Broker/BKController.m

//
//  BKController.m
//  Broker
//
//  Created by Andrew Smith on 1/8/14.
//  Copyright (c) 2014 Andrew B. Smith. All rights reserved.
//

#import "BKController.h"

#import "BKEntityMap.h"
#import "BKJSONController.h"
#import "BKEntityDescription.h"
#import "BKAttributeDescription.h"
#import "BrokerLog.h"

static NSString * const BROKER_INTERNAL_QUEUE = @"com.broker.queue";

@interface BKController ()

@property (nonatomic, strong, readwrite) BKEntityMap *entityMap;

/**
 Internal serial queue for core data processing off the main thread.
 */
@property (nonatomic, strong) NSOperationQueue *queue;

@end

@implementation BKController

+ (instancetype)controller
{
    BKController *controller = [self new];
    
    //
    // Entity Map
    //
    BKEntityMap *entityMap = [BKEntityMap entityMap];
    controller.entityMap = entityMap;
    
    //
    // Serial queue
    //
    NSOperationQueue *queue = [NSOperationQueue new];
    queue.maxConcurrentOperationCount = 1;
    controller.queue = queue;
    
    return controller;
}

#pragma mark BKJSONController

- (void)processJSONObject:(NSDictionary *)json
            asEntityNamed:(NSString *)entityName
                inContext:(NSManagedObjectContext *)context
          completionBlock:(void (^)())completionBlock
{
    NSOperation *operation = [self operationForContext:context
                                                  JSON:json
                                         withJSONBlock:^(id jsonCopy,
                                                         NSManagedObjectContext *backgroundContext,
                                                         BKJSONController *jsonController) {
                                             [jsonController processJSONObject:jsonCopy
                                                                 asEntityNamed:entityName];
                                         }];
    
    // Finish
    operation.completionBlock = completionBlock;
    
    // Queue it up
    [self.queue addOperation:operation];
}

- (void)processJSONObject:(NSDictionary *)json
                 onObject:(NSManagedObject *)object
          completionBlock:(void (^)())completionBlock
{
    NSManagedObjectID *objectId = object.objectID;

    NSOperation *operation = [self operationForContext:object.managedObjectContext
                                                  JSON:json
                                         withJSONBlock:^(id jsonCopy,
                                                         NSManagedObjectContext *backgroundContext,
                                                         BKJSONController *jsonController) {
                                             //
                                             // Use a newly fetched object from the background context so we don't modify
                                             // the passed in object, which could come from god knows where.
                                             //
                                             NSManagedObject *backgroundObject = [backgroundContext objectWithID:objectId];
                                             
                                             [jsonController processJSONObject:jsonCopy
                                                                      onObject:backgroundObject];
                                         }];
    
    // Finish
    operation.completionBlock = completionBlock;
    
    // Queue it up
    [self.queue addOperation:operation];

}

- (void)processJSON:(id)json
    forRelationship:(NSString *)relationshipName
           onObject:(NSManagedObject *)object
    completionBlock:(void (^)())completionBlock
{
    NSManagedObjectID *objectId = object.objectID;
    
    // Operation
    NSOperation *operation = [self operationForContext:object.managedObjectContext
                                                  JSON:json
                                         withJSONBlock:^(id jsonCopy,
                                                         NSManagedObjectContext *backgroundContext,
                                                         BKJSONController *jsonController) {
                                             //
                                             // Use a newly fetched object from the background context so we don't modify
                                             // the passed in object, which could come from god knows where.
                                             //
                                             NSManagedObject *backgroundObject = [backgroundContext objectWithID:objectId];
                                             
                                             [jsonController processJSON:jsonCopy
                                                         forRelationship:relationshipName
                                                                onObject:backgroundObject];
                                         }];
    
    // Finish
    operation.completionBlock = completionBlock;
    
    // Queue it up
    [self.queue addOperation:operation];
}

- (void)processJSONCollection:(NSArray *)json
              asEntitiesNamed:(NSString *)entityName
                    inContext:(NSManagedObjectContext *)context
              completionBlock:(void (^)())completionBlock
{
    // Operation
    NSOperation *operation = [self operationForContext:context
                                                  JSON:json
                                         withJSONBlock:^(id jsonCopy,
                                                         NSManagedObjectContext *backgroundContext,
                                                         BKJSONController *jsonController) {
                                             [jsonController processJSONCollection:jsonCopy
                                                                   asEntitiesNamed:entityName];
                                         }];
    
    // Finish
    operation.completionBlock = completionBlock;
    
    // Queue it up
    [self.queue addOperation:operation];
}

- (void)processJSON:(id)json
          workBlock:(void (^)(id jsonCopy, NSManagedObjectContext *childContext, BKJSONController *jsonController))workBlock
          inContext:(NSManagedObjectContext *)context
    completionBlock:(void (^)())completionBlock
{
    // Operation
    NSOperation *operation = [self operationForContext:context
                                                  JSON:json
                                         withJSONBlock:workBlock];
    
    // Finish
    operation.completionBlock = completionBlock;
    
    // Queue it up
    [self.queue addOperation:operation];
}

#pragma mark -

- (NSOperation *)operationForContext:(NSManagedObjectContext *)context
                                JSON:(id)json
                       withJSONBlock:(void (^)(id jsonCopy,
                                               NSManagedObjectContext *childContext,
                                               BKJSONController *jsonController))block
{
    __weak typeof(self) weakSelf = self;
    NSBlockOperation *operation = [NSBlockOperation blockOperationWithBlock:^{
        // Background context
        NSManagedObjectContext *backgroundContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];
        backgroundContext.parentContext = context;
        
        // Memory optimization
        backgroundContext.undoManager = nil;
        
        // Grab a new JSON controller
        BKJSONController *jsonController = [BKJSONController JSONControllerWithContext:backgroundContext
                                                                             entityMap:weakSelf.entityMap];
        
        // Copy JSON to make sure it doesn't get mutated underneath us
        id jsonCopy = [json copy];
        
        // Queue up a blocking call to make sure we play super nice with Apples Core Data concurrency
        [backgroundContext performBlockAndWait:^{
            /**
             
             Here is why an autorelease pool is necessary, per apple docs.
             
             https://developer.apple.com/library/ios/documentation/General/Conceptual/ConcurrencyProgrammingGuide/OperationQueues/OperationQueues.html#//apple_ref/doc/uid/TP40008091-CH102-SW18
             
             "If your block creates more than a few Objective-C objects, you might want to enclose parts
             of your block’s code in an @autorelease block to handle the memory management for those
             objects. Although GCD dispatch queues have their own autorelease pools, they make no
             guarantees as to when those pools are drained. If your application is memory constrained,
             creating your own autorelease pool allows you to free up the memory for autoreleased
             objects at more regular intervals."
             
             */
            @autoreleasepool {
                // Do the actual work
                if (block) block(jsonCopy, backgroundContext, jsonController);
                // Save background context. Does not automatically save parent context.
                NSError *error;
                [backgroundContext save:&error];
                if (error) {
                    BrokerLog(@"%@", error.localizedDescription);
                }
            }
        }];
    }];
    return operation;
}

@end