import { writable } from 'svelte/store';
import type { Unsubscriber, Subscriber, Invalidator } from 'svelte/store';

const isClient = typeof window !== 'undefined';

export function useUrlSearchParams<T extends Record<string,string>>(
	mode: 'history' | 'hash' | 'hash-params' = 'history',
	options?: {
		write?: boolean;
		writeMode?: 'replace'|'push';
		removeNullishValues?: boolean;
		removeFalsyValues?: boolean;
		initialValue?: Partial<T>;
		stringify?: (params: URLSearchParams) => string;
		windowRef?: Window;
	}
): {
		subscribe: (
			this: void, run: Subscriber<T>, invalidate?: Invalidator<T> | undefined) => Unsubscriber;
		setParams: (obj: Partial<T>) => void;
} {
	const {
		write = true,
		writeMode = 'replace',
		removeNullishValues = true,
		removeFalsyValues = false,
		initialValue = {} as Partial<T>,
		stringify,
		windowRef = isClient ? window : undefined as any
	} = options ?? {};
	const store = writable<T>({} as T);

	function read() {
		if (!isClient || !windowRef) return;
		let search = '';
		if (mode === 'history') search = windowRef.location.search;
		else if (mode === 'hash') search = windowRef.location.hash.replace(/^#/, '');
		else if (mode === 'hash-params') search = windowRef.location.hash.split('?')[1] ?? '';
		const params = new URLSearchParams(search);
		for (const [k,v] of Object.entries(initialValue)) {
			if (!params.has(k) && v !== undefined) params.set(k, String(v));
		}
		const obj: Record<string,string> = {};
		params.forEach((v,k) => {
			if (v === null && removeNullishValues) return;
			if (!v && removeFalsyValues) return;
			obj[k] = v;
		});
		store.set(obj as T);
	}

	function writeUrl(params: URLSearchParams) {
		if (!windowRef || !write) return;
		const q = stringify ? stringify(params) : params.toString();
		let url = '';

		if (mode === 'history') {
			url = `${windowRef.location.pathname}${q ? '?' + q : ''}`;
		} else if (mode === 'hash') {
			url = `#${q}`;
		} else {
			url = `${windowRef.location.pathname}#${q}`;
		}

		windowRef.history[writeMode + 'State']({}, '', url);
	}

	function updateStore(obj: Partial<T>): void {
		store.update(prev => {
			const next = { ...prev, ...obj } as T;
			const params = new URLSearchParams();

			Object.entries(next).forEach(([k,v])=> {
				if (v == null && removeNullishValues) return;
				if (!v && removeFalsyValues) return;
				params.set(k, String(v));
			});

			writeUrl(params);

			return next;
		});
	}

	if (isClient && windowRef) {
		windowRef.addEventListener('popstate', read);
		read();
	} else {
		store.set(initialValue as T);
	}

	return {
		subscribe: store.subscribe,
		setParams: updateStore,
	};
}