keyboard/CustomKeyboard/Utils/KBBackspaceLongPressHandler.m

//
//  KBBackspaceLongPressHandler.m
//  CustomKeyboard
//

#import "KBBackspaceLongPressHandler.h"
#import "KBResponderUtils.h"
#import "KBSkinManager.h"
#import "KBBackspaceUndoManager.h"
#import "KBInputBufferManager.h"

static const NSTimeInterval kKBBackspaceLongPressMinDuration = 0.35;
static const NSTimeInterval kKBBackspaceRepeatInterval = 0.06;
static const NSTimeInterval kKBBackspaceChunkStartDelay = 0.6;
static const NSTimeInterval kKBBackspaceChunkRepeatInterval = 0.1;
static const NSTimeInterval kKBBackspaceChunkFastDelay = 1.2;
static const NSInteger kKBBackspaceChunkSize = 8;
static const NSInteger kKBBackspaceChunkSizeFast = 16;
static const CGFloat kKBBackspaceClearLabelCornerRadius = 8.0;
static const CGFloat kKBBackspaceClearLabelHeight = 34;
static const CGFloat kKBBackspaceClearLabelPaddingX = 10.0;
static const CGFloat kKBBackspaceClearLabelTopGap = 6.0;
static const CGFloat kKBBackspaceClearLabelHorizontalInset = 6.0;
static const NSTimeInterval kKBBackspaceClearBatchInterval = 0.02;
static const NSInteger kKBBackspaceClearMaxDeletes = 10000;
static const NSInteger kKBBackspaceClearEmptyContextMaxRounds = 40;
static const NSInteger kKBBackspaceClearMaxStep = 80;
static const NSInteger kKBBackspaceClearDeletesPerTick = 10;

typedef NS_ENUM(NSInteger, KBBackspaceChunkClass) {
    KBBackspaceChunkClassUnknown = 0,
    KBBackspaceChunkClassWhitespace,
    KBBackspaceChunkClassASCIIWord,
    KBBackspaceChunkClassPunctuation,
    KBBackspaceChunkClassOther
};

typedef NS_ENUM(NSInteger, KBClearPhase) {
    KBClearPhaseSkipWhitespace = 0,
    KBClearPhaseSkipTrailingBoundary,
    KBClearPhaseDeleteUntilBoundary
};

@interface KBBackspaceLongPressHandler ()
@property (nonatomic, weak) UIView *containerView;
@property (nonatomic, weak) UIView *backspaceButton;
@property (nonatomic, strong) UILongPressGestureRecognizer *longPress;
@property (nonatomic, assign) BOOL showClearLabelEnabled;
@property (nonatomic, assign) BOOL backspaceHoldActive;
@property (nonatomic, assign) NSTimeInterval backspaceHoldStartTime;
@property (nonatomic, assign) BOOL backspaceChunkModeActive;
@property (nonatomic, assign) BOOL backspaceClearHighlighted;
@property (nonatomic, assign) NSUInteger backspaceHoldToken;
@property (nonatomic, assign) BOOL backspaceHasLastTouchPoint;
@property (nonatomic, assign) CGPoint backspaceLastTouchPointInSelf;
@property (nonatomic, assign) NSUInteger backspaceClearToken;
@property (nonatomic, strong) UILabel *backspaceClearLabel;
@property (nonatomic, copy) NSString *pendingClearBefore;
@property (nonatomic, copy) NSString *pendingClearAfter;
@property (nonatomic, assign) KBClearPhase backspaceClearPhase;
@end

@implementation KBBackspaceLongPressHandler

- (instancetype)initWithContainerView:(UIView *)containerView {
    if (self = [super init]) {
        _containerView = containerView;
        _backspaceClearPhase = KBClearPhaseSkipWhitespace;
    }
    return self;
}

