import { type ScrollingTimeframe } from "$lib/types";
import { type Writable, writable } from "svelte/store";

async function createStore(): Promise<Writable<ScrollingTimeframe> & { next: Function; prev: Function }> {
	const thism = new Date();
	const lastm = new Date();
	thism.setDate(1);
	lastm.setDate(1);
	thism.setMonth(thism.getMonth() - 1);
	lastm.setMonth(lastm.getMonth() - 2);

	const { subscribe, update, set } = writable({ from: lastm, to: thism });
	return {
		subscribe,
		update,
		set,
		next: () => {
			update((frame: ScrollingTimeframe) => {
				const newFrom = new Date(frame.from);
				const newTo = new Date(frame.to);
				newFrom.setMonth(newFrom.getMonth() + 1);
				newTo.setMonth(newTo.getMonth() + 1);
				return { from: newFrom, to: newTo };
			});
		},
		prev: () => {
			update((frame: ScrollingTimeframe) => {
				const newFrom = new Date(frame.from);
				const newTo = new Date(frame.to);
				newFrom.setMonth(newFrom.getMonth() - 1);
				newTo.setMonth(newTo.getMonth() - 1);
				return { from: newFrom, to: newTo };
			});
		},
	};
}

export const scrollingTimeFrameStore = await createStore();