ComponentTextKit/TextKit/CKTextKitTailTruncater.mm

/*
 *  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 <RenderCore/RCAssert.h>

#import <ComponentTextKit/CKTextKitContext.h>
#import <ComponentTextKit/CKTextKitTailTruncater.h>

@implementation CKTextKitTailTruncater
{
  __weak CKTextKitContext *_context;
  NSAttributedString *_truncationAttributedString;
  NSCharacterSet *_avoidTailTruncationSet;
  CGSize _constrainedSize;
}
@synthesize visibleRanges = _visibleRanges;
@synthesize truncationStringRect = _truncationStringRect;

- (instancetype)initWithContext:(CKTextKitContext *)context
     truncationAttributedString:(NSAttributedString *)truncationAttributedString
         avoidTailTruncationSet:(NSCharacterSet *)avoidTailTruncationSet
                constrainedSize:(CGSize)constrainedSize
{
  if (self = [super init]) {
    _context = context;
    _truncationAttributedString = truncationAttributedString;
    _avoidTailTruncationSet = avoidTailTruncationSet;
    _constrainedSize = constrainedSize;

    [self _truncate];
  }
  return self;
}

/**
 Calculates the intersection of the truncation message within the end of the last line.
 */
- (NSUInteger)_calculateCharacterIndexBeforeTruncationMessage:(NSLayoutManager *)layoutManager
                                                  textStorage:(NSTextStorage *)textStorage
                                                textContainer:(NSTextContainer *)textContainer
{
  CGRect constrainedRect = (CGRect){ .size = textContainer.size };

  NSRange visibleGlyphRange = [layoutManager glyphRangeForBoundingRect:constrainedRect
                                                       inTextContainer:textContainer];
  NSInteger lastVisibleGlyphIndex = (NSMaxRange(visibleGlyphRange) - 1);

  if (lastVisibleGlyphIndex < 0) {
    return NSNotFound;
  }

  CGRect lastLineRect = [layoutManager lineFragmentRectForGlyphAtIndex:lastVisibleGlyphIndex
                                                        effectiveRange:NULL];
  CGRect lastLineUsedRect = [layoutManager lineFragmentUsedRectForGlyphAtIndex:lastVisibleGlyphIndex
                                                                effectiveRange:NULL];
  NSParagraphStyle *paragraphStyle = [textStorage attributesAtIndex:[layoutManager characterIndexForGlyphAtIndex:lastVisibleGlyphIndex]
                                                     effectiveRange:NULL][NSParagraphStyleAttributeName];
  // We assume LTR so long as the writing direction is not
  BOOL rtlWritingDirection = paragraphStyle ? paragraphStyle.baseWritingDirection == NSWritingDirectionRightToLeft : NO;
  // We only want to treat the trunction rect as left-aligned in the case that we are right-aligned and our writing
  // direction is RTL.
  BOOL leftAligned = CGRectGetMinX(lastLineRect) == CGRectGetMinX(lastLineUsedRect) || !rtlWritingDirection;

  // Calculate the bounding rectangle for the truncation message
  CKTextKitContext *truncationContext = [[CKTextKitContext alloc] initWithAttributedString:_truncationAttributedString
                                                                             lineBreakMode:NSLineBreakByWordWrapping
                                                                      maximumNumberOfLines:1
                                                                           constrainedSize:constrainedRect.size
                                                                      layoutManagerFactory:nil];

  __block CGRect truncationUsedRect;

  [truncationContext performBlockWithLockedTextKitComponents:^(NSLayoutManager *truncationLayoutManager, NSTextStorage *truncationTextStorage, NSTextContainer *truncationTextContainer) {
    // Size the truncation message
    [truncationLayoutManager ensureLayoutForTextContainer:truncationTextContainer];
    NSRange truncationGlyphRange = [truncationLayoutManager glyphRangeForTextContainer:truncationTextContainer];
    truncationUsedRect = [truncationLayoutManager boundingRectForGlyphRange:truncationGlyphRange
                                                            inTextContainer:truncationTextContainer];
  }];
  CGFloat truncationOriginX = (leftAligned ?
                               CGRectGetMaxX(constrainedRect) - truncationUsedRect.size.width :
                               CGRectGetMinX(constrainedRect));
  CGRect translatedTruncationRect = CGRectMake(truncationOriginX,
                                               CGRectGetMinY(lastLineRect),
                                               truncationUsedRect.size.width,
                                               truncationUsedRect.size.height);