- (void)bindDeleteButton:(UIView *)button showClearLabel:(BOOL)showClearLabel {
    if (self.backspaceButton == button) { return; }

    if (self.longPress && self.backspaceButton) {
        [self.backspaceButton removeGestureRecognizer:self.longPress];
    }
    self.backspaceButton = button;
    self.showClearLabelEnabled = showClearLabel;
    self.backspaceHoldActive = NO;
    self.backspaceChunkModeActive = NO;
    self.backspaceClearHighlighted = NO;
    self.backspaceHasLastTouchPoint = NO;
    self.backspaceHoldToken += 1;
    [self kb_hideBackspaceClearLabel];
    self.pendingClearBefore = nil;
    self.pendingClearAfter = nil;

    if (!button) { return; }

    self.longPress = [[UILongPressGestureRecognizer alloc] initWithTarget:self
                                                                   action:@selector(onBackspaceLongPress:)];
    self.longPress.minimumPressDuration = kKBBackspaceLongPressMinDuration;
    self.longPress.allowableMovement = CGFLOAT_MAX;
    self.longPress.cancelsTouchesInView = YES;
    [button addGestureRecognizer:self.longPress];
}

- (void)performClearAction {
    [self kb_clearAllInput];
}

#pragma mark - Long Press

- (void)onBackspaceLongPress:(UILongPressGestureRecognizer *)gr {
    UIView *hostView = [self kb_hostView];
    if (!hostView) { return; }
    if (gr) {
        self.backspaceLastTouchPointInSelf = [gr locationInView:hostView];
        self.backspaceHasLastTouchPoint = YES;
    }
    switch (gr.state) {
        case UIGestureRecognizerStateBegan: {
            UIResponder *start = (UIResponder *)([self kb_hostView] ?: self.backspaceButton);
            UIInputViewController *ivc = KBFindInputViewController(start);
            if (ivc) {
                id<UITextDocumentProxy> proxy = ivc.textDocumentProxy;
                [[KBInputBufferManager shared] refreshFromProxyIfPossible:proxy];
                [[KBInputBufferManager shared] prepareSnapshotForDeleteWithContextBefore:proxy.documentContextBeforeInput
                                                                                   after:proxy.documentContextAfterInput];
            }
            if (self.showClearLabelEnabled) {
                [self kb_capturePendingClearSnapshotIfNeeded];
                [[KBInputBufferManager shared] beginPendingClearSnapshot];
            }
            self.backspaceHoldToken += 1;
            NSUInteger token = self.backspaceHoldToken;
            self.backspaceHoldActive = YES;
            self.backspaceHoldStartTime = [NSDate date].timeIntervalSinceReferenceDate;
            self.backspaceChunkModeActive = NO;
            [self kb_setBackspaceClearHighlighted:NO];
            [self kb_hideBackspaceClearLabel];
            if (self.showClearLabelEnabled) {
                [self kb_showBackspaceClearLabelIfNeeded];
            }
            [self kb_backspaceStepForToken:token];
        } break;
        case UIGestureRecognizerStateChanged: {
            [self kb_handleBackspaceLongPressChanged:gr];
        } break;
        case UIGestureRecognizerStateEnded:
        case UIGestureRecognizerStateCancelled:
        case UIGestureRecognizerStateFailed: {
            [self kb_handleBackspaceLongPressEnded:gr];
        } break;
        default: break;
    }
}

