FBSDKGraphRequest+Paging.h

## FBSDKGraphRequest+Paging.h
//
//  FBSDKGraphRequest+Paging.h
//  Facebook Paging Extension
//
//  Created by Yonat Sharon on 04.04.2016.
//  Copyright © 2016 Yonat Sharon. All rights reserved.
//

#import <FBSDKCoreKit/FBSDKCoreKit.h>

@interface FBSDKGraphRequest (Paging)

/// Page through results, executing the completion block for each page of results.
- (void)startPagingWithCompletionHandler:(void (^)(id result, NSError *error))completion;

@end

## FBSDKGraphRequest+Paging.m
//
//  FBSDKGraphRequest+Paging.m
//  Facebook Paging Extension
//
//  Created by Yonat Sharon on 04.04.2016.
//  Copyright © 2016 Yonat Sharon. All rights reserved.
//

#import "FBSDKGraphRequest+Paging.h"

@interface FBSDKGraphRequest (PagingPrivate)
- (void)pageJSON:(id)json completionHandler:(void (^)(id result, NSError *error))completion;
- (id)decodeJSONResult:(NSData *)data response:(NSURLResponse *)response error:(NSError *)error;
@end

@implementation FBSDKGraphRequest (Paging)

- (void)startPagingWithCompletionHandler:(void (^)(id result, NSError *error))completion {
  [self startWithCompletionHandler:^(FBSDKGraphRequestConnection *connection, id result, NSError *error) {
    if (error) {
      NSLog(@"Error executing facebook request %@ info: %@", self.graphPath, error.localizedDescription);
      completion(nil, error);
      return;
    };

    completion(result, nil);
    [self pageJSON:result completionHandler:completion];
  }];
}

@end

@implementation FBSDKGraphRequest (PagingPrivate)

- (void)pageJSON:(id)json completionHandler:(void (^)(id result, NSError *error))completion {
  NSString *nextPage = json[@"paging"][@"next"];
  if (!nextPage) return;
  [[[NSURLSession sharedSession] dataTaskWithURL:[NSURL URLWithString:nextPage] completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {
    id json = [self decodeJSONResult:data response:response error:error];
    if (!json) {
      completion(nil, error);
      return;
    }
    completion(json, nil);
    [self pageJSON:json completionHandler:completion];
  }] resume];
}

- (id)decodeJSONResult:(NSData *)data response:(NSURLResponse *)response error:(NSError *)error {
  if (error) {
    NSLog(@"Error executing facebook paging: %@", error.localizedDescription);
    return nil;
  };

  NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse *)response;
  if (httpResponse.statusCode != 200) {
    NSLog(@"facebook paging request returned status: %d", (int)httpResponse.statusCode);
    return nil;
  }

  NSError *jsonDecodingError = nil;
  id json = [NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:&jsonDecodingError];
  if (jsonDecodingError) {
    NSString *returnString = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
    if ([returnString isEqualToString:@"none"]) {
      json = [NSDictionary dictionary];
    }
    else {
      NSLog(@"facebook paging request returned malformed JSON: %@", returnString);
      return nil;
    }
  }
  return json;
}

@end