keyboard/CustomKeyboard/Utils/KBBackspaceUndoManager.m

//
//  KBBackspaceUndoManager.m
//  CustomKeyboard
//

#import "KBBackspaceUndoManager.h"
#import "KBResponderUtils.h"

NSNotificationName const KBBackspaceUndoStateDidChangeNotification = @"KBBackspaceUndoStateDidChangeNotification";

@interface KBBackspaceUndoManager ()
@property (nonatomic, strong) NSMutableArray<NSString *> *segments; // deletion order (last -> first)
@property (nonatomic, assign) BOOL lastActionWasClear;
@property (nonatomic, assign) BOOL hasUndo;
@end

@implementation KBBackspaceUndoManager

+ (instancetype)shared {
    static KBBackspaceUndoManager *mgr = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        mgr = [[KBBackspaceUndoManager alloc] init];
    });
    return mgr;
}

- (instancetype)init {
    if (self = [super init]) {
        _segments = [NSMutableArray array];
    }
    return self;
}

- (void)recordClearWithContext:(NSString *)context {
    if (context.length == 0) { return; }
    NSString *segment = [self kb_segmentForClearFromContext:context];
    if (segment.length == 0) { return; }

    if (!self.lastActionWasClear) {
        [self.segments removeAllObjects];
    }
    [self.segments addObject:segment];
    self.lastActionWasClear = YES;
    [self kb_updateHasUndo:YES];
}

- (void)performUndoFromResponder:(UIResponder *)responder {
    if (self.segments.count == 0) { return; }
    UIInputViewController *ivc = KBFindInputViewController(responder);
    if (!ivc) { return; }
    id<UITextDocumentProxy> proxy = ivc.textDocumentProxy;
    NSString *text = [self kb_buildUndoText];
    if (text.length == 0) { return; }
    [proxy insertText:text];

    [self.segments removeAllObjects];
    self.lastActionWasClear = NO;
    [self kb_updateHasUndo:NO];
}

- (void)registerNonClearAction {
    self.lastActionWasClear = NO;
    if (self.segments.count == 0) { return; }
    [self.segments removeAllObjects];
    [self kb_updateHasUndo:NO];
}

#pragma mark - Helpers

- (void)kb_updateHasUndo:(BOOL)hasUndo {
    if (self.hasUndo == hasUndo) { return; }
    self.hasUndo = hasUndo;
    [[NSNotificationCenter defaultCenter] postNotificationName:KBBackspaceUndoStateDidChangeNotification object:self];
}

- (NSString *)kb_segmentForClearFromContext:(NSString *)context {
    NSInteger length = context.length;
    if (length == 0) { return @""; }

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

    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;
        }
    }

    NSInteger start = (boundaryIndex == NSNotFound) ? 0 : (boundaryIndex + 1);
    if (start >= length) { return @""; }
    return [context substringFromIndex:start];
}

- (NSString *)kb_buildUndoText {
    if (self.segments.count == 0) { return @""; }
    NSArray<NSString *> *ordered = [[self.segments reverseObjectEnumerator] allObjects];
    NSMutableString *result = [NSMutableString string];
    for (NSInteger i = 0; i < ordered.count; i++) {
        NSString *segment = ordered[i] ?: @"";
        if (segment.length == 0) { continue; }
        if (i < ordered.count - 1) {
            segment = [self kb_replaceTrailingBoundaryWithComma:segment];
        }
        [result appendString:segment];
    }
    return result;
}

- (NSString *)kb_replaceTrailingBoundaryWithComma:(NSString *)segment {
    if (segment.length == 0) { return segment; }

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

    NSInteger idx = segment.length - 1;
    while (idx >= 0) {
        unichar ch = [segment characterAtIndex:idx];
        if ([whitespaceSet characterIsMember:ch]) {
            idx -= 1;
            continue;
        }
        if (![boundarySet characterIsMember:ch]) {
            return segment;
        }
        NSString *comma = [englishBoundarySet characterIsMember:ch] ? @"," : @"，";
        NSMutableString *mutable = [segment mutableCopy];
        NSRange r = NSMakeRange(idx, 1);
        [mutable replaceCharactersInRange:r withString:comma];
        return mutable;
    }

    return segment;
}

@end