    }] switchToLatest];

    // forceRestartServerRequestSubject has to start with nil because combineLatest needs at least one value
    // to start working.
    RACSignal *latestOrRefreshedSearchTerm = [RACSignal combineLatest:@[latestSearchTerm, [self.forceRestartServerRequestSubject startWith:nil]] reduce:^id(NSString *latestSearchTerm, id forceRefresh) {
        return latestSearchTerm;
    }];

    RACSignal *latestSearchResults = [[[latestOrRefreshedSearchTerm map:^id(NSString *searchTerm) {
        // This ensures that we immediately switch to a new search term if it's empty,
        // thus cancelling any running request for old search terms. An empty results table is immediately shown.
        if (searchTerm.length == 0) {
            return [RACSignal return:nil];
        }

        @strongify(self)
        RACSignal *serverResults = [[self serverSearchSignalWithSearchTerm:searchTerm] catch:^RACSignal *(NSError *error) {
            // Catch server errors and return an empty result set
            @strongify(self)
            self.error = error;
            return [RACSignal return:nil];
        }];

        // Return nil until the server results arrive, so the results table is emptied until results are there
        return [[RACSignal return:nil] concat:serverResults];
    }] switchToLatest] doNext:^(id x) {
        @strongify(self)
        self.isLoading = NO;
    }];

    return latestSearchResults;
}

- (void)forceRestartSearch {
    [self.forceRestartServerRequestSubject sendNext:nil];
}

// Override in subclass
- (RACSignal *)serverSearchSignalWithSearchTerm:(NSString *)term {
    return [RACSignal return: nil];
}

@end