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

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

NSNotificationName const KBBackspaceUndoStateDidChangeNotification = @"KBBackspaceUndoStateDidChangeNotification";

@interface KBBackspaceUndoManager ()
@property (nonatomic, copy) NSString *undoText;
@property (nonatomic, assign) NSInteger undoAfterLength;
@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]) {
        _undoText = @"";
        _undoAfterLength = 0;
    }
    return self;
}

- (void)recordDeletionSnapshotBefore:(NSString *)before after:(NSString *)after {
    if (self.undoText.length > 0) { return; }
    NSString *safeBefore = before ?: @"";
    NSString *safeAfter = after ?: @"";
    NSString *full = [safeBefore stringByAppendingString:safeAfter];
    if (full.length == 0) { return; }
    self.undoText = full;
    self.undoAfterLength = (NSInteger)safeAfter.length;
}

- (void)recordClearWithContextBefore:(NSString *)before after:(NSString *)after {
    if (self.undoText.length == 0) {
        NSString *safeBefore = before ?: @"";
        NSString *safeAfter = after ?: @"";
        NSString *full = [safeBefore stringByAppendingString:safeAfter];
        if (full.length > 0) {
            self.undoText = full;
            self.undoAfterLength = (NSInteger)safeAfter.length;
        }
    }
    if (self.undoText.length == 0) { return; }
    [self kb_updateHasUndo:YES];
}

- (void)performUndoFromResponder:(UIResponder *)responder {
    if (self.undoText.length == 0) { return; }
    UIInputViewController *ivc = KBFindInputViewController(responder);
    if (!ivc) { return; }
    id<UITextDocumentProxy> proxy = ivc.textDocumentProxy;
    [self kb_clearAllTextForProxy:proxy];
    [proxy insertText:self.undoText];
    if (self.undoAfterLength > 0 &&
        [proxy respondsToSelector:@selector(adjustTextPositionByCharacterOffset:)]) {
        [proxy adjustTextPositionByCharacterOffset:-self.undoAfterLength];
    }

    self.undoText = @"";
    self.undoAfterLength = 0;
    [self kb_updateHasUndo:NO];
}

- (void)registerNonClearAction {
    if (self.undoText.length == 0) { return; }
    self.undoText = @"";
    self.undoAfterLength = 0;
    [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];
}

static const NSInteger kKBUndoClearMaxRounds = 200;

- (void)kb_clearAllTextForProxy:(id<UITextDocumentProxy>)proxy {
    if (!proxy) { return; }

    if ([proxy respondsToSelector:@selector(adjustTextPositionByCharacterOffset:)]) {
        NSInteger guard = 0;
        NSString *contextAfter = proxy.documentContextAfterInput ?: @"";
        while (contextAfter.length > 0 && guard < kKBUndoClearMaxRounds) {
            NSInteger offset = (NSInteger)contextAfter.length;
            [proxy adjustTextPositionByCharacterOffset:offset];
            for (NSUInteger i = 0; i < contextAfter.length; i++) {
                [proxy deleteBackward];
            }
            guard += 1;
            contextAfter = proxy.documentContextAfterInput ?: @"";
        }
    }

    NSInteger guard = 0;
    NSString *contextBefore = proxy.documentContextBeforeInput ?: @"";
    while (contextBefore.length > 0 && guard < kKBUndoClearMaxRounds) {
        for (NSUInteger i = 0; i < contextBefore.length; i++) {
            [proxy deleteBackward];
        }
        guard += 1;
        contextBefore = proxy.documentContextBeforeInput ?: @"";
    }
}

@end