ASEditableTextNode.mm

//
//  ASEditableTextNode.mm
//  Texture
//
//  Copyright (c) Facebook, Inc. and its affiliates.  All rights reserved.
//  Changes after 4/13/2017 are: Copyright (c) Pinterest, Inc.  All rights reserved.
//  Licensed under Apache 2.0: http://www.apache.org/licenses/LICENSE-2.0
//

#import <AsyncDisplayKit/ASEditableTextNode.h>

#import <tgmath.h>

#import <AsyncDisplayKit/ASDisplayNode+Subclasses.h>
#import <AsyncDisplayKit/ASEqualityHelpers.h>
#import <AsyncDisplayKit/ASTextKitComponents.h>
#import <AsyncDisplayKit/ASTextNodeWordKerner.h>
#import <AsyncDisplayKit/ASThread.h>

/**
 @abstract Object to hold UITextView's pending UITextInputTraits
**/
@interface _ASTextInputTraitsPendingState : NSObject

@property UITextAutocapitalizationType autocapitalizationType;
@property UITextAutocorrectionType autocorrectionType;
@property UITextSpellCheckingType spellCheckingType;
@property UIKeyboardAppearance keyboardAppearance;
@property UIKeyboardType keyboardType;
@property UIReturnKeyType returnKeyType;
@property BOOL enablesReturnKeyAutomatically;
@property (getter=isSecureTextEntry) BOOL secureTextEntry;

@end

@implementation _ASTextInputTraitsPendingState

- (instancetype)init
{
  if (!(self = [super init]))
    return nil;
  
  // set default values, as defined in Apple's comments in UITextInputTraits.h
  _autocapitalizationType = UITextAutocapitalizationTypeSentences;
  _autocorrectionType = UITextAutocorrectionTypeDefault;
  _spellCheckingType = UITextSpellCheckingTypeDefault;
  _keyboardAppearance = UIKeyboardAppearanceDefault;
  _keyboardType = UIKeyboardTypeDefault;
  _returnKeyType = UIReturnKeyDefault;
  
  return self;
}

@end

/**
 @abstract As originally reported in rdar://14729288, when scrollEnabled = NO,
   UITextView does not calculate its contentSize. This makes it difficult 
   for a client to embed a UITextView inside a different scroll view with 
   other content (setting scrollEnabled = NO on the UITextView itself,
   because the containing scroll view will handle the gesture)...
   because accessing contentSize is typically necessary to perform layout.
   Apple later closed the issue as expected behavior. This works around
   the issue by ensuring that contentSize is always calculated, while
   still providing control over the UITextView's scrolling.

 See issue: https://github.com/facebook/AsyncDisplayKit/issues/1063
 */
@interface ASPanningOverriddenUITextView : ASTextKitComponentsTextView
{
  BOOL _shouldBlockPanGesture;
}
@end

@implementation ASPanningOverriddenUITextView

#if TARGET_OS_IOS
 // tvOS doesn't support self.scrollsToTop
- (BOOL)scrollEnabled
{
  return _shouldBlockPanGesture;
}

- (void)setScrollEnabled:(BOOL)scrollEnabled
{
  _shouldBlockPanGesture = !scrollEnabled;
  self.scrollsToTop = scrollEnabled;

  [super setScrollEnabled:YES];
}
#endif

- (BOOL)gestureRecognizerShouldBegin:(UIGestureRecognizer *)gestureRecognizer
{
  // Never allow our pans to begin when _shouldBlockPanGesture is true.
  if (_shouldBlockPanGesture && gestureRecognizer == self.panGestureRecognizer)
    return NO;

  // Otherwise, proceed as usual.
  if ([UITextView instancesRespondToSelector:_cmd])
    return [super gestureRecognizerShouldBegin:gestureRecognizer];
  return YES;
}

@end

#pragma mark -
@interface ASEditableTextNode () <UITextViewDelegate, NSLayoutManagerDelegate>
{
  @private
  // Configuration.
  NSDictionary *_typingAttributes;

  // Core.
  id <ASEditableTextNodeDelegate> __weak _delegate;

  // TextKit.
  AS::RecursiveMutex _textKitLock;
  ASTextKitComponents *_textKitComponents;
  ASTextKitComponents *_placeholderTextKitComponents;
  // Forwards NSLayoutManagerDelegate methods related to word kerning
  ASTextNodeWordKerner *_wordKerner;
  
