#import "KBInputBufferManager.h"
#import <UIKit/UIKit.h>

#if DEBUG
static NSString *KBLogString2(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_BUF_LOG(tag, text) NSLog(@"❤️=%@", KBLogString2((tag), (text)))
#else
#define KB_BUF_LOG(tag, text) do {} while(0)
#endif

@interface KBInputBufferManager ()
@property (nonatomic, copy, readwrite) NSString *liveText;
@property (nonatomic, copy, readwrite) NSString *manualSnapshot;
@property (nonatomic, copy, readwrite) NSString *pendingClearSnapshot;
@property (nonatomic, assign) BOOL manualSnapshotDirty;
@end

@implementation KBInputBufferManager

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

- (instancetype)init {
    if (self = [super init]) {
        _liveText = @"";
        _manualSnapshot = @"";
        _pendingClearSnapshot = @"";
        _manualSnapshotDirty = NO;
    }
    return self;
}

- (void)seedIfEmptyWithContextBefore:(NSString *)before after:(NSString *)after {
    if (self.liveText.length > 0 || self.manualSnapshot.length > 0) { return; }
    NSString *safeBefore = before ?: @"";
    NSString *safeAfter = after ?: @"";
    NSString *full = [safeBefore stringByAppendingString:safeAfter];
    if (full.length == 0) { return; }
    self.liveText = full;
    self.manualSnapshot = full;
    self.manualSnapshotDirty = NO;
    KB_BUF_LOG(@"seedIfEmpty", full);
}

- (void)updateFromExternalContextBefore:(NSString *)before after:(NSString *)after {
    NSString *safeBefore = before ?: @"";
    NSString *safeAfter = after ?: @"";
    NSString *context = [safeBefore stringByAppendingString:safeAfter];
    if (context.length == 0) { return; }

    // 微信/QQ 等宿主通常只提供光标附近“截断窗口”，不应当作为全文快照。
    // 这里只更新 liveText，给删除/清空逻辑做参考；manualSnapshot 仅由键盘自身输入/撤销来维护。
    self.liveText = context;
    self.manualSnapshotDirty = YES;
#if DEBUG
    static NSUInteger sExternalLogCounter = 0;
    sExternalLogCounter += 1;
    if (sExternalLogCounter % 12 == 0) {
        KB_BUF_LOG(@"updateFromExternalContext/liveOnly", context);
    }
#endif
}

- (void)refreshFromProxyIfPossible:(id<UITextDocumentProxy>)proxy {
    NSString *harvested = [self kb_harvestFullTextFromProxy:proxy];
    if (harvested.length == 0) {
        KB_BUF_LOG(@"refreshFromProxy/failedOrUnsupported", @"");
        return;
    }

    BOOL manualEmpty = (self.manualSnapshot.length == 0);
    BOOL longerThanManual = (harvested.length > self.manualSnapshot.length);
    if (!(manualEmpty || longerThanManual)) {
        KB_BUF_LOG(@"refreshFromProxy/ignoredShorter", harvested);
        return;
    }

    self.liveText = harvested;
    self.manualSnapshot = harvested;
    self.manualSnapshotDirty = NO;
    KB_BUF_LOG(@"refreshFromProxy/accepted", harvested);
}

- (void)prepareSnapshotForDeleteWithContextBefore:(NSString *)before
                                            after:(NSString *)after {
    NSString *safeBefore = before ?: @"";
    NSString *safeAfter = after ?: @"";
    NSString *context = [safeBefore stringByAppendingString:safeAfter];

    BOOL manualValid = (self.manualSnapshot.length > 0 &&
                        (context.length == 0 ||
                         (self.manualSnapshot.length >= context.length &&
                          [self.manualSnapshot rangeOfString:context].location != NSNotFound)));
    if (manualValid) { return; }

    if (self.liveText.length > 0) {
        self.manualSnapshot = self.liveText;
        self.manualSnapshotDirty = NO;
        KB_BUF_LOG(@"prepareSnapshotForDelete/fromLiveText", self.manualSnapshot);
        return;
    }
    if (context.length > 0) {
        self.manualSnapshot = context;
        self.manualSnapshotDirty = NO;
        KB_BUF_LOG(@"prepareSnapshotForDelete/fromContext", self.manualSnapshot);
    }
}

- (void)beginPendingClearSnapshot {
    if (self.pendingClearSnapshot.length > 0) { return; }
    if (self.manualSnapshot.length > 0) {
        self.pendingClearSnapshot = self.manualSnapshot;
        KB_BUF_LOG(@"beginPendingClearSnapshot/fromManual", self.pendingClearSnapshot);
        return;
    }
    if (self.liveText.length > 0) {
        self.pendingClearSnapshot = self.liveText;
        KB_BUF_LOG(@"beginPendingClearSnapshot/fromLive", self.pendingClearSnapshot);
    }
}

- (void)clearPendingClearSnapshot {
    self.pendingClearSnapshot = @"";
}

- (void)resetWithText:(NSString *)text {
    NSString *safe = text ?: @"";
    self.liveText = safe;
    self.manualSnapshot = safe;
    self.pendingClearSnapshot = @"";
    self.manualSnapshotDirty = NO;
    KB_BUF_LOG(@"resetWithText", safe);
}

