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

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

NSNotificationName const KBBackspaceUndoStateDidChangeNotification = @"KBBackspaceUndoStateDidChangeNotification";

#if DEBUG
static NSString *KBLogString(NSString *tag, NSString *text) {
    NSString *safeTag = tag ?: @"";
    NSString *safeText = text ?: @"";
    if (safeText.length <= 2000) {
        return [NSString stringWithFormat:@"[%@] len=%lu text=%@", safeTag, (unsigned long)safeText.length, safeText];
    }
    NSString *head = [safeText substringToIndex:800];
    NSString *tail = [safeText substringFromIndex:safeText.length - 800];
    return [NSString stringWithFormat:@"[%@] len=%lu head=%@ ... tail=%@", safeTag, (unsigned long)safeText.length, head, tail];
}
#define KB_UNDO_LOG(tag, text) NSLog(@"%@", KBLogString((tag), (text)))
#else
#define KB_UNDO_LOG(tag, text) do {} while(0)
#endif

typedef NS_ENUM(NSInteger, KBUndoSnapshotSource) {
    KBUndoSnapshotSourceNone = 0,
    KBUndoSnapshotSourceDeletionSnapshot,
    KBUndoSnapshotSourceClear
};

@interface KBBackspaceUndoManager ()
@property (nonatomic, copy) NSString *undoText;
@property (nonatomic, assign) NSInteger undoAfterLength;
@property (nonatomic, assign) BOOL hasUndo;
@property (nonatomic, assign) KBUndoSnapshotSource snapshotSource;
@property (nonatomic, strong) NSMutableArray<NSString *> *undoDeletedPieces;
@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;
        _snapshotSource = KBUndoSnapshotSourceNone;
        _undoDeletedPieces = [NSMutableArray array];
    }
    return self;
}

- (void)captureAndDeleteBackwardFromProxy:(id<UITextDocumentProxy>)proxy count:(NSUInteger)count {
    if (!proxy || count == 0) { return; }

    NSString *selected = proxy.selectedText ?: @"";
    NSString *ctxBefore = proxy.documentContextBeforeInput ?: @"";
    NSString *ctxAfter = proxy.documentContextAfterInput ?: @"";
    NSUInteger ctxLen = ctxBefore.length + ctxAfter.length;
    BOOL isSelectAllLike = (selected.length > 0 &&
                            (ctxLen == 0 || selected.length >= MAX((NSUInteger)40, ctxLen * 2)));
    if (isSelectAllLike) {
        // “全选删除”在微信/QQ中通常拿不到可靠的全文，因此禁用撤销，避免插回错误/不完整内容。
        if (self.hasUndo) {
            [self registerNonClearAction];
        }
#if DEBUG
        KB_UNDO_LOG(@"captureAndDelete/selectAllDisableUndo", selected);
#endif
        [proxy deleteBackward];
        [[KBInputBufferManager shared] resetWithText:@""];
        return;
    }

    if (!self.hasUndo) {
        [self.undoDeletedPieces removeAllObjects];
        self.undoText = @"";
        self.undoAfterLength = 0;
        self.snapshotSource = KBUndoSnapshotSourceDeletionSnapshot;
        [self kb_updateHasUndo:YES];
    }

    BOOL didAppend = NO;
    NSString *lastObservedBefore = nil;
    for (NSUInteger i = 0; i < count; i++) {
        NSString *before = proxy.documentContextBeforeInput ?: @"";
        if (before.length > 0) {
            // 若宿主在同一 runloop 内不更新 context，则跳过记录，避免把同一个字符重复记录成“多句”。
            if (lastObservedBefore && [before isEqualToString:lastObservedBefore]) {
                // still delete, but don't record
            } else {
                NSString *piece = [self kb_lastComposedCharacterFromString:before];
                if (piece.length > 0) {
                    [self.undoDeletedPieces addObject:piece];
                    didAppend = YES;
                }
                lastObservedBefore = before;
            }
        }
        [proxy deleteBackward];
    }

#if DEBUG
    if (didAppend) {
        NSUInteger piecesCount = self.undoDeletedPieces.count;
        if (piecesCount <= 20) {
            KB_UNDO_LOG(@"captureAndDelete/undoInsertTextNow", [self kb_buildUndoInsertTextFromPieces]);
        } else if (piecesCount % 50 == 0) {
            NSString *lastPiece = self.undoDeletedPieces.lastObject ?: @"";
            NSLog(@"[captureAndDelete/undoPieces] pieces=%lu lastPiece=%@",
                  (unsigned long)piecesCount,
                  lastPiece);
        }
    }
#endif
}

- (void)recordDeletionSnapshotBefore:(NSString *)before after:(NSString *)after {
    if (self.hasUndo) { return; }
    NSString *pending = [KBInputBufferManager shared].pendingClearSnapshot;
    NSString *manual = [KBInputBufferManager shared].manualSnapshot;
    NSString *fallbackText = (pending.length > 0) ? pending : ((manual.length > 0) ? manual : [KBInputBufferManager shared].liveText);
    if (fallbackText.length > 0) {
        self.undoText = fallbackText;
        self.undoAfterLength = 0;
        self.snapshotSource = KBUndoSnapshotSourceDeletionSnapshot;
        KB_UNDO_LOG(@"recordDeletionSnapshot/fallback", self.undoText);
        [self kb_updateHasUndo:YES];
        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;
    self.snapshotSource = KBUndoSnapshotSourceDeletionSnapshot;
    KB_UNDO_LOG(@"recordDeletionSnapshot/context", self.undoText);
    [self kb_updateHasUndo:YES];
}