#pragma mark - Delete Steps

- (void)kb_backspaceStepForToken:(NSUInteger)token {
    if (!self.backspaceHoldActive) { return; }
    if (token != self.backspaceHoldToken) { return; }
    UIResponder *start = (UIResponder *)([self kb_hostView] ?: self.backspaceButton);
    UIInputViewController *ivc = KBFindInputViewController(start);
    if (!ivc) { self.backspaceHoldActive = NO; return; }
    id<UITextDocumentProxy> proxy = ivc.textDocumentProxy;
    NSString *before = proxy.documentContextBeforeInput ?: @"";
    if (before.length == 0) { before = [KBInputBufferManager shared].liveText ?: @""; }
    NSTimeInterval elapsed = [NSDate date].timeIntervalSinceReferenceDate - self.backspaceHoldStartTime;
    NSInteger deleteCount = 1;
    if (before.length > 0) {
        deleteCount = [self kb_backspaceDeleteCountForContext:before elapsed:elapsed];
    }
    if (!self.backspaceChunkModeActive && elapsed >= kKBBackspaceChunkStartDelay) {
        self.backspaceChunkModeActive = YES;
        if (self.showClearLabelEnabled) {
            [self kb_showBackspaceClearLabelIfNeeded];
        }
    }
    [[KBBackspaceUndoManager shared] captureAndDeleteBackwardFromProxy:proxy count:(NSUInteger)deleteCount];
    [[KBInputBufferManager shared] applyHoldDeleteCount:(NSUInteger)deleteCount];

    NSTimeInterval interval = [self kb_backspaceRepeatIntervalForElapsed:elapsed];
    __weak typeof(self) weakSelf = self;
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW,
                                 (int64_t)(interval * NSEC_PER_SEC)),
                   dispatch_get_main_queue(), ^{
        __strong typeof(weakSelf) selfStrong = weakSelf;
        [selfStrong kb_backspaceStepForToken:token];
    });
}

- (NSTimeInterval)kb_backspaceRepeatIntervalForElapsed:(NSTimeInterval)elapsed {
    if (elapsed >= kKBBackspaceChunkStartDelay) {
        return kKBBackspaceChunkRepeatInterval;
    }
    return kKBBackspaceRepeatInterval;
}

- (NSInteger)kb_backspaceDeleteCountForContext:(NSString *)context elapsed:(NSTimeInterval)elapsed {
    if (elapsed < kKBBackspaceChunkStartDelay) {
        return 1;
    }
    NSInteger maxCount = (elapsed >= kKBBackspaceChunkFastDelay)
                         ? kKBBackspaceChunkSizeFast : kKBBackspaceChunkSize;
    return [self kb_backspaceChunkDeleteCountForContext:context maxCount:maxCount];
}

- (NSInteger)kb_backspaceChunkDeleteCountForContext:(NSString *)context maxCount:(NSInteger)maxCount {
    if (context.length == 0) { return 1; }

    static NSCharacterSet *whitespaceSet = nil;
    static NSCharacterSet *asciiWordSet = nil;
    static NSCharacterSet *punctuationSet = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        whitespaceSet = [NSCharacterSet whitespaceAndNewlineCharacterSet];
        asciiWordSet = [NSCharacterSet characterSetWithCharactersInString:
                        @"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789_"];
        NSMutableCharacterSet *punct = [[NSCharacterSet punctuationCharacterSet] mutableCopy];
        // 补齐常见中文/全角标点（避免 chunk 总是只删 1 个符号）
        [punct addCharactersInString:@"，。！？；：、（）【】《》“”‘’·…—"];
        punctuationSet = [punct copy];
    });

    __block NSInteger deleteCount = 0;
    typedef NS_ENUM(NSInteger, KBBackspaceChunkPhase) {
        KBBackspaceChunkPhaseWhitespace = 0,
        KBBackspaceChunkPhasePunctuation,
        KBBackspaceChunkPhaseCore
    };
    __block KBBackspaceChunkPhase phase = KBBackspaceChunkPhaseWhitespace;
    __block KBBackspaceChunkClass coreClass = KBBackspaceChunkClassUnknown;

    [context enumerateSubstringsInRange:NSMakeRange(0, context.length)
                                options:NSStringEnumerationByComposedCharacterSequences | NSStringEnumerationReverse
                             usingBlock:^(NSString *substring, __unused NSRange substringRange, __unused NSRange enclosingRange, BOOL *stop) {
        if (substring.length == 0) { return; }
        if (deleteCount >= maxCount) {
            *stop = YES;
            return;
        }