  // UITextInputTraits
  AS::RecursiveMutex _textInputTraitsLock;
  _ASTextInputTraitsPendingState *_textInputTraits;

  // Misc. State.
  BOOL _displayingPlaceholder; // Defaults to YES.
  BOOL _isPreservingSelection;
  BOOL _selectionChangedForEditedText;
  BOOL _delegateDidUpdateEnqueued;
  BOOL _scrollEnabled;

  NSRange _previousSelectedRange;
}

@property (nonatomic, readonly) _ASTextInputTraitsPendingState *textInputTraits;

@end

@implementation ASEditableTextNode

#pragma mark - NSObject Overrides
- (instancetype)init
{
  return [self initWithTextKitComponents:[ASTextKitComponents componentsWithAttributedSeedString:nil textContainerSize:CGSizeZero]
            placeholderTextKitComponents:[ASTextKitComponents componentsWithAttributedSeedString:nil textContainerSize:CGSizeZero]];
}

- (instancetype)initWithTextKitComponents:(ASTextKitComponents *)textKitComponents
             placeholderTextKitComponents:(ASTextKitComponents *)placeholderTextKitComponents
{
  if (!(self = [super init]))
    return nil;

  _displayingPlaceholder = YES;
  _scrollEnabled = YES;

  // Create the scaffolding for the text view.
  _textKitComponents = textKitComponents;
  _textKitComponents.layoutManager.delegate = self;
  _wordKerner = [[ASTextNodeWordKerner alloc] init];
  _textContainerInset = UIEdgeInsetsZero;
  
  // Create the placeholder scaffolding.
  _placeholderTextKitComponents = placeholderTextKitComponents;
  _placeholderTextKitComponents.layoutManager.delegate = self;
  
  return self;
}

#pragma mark - ASDisplayNode Overrides
- (void)didLoad
{
  [super didLoad];

  void (^configureTextView)(UITextView *) = ^(UITextView *textView) {
    if (!self->_displayingPlaceholder || textView != self->_textKitComponents.textView) {
      // If showing the placeholder, don't propagate backgroundColor/opaque to the editable textView.  It is positioned over the placeholder to accept taps to begin editing, and if it's opaque/colored then it'll obscure the placeholder.
      textView.backgroundColor = self.backgroundColor;
      textView.opaque = self.opaque;
    } else if (self->_displayingPlaceholder && textView == self->_textKitComponents.textView) {
      // The default backgroundColor for a textView is white.  Due to the reason described above, make sure the editable textView starts out transparent.
      textView.backgroundColor = nil;
      textView.opaque = NO;
    }
    textView.textContainerInset = self.textContainerInset;
    
    // Configure textView with UITextInputTraits
    {
      AS::MutexLocker l(self->_textInputTraitsLock);
      if (self->_textInputTraits) {
        textView.autocapitalizationType         = self->_textInputTraits.autocapitalizationType;
        textView.autocorrectionType             = self->_textInputTraits.autocorrectionType;
        textView.spellCheckingType              = self->_textInputTraits.spellCheckingType;
        textView.keyboardType                   = self->_textInputTraits.keyboardType;
        textView.keyboardAppearance             = self->_textInputTraits.keyboardAppearance;
        textView.returnKeyType                  = self->_textInputTraits.returnKeyType;
        textView.enablesReturnKeyAutomatically  = self->_textInputTraits.enablesReturnKeyAutomatically;
        textView.secureTextEntry                = self->_textInputTraits.isSecureTextEntry;
      }
    }
    
    [self.view addSubview:textView];
  };

  AS::MutexLocker l(_textKitLock);

  // Create and configure the placeholder text view.
  _placeholderTextKitComponents.textView = [[ASTextKitComponentsTextView alloc] initWithFrame:CGRectZero textContainer:_placeholderTextKitComponents.textContainer];
  _placeholderTextKitComponents.textView.userInteractionEnabled = NO;
  _placeholderTextKitComponents.textView.accessibilityElementsHidden = YES;
  configureTextView(_placeholderTextKitComponents.textView);

