ReadViewSDK/Doc/WXRead/decompiled/DTCoreTextLayouter.m

//
//  DTCoreTextLayouter.m
//  WeRead
//
//  Reverse-engineered from binary analysis
//  Based on DTCoreText open-source library, customized by WeRead
//
//  This file contains pseudo-code reconstruction of the DTCoreTextLayouter
//  class based on ivar analysis, method signatures, and the open-source DTCoreText library.
//

#import "DTCoreTextLayouter.h"
#import "DTCoreTextLayoutFrame.h"
#import <CoreText/CoreText.h>

#pragma mark - Private Interface

@interface DTCoreTextLayouter () {
    // CoreText typesetter - the core text processing engine
    CTTypesetterRef _typesetter;

    // Track whether the typesetter is valid
    BOOL _typesetterValid;

    // Internal lock for thread safety
    NSLock *_lock;
}

@end

#pragma mark - DTCoreTextLayouter Implementation

@implementation DTCoreTextLayouter

#pragma mark - Lifecycle

- (instancetype)init {
    self = [super init];
    if (self) {
        _layoutFrameCache = [[NSCache alloc] init];
        _layoutFrameCache.countLimit = 20; // Cache up to 20 layout frames
        _layoutFrames = [NSMutableArray array];
        _typesetterValid = NO;
        _lock = [[NSLock alloc] init];
    }
    return self;
}

- (instancetype)initWithAttributedString:(NSAttributedString *)attributedString {
    self = [self init];
    if (self) {
        _attributedString = attributedString;
    }
    return self;
}

- (void)dealloc {
    if (_typesetter) {
        CFRelease(_typesetter);
        _typesetter = NULL;
    }
}

#pragma mark - Property Accessors

- (void)setAttributedString:(NSAttributedString *)attributedString {
    [_lock lock];

    _attributedString = attributedString;

    // Invalidate the typesetter when the string changes
    _typesetterValid = NO;

    // Clear the layout frames array
    [_layoutFrames removeAllObjects];

    [_lock unlock];
}

#pragma mark - Typesetter Management

/**
 * Returns the internal CTTypesetter, creating it if necessary.
 *
 * CTTypesetter is the low-level CoreText object that performs glyph layout.
 * It analyzes the attributed string and prepares it for line-by-line layout.
 *
 * @return The CTTypesetter reference
 */
- (CTTypesetterRef)typesetter {
    [_lock lock];

    if (!_typesetterValid || !_typesetter) {
        // Release old typesetter if any
        if (_typesetter) {
            CFRelease(_typesetter);
            _typesetter = NULL;
        }

        if (_attributedString) {
            // Create new typesetter from the attributed string
            _typesetter = CTTypesetterCreateWithAttributedString(
                (__bridge CFAttributedStringRef)_attributedString
            );
            _typesetterValid = YES;
        }
    }

    CTTypesetterRef result = _typesetter;

    [_lock unlock];

    return result;
}

/**
 * Invalidates the current typesetter.
 * Forces recreation on next access.
 */
- (void)invalidateTypesetter {
    [_lock lock];
    _typesetterValid = NO;
    [_lock unlock];
}

#pragma mark - Layout Frame Creation

/**
 * Creates a DTCoreTextLayoutFrame for a given string range.
 *
 * This method creates a layout frame by:
 * 1. Getting the typesetter
 * 2. Creating a CTFrame for the range within the given rect
 * 3. Wrapping it in a DTCoreTextLayoutFrame
 *
 * @param range Range of the attributed string to lay out
 * @param frame Bounding rectangle for the layout
 * @return A new DTCoreTextLayoutFrame
 */
- (DTCoreTextLayoutFrame *)layoutFrameWithRange:(NSRange)range
                                          frame:(CGRect)frame {
    CTTypesetterRef typesetter = [self typesetter];

    if (!typesetter || range.length == 0) {
        return nil;
    }

    [_lock lock];

    // Create a CGPath for the frame bounds
    CGMutablePathRef path = CGPathCreateMutable();
    CGPathAddRect(path, NULL, frame);

    // Create CTFrame from the typesetter
    CTFrameRef ctFrame = CTTypesetterCreateFrame(
        typesetter,
        CFRangeMake(range.location, range.length),
        path,
        NULL
    );

    CGPathRelease(path);

    if (!ctFrame) {
        [_lock unlock];
        return nil;
    }

    // Create layout frame wrapper
    DTCoreTextLayoutFrame *layoutFrame = [[DTCoreTextLayoutFrame alloc]
        initWithAttributedString:_attributedString
                            range:range
                         ctFrame:ctFrame];

    CFRelease(ctFrame);

    [_layoutFrames addObject:layoutFrame];

    [_lock unlock];

    return layoutFrame;
}

/**
 * Suggests a line break for the given start index and width.
 *
 * Uses CTTypesetterSuggestLineBreak to determine how many characters
 * fit within the given width.
 *
 * @param startIndex The starting index in the string
 * @param width The available width
 * @return The suggested line break index
 */
- (NSUInteger)suggestLineBreakStartIndex:(NSUInteger)startIndex
                                   width:(CGFloat)width {
    CTTypesetterRef typesetter = [self typesetter];

    if (!typesetter) {
        return 0;
    }

    // CTTypesetterSuggestLineBreak returns the number of characters
    // that fit in the given width starting from startIndex
    CFIndex breakIndex = CTTypesetterSuggestLineBreak(
        typesetter,
        startIndex,
        width
    );

    return (NSUInteger)breakIndex;
}

/**
 * Suggests a fitting string length for pagination.
 *
 * This method simulates pagination to determine how much text
 * fits within the given constraints.
 *
 * @param width The available width
 * @param startIndex The starting index
 * @return The suggested fitting length
 */
- (NSUInteger)stringIndexFittingLengthForWidth:(CGFloat)width
                                    startIndex:(NSUInteger)startIndex {
    CTTypesetterRef typesetter = [self typesetter];

    if (!_attributedString || !typesetter) {
        return 0;
    }

    NSUInteger totalLength = [_attributedString length];
    NSUInteger currentIndex = startIndex;
    NSUInteger totalFitted = 0;

    // Simulate line-by-line layout to find total fitting length
    while (currentIndex < totalLength) {
        CFIndex lineBreak = CTTypesetterSuggestLineBreak(
            typesetter,
            currentIndex,
            width
        );

        if (lineBreak <= 0) {
            break;
        }

        totalFitted += lineBreak;
        currentIndex += lineBreak;
    }

    return totalFitted;
}

#pragma mark - Frame Caching

/**
 * Returns a cached layout frame for the given key.
 */
- (DTCoreTextLayoutFrame *)cachedLayoutFrameForKey:(NSString *)key {
    return [_layoutFrameCache objectForKey:key];
}

/**
 * Caches a layout frame with the given key.
 */
- (void)cacheLayoutFrame:(DTCoreTextLayoutFrame *)frame
                  forKey:(NSString *)key {
    if (frame && key) {
        [_layoutFrameCache setObject:frame forKey:key];
    }
}

/**
 * Clears the layout frame cache.
 */
- (void)clearLayoutFrameCache {
    [_layoutFrameCache removeAllObjects];
}

@end