import { useMemo } from "react";

export type UseVirtualTextOptions = {
	text: string[];
	viewportHeight: number;
	scrollOffset: number;
};

export type UseVirtualTextResult = {
	visibleText: string[];
	totalLines: number;
	offset: number;
};

export function useVirtualText({ text, viewportHeight, scrollOffset }: UseVirtualTextOptions): UseVirtualTextResult {
	return useMemo(() => {
		let totalLines = text.length;
		if (viewportHeight <= 0) {
			return { visibleText: [], totalLines, offset: 0 };
		}

		let maxOffset = Math.max(totalLines - viewportHeight, 0);
		let clampedOffset = Math.min(Math.max(scrollOffset, 0), maxOffset);
		let end = Math.min(clampedOffset + viewportHeight, totalLines);

		return {
			visibleText: text.slice(clampedOffset, end),
			totalLines,
			offset: clampedOffset,
		};
	}, [scrollOffset, text, viewportHeight]);
}