  // Create and configure our text view.
  _textKitComponents.textView = [[ASPanningOverriddenUITextView alloc] initWithFrame:CGRectZero textContainer:_textKitComponents.textContainer];
  _textKitComponents.textView.scrollEnabled = _scrollEnabled;
  _textKitComponents.textView.delegate = self;
  #if TARGET_OS_IOS
  _textKitComponents.textView.editable = YES;
  #endif
  _textKitComponents.textView.typingAttributes = _typingAttributes;
  _textKitComponents.textView.accessibilityHint = _placeholderTextKitComponents.textStorage.string;
  configureTextView(_textKitComponents.textView);

  [self _updateDisplayingPlaceholder];
    
  // once view is loaded, setters set directly on view
  _textInputTraits = nil;
}

- (CGSize)calculateSizeThatFits:(CGSize)constrainedSize
{
  ASTextKitComponents *displayedComponents = [self isDisplayingPlaceholder] ? _placeholderTextKitComponents : _textKitComponents;
  
  CGSize textSize;
  
  if (_maximumLinesToDisplay > 0) {
    textSize = [displayedComponents sizeForConstrainedWidth:constrainedSize.width
                                        forMaxNumberOfLines: _maximumLinesToDisplay];
  } else {
    textSize = [displayedComponents sizeForConstrainedWidth:constrainedSize.width];
  }
  
  CGFloat width = std::ceil(textSize.width + _textContainerInset.left + _textContainerInset.right);
  CGFloat height = std::ceil(textSize.height + _textContainerInset.top + _textContainerInset.bottom);
  return CGSizeMake(std::fmin(width, constrainedSize.width), std::fmin(height, constrainedSize.height));
}

- (void)layout
{
  ASDisplayNodeAssertMainThread();

  [super layout];
  [self _layoutTextView];
}

- (void)setBackgroundColor:(UIColor *)backgroundColor
{
  [super setBackgroundColor:backgroundColor];

  AS::MutexLocker l(_textKitLock);

  // If showing the placeholder, don't propagate backgroundColor/opaque to the editable textView.  It is positioned over the placeholder to accept taps to begin editing, and if it's opaque/colored then it'll obscure the placeholder.
  // The backgroundColor/opaque will be propagated to the editable textView when editing begins.
  if (!_displayingPlaceholder) {
    _textKitComponents.textView.backgroundColor = backgroundColor;
  }
  _placeholderTextKitComponents.textView.backgroundColor = backgroundColor;
}

- (void)setTextContainerInset:(UIEdgeInsets)textContainerInset
{
  AS::MutexLocker l(_textKitLock);

  _textContainerInset = textContainerInset;
  _textKitComponents.textView.textContainerInset = textContainerInset;
  _placeholderTextKitComponents.textView.textContainerInset = textContainerInset;
}

- (void)setOpaque:(BOOL)opaque
{
  [super setOpaque:opaque];

  AS::MutexLocker l(_textKitLock);

  // If showing the placeholder, don't propagate backgroundColor/opaque to the editable textView.  It is positioned over the placeholder to accept taps to begin editing, and if it's opaque/colored then it'll obscure the placeholder.
  // The backgroundColor/opaque will be propagated to the editable textView when editing begins.
  if (!_displayingPlaceholder) {
    _textKitComponents.textView.opaque = opaque;
  }
  _placeholderTextKitComponents.textView.opaque = opaque;
}

- (void)setLayerBacked:(BOOL)layerBacked
{
  ASDisplayNodeAssert(!layerBacked, @"Cannot set layerBacked to YES on ASEditableTextNode – instances must be view-backed in order to ensure touch events can be passed to the internal UITextView during editing.");
  [super setLayerBacked:layerBacked];
}

- (BOOL)supportsLayerBacking
{
  return NO;
}

#pragma mark - Configuration
@synthesize delegate = _delegate;

- (void)setScrollEnabled:(BOOL)scrollEnabled
{
  AS::MutexLocker l(_textKitLock);
  _scrollEnabled = scrollEnabled;
  [_textKitComponents.textView setScrollEnabled:_scrollEnabled];
}

- (UITextView *)textView
{
  ASDisplayNodeAssertMainThread();
  [self view];
  ASDisplayNodeAssert(_textKitComponents.textView != nil, @"UITextView must be created in -[ASEditableTextNode didLoad]");
  return _textKitComponents.textView;
}

- (void)setMaximumLinesToDisplay:(NSUInteger)maximumLines
{
  _maximumLinesToDisplay = maximumLines;
  [self setNeedsLayout];
}

