#import <AppKit/AppKit.h>
#import <WebKit/WebKit.h>
#import <objc/runtime.h>

// Keep AppKit's system swipe preferences and cancellation thresholds, but use
// script history traversal so asynchronously created Inertia entries aren't skipped.
@interface KanbanNavigation : NSObject
@property(nonatomic, weak) WKWebView *webview;
@property(nonatomic, strong) id monitor;
@property(nonatomic) BOOL pending;
@property(nonatomic) BOOL tracking;
@property(nonatomic) BOOL blocked;
@property(nonatomic) NSUInteger sequence;
@end

@implementation KanbanNavigation
- (BOOL)swipeTrackingEnabled {
    return NSEvent.isSwipeTrackingFromScrollEventsEnabled;
}

- (void)dealloc {
    if (_monitor) [NSEvent removeMonitor:_monitor];
}

- (NSEvent *)handleEvent:(NSEvent *)event {
    WKWebView *webview = self.webview;
    if (!webview || event.window != webview.window || !webview.window.isKeyWindow ||
        webview.hidden || ![self swipeTrackingEnabled]) return event;
    if (event.phase == NSEventPhaseBegan) {
        self.sequence++;
        self.blocked = NO;
        self.pending = NO;
        self.tracking = NO;
    }
    if (self.tracking) return nil;
    if (event.phase == NSEventPhaseEnded || event.phase == NSEventPhaseCancelled) {
        self.sequence++;
        self.pending = NO;
        return event;
    }
    if (self.blocked || self.pending || event.momentumPhase != NSEventPhaseNone ||
        !(event.phase & (NSEventPhaseBegan | NSEventPhaseChanged)) || !event.hasPreciseScrollingDeltas) return event;
    if (fabs(event.scrollingDeltaX) <= fabs(event.scrollingDeltaY)) {
        if (fabs(event.scrollingDeltaY) > 0) self.blocked = YES;
        return event;
    }
    NSPoint point = [webview convertPoint:event.locationInWindow fromView:nil];
    if (!NSPointInRect(point, webview.bounds)) return event;
    if (!webview.isFlipped) point.y = webview.bounds.size.height - point.y;
    NSString *script = [NSString stringWithFormat:@"window.__kanbanNavigation?.canSwipe(%f, %f) === true", point.x, point.y];
    self.pending = YES;
    NSUInteger sequence = self.sequence;
    NSURL *page = webview.URL;
    __weak KanbanNavigation *weakSelf = self;
    [webview evaluateJavaScript:script completionHandler:^(id allowed, NSError *error) {
        KanbanNavigation *owner = weakSelf;
        if (!owner || owner.sequence != sequence) return;
        owner.pending = NO;
        owner.blocked = YES;
        if (error || ![allowed isEqual:@YES] || ![webview.URL isEqual:page] ||
            (!webview.canGoBack && !webview.canGoForward)) return;
        owner.tracking = YES;
        [event trackSwipeEventWithOptions:NSEventSwipeTrackingLockDirection | NSEventSwipeTrackingClampGestureAmount
                dampenAmountThresholdMin:webview.canGoForward ? -1 : 0
                                    max:webview.canGoBack ? 1 : 0
                           usingHandler:^(CGFloat amount, NSEventPhase phase, BOOL complete, BOOL *stop) {
            KanbanNavigation *current = weakSelf;
            if (current.sequence != sequence) {
                *stop = YES;
                return;
            }
            if (!current || !webview.window.isKeyWindow || ![webview.URL isEqual:page]) {
                current.tracking = NO;
                *stop = YES;
                return;
            }
            if (!complete) return;
            current.tracking = NO;
            if (phase == NSEventPhaseCancelled) return;
            NSInteger direction = amount >= 1 ? -1 : amount <= -1 ? 1 : 0;
            if ((direction == -1 && webview.canGoBack) || (direction == 1 && webview.canGoForward)) {
                NSString *navigate = [NSString stringWithFormat:@"if (%@) window.__kanbanNavigation.step(%ld)", script, (long)direction];
                [webview evaluateJavaScript:navigate completionHandler:nil];
            }
        }];
    }];
    return event;
}
@end

void install_workspace_navigation(void *pointer) {
    WKWebView *webview = (__bridge WKWebView *)pointer;
    webview.allowsBackForwardNavigationGestures = NO;
    KanbanNavigation *navigation = [KanbanNavigation new];
    navigation.webview = webview;
    __weak KanbanNavigation *weakNavigation = navigation;
    navigation.monitor = [NSEvent addLocalMonitorForEventsMatchingMask:NSEventMaskScrollWheel handler:^NSEvent *(NSEvent *event) {
        KanbanNavigation *owner = weakNavigation;
        return owner ? [owner handleEvent:event] : event;
    }];
    objc_setAssociatedObject(webview, @selector(handleEvent:), navigation, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}