        KBBackspaceChunkClass currentClass = KBBackspaceChunkClassOther;
        if ([substring rangeOfCharacterFromSet:whitespaceSet].location != NSNotFound) {
            currentClass = KBBackspaceChunkClassWhitespace;
        } else if ([substring rangeOfCharacterFromSet:punctuationSet].location != NSNotFound) {
            currentClass = KBBackspaceChunkClassPunctuation;
        } else if ([substring rangeOfCharacterFromSet:asciiWordSet].location != NSNotFound) {
            currentClass = KBBackspaceChunkClassASCIIWord;
        }

        BOOL consumed = NO;
        while (!consumed) {
            if (phase == KBBackspaceChunkPhaseWhitespace) {
                if (currentClass == KBBackspaceChunkClassWhitespace) {
                    deleteCount += 1;
                    consumed = YES;
                } else {
                    phase = KBBackspaceChunkPhasePunctuation;
                }
                continue;
            }

            if (phase == KBBackspaceChunkPhasePunctuation) {
                if (currentClass == KBBackspaceChunkClassPunctuation) {
                    deleteCount += 1;
                    consumed = YES;
                } else {
                    phase = KBBackspaceChunkPhaseCore;
                }
                continue;
            }

            // phase == Core：连续删同一类（ASCII 单词 / 其它），让效果更像微信“几个字一组”
            if (coreClass == KBBackspaceChunkClassUnknown) {
                coreClass = currentClass;
            }
            if (currentClass != coreClass) {
                *stop = YES;
                consumed = YES;
                continue;
            }
            deleteCount += 1;
            consumed = YES;
        }

        if (deleteCount >= maxCount) {
            *stop = YES;
            return;
        }
    }];

    return MAX(deleteCount, 1);
}

- (NSInteger)kb_clearDeleteCountForContext:(NSString *)context
                               hitBoundary:(BOOL *)hitBoundary {
    if (context.length == 0) {
        if (hitBoundary) { *hitBoundary = NO; }
        return 1;
    }

    static NSCharacterSet *sentenceBoundarySet = nil;
    static NSCharacterSet *whitespaceSet = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        sentenceBoundarySet = [NSCharacterSet characterSetWithCharactersInString:@".!?。！？"];
        whitespaceSet = [NSCharacterSet whitespaceAndNewlineCharacterSet];
    });

    NSInteger length = context.length;
    NSInteger end = length;
    while (end > 0) {
        unichar ch = [context characterAtIndex:end - 1];
        if ([whitespaceSet characterIsMember:ch]) {
            end -= 1;
        } else {
            break;
        }
    }
    NSInteger searchEnd = end;
    while (searchEnd > 0) {
        unichar ch = [context characterAtIndex:searchEnd - 1];
        if ([sentenceBoundarySet characterIsMember:ch]) {
            searchEnd -= 1;
        } else {
            break;
        }
    }

    NSInteger boundaryIndex = NSNotFound;
    for (NSInteger i = searchEnd - 1; i >= 0; i--) {
        unichar ch = [context characterAtIndex:i];
        if ([sentenceBoundarySet characterIsMember:ch]) {
            boundaryIndex = i;
            break;
        }
    }

    BOOL boundaryFound = (boundaryIndex != NSNotFound);
    NSInteger deleteCount = length;
    if (boundaryIndex != NSNotFound) {
        deleteCount = length - (boundaryIndex + 1);
    }
    deleteCount = MAX(deleteCount, 1);
    if (hitBoundary) {
        *hitBoundary = boundaryFound;
    }
    return MIN(deleteCount, kKBBackspaceClearMaxStep);
}