#pragma mark -
@dynamic typingAttributes;

- (NSDictionary *)typingAttributes
{
  return _typingAttributes;
}

- (void)setTypingAttributes:(NSDictionary *)typingAttributes
{
  if (ASObjectIsEqual(typingAttributes, _typingAttributes))
    return;

  _typingAttributes = [typingAttributes copy];

  AS::MutexLocker l(_textKitLock);

  _textKitComponents.textView.typingAttributes = _typingAttributes;
}

#pragma mark -
@dynamic selectedRange;

- (NSRange)selectedRange
{
  AS::MutexLocker l(_textKitLock);
  return _textKitComponents.textView.selectedRange;
}

- (void)setSelectedRange:(NSRange)selectedRange
{
  AS::MutexLocker l(_textKitLock);
  _textKitComponents.textView.selectedRange = selectedRange;
}

#pragma mark - Placeholder
- (BOOL)isDisplayingPlaceholder
{
  return _displayingPlaceholder;
}

#pragma mark -
@dynamic attributedPlaceholderText;
- (NSAttributedString *)attributedPlaceholderText
{
  AS::MutexLocker l(_textKitLock);

  return [_placeholderTextKitComponents.textStorage copy];
}

- (void)setAttributedPlaceholderText:(NSAttributedString *)attributedPlaceholderText
{
  AS::MutexLocker l(_textKitLock);

  if (ASObjectIsEqual(_placeholderTextKitComponents.textStorage, attributedPlaceholderText))
    return;

  [_placeholderTextKitComponents.textStorage setAttributedString:attributedPlaceholderText ? : [[NSAttributedString alloc] initWithString:@""]];
  _textKitComponents.textView.accessibilityHint = attributedPlaceholderText.string;
}

#pragma mark - Modifying User Text
@dynamic attributedText;
- (NSAttributedString *)attributedText
{
  // Per contract in our header, this value is nil when the placeholder is displayed.
  if ([self isDisplayingPlaceholder])
    return nil;

  AS::MutexLocker l(_textKitLock);

  return [_textKitComponents.textStorage copy];
}

- (void)setAttributedText:(NSAttributedString *)attributedText
{
  AS::MutexLocker l(_textKitLock);

  // If we (_cmd) are called while the text view itself is updating (-textViewDidUpdate:), you cannot update the text storage and expect perfect propagation to the text view.
  // Thus, we always update the textview directly if it's been created already.
  if (ASObjectIsEqual((_textKitComponents.textView.attributedText ? : _textKitComponents.textStorage), attributedText))
    return;

  // If the cursor isn't at the end of the text, we need to preserve the selected range to avoid moving the cursor.
  NSRange selectedRange = _textKitComponents.textView.selectedRange;
  BOOL preserveSelectedRange = (selectedRange.location != _textKitComponents.textStorage.length);

  NSAttributedString *attributedStringToDisplay = nil;

  if (attributedText)
    attributedStringToDisplay = attributedText;
  // Otherwise, note that we don't simply nil out attributed text. Because the insertion point is guided by the attributes at index 0, we need to attribute an empty string to ensure the insert point obeys our typing attributes.
  else
    attributedStringToDisplay = [[NSAttributedString alloc] initWithString:@"" attributes:self.typingAttributes];

  // Always prefer updating the text view directly if it's been created (see above).
  if (_textKitComponents.textView)
    [_textKitComponents.textView setAttributedText:attributedStringToDisplay];
  else
    [_textKitComponents.textStorage setAttributedString:attributedStringToDisplay];

  // Calculated size depends on the seeded text.
  [self setNeedsLayout];

  // Update if placeholder is shown.
  [self _updateDisplayingPlaceholder];

  // Preserve cursor range, if necessary.
  if (preserveSelectedRange) {
    _isPreservingSelection = YES; // Used in -textViewDidChangeSelection: to avoid informing our delegate about our preservation.
    [_textKitComponents.textView setSelectedRange:selectedRange];
    _isPreservingSelection = NO;
  }
}

#pragma mark - Core
- (void)_updateDisplayingPlaceholder
{
  AS::MutexLocker l(_textKitLock);

  // Show the placeholder if necessary.
  _displayingPlaceholder = (_textKitComponents.textStorage.length == 0);
  _placeholderTextKitComponents.textView.hidden = !_displayingPlaceholder;

