/**
 Copyright (c) 2014-present, Facebook, Inc.
 All rights reserved.
 
 This source code is licensed under the BSD-style license found in the
 LICENSE file in the root directory of this source tree. An additional grant
 of patent rights can be found in the PATENTS file in the same directory.
 */

#import "FBKVOController.h"

#import <libkern/OSAtomic.h>
#import <objc/message.h>

#if !__has_feature(objc_arc)
#error This file must be compiled with ARC. Convert your project to ARC or specify the -fobjc-arc flag.
#endif

#pragma mark Utilities -

static NSString *describe_option(NSKeyValueObservingOptions option)
{
  switch (option) {
    case NSKeyValueObservingOptionNew:
      return @"NSKeyValueObservingOptionNew";
      break;
    case NSKeyValueObservingOptionOld:
      return @"NSKeyValueObservingOptionOld";
      break;
    case NSKeyValueObservingOptionInitial:
      return @"NSKeyValueObservingOptionInitial";
      break;
    case NSKeyValueObservingOptionPrior:
      return @"NSKeyValueObservingOptionPrior";
      break;
    default:
      NSCAssert(NO, @"unexpected option %tu", option);
      break;
  }
  return nil;
}

static void append_option_description(NSMutableString *s, NSUInteger option)
{
  if (0 == s.length) {
    [s appendString:describe_option(option)];
  } else {
    [s appendString:@"|"];
    [s appendString:describe_option(option)];
  }
}

static NSUInteger enumerate_flags(NSUInteger *ptrFlags)
{
  NSCAssert(ptrFlags, @"expected ptrFlags");
  if (!ptrFlags) {
    return 0;
  }
  
  NSUInteger flags = *ptrFlags;
  if (!flags) {
    return 0;
  }
  
  NSUInteger flag = 1 << __builtin_ctzl(flags);
  flags &= ~flag;
  *ptrFlags = flags;
  return flag;
}

static NSString *describe_options(NSKeyValueObservingOptions options)
{
  NSMutableString *s = [NSMutableString string];
  NSUInteger option;
  while (0 != (option = enumerate_flags(&options))) {
    append_option_description(s, option);
  }
  return s;
}

#pragma mark _FBKVOInfo -

/**
 @abstract The key-value observation info.
 @discussion Object equality is only used within the scope of a controller instance. Safely omit controller from equality definition.
 */
@interface _FBKVOInfo : NSObject
@end

@implementation _FBKVOInfo
{
@public
  __weak FBKVOController *_controller;
  NSString *_keyPath;
  NSKeyValueObservingOptions _options;
  SEL _action;
  void *_context;
  FBKVONotificationBlock _block;
}

- (instancetype)initWithController:(FBKVOController *)controller keyPath:(NSString *)keyPath options:(NSKeyValueObservingOptions)options block:(FBKVONotificationBlock)block action:(SEL)action context:(void *)context
{
  self = [super init];
  if (nil != self) {
    _controller = controller;
    _block = [block copy];
    _keyPath = [keyPath copy];
    _options = options;
    _action = action;
    _context = context;
  }
  return self;
}

- (instancetype)initWithController:(FBKVOController *)controller keyPath:(NSString *)keyPath options:(NSKeyValueObservingOptions)options block:(FBKVONotificationBlock)block
{
  return [self initWithController:controller keyPath:keyPath options:options block:block action:NULL context:NULL];
}

- (instancetype)initWithController:(FBKVOController *)controller keyPath:(NSString *)keyPath options:(NSKeyValueObservingOptions)options action:(SEL)action
{
  return [self initWithController:controller keyPath:keyPath options:options block:NULL action:action context:NULL];
}

- (instancetype)initWithController:(FBKVOController *)controller keyPath:(NSString *)keyPath options:(NSKeyValueObservingOptions)options context:(void *)context
{
  return [self initWithController:controller keyPath:keyPath options:options block:NULL action:NULL context:context];
}

- (instancetype)initWithController:(FBKVOController *)controller keyPath:(NSString *)keyPath
{
  return [self initWithController:controller keyPath:keyPath options:0 block:NULL action:NULL context:NULL];
}

- (NSUInteger)hash
{
  return [_keyPath hash];
}

- (BOOL)isEqual:(id)object
{
  if (nil == object) {
    return NO;
  }
  if (self == object) {
    return YES;
  }
  if (![object isKindOfClass:[self class]]) {
    return NO;
  }
  return [_keyPath isEqualToString:((_FBKVOInfo *)object)->_keyPath];
}

