Web:Component:Cron Added a method for getting the time of the next synchronization

packages/components/Cron/Cron.stories.tsx

@@ -1,6 +1,8 @@
-import React, { useEffect, useState } from "react";
-import i18n from "i18next";
+import React, { useEffect, useMemo, useState } from "react";
 import { initReactI18next } from "react-i18next";
+import i18n from "i18next";
+
+import Cron, { getNextSynchronization } from ".";
 
 import type { Meta, StoryObj } from "@storybook/react";
 
@@ -53,8 +55,6 @@ i18n.use(initReactI18next).init({
   },
 });
 
-import Cron from ".";
-
 type CronType = typeof Cron;
 
 type Story = StoryObj<CronType>;
@@ -88,9 +88,14 @@ export const Default: Story = {
       setValue(defaultValue);
     }, [defaultValue]);
 
+    const date = useMemo(() => cron && getNextSynchronization(cron), [cron]);
+
     return (
       <div>
         <input
+          style={{
+            borderColor: error ? "red" : "black",
+          }}
           value={input}
           onChange={(e) => setInput(e.target.value)}
           onBlur={(e) => setCron(e.target.value)}
@@ -102,6 +107,12 @@ export const Default: Story = {
         <p>
           <strong>Error message: </strong> {error?.message ?? "undefined"}
         </p>
+        {date && (
+          <p>
+            <strong>Next synchronization: </strong>{" "}
+            {date.toUTC().setLocale("en-GB").toFormat("DDDD tt")}
+          </p>
+        )}
       </div>
     );
   },

packages/components/Cron/index.ts

@@ -1 +1,2 @@
 export { default } from "./Cron";
+export { getNextSynchronization } from "./part";

packages/components/Cron/part.ts

@@ -1,8 +1,14 @@
+import { DateTime } from "luxon";
 import { Options, PeriodType } from "./types";
 import { defaultOptions, units } from "./constants";
-import { arrayToStringPart, assertValidArray, stringToArrayPart } from "./util";
+import {
+  arrayToStringPart,
+  assertValidArray,
+  findDate,
+  stringToArrayPart,
+} from "./util";
 
-export const stringToArray = (str: string) => {
+export const stringToArray = (str: string, full = false) => {
   if (typeof str !== "string") {
     throw new Error("Invalid cron string");
   }
@@ -10,7 +16,7 @@ export const stringToArray = (str: string) => {
   if (parts.length !== 5) {
     throw new Error("Invalid cron string format");
   } else {
-    return parts.map((str, idx) => stringToArrayPart(str, units[idx]));
+    return parts.map((str, idx) => stringToArrayPart(str, units[idx], full));
   }
 };
 
@@ -51,3 +57,25 @@ export function getCronStringFromValues(
 
   return parsedArray;
 }
+
+export const getNextSynchronization = (
+  cronString: string,
+  timezone?: string
+) => {
+  const cron = stringToArray(cronString, true);
+  assertValidArray(cron);
+  let date = DateTime.now();
+
+  if (timezone) date = date.setZone(timezone);
+
+  if (!date.isValid) {
+    throw new Error("Invalid timezone provided");
+  }
+
+  if (date.second > 0) {
+    // plus a minute to the date to prevent returning dates in the past
+    date = date.plus({ minute: 1 });
+  }
+
+  return findDate(cron, date);
+};

packages/components/Cron/util.ts

@@ -1,3 +1,4 @@
+import { DateTime } from "luxon";
 import { Options, PeriodType, Unit } from "./types";
 
 export const parseNumber = (value: unknown) => {
@@ -17,7 +18,7 @@ export const parseNumber = (value: unknown) => {
   return undefined;
 };
 
-export const assertValidArray = (arr: unknown) => {
+export const assertValidArray = (arr: unknown): void | never => {
   if (
     arr === undefined ||
     !Array.isArray(arr) ||
@@ -100,8 +101,8 @@ export const arrayToStringPart = (
   return toString(values, unit, options);
 };
 
-export const stringToArrayPart = (str: string, unit: Unit) => {
-  if (str === "*" || str === "*/1") {
+export const stringToArrayPart = (str: string, unit: Unit, full = false) => {
+  if ((str === "*" || str === "*/1") && !full) {
     return [];
   }
 
@@ -332,3 +333,72 @@ const getStep = (values: number[]) => {
 const isFull = (values: number[], unit: Unit) => {
   return values.length === unit.max - unit.min + 1;
 };
+
+const shiftMonth = (arr: number[][], date: DateTime) => {
+  while (arr[3].indexOf(date.month) === -1) {
+    date = date.plus({ months: 1 }).startOf("month");
+  }
+  return date;
+};
+
+const shiftDay = (arr: number[][], date: DateTime): [DateTime, boolean] => {
+  const currentMonth = date.month;
+  while (
+    arr[2].indexOf(date.day) === -1 ||
+    // luxon uses 1-7 for weekdays, but we use 0-6
+    arr[4].indexOf(date.weekday === 7 ? 0 : date.weekday) === -1
+  ) {
+    date = date.plus({ days: 1 }).startOf("day");
+    if (currentMonth !== date.month) {
+      return [date, true];
+    }
+  }
+  return [date, false];
+};
+
+const shiftHour = (arr: number[][], date: DateTime): [DateTime, boolean] => {
+  const currentDay = date.day;
+  while (arr[1].indexOf(date.hour) === -1) {
+    date = date.plus({ hours: 1 }).startOf("hour");
+    if (currentDay !== date.day) {
+      return [date, true];
+    }
+  }
+  return [date, false];
+};
+
+const shiftMinute = (arr: number[][], date: DateTime): [DateTime, boolean] => {
+  const currentHour = date.hour;
+  while (arr[0].indexOf(date.minute) === -1) {
+    date = date.plus({ minutes: 1 }).startOf("minute");
+    if (currentHour !== date.hour) {
+      return [date, true];
+    }
+  }
+  return [date, false];
+};
+
+export const findDate = (arr: number[][], date: DateTime) => {
+  let retry = 24;
+  let monthChanged: boolean;
+  let dayChanged: boolean;
+  let hourChanged: boolean;
+
+  while (--retry) {
+    date = shiftMonth(arr, date);
+    [date, monthChanged] = shiftDay(arr, date);
+    if (!monthChanged) {
+      [date, dayChanged] = shiftHour(arr, date);
+      if (!dayChanged) {
+        [date, hourChanged] = shiftMinute(arr, date);
+        if (!hourChanged) {
+          break;
+        }
+      }
+    }
+  }
+  if (!retry) {
+    throw new Error("Unable to find execution time for schedule");
+  }
+  return date.set({ second: 0, millisecond: 0 });
+};