  // If hiding the placeholder, propagate backgroundColor/opaque to the editable textView.  It is positioned over the placeholder to accept taps to begin editing, and was kept transparent so it doesn't obscure the placeholder text.  Now that we're editing it and the placeholder is hidden, we can make it opaque to avoid unnecessary blending.
  if (!_displayingPlaceholder) {
    _textKitComponents.textView.opaque = self.isOpaque;
    _textKitComponents.textView.backgroundColor = self.backgroundColor;
  } else {
    _textKitComponents.textView.opaque = NO;
    _textKitComponents.textView.backgroundColor = nil;
  }
}

- (void)_layoutTextView
{
  AS::MutexLocker l(_textKitLock);

  // Layout filling our bounds.
  _textKitComponents.textView.frame = self.bounds;
  _placeholderTextKitComponents.textView.frame = self.bounds;

  // Note that both of these won't be necessary once we can disable scrolling, pending rdar://14729288
  // When we resize to fit (above) the prior layout becomes invalid. For whatever reason, UITextView doesn't invalidate its layout when its frame changes on its own, so we have to do so ourselves.
  [_textKitComponents.layoutManager invalidateLayoutForCharacterRange:NSMakeRange(0, [_textKitComponents.textStorage length]) actualCharacterRange:NULL];

  // When you type beyond UITextView's bounds it scrolls you down a line. We need to remain at the top.
  [_textKitComponents.textView setContentOffset:CGPointZero animated:NO];
}

#pragma mark - Keyboard
@dynamic textInputMode;
- (UITextInputMode *)textInputMode
{
  AS::MutexLocker l(_textKitLock);
  return [_textKitComponents.textView textInputMode];
}

- (BOOL)isFirstResponder
{
  AS::MutexLocker l(_textKitLock);
  return [_textKitComponents.textView isFirstResponder];
}

- (BOOL)canBecomeFirstResponder {
    AS::MutexLocker l(_textKitLock);
    return [_textKitComponents.textView canBecomeFirstResponder];
}

- (BOOL)becomeFirstResponder
{
  AS::MutexLocker l(_textKitLock);
  return [_textKitComponents.textView becomeFirstResponder];
}

- (BOOL)canResignFirstResponder {
    AS::MutexLocker l(_textKitLock);
    return [_textKitComponents.textView canResignFirstResponder];
}

- (BOOL)resignFirstResponder
{
  AS::MutexLocker l(_textKitLock);
  return [_textKitComponents.textView resignFirstResponder];
}

#pragma mark - UITextInputTraits

- (_ASTextInputTraitsPendingState *)textInputTraits
{
  if (!_textInputTraits) {
    _textInputTraits = [[_ASTextInputTraitsPendingState alloc] init];
  }
  return _textInputTraits;
}

- (void)setAutocapitalizationType:(UITextAutocapitalizationType)autocapitalizationType
{
  AS::MutexLocker l(_textInputTraitsLock);
  if (self.isNodeLoaded) {
    [self.textView setAutocapitalizationType:autocapitalizationType];
  } else {
    [self.textInputTraits setAutocapitalizationType:autocapitalizationType];
  }
}

- (UITextAutocapitalizationType)autocapitalizationType
{
  AS::MutexLocker l(_textInputTraitsLock);
  if (self.isNodeLoaded) {
    return [self.textView autocapitalizationType];
  } else {
    return [self.textInputTraits autocapitalizationType];
  }
}

- (void)setAutocorrectionType:(UITextAutocorrectionType)autocorrectionType
{
  AS::MutexLocker l(_textInputTraitsLock);
  if (self.isNodeLoaded) {
    [self.textView setAutocorrectionType:autocorrectionType];
  } else {
    [self.textInputTraits setAutocorrectionType:autocorrectionType];
  }
}

- (UITextAutocorrectionType)autocorrectionType
{
  AS::MutexLocker l(_textInputTraitsLock);
  if (self.isNodeLoaded) {
    return [self.textView autocorrectionType];
  } else {
    return [self.textInputTraits autocorrectionType];
  }
}

- (void)setSpellCheckingType:(UITextSpellCheckingType)spellCheckingType
{
  AS::MutexLocker l(_textInputTraitsLock);
  if (self.isNodeLoaded) {
    [self.textView setSpellCheckingType:spellCheckingType];
  } else {
    [self.textInputTraits setSpellCheckingType:spellCheckingType];
  }
}