- (NSString *)debugDescription
{
  NSMutableString *s = [NSMutableString stringWithFormat:@"<%@:%p keyPath:%@", NSStringFromClass([self class]), self, _keyPath];
  if (0 != _options) {
    [s appendFormat:@" options:%@", describe_options(_options)];
  }
  if (NULL != _action) {
    [s appendFormat:@" action:%@", NSStringFromSelector(_action)];
  }
  if (NULL != _context) {
    [s appendFormat:@" context:%p", _context];
  }
  if (NULL != _block) {
    [s appendFormat:@" block:%p", _block];
  }
  [s appendString:@">"];
  return s;
}

@end

#pragma mark _FBKVOSharedController -

/**
 @abstract The shared KVO controller instance.
 @discussion Acts as a receptionist, receiving and forwarding KVO notifications.
 */
@interface _FBKVOSharedController : NSObject

/** A shared instance that never deallocates. */
+ (instancetype)sharedController;

/** observe an object, info pair */
- (void)observe:(id)object info:(_FBKVOInfo *)info;

/** unobserve an object, info pair */
- (void)unobserve:(id)object info:(_FBKVOInfo *)info;

/** unobserve an object with a set of infos */
- (void)unobserve:(id)object infos:(NSSet *)infos;

@end

@implementation _FBKVOSharedController
{
  NSHashTable *_infos;
  OSSpinLock _lock;
}

+ (instancetype)sharedController
{
  static _FBKVOSharedController *_controller = nil;
  static dispatch_once_t onceToken;
  dispatch_once(&onceToken, ^{
    _controller = [[_FBKVOSharedController alloc] init];
  });
  return _controller;
}

- (instancetype)init
{
  self = [super init];
  if (nil != self) {
    NSHashTable *infos = [NSHashTable alloc];
#ifdef __IPHONE_OS_VERSION_MIN_REQUIRED
    _infos = [infos initWithOptions:NSPointerFunctionsWeakMemory|NSPointerFunctionsObjectPointerPersonality capacity:0];
#elif defined(__MAC_OS_X_VERSION_MIN_REQUIRED)
    if ([NSHashTable respondsToSelector:@selector(weakObjectsHashTable)]) {
      _infos = [infos initWithOptions:NSPointerFunctionsWeakMemory|NSPointerFunctionsObjectPointerPersonality capacity:0];
    } else {
      // silence deprecated warnings
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wdeprecated-declarations"
      _infos = [infos initWithOptions:NSPointerFunctionsZeroingWeakMemory|NSPointerFunctionsObjectPointerPersonality capacity:0];
#pragma clang diagnostic pop
    }
    
#endif
    _lock = OS_SPINLOCK_INIT;
  }
  return self;
}

- (NSString *)debugDescription
{
  NSMutableString *s = [NSMutableString stringWithFormat:@"<%@:%p", NSStringFromClass([self class]), self];
  
  // lock
  OSSpinLockLock(&_lock);
  
  NSMutableArray *infoDescriptions = [NSMutableArray arrayWithCapacity:_infos.count];
  for (_FBKVOInfo *info in _infos) {
    [infoDescriptions addObject:info.debugDescription];
  }
  
  [s appendFormat:@" contexts:%@", infoDescriptions];
  
  // unlock
  OSSpinLockUnlock(&_lock);
  
  [s appendString:@">"];
  return s;
}

- (void)observe:(id)object info:(_FBKVOInfo *)info
{
  if (nil == info) {
    return;
  }
  
  // register info
  OSSpinLockLock(&_lock);
  [_infos addObject:info];
  OSSpinLockUnlock(&_lock);
  
  // add observer
  [object addObserver:self forKeyPath:info->_keyPath options:info->_options context:(void *)info];
}

- (void)unobserve:(id)object info:(_FBKVOInfo *)info
{
  if (nil == info) {
    return;
  }
  
  // unregister info
  OSSpinLockLock(&_lock);
  [_infos removeObject:info];
  OSSpinLockUnlock(&_lock);
  
  // remove observer
  [object removeObserver:self forKeyPath:info->_keyPath context:(void *)info];
}

- (void)unobserve:(id)object infos:(NSSet *)infos
{
  if (0 == infos.count) {
    return;
  }
  
  // unregister info
  OSSpinLockLock(&_lock);
  for (_FBKVOInfo *info in infos) {
    [_infos removeObject:info];
  }
  OSSpinLockUnlock(&_lock);
  
  // remove observer
  for (_FBKVOInfo *info in infos) {
    [object removeObserver:self forKeyPath:info->_keyPath context:(void *)info];
  }
}

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
  NSAssert(context, @"missing context keyPath:%@ object:%@ change:%@", keyPath, object, change);
  
  _FBKVOInfo *info;
  
  {
    // lookup context in registered infos, taking out a strong reference only if it exists
    OSSpinLockLock(&_lock);
    info = [_infos member:(__bridge id)context];
    OSSpinLockUnlock(&_lock);
  }
  
  if (nil != info) {
    
    // take strong reference to controller
    FBKVOController *controller = info->_controller;
    if (nil != controller) {
      
