export const keys = (ks, obj) =>
	ks.reduce(
		(ret, k) =>
			obj.hasOwnProperty(k) ?  {...ret, [k]: obj[k]} : ret,
		{},
	);

export const difference = (a, b) => {
	const diff = new Set(a);
	for (const el of b) {
		diff.delete(el);
	}
	return diff;
};

export const assocIn = (obj, path, value) =>
	path.length === 0 ?  obj :
		path.length === 1 ? { ...obj, [path[0]]: value } :
			{
				...obj,
				[path[0]]: assocIn(
					(obj[path[0]] || {}),
					path.slice(1),
					value
				)
			};

export const dissoc = (obj, key) => {
	const ret = { ...obj };
	delete ret[key]
	return ret;
};

export const getIn = (obj, path) =>
	path.length === 0 ? obj :
		getIn(obj?.[path[0]], path.slice(1));

export const findFirst = (arr, fn) => {
	for (const x of arr) {
		const ret = fn(x);
		if (ret) {
			return ret;
		}
	}

	return null;
};

export const partial = (fn, ...startArgs) =>
	(...endArgs) =>
		fn(...startArgs, ...endArgs);

export const strSortFn = (a, b) => a.localeCompare(b, "POSIX");

export const undefinedAsNull = x => x === undefined ? null : x;

export const first   = a => a[0];
export const rest    = a => a.slice(1);
export const butlast = a => a.slice(a, a.length - 1);
export const last    = a => a[a.length - 1];