- (UITextSpellCheckingType)spellCheckingType
{
  AS::MutexLocker l(_textInputTraitsLock);
  if (self.isNodeLoaded) {
    return [self.textView spellCheckingType];
  } else {
    return [self.textInputTraits spellCheckingType];
  }
}

- (void)setEnablesReturnKeyAutomatically:(BOOL)enablesReturnKeyAutomatically
{
  AS::MutexLocker l(_textInputTraitsLock);
  if (self.isNodeLoaded) {
    [self.textView setEnablesReturnKeyAutomatically:enablesReturnKeyAutomatically];
  } else {
    [self.textInputTraits setEnablesReturnKeyAutomatically:enablesReturnKeyAutomatically];
  }
}

- (BOOL)enablesReturnKeyAutomatically
{
  AS::MutexLocker l(_textInputTraitsLock);
  if (self.isNodeLoaded) {
    return [self.textView enablesReturnKeyAutomatically];
  } else {
    return [self.textInputTraits enablesReturnKeyAutomatically];
  }
}

- (void)setKeyboardAppearance:(UIKeyboardAppearance)setKeyboardAppearance
{
  AS::MutexLocker l(_textInputTraitsLock);
  if (self.isNodeLoaded) {
    [self.textView setKeyboardAppearance:setKeyboardAppearance];
  } else {
    [self.textInputTraits setKeyboardAppearance:setKeyboardAppearance];
  }
}

- (UIKeyboardAppearance)keyboardAppearance
{
  AS::MutexLocker l(_textInputTraitsLock);
  if (self.isNodeLoaded) {
    return [self.textView keyboardAppearance];
  } else {
    return [self.textInputTraits keyboardAppearance];
  }
}

- (void)setKeyboardType:(UIKeyboardType)keyboardType
{
  AS::MutexLocker l(_textInputTraitsLock);
  if (self.isNodeLoaded) {
    [self.textView setKeyboardType:keyboardType];
  } else {
    [self.textInputTraits setKeyboardType:keyboardType];
  }
}

- (UIKeyboardType)keyboardType
{
  AS::MutexLocker l(_textInputTraitsLock);
  if (self.isNodeLoaded) {
    return [self.textView keyboardType];
  } else {
    return [self.textInputTraits keyboardType];
  }
}

- (void)setReturnKeyType:(UIReturnKeyType)returnKeyType
{
  AS::MutexLocker l(_textInputTraitsLock);
  if (self.isNodeLoaded) {
    [self.textView setReturnKeyType:returnKeyType];
  } else {
    [self.textInputTraits setReturnKeyType:returnKeyType];
  }
}

- (UIReturnKeyType)returnKeyType
{
  AS::MutexLocker l(_textInputTraitsLock);
  if (self.isNodeLoaded) {
    return [self.textView returnKeyType];
  } else {
    return [self.textInputTraits returnKeyType];
  }
}

- (void)setSecureTextEntry:(BOOL)secureTextEntry
{
  AS::MutexLocker l(_textInputTraitsLock);
  if (self.isNodeLoaded) {
    [self.textView setSecureTextEntry:secureTextEntry];
  } else {
    [self.textInputTraits setSecureTextEntry:secureTextEntry];
  }
}

- (BOOL)isSecureTextEntry
{
  AS::MutexLocker l(_textInputTraitsLock);
  if (self.isNodeLoaded) {
    return [self.textView isSecureTextEntry];
  } else {
    return [self.textInputTraits isSecureTextEntry];
  }
}

#pragma mark - UITextView Delegate
- (BOOL)textViewShouldBeginEditing:(UITextView *)textView
{
  // Delegateify.
  return [self _delegateShouldBeginEditing];
}

- (void)textViewDidBeginEditing:(UITextView *)textView
{
  // Delegateify.
  [self _delegateDidBeginEditing];
}

- (BOOL)textView:(UITextView *)textView shouldChangeTextInRange:(NSRange)range replacementText:(NSString *)text
{
  // Delegateify.
  return [self _delegateShouldChangeTextInRange:range replacementText:text];
}

- (void)textViewDidChange:(UITextView *)textView
{
  AS::MutexLocker l(_textKitLock);