#pragma mark - Long Press State

- (void)kb_handleBackspaceLongPressChanged:(UILongPressGestureRecognizer *)gr {
    if (!self.backspaceHoldActive) { return; }
    if (!self.showClearLabelEnabled) { return; }
    [self kb_showBackspaceClearLabelIfNeeded];
    UIView *hostView = [self kb_hostView];
    if (!hostView) { return; }
    CGPoint point = [gr locationInView:hostView];
    self.backspaceLastTouchPointInSelf = point;
    self.backspaceHasLastTouchPoint = YES;
    BOOL inside = [self kb_isPointInsideBackspaceClearLabel:point];
    [self kb_setBackspaceClearHighlighted:inside];
}

- (void)kb_handleBackspaceLongPressEnded:(UILongPressGestureRecognizer *)gr {
    BOOL shouldClear = NO;
    if (self.showClearLabelEnabled) {
        shouldClear = self.backspaceClearHighlighted;
        if (!shouldClear) {
            UIView *hostView = [self kb_hostView];
            CGPoint point = CGPointZero;
            if (gr && hostView) {
                point = [gr locationInView:hostView];
            } else if (self.backspaceHasLastTouchPoint) {
                point = self.backspaceLastTouchPointInSelf;
            }
            shouldClear = [self kb_isPointInsideBackspaceClearLabel:point];
        }
    }
#if DEBUG
    NSLog(@"[kb_handleBackspaceLongPressEnded] shouldClear=%@ highlighted=%@ labelHidden=%@",
          shouldClear ? @"YES" : @"NO",
          self.backspaceClearHighlighted ? @"YES" : @"NO",
          self.backspaceClearLabel.hidden ? @"YES" : @"NO");
#endif
    self.backspaceHoldActive = NO;
    self.backspaceChunkModeActive = NO;
    self.backspaceHoldToken += 1;
    self.backspaceHasLastTouchPoint = NO;
    [self kb_hideBackspaceClearLabel];
    if (shouldClear) {
        [self kb_clearAllInput];
    } else {
        self.pendingClearBefore = nil;
        self.pendingClearAfter = nil;
        [[KBInputBufferManager shared] clearPendingClearSnapshot];
        [[KBInputBufferManager shared] commitLiveToManual];
    }
}

#pragma mark - Clear Label

- (void)kb_showBackspaceClearLabelIfNeeded {
    UIView *hostView = [self kb_hostView];
    if (!hostView || !self.backspaceButton) { return; }
    UILabel *label = self.backspaceClearLabel;
    [self kb_refreshBackspaceClearLabelColors];
    if (!label.superview) {
        [hostView addSubview:label];
    }
    [self kb_updateBackspaceClearLabelFrame];
    [hostView bringSubviewToFront:label];
    if (label.hidden) {
        label.alpha = 0.0;
        label.hidden = NO;
        [self kb_playLightHaptic];
        [UIView animateWithDuration:0.12 animations:^{
            label.alpha = 1.0;
        }];
    }
}

- (void)kb_hideBackspaceClearLabel {
    if (!_backspaceClearLabel || _backspaceClearLabel.hidden) { return; }
    _backspaceClearLabel.hidden = YES;
    _backspaceClearLabel.alpha = 1.0;
    [self kb_setBackspaceClearHighlighted:NO];
}

- (void)kb_updateBackspaceClearLabelFrame {
    UIView *hostView = [self kb_hostView];
    if (!hostView || !self.backspaceButton || !self.backspaceClearLabel) { return; }
    CGRect btnFrame = [self.backspaceButton convertRect:self.backspaceButton.bounds toView:hostView];
    UILabel *label = self.backspaceClearLabel;
    CGSize textSize = [label sizeThatFits:CGSizeMake(CGFLOAT_MAX, kKBBackspaceClearLabelHeight)];
    CGFloat width = MAX(textSize.width + kKBBackspaceClearLabelPaddingX * 2.0, 60.0);
    CGFloat height = kKBBackspaceClearLabelHeight;
    CGFloat x = CGRectGetMidX(btnFrame) - width * 0.5;
    CGFloat y = CGRectGetMinY(btnFrame) - height - kKBBackspaceClearLabelTopGap;
    if (x < kKBBackspaceClearLabelHorizontalInset) { x = kKBBackspaceClearLabelHorizontalInset; }
    CGFloat maxX = CGRectGetWidth(hostView.bounds) - kKBBackspaceClearLabelHorizontalInset - width;
    if (x > maxX) { x = maxX; }
    if (y < 0) { y = 0; }
    label.frame = CGRectIntegral(CGRectMake(x, y, width, height));
}