      // take strong reference to observer
      id observer = controller.observer;
      if (nil != observer) {
        
        // dispatch custom block or action, fall back to default action
        if (info->_block) {
          info->_block(observer, object, change);
        } else if (info->_action) {
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Warc-performSelector-leaks"
          [observer performSelector:info->_action withObject:change withObject:object];
#pragma clang diagnostic pop
        } else {
          [observer observeValueForKeyPath:keyPath ofObject:object change:change context:info->_context];
        }
      }
    }
  }
}

@end

#pragma mark FBKVOController -

@implementation FBKVOController
{
  NSMapTable *_objectInfosMap;
  OSSpinLock _lock;
}

#pragma mark Lifecycle -

+ (instancetype)controllerWithObserver:(id)observer
{
  return [[self alloc] initWithObserver:observer];
}

- (instancetype)initWithObserver:(id)observer retainObserved:(BOOL)retainObserved
{
  self = [super init];
  if (nil != self) {
    _observer = observer;
    NSPointerFunctionsOptions keyOptions = retainObserved ? NSPointerFunctionsStrongMemory|NSPointerFunctionsObjectPointerPersonality : NSPointerFunctionsWeakMemory|NSPointerFunctionsObjectPointerPersonality;
    _objectInfosMap = [[NSMapTable alloc] initWithKeyOptions:keyOptions valueOptions:NSPointerFunctionsStrongMemory|NSPointerFunctionsObjectPersonality capacity:0];
    _lock = OS_SPINLOCK_INIT;
  }
  return self;
}

- (instancetype)initWithObserver:(id)observer
{
  return [self initWithObserver:observer retainObserved:YES];
}

- (void)dealloc
{
  [self unobserveAll];
}

#pragma mark Properties -

- (NSString *)debugDescription
{
  NSMutableString *s = [NSMutableString stringWithFormat:@"<%@:%p", NSStringFromClass([self class]), self];
  [s appendFormat:@" observer:<%@:%p>", NSStringFromClass([_observer class]), _observer];
  
  // lock
  OSSpinLockLock(&_lock);
  
  if (0 != _objectInfosMap.count) {
    [s appendString:@"\n  "];
  }
  
  for (id object in _objectInfosMap) {
    NSMutableSet *infos = [_objectInfosMap objectForKey:object];
    NSMutableArray *infoDescriptions = [NSMutableArray arrayWithCapacity:infos.count];
    [infos enumerateObjectsUsingBlock:^(_FBKVOInfo *info, BOOL *stop) {
      [infoDescriptions addObject:info.debugDescription];
    }];
    [s appendFormat:@"%@ -> %@", object, infoDescriptions];
  }
  
  // unlock
  OSSpinLockUnlock(&_lock);
  
  [s appendString:@">"];
  return s;
}

#pragma mark Utilities -

- (void)_observe:(id)object info:(_FBKVOInfo *)info
{
  // lock
  OSSpinLockLock(&_lock);
  
  NSMutableSet *infos = [_objectInfosMap objectForKey:object];
  
  // check for info existence
  _FBKVOInfo *existingInfo = [infos member:info];
  if (nil != existingInfo) {
    NSLog(@"observation info already exists %@", existingInfo);
    
    // unlock and return
    OSSpinLockUnlock(&_lock);
    return;
  }
  
  // lazilly create set of infos
  if (nil == infos) {
    infos = [NSMutableSet set];
    [_objectInfosMap setObject:infos forKey:object];
  }
  
  // add info and oberve
  [infos addObject:info];
  
  // unlock prior to callout
  OSSpinLockUnlock(&_lock);
  
  [[_FBKVOSharedController sharedController] observe:object info:info];
}

- (void)_unobserve:(id)object info:(_FBKVOInfo *)info
{
  // lock
  OSSpinLockLock(&_lock);
  
  // get observation infos
  NSMutableSet *infos = [_objectInfosMap objectForKey:object];
  
  // lookup registered info instance
  _FBKVOInfo *registeredInfo = [infos member:info];
  
  if (nil != registeredInfo) {
    [infos removeObject:registeredInfo];
    
    // remove no longer used infos
    if (0 == infos.count) {
      [_objectInfosMap removeObjectForKey:object];
    }
  }
  
  // unlock
  OSSpinLockUnlock(&_lock);
  
  // unobserve
  [[_FBKVOSharedController sharedController] unobserve:object info:registeredInfo];
}

- (void)_unobserve:(id)object
{
  // lock
  OSSpinLockLock(&_lock);
  
  NSMutableSet *infos = [_objectInfosMap objectForKey:object];
  
  // remove infos
  [_objectInfosMap removeObjectForKey:object];
  
  // unlock
  OSSpinLockUnlock(&_lock);
  