  // Note we received a text changed event.
  // This is used by _delegateDidChangeSelectionFromSelectedRange:toSelectedRange: to distinguish between selection changes that happen because of editing or pure selection changes.
  _selectionChangedForEditedText = YES;

  // Update if the placeholder is visible.
  [self _updateDisplayingPlaceholder];

  // Invalidate, as our calculated size depends on the textview's seeded text.
  [self invalidateCalculatedLayout];

  // Delegateify.
  [self _delegateDidUpdateText];
}

- (void)textViewDidChangeSelection:(UITextView *)textView
{
  // Typing attributes get reset when selection changes. Reapply them so they actually obey our header.
  _textKitComponents.textView.typingAttributes = _typingAttributes;

  // If we're only changing selection to preserve it, don't notify about anything.
  if (_isPreservingSelection)
    return;

  // Note if we receive a -textDidChange: between now and when we delegatify.
  // This is used by _delegateDidChangeSelectionFromSelectedRange:toSelectedRange: to distinguish between selection changes that happen because of editing or pure selection changes.
  _selectionChangedForEditedText = NO;

  NSRange fromSelectedRange = _previousSelectedRange;
  NSRange toSelectedRange = self.selectedRange;
  _previousSelectedRange = toSelectedRange;

  // Delegateify.
  [self _delegateDidChangeSelectionFromSelectedRange:fromSelectedRange toSelectedRange:toSelectedRange];
}

- (void)textViewDidEndEditing:(UITextView *)textView
{
  // Delegateify.
  [self _delegateDidFinishEditing];
}

#pragma mark - NSLayoutManager Delegate

- (NSUInteger)layoutManager:(NSLayoutManager *)layoutManager shouldGenerateGlyphs:(const CGGlyph *)glyphs properties:(const NSGlyphProperty *)properties characterIndexes:(const NSUInteger *)characterIndexes font:(UIFont *)aFont forGlyphRange:(NSRange)glyphRange
{
  return [_wordKerner layoutManager:layoutManager shouldGenerateGlyphs:glyphs properties:properties characterIndexes:characterIndexes font:aFont forGlyphRange:glyphRange];
}

- (NSControlCharacterAction)layoutManager:(NSLayoutManager *)layoutManager shouldUseAction:(NSControlCharacterAction)defaultAction forControlCharacterAtIndex:(NSUInteger)characterIndex
{
  return [_wordKerner layoutManager:layoutManager shouldUseAction:defaultAction forControlCharacterAtIndex:characterIndex];
}

- (CGRect)layoutManager:(NSLayoutManager *)layoutManager boundingBoxForControlGlyphAtIndex:(NSUInteger)glyphIndex forTextContainer:(NSTextContainer *)textContainer proposedLineFragment:(CGRect)proposedRect glyphPosition:(CGPoint)glyphPosition characterIndex:(NSUInteger)characterIndex
{
  return [_wordKerner layoutManager:layoutManager boundingBoxForControlGlyphAtIndex:glyphIndex forTextContainer:textContainer proposedLineFragment:proposedRect glyphPosition:glyphPosition characterIndex:characterIndex];
}

#pragma mark - Geometry
- (CGRect)frameForTextRange:(NSRange)textRange
{
  AS::MutexLocker l(_textKitLock);

  // Bail on invalid range.
  if (NSMaxRange(textRange) > [_textKitComponents.textStorage length]) {
    ASDisplayNodeAssert(NO, @"Invalid range");
    return CGRectZero;
  }

  // Force glyph generation and layout.
  [_textKitComponents.layoutManager ensureLayoutForTextContainer:_textKitComponents.textContainer];

  NSRange glyphRange = [_textKitComponents.layoutManager glyphRangeForCharacterRange:textRange actualCharacterRange:NULL];
  CGRect textRect = [_textKitComponents.layoutManager boundingRectForGlyphRange:glyphRange inTextContainer:_textKitComponents.textContainer];
  return [_textKitComponents.textView convertRect:textRect toView:self.view];
}

#pragma mark -
- (BOOL)_delegateShouldBeginEditing
{
  if ([_delegate respondsToSelector:@selector(editableTextNodeShouldBeginEditing:)]) {
    return [_delegate editableTextNodeShouldBeginEditing:self];
  }
  return YES;
}

