Chapter 11 - Chat App/ChatAppFinished/Pods/FirebaseCore/Firebase/Core/FIRComponentContainer.m
/*
 * Copyright 2018 Google
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#import "Private/FIRComponentContainer.h"

#import "Private/FIRAppInternal.h"
#import "Private/FIRComponent.h"
#import "Private/FIRLibrary.h"
#import "Private/FIRLogger.h"

NS_ASSUME_NONNULL_BEGIN

@interface FIRComponentContainer ()

/// The dictionary of components that are registered for a particular app. The key is an NSString
/// of the protocol.
@property(nonatomic, strong) NSMutableDictionary<NSString *, FIRComponentCreationBlock> *components;

/// Cached instances of components that requested to be cached.
@property(nonatomic, strong) NSMutableDictionary<NSString *, id> *cachedInstances;

@end

@implementation FIRComponentContainer

// Collection of all classes that register to provide components.
static NSMutableSet<Class> *sFIRComponentRegistrants;

#pragma mark - Public Registration

+ (void)registerAsComponentRegistrant:(Class<FIRLibrary>)klass {
  static dispatch_once_t onceToken;
  dispatch_once(&onceToken, ^{
    sFIRComponentRegistrants = [[NSMutableSet<Class> alloc] init];
  });

  [self registerAsComponentRegistrant:klass inSet:sFIRComponentRegistrants];
}

+ (void)registerAsComponentRegistrant:(Class<FIRLibrary>)klass
                                inSet:(NSMutableSet<Class> *)allRegistrants {
  [allRegistrants addObject:klass];
}

#pragma mark - Internal Initialization

- (instancetype)initWithApp:(FIRApp *)app {
  return [self initWithApp:app registrants:sFIRComponentRegistrants];
}

- (instancetype)initWithApp:(FIRApp *)app registrants:(NSMutableSet<Class> *)allRegistrants {
  self = [super init];
  if (self) {
    _app = app;
    _cachedInstances = [NSMutableDictionary<NSString *, id> dictionary];
    _components = [NSMutableDictionary<NSString *, FIRComponentCreationBlock> dictionary];

    [self populateComponentsFromRegisteredClasses:allRegistrants forApp:app];
  }
  return self;
}

- (void)populateComponentsFromRegisteredClasses:(NSSet<Class> *)classes forApp:(FIRApp *)app {
  // Loop through the verified component registrants and populate the components array.
  for (Class<FIRLibrary> klass in classes) {
    // Loop through all the components being registered and store them as appropriate.
    // Classes which do not provide functionality should use a dummy FIRComponentRegistrant
    // protocol.
    for (FIRComponent *component in [klass componentsToRegister]) {
      // Check if the component has been registered before, and error out if so.
      NSString *protocolName = NSStringFromProtocol(component.protocol);
      if (self.components[protocolName]) {
        FIRLogError(kFIRLoggerCore, @"I-COR000029",
                    @"Attempted to register protocol %@, but it already has an implementation.",
                    protocolName);
        continue;
      }

      // Store the creation block for later usage.
      self.components[protocolName] = component.creationBlock;

      // Instantiate the
      BOOL shouldInstantiateEager =
          (component.instantiationTiming == FIRInstantiationTimingAlwaysEager);
      BOOL shouldInstantiateDefaultEager =
          (component.instantiationTiming == FIRInstantiationTimingEagerInDefaultApp &&
           [app isDefaultApp]);
      if (shouldInstantiateEager || shouldInstantiateDefaultEager) {
        [self instantiateInstanceForProtocol:component.protocol withBlock:component.creationBlock];
      }
    }
  }
}

#pragma mark - Instance Creation

/// Instantiate an instance of a class that conforms to the specified protocol.
/// This will:
///   - Call the block to create an instance if possible,
///   - Validate that the instance returned conforms to the protocol it claims to,
///   - Cache the instance if the block requests it
- (nullable id)instantiateInstanceForProtocol:(Protocol *)protocol
                                    withBlock:(FIRComponentCreationBlock)creationBlock {
  if (!creationBlock) {
    return nil;
  }

  // Create an instance using the creation block.
  BOOL shouldCache = NO;
  id instance = creationBlock(self, &shouldCache);
  if (!instance) {
    return nil;
  }

  // An instance was created, validate that it conforms to the protocol it claims to.
  NSString *protocolName = NSStringFromProtocol(protocol);
  if (![instance conformsToProtocol:protocol]) {
    FIRLogError(kFIRLoggerCore, @"I-COR000030",
                @"An instance conforming to %@ was requested, but the instance provided does not "
                @"conform to the protocol",
                protocolName);
  }

  // The instance is ready to be returned, but check if it should be cached first before returning.
  if (shouldCache) {
    self.cachedInstances[protocolName] = instance;
  }

  return instance;
}

#pragma mark - Internal Retrieval

- (nullable id)instanceForProtocol:(Protocol *)protocol {
  // Check if there is a cached instance, and return it if so.
  NSString *protocolName = NSStringFromProtocol(protocol);
  id cachedInstance = self.cachedInstances[protocolName];
  if (cachedInstance) {
    return cachedInstance;
  }

  // Use the creation block to instantiate an instance and return it.
  FIRComponentCreationBlock creationBlock = self.components[protocolName];
  return [self instantiateInstanceForProtocol:protocol withBlock:creationBlock];
}

#pragma mark - Lifecycle

- (void)removeAllCachedInstances {
  // Loop through the cache and notify each instance that is a maintainer to clean up after itself.
  for (id instance in self.cachedInstances.allValues) {
    if ([instance conformsToProtocol:@protocol(FIRComponentLifecycleMaintainer)] &&
        [instance respondsToSelector:@selector(appWillBeDeleted:)]) {
      [instance appWillBeDeleted:self.app];
    }
  }

  [self.cachedInstances removeAllObjects];
}

@end

NS_ASSUME_NONNULL_END