  // unobserve
  [[_FBKVOSharedController sharedController] unobserve:object infos:infos];
}

- (void)_unobserveAll
{
  // lock
  OSSpinLockLock(&_lock);
  
  NSMapTable *objectInfoMaps = [_objectInfosMap copy];
  
  // clear table and map
  [_objectInfosMap removeAllObjects];
  
  // unlock
  OSSpinLockUnlock(&_lock);
  
  _FBKVOSharedController *shareController = [_FBKVOSharedController sharedController];
  
  for (id object in objectInfoMaps) {
    // unobserve each registered object and infos
    NSSet *infos = [objectInfoMaps objectForKey:object];
    [shareController unobserve:object infos:infos];
  }
}

#pragma mark API -

- (void)observe:(id)object keyPath:(NSString *)keyPath options:(NSKeyValueObservingOptions)options block:(FBKVONotificationBlock)block
{
  NSAssert(0 != keyPath.length && NULL != block, @"missing required parameters observe:%@ keyPath:%@ block:%p", object, keyPath, block);
  if (nil == object || 0 == keyPath.length || NULL == block) {
    return;
  }
  
  // create info
  _FBKVOInfo *info = [[_FBKVOInfo alloc] initWithController:self keyPath:keyPath options:options block:block];
  
  // observe object with info
  [self _observe:object info:info];
}


- (void)observe:(id)object keyPaths:(NSArray *)keyPaths options:(NSKeyValueObservingOptions)options block:(FBKVONotificationBlock)block
{
  NSAssert(0 != keyPaths.count && NULL != block, @"missing required parameters observe:%@ keyPath:%@ block:%p", object, keyPaths, block);
  if (nil == object || 0 == keyPaths.count || NULL == block) {
    return;
  }
  
  for (NSString *keyPath in keyPaths)
  {
    [self observe:object keyPath:keyPath options:options block:block];
  }
}

- (void)observe:(id)object keyPath:(NSString *)keyPath options:(NSKeyValueObservingOptions)options action:(SEL)action
{
  NSAssert(0 != keyPath.length && NULL != action, @"missing required parameters observe:%@ keyPath:%@ action:%@", object, keyPath, NSStringFromSelector(action));
  NSAssert([_observer respondsToSelector:action], @"%@ does not respond to %@", _observer, NSStringFromSelector(action));
  if (nil == object || 0 == keyPath.length || NULL == action) {
    return;
  }
  
  // create info
  _FBKVOInfo *info = [[_FBKVOInfo alloc] initWithController:self keyPath:keyPath options:options action:action];
  
  // observe object with info
  [self _observe:object info:info];
}

- (void)observe:(id)object keyPaths:(NSArray *)keyPaths options:(NSKeyValueObservingOptions)options action:(SEL)action
{
  NSAssert(0 != keyPaths.count && NULL != action, @"missing required parameters observe:%@ keyPath:%@ action:%@", object, keyPaths, NSStringFromSelector(action));
  NSAssert([_observer respondsToSelector:action], @"%@ does not respond to %@", _observer, NSStringFromSelector(action));
  if (nil == object || 0 == keyPaths.count || NULL == action) {
    return;
  }
  
  for (NSString *keyPath in keyPaths)
  {
    [self observe:object keyPath:keyPath options:options action:action];
  }
}

- (void)observe:(id)object keyPath:(NSString *)keyPath options:(NSKeyValueObservingOptions)options context:(void *)context
{
  NSAssert(0 != keyPath.length, @"missing required parameters observe:%@ keyPath:%@", object, keyPath);
  if (nil == object || 0 == keyPath.length) {
    return;
  }
  
  // create info
  _FBKVOInfo *info = [[_FBKVOInfo alloc] initWithController:self keyPath:keyPath options:options context:context];
  
  // observe object with info
  [self _observe:object info:info];
}

- (void)observe:(id)object keyPaths:(NSArray *)keyPaths options:(NSKeyValueObservingOptions)options context:(void *)context
{
  NSAssert(0 != keyPaths.count, @"missing required parameters observe:%@ keyPath:%@", object, keyPaths);
  if (nil == object || 0 == keyPaths.count) {
    return;
  }
  
  for (NSString *keyPath in keyPaths)
  {
    [self observe:object keyPath:keyPath options:options context:context];
  }
}

- (void)unobserve:(id)object keyPath:(NSString *)keyPath
{
  // create representative info
  _FBKVOInfo *info = [[_FBKVOInfo alloc] initWithController:self keyPath:keyPath];
  
  // unobserve object property
  [self _unobserve:object info:info];
}

- (void)unobserve:(id)object
{
  if (nil == object) {
    return;
  }
  
  [self _unobserve:object];
}

- (void)unobserveAll
{
  [self _unobserveAll];
}

@end