// @flow

/**
 * SET_INTERVAL constant is used to set interval and it is set in
 * the id property of the request.data property. TimeMs property must
 * also be set. Request.data example:
 *
 * {
 *      id: SET_INTERVAL,
 *      timeMs: 33
 * }.
 */
export const SET_INTERVAL = 1;

/**
 * CLEAR_INTERVAL constant is used to clear the interval and it is set in
 * the id property of the request.data property.
 *
 * {
 *      id: CLEAR_INTERVAL
 * }.
 */
export const CLEAR_INTERVAL = 2;

/**
 * INTERVAL_TIMEOUT constant is used as response and it is set in the id
 * property.
 *
 * {
 *      id: INTERVAL_TIMEOUT
 * }.
 */
export const INTERVAL_TIMEOUT = 3;

/**
 * The following code is needed as string to create a URL from a Blob.
 * The URL is then passed to a WebWorker. Reason for this is to enable
 * use of setInterval that is not throttled when tab is inactive.
 */
const code = `
    var timer;

    onmessage = function(request) {
        switch (request.data.id) {
        case ${SET_INTERVAL}: {
            timer = setInterval(() => {
                postMessage({ id: ${INTERVAL_TIMEOUT} });
            }, request.data.timeMs);
            break;
        }
        case ${CLEAR_INTERVAL}: {
            if (timer) {
                clearInterval(timer);
            }
            break;
        }
        }
    };
`;

export const timerWorkerScript
    = URL.createObjectURL(new Blob([ code ], { type: 'application/javascript' }));