- (BOOL)kb_isPointInsideBackspaceClearLabel:(CGPoint)point {
    if (!self.backspaceClearLabel || self.backspaceClearLabel.hidden) { return NO; }
    [self kb_updateBackspaceClearLabelFrame];
    CGRect hitFrame = CGRectInset(self.backspaceClearLabel.frame, -12.0, -10.0);
    return CGRectContainsPoint(hitFrame, point);
}

- (void)kb_setBackspaceClearHighlighted:(BOOL)highlighted {
    if (self.backspaceClearHighlighted == highlighted) { return; }
    self.backspaceClearHighlighted = highlighted;
    [self kb_refreshBackspaceClearLabelColors];
}

- (void)kb_refreshBackspaceClearLabelColors {
    UILabel *label = self.backspaceClearLabel;
    label.textColor = [KBSkinManager shared].current.keyTextColor ?: UIColor.blackColor;
    label.backgroundColor = self.backspaceClearHighlighted
                            ? [self kb_backspaceClearLabelHighlightedColor]
                            : [self kb_backspaceClearLabelNormalColor];
}

- (UIColor *)kb_backspaceClearLabelNormalColor {
    KBSkinTheme *t = [KBSkinManager shared].current;
    return t.keyHighlightBackground ?: [UIColor colorWithWhite:0.9 alpha:1.0];
}

- (UIColor *)kb_backspaceClearLabelHighlightedColor {
    KBSkinTheme *t = [KBSkinManager shared].current;
    return t.accentColor ?: t.keyHighlightBackground ?: [UIColor colorWithWhite:0.8 alpha:1.0];
}

- (void)kb_playLightHaptic {
    if (@available(iOS 10.0, *)) {
        UIImpactFeedbackGenerator *gen = [[UIImpactFeedbackGenerator alloc] initWithStyle:UIImpactFeedbackStyleLight];
        [gen prepare];
        [gen impactOccurred];
    }
}

- (UILabel *)backspaceClearLabel {
    if (!_backspaceClearLabel) {
        UILabel *label = [[UILabel alloc] initWithFrame:CGRectZero];
        label.text = KBLocalized(@"Clear");
        label.textAlignment = NSTextAlignmentCenter;
        label.font = [UIFont systemFontOfSize:16 weight:UIFontWeightSemibold];
        label.textColor = [KBSkinManager shared].current.keyTextColor ?: UIColor.blackColor;
        label.backgroundColor = [self kb_backspaceClearLabelNormalColor];
        label.layer.cornerRadius = kKBBackspaceClearLabelCornerRadius;
        label.layer.masksToBounds = YES;
        label.hidden = YES;
        label.userInteractionEnabled = NO;
        _backspaceClearLabel = label;
    }
    return _backspaceClearLabel;
}

#pragma mark - Clear

- (void)kb_clearAllInput {
    UIResponder *start = (UIResponder *)([self kb_hostView] ?: self.backspaceButton);
    UIInputViewController *ivc = KBFindInputViewController(start);
    if (ivc) {
        id<UITextDocumentProxy> proxy = ivc.textDocumentProxy;
        [[KBInputBufferManager shared] refreshFromProxyIfPossible:proxy];
    }
    self.pendingClearBefore = nil;
    self.pendingClearAfter = nil;
    [[KBInputBufferManager shared] clearPendingClearSnapshot];
    self.backspaceClearToken += 1;
    self.backspaceClearPhase = KBClearPhaseSkipWhitespace;
    NSUInteger token = self.backspaceClearToken;
    [self kb_clearAllInputStepForToken:token guard:0 emptyRounds:0];
}