- (void)_delegateDidBeginEditing
{
  if ([_delegate respondsToSelector:@selector(editableTextNodeDidBeginEditing:)])
    [_delegate editableTextNodeDidBeginEditing:self];
}

- (BOOL)_delegateShouldChangeTextInRange:(NSRange)range replacementText:(NSString *)text
{
  if ([_delegate respondsToSelector:@selector(editableTextNode:shouldChangeTextInRange:replacementText:)]) {
    return [_delegate editableTextNode:self shouldChangeTextInRange:range replacementText:text];
  }

  return YES;
}

- (void)_delegateDidChangeSelectionFromSelectedRange:(NSRange)fromSelectedRange toSelectedRange:(NSRange)toSelectedRange
{
  // There are two reasons we're invoking the delegate on the next run of the runloop.
  // 1. UITextView invokes its delegate methods when it's in the middle of text-processing. For example, -textViewDidChange: is invoked before you can truly rely on the changes being propagated throughout the Text Kit hierarchy.
  // 2. This delegate method (-textViewDidChangeSelection:) is called both before -textViewDidChange: and before the layout manager/etc. has necessarily generated+laid out its glyphs. Because of the former, we need to wait until -textViewDidChange: has had an opportunity to be called so can accurately determine whether this selection change is due to editing (_selectionChangedForEditedText).
  // Thus, to avoid calling out to client code in the middle of UITextView's processing, we call the delegate on the next run of the runloop, when all such internal processing is surely done.
  dispatch_async(dispatch_get_main_queue(), ^{
    if ([self->_delegate respondsToSelector:@selector(editableTextNodeDidChangeSelection:fromSelectedRange:toSelectedRange:dueToEditing:)])
      [self->_delegate editableTextNodeDidChangeSelection:self fromSelectedRange:fromSelectedRange toSelectedRange:toSelectedRange dueToEditing:self->_selectionChangedForEditedText];
  });
}

- (void)_delegateDidUpdateText
{
  // Note that because -editableTextNodeDidUpdateText: passes no state, the current state of the receiver will be accessed. Thus, it's not useful to enqueue a second delegation call if the first hasn't happened yet -- doing so will result in the delegate receiving -editableTextNodeDidUpdateText: when the "updated text" has already been processed. This may sound innocuous, but because our delegation may cause additional updates to the textview's string, and because such updates discard spelling suggestions and autocompletions (like double-space to `.`), it can actually be quite dangerous!
  if (_delegateDidUpdateEnqueued)
    return;

  _delegateDidUpdateEnqueued = YES;

  // UITextView invokes its delegate methods when it's in the middle of text-processing. For example, -textViewDidChange: is invoked before you can truly rely on the changes being propagated throughout the Text Kit hierarchy.
  // Thus, to avoid calling out to client code in the middle of UITextView's processing, we call the delegate on the next run of the runloop, when all such internal processing is surely done.
  dispatch_async(dispatch_get_main_queue(), ^{
    self->_delegateDidUpdateEnqueued = NO;
    if ([self->_delegate respondsToSelector:@selector(editableTextNodeDidUpdateText:)])
      [self->_delegate editableTextNodeDidUpdateText:self];
  });
}

- (void)_delegateDidFinishEditing
{
  if ([_delegate respondsToSelector:@selector(editableTextNodeDidFinishEditing:)])
    [_delegate editableTextNodeDidFinishEditing:self];
}

#pragma mark - UIAccessibilityContainer

- (NSInteger)accessibilityElementCount
{
  if (!self.isNodeLoaded) {
    ASDisplayNodeFailAssert(@"Cannot access accessibilityElementCount since ASEditableTextNode is not loaded");
    return 0;
  }
  return 1;
}

- (NSArray *)accessibilityElements
{
  if (!self.isNodeLoaded) {
    ASDisplayNodeFailAssert(@"Cannot access accessibilityElements since ASEditableTextNode is not loaded");
    return @[];
  }
  return @[self.textView];
}

- (id)accessibilityElementAtIndex:(NSInteger)index
{
  if (!self.isNodeLoaded) {
    ASDisplayNodeFailAssert(@"Cannot access accessibilityElementAtIndex: since ASEditableTextNode is not loaded");
    return nil;
  }
  return self.textView;
}

- (NSInteger)indexOfAccessibilityElement:(id)element
{
  return 0;
}

@end