import { ScrollView, type Component } from "@earendil-works/pi-tui";

/** Overlay-local clipping: ordinary overlays do not enter Pi's scroll layout traversal. */
export class FleetViewport {
	private readonly body: Component & { lines: string[] } = {
		lines: [],
		render() { return this.lines; },
		invalidate() {},
	};
	readonly scroll = new ScrollView(this.body, { follow: "end", overscroll: "contain" });

	private readonly requestRender: () => void;
	private resetTopOnLayout = false;

	constructor(requestRender: () => void) {
		this.requestRender = requestRender;
	}

	render(lines: string[], width: number, height: number): string[] {
		this.body.lines = lines;
		const rendered = this.scroll.render(width);
		this.scroll.updateLayout(rendered.length, height, this.requestRender);
		if (this.resetTopOnLayout) {
			this.resetTopOnLayout = false;
			this.scroll.scrollTo(0, { disableFollow: true });
		}
		return rendered.slice(this.scroll.scrollTop, this.scroll.scrollTop + this.scroll.viewportHeight);
	}

	resetTop(): void {
		// Apply again after the new view's dimensions arrive: disableFollow suppresses following
		// at the actual content end, which may differ from the previous view's end.
		this.resetTopOnLayout = true;
		this.scroll.scrollTo(0, { disableFollow: true });
	}

	follow(): void {
		this.resetTopOnLayout = false;
		this.scroll.scrollToEnd();
	}
}