- (void)kb_clearAllInputStepForToken:(NSUInteger)token
                               guard:(NSInteger)guard
                         emptyRounds:(NSInteger)emptyRounds {
    if (token != self.backspaceClearToken) { return; }
    UIResponder *start = (UIResponder *)([self kb_hostView] ?: self.backspaceButton);
    UIInputViewController *ivc = KBFindInputViewController(start);
    if (!ivc) { return; }
    id<UITextDocumentProxy> proxy = ivc.textDocumentProxy;
    NSInteger nextEmptyRounds = emptyRounds;
    static NSCharacterSet *stopBoundarySet = nil;
    static NSCharacterSet *trailingBoundarySet = nil;
    static NSCharacterSet *trailingWhitespaceSet = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        // stopBoundary: 遇到这些符号就停（不删除它）
        // - 句末符号：. ! ? 。！？
        // - 省略号：…（中文里“……”常用作句/段落的停顿）
        // - 换行：\n \r（段落边界，避免一次“清空”跨段把全文删完）
        stopBoundarySet = [NSCharacterSet characterSetWithCharactersInString:@".!?。！？…\n\r\u2028\u2029"];

        // trailingBoundary: 允许作为“尾部句末符号”先删掉，再继续删上一句（更接近微信体验）
        // 注意：不要把换行/省略号放进来，否则可能跨段/跨停顿继续删。
        trailingBoundarySet = [NSCharacterSet characterSetWithCharactersInString:@".!?。！？"];

        // trailingWhitespace: 只跳过空格/Tab（不包含换行，换行由 stopBoundarySet 处理）
        trailingWhitespaceSet = [NSCharacterSet whitespaceCharacterSet];
    });
    KBClearPhase phase = self.backspaceClearPhase;

    NSInteger deletedThisTick = 0;
    BOOL shouldStop = NO;
    NSString *lastBefore = nil;
    for (NSInteger i = 0; i < kKBBackspaceClearDeletesPerTick; i++) {
        NSString *before = proxy.documentContextBeforeInput ?: @"";
        if (before.length == 0) {
            nextEmptyRounds += 1;
            // 宿主（微信/QQ 等）可能在长文本场景下返回空 context，即使还有很多内容。
            // 为了避免一次“清空”误删全文：一旦拿不到 before，就立刻停止本次清空。
            shouldStop = YES;
            break;
        }
        nextEmptyRounds = 0;

        if (lastBefore && [before isEqualToString:lastBefore] && deletedThisTick > 0) {
            // 宿主未及时刷新 context，留到下一 tick 再继续，避免越界/重复记录
            break;
        }
        lastBefore = before;

        // 取最后一个组合字符
        __block NSString *lastChar = @"";
        [before enumerateSubstringsInRange:NSMakeRange(0, before.length)
                                   options:NSStringEnumerationByComposedCharacterSequences | NSStringEnumerationReverse
                                usingBlock:^(NSString *substring, __unused NSRange substringRange, __unused NSRange enclosingRange, BOOL *stop) {
            lastChar = substring ?: @"";
            *stop = YES;
        }];
        if (lastChar.length == 0) { break; }

