//
//  WRChapterPageCount.m
//  WeRead (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