- (void)recordClearWithContextBefore:(NSString *)before after:(NSString *)after {
    NSString *pending = [KBInputBufferManager shared].pendingClearSnapshot;
    NSString *manual = [KBInputBufferManager shared].manualSnapshot;
    NSString *fallbackText = (pending.length > 0) ? pending : ((manual.length > 0) ? manual : [KBInputBufferManager shared].liveText);

    NSString *safeBefore = before ?: @"";
    NSString *safeAfter = after ?: @"";
    NSString *contextText = [[safeBefore stringByAppendingString:safeAfter] copy];

    NSString *candidate = (fallbackText.length > 0) ? fallbackText : contextText;
    NSInteger candidateAfterLen = (fallbackText.length > 0) ? 0 : (NSInteger)safeAfter.length;

    if (candidate.length == 0) { return; }

    KB_UNDO_LOG(@"recordClear/candidate", candidate);

    if (self.undoText.length > 0) {
        if (self.snapshotSource == KBUndoSnapshotSourceClear) {
            KB_UNDO_LOG(@"recordClear/ignored(alreadyClear)", self.undoText);
            [self kb_updateHasUndo:YES];
            return;
        }
        if (self.snapshotSource == KBUndoSnapshotSourceDeletionSnapshot) {
            if (candidate.length > self.undoText.length) {
                self.undoText = candidate;
                self.undoAfterLength = candidateAfterLen;
                KB_UNDO_LOG(@"recordClear/upgradedFromDeletion", self.undoText);
            } else {
                KB_UNDO_LOG(@"recordClear/keepDeletionSnapshot", self.undoText);
            }
            self.snapshotSource = KBUndoSnapshotSourceClear;
            [self kb_updateHasUndo:YES];
            return;
        }
    }

    self.undoText = candidate;
    self.undoAfterLength = candidateAfterLen;
    self.snapshotSource = KBUndoSnapshotSourceClear;
    KB_UNDO_LOG(@"recordClear/set", self.undoText);
    [self kb_updateHasUndo:YES];
}

- (void)performUndoFromResponder:(UIResponder *)responder {
    if (!self.hasUndo) { return; }
    UIInputViewController *ivc = KBFindInputViewController(responder);
    if (!ivc) { return; }
    id<UITextDocumentProxy> proxy = ivc.textDocumentProxy;
    NSString *curBefore = proxy.documentContextBeforeInput ?: @"";
    NSString *curAfter = proxy.documentContextAfterInput ?: @"";
    KB_UNDO_LOG(@"performUndo/currentBefore", curBefore);
    KB_UNDO_LOG(@"performUndo/currentAfter", curAfter);
    NSString *insertText = [self kb_buildUndoInsertTextFromPieces];
    if (insertText.length > 0) {
        KB_UNDO_LOG(@"performUndo/insertDeletedText", insertText);
        [proxy insertText:insertText];
        [[KBInputBufferManager shared] appendText:insertText];
    } else if (self.undoText.length > 0) {
        KB_UNDO_LOG(@"performUndo/fallbackUndoText", self.undoText);
        [self kb_clearAllTextForProxy:proxy];
        [proxy insertText:self.undoText];
        if (self.undoAfterLength > 0 &&
            [proxy respondsToSelector:@selector(adjustTextPositionByCharacterOffset:)]) {
            [proxy adjustTextPositionByCharacterOffset:-self.undoAfterLength];
        }
        [[KBInputBufferManager shared] resetWithText:self.undoText];
    } else {
        return;
    }
    self.undoText = @"";
    self.undoAfterLength = 0;
    self.snapshotSource = KBUndoSnapshotSourceNone;
    [self.undoDeletedPieces removeAllObjects];
    [self kb_updateHasUndo:NO];
}

- (void)registerNonClearAction {
    if (!self.hasUndo) { return; }
    if (self.undoText.length > 0) {
        KB_UNDO_LOG(@"registerNonClearAction/clearUndoText", self.undoText);
    }
    if (self.undoDeletedPieces.count > 0) {
        KB_UNDO_LOG(@"registerNonClearAction/clearDeletedPieces", [self kb_buildUndoInsertTextFromPieces]);
    }
    self.undoText = @"";
    self.undoAfterLength = 0;
    self.snapshotSource = KBUndoSnapshotSourceNone;
    [self.undoDeletedPieces 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_lastComposedCharacterFromString:(NSString *)text {
     if (text.length == 0) { return @""; }
     __block NSString *last = @"";
     [text enumerateSubstringsInRange:NSMakeRange(0, text.length)
                              options:NSStringEnumerationByComposedCharacterSequences | NSStringEnumerationReverse
                           usingBlock:^(NSString *substring, __unused NSRange substringRange, __unused NSRange enclosingRange, BOOL *stop) {
         last = substring ?: @"";
         *stop = YES;
     }];
     return last ?: @"";
 }

- (NSString *)kb_buildUndoInsertTextFromPieces {
    if (self.undoDeletedPieces.count == 0) { return @""; }
    NSMutableString *result = [NSMutableString string];
    for (NSInteger i = (NSInteger)self.undoDeletedPieces.count - 1; i >= 0; i--) {
         NSString *piece = self.undoDeletedPieces[(NSUInteger)i] ?: @"";
         if (piece.length == 0) { continue; }
         [result appendString:piece];
     }
     return result;
 }

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