import { VirtualScroll } from '@web/base';

export const createScrollManager = (container, state, onRenderedListChange) => {
    const vs = VirtualScroll();
    let scrollEl = null;

    const refresh = () => {
        if (!scrollEl) return;
        // Expand the virtual viewport to 1.6x height to create a buffer
        const virtualContainer = { 
            clientHeight: scrollEl.clientHeight * 1.6, 
            scrollTop: scrollEl.scrollTop 
        };
        const res = vs.calc(virtualContainer, state.list);
        if (res) {
            Object.assign(state, {
                prevHeight: res.prevHeight,
                postHeight: res.postHeight,
                _listStartIndex: res.listStartIndex,
                _renderedList: res.renderedList
            });
            onRenderedListChange?.(res.renderedList.length);
        }
    };

    return {
        init: () => {
            scrollEl = container.querySelector('.dt-main');
        },
        reset: (list) => {
            state._listStartIndex = 0;
            state._renderedList = vs.reset(list, scrollEl || container) || [];
            if (state.list === list) {
                vs.init(list, refresh);
            }
        },
        updateRowHeight: (index, node) => {
            // Restore this call so VirtualScroll can learn the actual height
            // of the rows instead of using its 32px default. This fixes
            // layout shifts/jumps when scrolling past the first group.
            vs.update(index + (state._listStartIndex || 0), node);
        },
        refresh,
        onScroll: refresh
    };
};