Epub阅读器0.0.1

2026-05-21 19:40:51 +08:00
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+//
+//  WRChapterPageCount.m
+//  WeRead (微信读书)
+//
+//  Detailed pseudo-code reconstruction of the pagination calculator.
+//  Computes page breaks by simulating CoreText line layout and fitting
+//  lines into the available vertical space.
+//
+
+#import "WRChapterPageCount.h"
+#import <CoreText/CoreText.h>
+
+// ============================================================================
+#pragma mark - Constants
+// ============================================================================
+
+/// Prefix for pagination cache keys.
+static NSString *const kPageCountCachePrefix = @"weread_pagcount";
+
+/// Separator used in cache key components.
+static NSString *const kCacheKeySeparator = @"_";
+
+// ============================================================================
+#pragma mark - WRChapterPageCount ()
+// ============================================================================
+
+@interface WRChapterPageCount ()
+
+/// Precomputed page ranges (cached after calculation).
+@property (nonatomic, strong) NSMutableArray<NSValue *> *mutablePageRanges;
+
+@end
+
+// ============================================================================
+#pragma mark - WRChapterPageCount Implementation
+// ============================================================================
+
+@implementation WRChapterPageCount
+
+// ============================================================================
+#pragma mark - Initialization
+// ============================================================================
+
+- (instancetype)init {
+    self = [super init];
+    if (self) {
+        _mutablePageRanges = [NSMutableArray array];
+    }
+    return self;
+}
+
+// ============================================================================
+#pragma mark - Class Methods
+// ============================================================================
+
+///
+/// Generates a cache key that encodes the book ID together with the current
+/// typesetter configuration (font size, line spacing, margins, page size).
+/// When any of these change, the cache key changes, invalidating old data.
+///
+/// Typical format:
+///   weread_pagcount_{bookId}_{fontSize}_{lineSpacing}_{pageWidth}_{pageHeight}
+///
+ (NSString *)currentCacheKeyWithBookId:(NSString *)bookId {
+    if (!bookId) return kPageCountCachePrefix;
+
+    // Read current typesetter settings from NSUserDefaults or a global config.
+    NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
+
+    CGFloat fontSize   = [defaults floatForKey:@"WRTypesetterFontSize"] ?: 18.0;
+    CGFloat lineSpacing = [defaults floatForKey:@"WRTypesetterLineSpacing"] ?: 1.5;
+    CGFloat pageWidth  = [defaults floatForKey:@"WRTypesetterPageWidth"] ?: 375.0;
+    CGFloat pageHeight = [defaults floatForKey:@"WRTypesetterPageHeight"] ?: 667.0;
+
+    // Build the key. Use integer representations to avoid locale issues.
+    NSString *key = [NSString stringWithFormat:@"%@%@%@%@%.0f%@%.1f%@%.0f%@%.0f",
+                     kPageCountCachePrefix,
+                     kCacheKeySeparator,
+                     bookId,
+                     kCacheKeySeparator,
+                     fontSize * 10,   // e.g., 180 for 18.0pt
+                     kCacheKeySeparator,
+                     lineSpacing * 10, // e.g., 15 for 1.5
+                     kCacheKeySeparator,
+                     pageWidth,
+                     kCacheKeySeparator,
+                     pageHeight];
+
+    return key;
+}
+
+///
+/// Converts a page info dictionary (from server or local computation)
+/// into an array of NSValue-wrapped NSRange objects.
+///
+/// Expected pageInfo format:
+///   {
+///       @"ranges": @[
+///           @{@"location": @0,    @"length": @500},
+///           @{@"location": @500,  @"length": @480},
+///           ...
+///       ]
+///   }
+///
+/// Or alternatively, an array of two-element arrays:
+///   {
+///       @"ranges": @[@[@0, @500], @[@500, @480], ...]
+///   }
+///
+ (NSArray<NSValue *> *)rangeValueWithPageInfo:(NSDictionary *)pageInfo {
+    NSMutableArray<NSValue *> *result = [NSMutableArray array];
+    if (!pageInfo) return [result copy];
+
+    NSArray *ranges = pageInfo[@"ranges"];
+    if (!ranges || ![ranges isKindOfClass:[NSArray class]]) return [result copy];
+
+    for (id entry in ranges) {
+        NSRange range = NSMakeRange(NSNotFound, 0);
+
+        if ([entry isKindOfClass:[NSDictionary class]]) {
+            // Dictionary format: {location, length}
+            NSDictionary *dict = (NSDictionary *)entry;
+            NSUInteger loc = [dict[@"location"] unsignedIntegerValue];
+            NSUInteger len = [dict[@"length"] unsignedIntegerValue];
+            range = NSMakeRange(loc, len);
+
+        } else if ([entry isKindOfClass:[NSArray class]]) {
+            // Array format: [location, length]
+            NSArray *arr = (NSArray *)entry;
+            if (arr.count >= 2) {
+                NSUInteger loc = [arr[0] unsignedIntegerValue];
+                NSUInteger len = [arr[1] unsignedIntegerValue];
+                range = NSMakeRange(loc, len);
+            }
+
+        } else if ([entry isKindOfClass:[NSValue class]]) {
+            // Already an NSValue wrapping NSRange.
+            range = [(NSValue *)entry rangeValue];
+        }
+
+        if (range.location != NSNotFound) {
+            [result addObject:[NSValue valueWithRange:range]];
+        }
+    }
+
+    return [result copy];
+}
+
+// ============================================================================
+#pragma mark - Instance Methods
+// ============================================================================
+
+/// Returns the character range for the page at the given index.