- (void)appendText:(NSString *)text {
    if (text.length == 0) { return; }
    [self kb_syncManualSnapshotIfNeeded];
    self.liveText = [self.liveText stringByAppendingString:text];
    self.manualSnapshot = [self.manualSnapshot stringByAppendingString:text];
}

- (void)deleteBackwardByCount:(NSUInteger)count {
    if (count == 0) { return; }
    self.liveText = [self kb_stringByDeletingComposedCharacters:count from:self.liveText];
    self.manualSnapshot = [self kb_stringByDeletingComposedCharacters:count from:self.manualSnapshot];
}

- (void)replaceTailWithText:(NSString *)text deleteCount:(NSUInteger)count {
    [self kb_syncManualSnapshotIfNeeded];
    [self deleteBackwardByCount:count];
    [self appendText:text];
}

- (void)applyHoldDeleteCount:(NSUInteger)count {
    if (count == 0) { return; }
    self.liveText = [self kb_stringByDeletingComposedCharacters:count from:self.liveText];
    self.manualSnapshotDirty = YES;
}

- (void)applyClearDeleteCount:(NSUInteger)count {
    if (count == 0) { return; }
    self.liveText = [self kb_stringByDeletingComposedCharacters:count from:self.liveText];
    self.manualSnapshotDirty = YES;
}

- (void)clearAllLiveText {
    self.liveText = @"";
    self.pendingClearSnapshot = @"";
    self.manualSnapshotDirty = YES;
}

- (void)commitLiveToManual {
    self.manualSnapshot = self.liveText ?: @"";
    self.manualSnapshotDirty = NO;
    KB_BUF_LOG(@"commitLiveToManual", self.manualSnapshot);
}

- (void)restoreManualSnapshot {
    self.liveText = self.manualSnapshot ?: @"";
}

#pragma mark - Helpers

- (void)kb_syncManualSnapshotIfNeeded {
    if (!self.manualSnapshotDirty) { return; }
    self.manualSnapshot = self.liveText ?: @"";
    self.manualSnapshotDirty = NO;
}

- (NSString *)kb_stringByDeletingComposedCharacters:(NSUInteger)count
                                               from:(NSString *)text {
    if (count == 0) { return text ?: @""; }
    NSString *source = text ?: @"";
    if (source.length == 0) { return @""; }

    __block NSUInteger removed = 0;
    __block NSUInteger endIndex = source.length;
    [source enumerateSubstringsInRange:NSMakeRange(0, source.length)
                               options:NSStringEnumerationByComposedCharacterSequences | NSStringEnumerationReverse
                            usingBlock:^(__unused NSString *substring, NSRange substringRange, __unused NSRange enclosingRange, BOOL *stop) {
        removed += 1;
        endIndex = substringRange.location;
        if (removed >= count) {
            *stop = YES;
        }
    }];
    if (removed < count) { return @""; }
    return [source substringToIndex:endIndex];
}

- (NSString *)kb_harvestFullTextFromProxy:(id<UITextDocumentProxy>)proxy {
    if (!proxy) { return @""; }
    if (![proxy respondsToSelector:@selector(adjustTextPositionByCharacterOffset:)]) { return @""; }

    static const NSInteger kKBHarvestMaxRounds = 160;
    static const NSInteger kKBHarvestMaxChars = 50000;

    NSInteger movedToEnd = 0;
    NSInteger movedLeft = 0;
    NSMutableArray<NSString *> *chunks = [NSMutableArray array];
    NSInteger totalChars = 0;

    @try {
        NSInteger guard = 0;
        NSString *after = proxy.documentContextAfterInput ?: @"";
        while (after.length > 0 && guard < kKBHarvestMaxRounds) {
            NSInteger step = (NSInteger)after.length;
            [(id)proxy adjustTextPositionByCharacterOffset:step];
            movedToEnd += step;
            guard += 1;
            after = proxy.documentContextAfterInput ?: @"";
        }

        guard = 0;
        NSString *before = proxy.documentContextBeforeInput ?: @"";
        while (before.length > 0 && guard < kKBHarvestMaxRounds && totalChars < kKBHarvestMaxChars) {
            [chunks addObject:before];
            totalChars += (NSInteger)before.length;
            NSInteger step = (NSInteger)before.length;
            [(id)proxy adjustTextPositionByCharacterOffset:-step];
            movedLeft += step;
            guard += 1;
            before = proxy.documentContextBeforeInput ?: @"";
        }
    } @finally {
        if (movedLeft != 0) {
            [(id)proxy adjustTextPositionByCharacterOffset:movedLeft];
        }
        if (movedToEnd != 0) {
            [(id)proxy adjustTextPositionByCharacterOffset:-movedToEnd];
        }
    }

    if (chunks.count == 0) { return @""; }
    NSMutableString *result = [NSMutableString stringWithCapacity:(NSUInteger)totalChars];
    for (NSInteger i = (NSInteger)chunks.count - 1; i >= 0; i--) {
        NSString *part = chunks[(NSUInteger)i] ?: @"";
        if (part.length == 0) { continue; }
        [result appendString:part];
    }
    return result;
}

@end