import { Clutter, St } from '../gi/ext';
import { getEventCoords } from './gnomesupport';

export default class TouchEventHelper {
    private readonly TOUCH_SCROLL_THRESHOLD = 10;

    private _touchStartY: number | null = null;
    private _scrollStartY: number = 0;
    private _isDragging: boolean = false;

    convertPanToScroll(
        event: Clutter.Event,
        scrollView: St.ScrollView,
    ): boolean {
        if (!scrollView.vadjustment) return Clutter.EVENT_PROPAGATE;

        const eventType = event.type();
        const [, y] = getEventCoords(event);

        switch (eventType) {
            case Clutter.EventType.TOUCH_BEGIN:
                this._touchStartY = y;
                this._scrollStartY = scrollView.vadjustment.value;
                this._isDragging = false;
                return Clutter.EVENT_STOP;

            case Clutter.EventType.TOUCH_UPDATE: {
                if (this._touchStartY === null) return Clutter.EVENT_STOP;

                const deltaY = this._touchStartY - y;
                const newScrollYValue = this._scrollStartY + deltaY;
                const adjustment = scrollView.vadjustment;
                const clampedValue = Math.max(
                    0,
                    Math.min(
                        newScrollYValue,
                        adjustment.upper - adjustment.page_size,
                    ),
                );
                adjustment.set_value(clampedValue);

                if (Math.abs(deltaY) > this.TOUCH_SCROLL_THRESHOLD)
                    this._isDragging = true;

                return Clutter.EVENT_STOP;
            }

            case Clutter.EventType.TOUCH_END: {
                const wasDragging = this._isDragging;
                this._touchStartY = null;
                this._isDragging = false;

                // Propagate touch event if we weren't dragging
                return wasDragging
                    ? Clutter.EVENT_STOP
                    : Clutter.EVENT_PROPAGATE;
            }

            default:
                return Clutter.EVENT_PROPAGATE;
        }
    }
}