+- (NSRange)rangeForPageAtIndex:(NSUInteger)pageIndex {
+    NSArray<NSValue *> *ranges = self.pageRanges ?: self.mutablePageRanges;
+    if (pageIndex >= ranges.count) {
+        return NSMakeRange(NSNotFound, 0);
+    }
+    return [ranges[pageIndex] rangeValue];
+}
+
+/// Binary-search-style lookup: finds the page index containing the given
+/// character index. Pages are contiguous, so we can use binary search.
+- (NSUInteger)pageIndexForCharacterIndex:(NSUInteger)charIndex {
+    NSArray<NSValue *> *ranges = self.pageRanges ?: self.mutablePageRanges;
+    if (ranges.count == 0) return 0;
+
+    NSUInteger lo = 0;
+    NSUInteger hi = ranges.count - 1;
+
+    while (lo <= hi) {
+        NSUInteger mid = lo + (hi - lo) / 2;
+        NSRange midRange = [ranges[mid] rangeValue];
+
+        if (charIndex >= midRange.location &&
+            charIndex < NSMaxRange(midRange)) {
+            return mid;
+        } else if (charIndex < midRange.location) {
+            if (mid == 0) break;
+            hi = mid - 1;
+        } else {
+            lo = mid + 1;
+        }
+    }
+
+    // If not found, return the last page (clamp).
+    return ranges.count - 1;
+}
+
+///
+/// Recalculates page ranges by simulating CoreText typesetting.
+/// This is the core pagination algorithm:
+///
+///   1. Create a CTFramesetter from the attributed string.
+///   2. For each page, create a CTFrame with the available height.
+///   3. Count how many lines fit in the frame.
+///   4. Sum the character counts of those lines to get the page range.
+///   5. Advance the start position and repeat.
+///
+- (void)recalculatePageRangesForAttributedString:(NSAttributedString *)attributedString
+                                     drawingSize:(CGSize)drawingSize
+                                         margins:(UIEdgeInsets)margins {
+    [self.mutablePageRanges removeAllObjects];
+
+    if (!attributedString || attributedString.length == 0) {
+        self.pageRanges = @[];
+        return;
+    }
+
+    // ---- Step 1: Create the CTFramesetter ----
+    CTFramesetterRef framesetter =
+        CTFramesetterCreateWithAttributedString((__bridge CFAttributedStringRef)attributedString);
+    if (!framesetter) {
+        self.pageRanges = @[];
+        return;
+    }
+
+    // ---- Step 2: Compute the usable drawing area ----
+    CGFloat usableWidth  = drawingSize.width - margins.left - margins.right;
+    CGFloat usableHeight = drawingSize.height - margins.top - margins.bottom;
+
+    if (usableWidth <= 0 || usableHeight <= 0) {
+        CFRelease(framesetter);
+        self.pageRanges = @[];
+        return;
+    }
+
+    // ---- Step 3: Paginate ----
+    NSUInteger totalLength = attributedString.length;
+    NSUInteger currentLocation = 0;
+
+    while (currentLocation < totalLength) {
+        // Create a path for this page's drawing area.
+        CGRect pathRect = CGRectMake(margins.left, margins.bottom,
+                                     usableWidth, usableHeight);
+        CGMutablePathRef path = CGPathCreateMutable();
+        CGPathAddRect(path, NULL, pathRect);
+
+        // Create a frame for the remaining text.
+        // The frame will typeset as much text as fits in the path.
+        CFRange frameRange = CFRangeMake((CFIndex)currentLocation, 0); // 0 = until end
+        CTFrameRef frame = CTFramesetterCreateFrame(framesetter,
+                                                     frameRange,
+                                                     path, NULL);
+        CGPathRelease(path);
+
+        if (!frame) break;
+
+        // Get the lines that fit in this page.
+        NSArray *lines = (__bridge_transfer NSArray *)CTFrameGetLines(frame);
+        if (lines.count == 0) {
+            CFRelease(frame);
+            break;
+        }
+
+        // Get the line origins to determine which lines are fully within bounds.
+        CGPoint *origins = (CGPoint *)calloc(lines.count, sizeof(CGPoint));
+        CTFrameGetLineOrigins(frame, CFRangeMake(0, 0), origins);
+
+        NSUInteger pageCharCount = 0;
+        for (NSUInteger i = 0; i < lines.count; i++) {
+            CTLineRef line = (__bridge CTLineRef)lines[i];
+            CFRange lineRange = CTLineGetStringRange(line);
+
+            // Check if this line's origin is within the usable area.
+            // CoreText origins are from the bottom of the frame.
+            CGFloat lineY = origins[i].y;
+            CGFloat lineHeight = 0.0;
+            CGFloat descent = 0.0;
+            CTLineGetTypographicBounds(line, &lineHeight, &descent, NULL);
+
+            // If the line's top is above the top of the frame, it doesn't fit.
+            if (lineY - lineHeight > usableHeight) {
+                break; // This line doesn't fit; stop here.
+            }
+
+            pageCharCount += (NSUInteger)lineRange.length;
+        }
+
+        free(origins);
+        CFRelease(frame);
+
+        // If no characters fit (shouldn't happen normally), advance by 1 to avoid infinite loop.
+        if (pageCharCount == 0) {
+            pageCharCount = 1;
+        }
+
+        // Record this page's range.
+        NSRange pageRange = NSMakeRange(currentLocation, pageCharCount);
+        [self.mutablePageRanges addObject:[NSValue valueWithRange:pageRange]];
+
+        currentLocation += pageCharCount;
+    }
+
+    CFRelease(framesetter);
+
+    self.pageRanges = [self.mutablePageRanges copy];
+}
+
+// ============================================================================
+#pragma mark - Computed Properties
+// ============================================================================
+
+- (NSUInteger)totalPages {
+    return self.pageRanges.count;
+}
+
+@end