        BOOL isWhitespace = ([lastChar rangeOfCharacterFromSet:trailingWhitespaceSet].location != NSNotFound);
        BOOL isStopBoundary = ([lastChar rangeOfCharacterFromSet:stopBoundarySet].location != NSNotFound);
        BOOL isTrailingBoundary = ([lastChar rangeOfCharacterFromSet:trailingBoundarySet].location != NSNotFound);

        if (phase == KBClearPhaseSkipWhitespace) {
            if (isWhitespace) {
                [[KBBackspaceUndoManager shared] captureAndDeleteBackwardFromProxy:proxy count:1];
                [[KBInputBufferManager shared] applyClearDeleteCount:1];
                deletedThisTick += 1;
                continue;
            }
            phase = KBClearPhaseSkipTrailingBoundary;
        }

        if (phase == KBClearPhaseSkipTrailingBoundary) {
            if (isTrailingBoundary) {
                [[KBBackspaceUndoManager shared] captureAndDeleteBackwardFromProxy:proxy count:1];
                [[KBInputBufferManager shared] applyClearDeleteCount:1];
                deletedThisTick += 1;
                continue;
            }
            phase = KBClearPhaseDeleteUntilBoundary;
        }

        // phase == DeleteUntilBoundary
        if (isStopBoundary) {
            shouldStop = YES; // 保留该句末符号
            break;
        }
        [[KBBackspaceUndoManager shared] captureAndDeleteBackwardFromProxy:proxy count:1];
        [[KBInputBufferManager shared] applyClearDeleteCount:1];
        deletedThisTick += 1;
        if (guard + deletedThisTick >= kKBBackspaceClearMaxDeletes) { break; }
        if (deletedThisTick >= kKBBackspaceClearMaxStep) { break; }
    }

    self.backspaceClearPhase = phase;
    NSInteger nextGuard = guard + deletedThisTick;
    if (nextGuard >= kKBBackspaceClearMaxDeletes ||
        nextEmptyRounds > kKBBackspaceClearEmptyContextMaxRounds ||
        shouldStop) {
        return;
    }

    __weak typeof(self) weakSelf = self;
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW,
                                 (int64_t)(kKBBackspaceClearBatchInterval * NSEC_PER_SEC)),
                   dispatch_get_main_queue(), ^{
        __strong typeof(weakSelf) selfStrong = weakSelf;
        [selfStrong kb_clearAllInputStepForToken:token
                                           guard:nextGuard
                                     emptyRounds:nextEmptyRounds];
    });
}

#pragma mark - Helpers

- (UIView *)kb_hostView {
    if (self.containerView) { return self.containerView; }
    return self.backspaceButton.superview;
}

- (void)kb_captureDeletionSnapshotIfNeeded {
    if ([KBBackspaceUndoManager shared].hasUndo) { return; }
    UIResponder *start = (UIResponder *)([self kb_hostView] ?: self.backspaceButton);
    UIInputViewController *ivc = KBFindInputViewController(start);
    if (!ivc) { return; }
    id<UITextDocumentProxy> proxy = ivc.textDocumentProxy;
    [[KBBackspaceUndoManager shared] recordDeletionSnapshotBefore:proxy.documentContextBeforeInput
                                                             after:proxy.documentContextAfterInput];
}

- (void)kb_capturePendingClearSnapshotIfNeeded {
    if (self.pendingClearBefore.length > 0 || self.pendingClearAfter.length > 0) { return; }
    UIResponder *start = (UIResponder *)([self kb_hostView] ?: self.backspaceButton);
    UIInputViewController *ivc = KBFindInputViewController(start);
    if (!ivc) { return; }
    id<UITextDocumentProxy> proxy = ivc.textDocumentProxy;
    self.pendingClearBefore = proxy.documentContextBeforeInput ?: @"";
    self.pendingClearAfter = proxy.documentContextAfterInput ?: @"";
#if DEBUG
    NSLog(@"[kb_capturePendingClearSnapshotIfNeeded/before] len=%lu text=%@", (unsigned long)self.pendingClearBefore.length, self.pendingClearBefore);
    NSLog(@"[kb_capturePendingClearSnapshotIfNeeded/after] len=%lu text=%@", (unsigned long)self.pendingClearAfter.length, self.pendingClearAfter);
#endif
}

@end