export function noop() {}

export const identity = x => x;

export function assign<T, S>(tar:T, src:S): T & S {
	// @ts-ignore
	for (const k in src) tar[k] = src[k];
	return tar as T & S;
}

export function is_promise<T = any>(value: any): value is PromiseLike<T> {
	return value && typeof value === 'object' && typeof value.then === 'function';
}

export function add_location(element, file, line, column, char) {
	element.__svelte_meta = {
		loc: { file, line, column, char }
	};
}

export function run(fn) {
	return fn();
}

export function blank_object() {
	return Object.create(null);
}

export function run_all(fns) {
	fns.forEach(run);
}

export function is_function(thing: any): thing is Function {
	return typeof thing === 'function';
}

export function safe_not_equal(a, b) {
	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
}

export function not_equal(a, b) {
	return a != a ? b == b : a !== b;
}

export function validate_store(store, name) {
	if (!store || typeof store.subscribe !== 'function') {
		throw new Error(`'${name}' is not a store with a 'subscribe' method`);
	}
}

export function subscribe(component, store, callback) {
	const unsub = store.subscribe(callback);

	component.$$.on_destroy.push(unsub.unsubscribe
		? () => unsub.unsubscribe()
		: unsub);
}

export function create_slot(definition, ctx, fn) {
	if (definition) {
		const slot_ctx = get_slot_context(definition, ctx, fn);
		return definition[0](slot_ctx);
	}
}

export function get_slot_context(definition, ctx, fn) {
	return definition[1]
		? assign({}, assign(ctx.$$scope.ctx, definition[1](fn ? fn(ctx) : {})))
		: ctx.$$scope.ctx;
}

export function get_slot_changes(definition, ctx, changed, fn) {
	return definition[1]
		? assign({}, assign(ctx.$$scope.changed || {}, definition[1](fn ? fn(changed) : {})))
		: ctx.$$scope.changed || {};
}

export function exclude_internal_props(props) {
	const result = {};
	for (const k in props) if (k[0] !== '$') result[k] = props[k];
	return result;
}

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

export let now: () => number = is_client
	? () => window.performance.now()
	: () => Date.now();

export let raf = is_client ? requestAnimationFrame : noop;

// used internally for testing
export function set_now(fn) {
	now = fn;
}

export function set_raf(fn) {
	raf = fn;
}