export class Backoff {

// For testing purposes, assign to overwrite the provided value by param

static __TEST__BASE_MILLIS?: number;

static __TEST__MAX_MILLIS?: number;

static DEFAULT_BASE_MILLIS = 1000; // 1 second

static DEFAULT_MAX_MILLIS = 1800000; // 30 minutes

baseMillis: number;

maxMillis: number;

attempts: number;

cb: (...args: any[]) => any;

timeoutID: ReturnType<typeof setTimeout> | undefined;

/**

* Schedule function calls with exponential backoff

*/

constructor(cb: (...args: any[]) => any, baseMillis?: number, maxMillis?: number) {

this.baseMillis = Backoff.__TEST__BASE_MILLIS || baseMillis || Backoff.DEFAULT_BASE_MILLIS;

this.maxMillis = Backoff.__TEST__MAX_MILLIS || maxMillis || Backoff.DEFAULT_MAX_MILLIS;

this.attempts = 0;

this.cb = cb;

}

/**

* Schedule a next call to `cb`

* @returns scheduled delay in milliseconds

*/

scheduleCall() {

let delayInMillis = Math.min(this.baseMillis * Math.pow(2, this.attempts), this.maxMillis);

if (this.timeoutID) clearTimeout(this.timeoutID);

this.timeoutID = setTimeout(() => {

this.timeoutID = undefined;

this.cb();

}, delayInMillis);

this.attempts++;

return delayInMillis;

}

reset() {

this.attempts = 0;

if (this.timeoutID) {

clearTimeout(this.timeoutID);

this.timeoutID = undefined;

}

}

}