  // Determine which glyph is the first to be clipped / overlaps the truncation message.
  CGFloat truncationMessageX = (leftAligned ?
                                CGRectGetMinX(translatedTruncationRect) :
                                CGRectGetMaxX(translatedTruncationRect));
  CGPoint beginningOfTruncationMessage = CGPointMake(truncationMessageX,
                                                     CGRectGetMidY(translatedTruncationRect));
  NSUInteger firstClippedGlyphIndex = [layoutManager glyphIndexForPoint:beginningOfTruncationMessage
                                                        inTextContainer:textContainer
                                         fractionOfDistanceThroughGlyph:NULL];
  // If it didn't intersect with any text then it should just return the last visible character index, since the
  // truncation rect can fully fit on the line without clipping any other text.
  if (firstClippedGlyphIndex == NSNotFound) {
    return [layoutManager characterIndexForGlyphAtIndex:lastVisibleGlyphIndex];
  }
  NSUInteger firstCharacterIndexToReplace = [layoutManager characterIndexForGlyphAtIndex:firstClippedGlyphIndex];
  if (firstCharacterIndexToReplace == NSNotFound) {
    return NSNotFound;
  }

  // Break on word boundaries
  return [self _findTruncationInsertionPointAtOrBeforeCharacterIndex:firstCharacterIndexToReplace
                                                       layoutManager:layoutManager
                                                         textStorage:textStorage];
}

/**
 Finds the first whitespace at or before the character index do we don't truncate in the middle of words
 If there are multiple whitespaces together (say a space and a newline), this will backtrack to the first one
 */
- (NSUInteger)_findTruncationInsertionPointAtOrBeforeCharacterIndex:(NSUInteger)firstCharacterIndexToReplace
                                                      layoutManager:(NSLayoutManager *)layoutManager
                                                        textStorage:(NSTextStorage *)textStorage
{
  // Don't attempt to truncate beyond the end of the string
  if (firstCharacterIndexToReplace >= textStorage.length) {
    return 0;
  }

  // Find the glyph range of the line fragment containing the first character to replace.
  NSRange lineGlyphRange;
  [layoutManager lineFragmentRectForGlyphAtIndex:[layoutManager glyphIndexForCharacterAtIndex:firstCharacterIndexToReplace]
                                  effectiveRange:&lineGlyphRange];

  // Look for the first whitespace from the end of the line, starting from the truncation point
  NSUInteger startingSearchIndex = [layoutManager characterIndexForGlyphAtIndex:lineGlyphRange.location];
  NSUInteger endingSearchIndex = firstCharacterIndexToReplace;
  NSRange rangeToSearch = NSMakeRange(startingSearchIndex, (endingSearchIndex - startingSearchIndex));

  NSRange rangeOfLastVisibleAvoidedChars = { .location = NSNotFound };
  if (_avoidTailTruncationSet) {
    rangeOfLastVisibleAvoidedChars = [textStorage.string rangeOfCharacterFromSet:_avoidTailTruncationSet
                                                                         options:NSBackwardsSearch
                                                                           range:rangeToSearch];
  }

  // Couldn't find a good place to truncate. Might be because there is no whitespace in the text, or we're dealing
  // with a foreign language encoding. Settle for truncating at the original place, which may be mid-word.
  if (rangeOfLastVisibleAvoidedChars.location == NSNotFound) {
    return firstCharacterIndexToReplace;
  } else {
    return rangeOfLastVisibleAvoidedChars.location;
  }
}

- (void)_truncate
{
  [_context performBlockWithLockedTextKitComponents:^(NSLayoutManager *layoutManager, NSTextStorage *textStorage, NSTextContainer *textContainer) {
    NSUInteger originalStringLength = textStorage.length;

    [layoutManager ensureLayoutForTextContainer:textContainer];

    NSRange visibleGlyphRange = [layoutManager glyphRangeForBoundingRect:{ .size = textContainer.size }
                                                         inTextContainer:textContainer];
    NSRange visibleCharacterRange = [layoutManager characterRangeForGlyphRange:visibleGlyphRange
                                                              actualGlyphRange:NULL];

    // Check if text is truncated, and if so apply our truncation string
    if (visibleCharacterRange.length < originalStringLength && _truncationAttributedString.length > 0) {
      NSInteger firstCharacterIndexToReplace = [self _calculateCharacterIndexBeforeTruncationMessage:layoutManager
                                                                                         textStorage:textStorage
                                                                                       textContainer:textContainer];
      if (firstCharacterIndexToReplace == 0 || firstCharacterIndexToReplace >= textStorage.length) {
        // Either nothing is visible, or everything is; nothing for us to do here
        return;
      }

      // Update/truncate the visible range of text
      visibleCharacterRange = NSMakeRange(0, firstCharacterIndexToReplace);
      NSRange truncationReplacementRange = NSMakeRange(firstCharacterIndexToReplace,
                                                       textStorage.length - firstCharacterIndexToReplace);
      // Replace the end of the visible message with the truncation string
      [textStorage replaceCharactersInRange:truncationReplacementRange
                       withAttributedString:_truncationAttributedString];
    }

    _visibleRanges = { visibleCharacterRange };
  }];
}

@end