[N8N-4339] Unify all Cron-specific code. Improve typing, and add tests. (#3887)

packages/workflow/src/Cron.ts

@@ -0,0 +1,68 @@
+interface BaseTriggerTime<T extends string> {
+	mode: T;
+}
+
+type CronExpression = string;
+interface CustomTrigger extends BaseTriggerTime<'custom'> {
+	cronExpression: CronExpression;
+}
+
+interface EveryX<U extends string> extends BaseTriggerTime<'everyX'> {
+	unit: U;
+	value: number;
+}
+
+type EveryMinute = BaseTriggerTime<'everyMinute'>;
+type EveryXMinutes = EveryX<'minutes'>;
+
+interface EveryHour extends BaseTriggerTime<'everyHour'> {
+	minute: number; // 0 - 59
+}
+type EveryXHours = EveryX<'hours'>;
+
+interface EveryDay extends BaseTriggerTime<'everyDay'> {
+	hour: number; // 0 - 23
+	minute: number; // 0 - 59
+}
+
+interface EveryWeek extends BaseTriggerTime<'everyWeek'> {
+	hour: number; // 0 - 23
+	minute: number; // 0 - 59
+	weekday: number; // 0 - 6(Sun - Sat)
+}
+
+interface EveryMonth extends BaseTriggerTime<'everyMonth'> {
+	hour: number; // 0 - 23
+	minute: number; // 0 - 59
+	dayOfMonth: number; // 1 - 31
+}
+
+export type TriggerTime =
+	| CustomTrigger
+	| EveryMinute
+	| EveryXMinutes
+	| EveryHour
+	| EveryXHours
+	| EveryDay
+	| EveryWeek
+	| EveryMonth;
+
+const randomSecond = () => Math.floor(Math.random() * 60).toString();
+
+export const toCronExpression = (item: TriggerTime): CronExpression => {
+	if (item.mode === 'everyMinute') return `${randomSecond()} * * * * *`;
+	if (item.mode === 'everyHour') return `${randomSecond()} ${item.minute} * * * *`;
+
+	if (item.mode === 'everyX') {
+		if (item.unit === 'minutes') return `${randomSecond()} */${item.value} * * * *`;
+		if (item.unit === 'hours') return `${randomSecond()} 0 */${item.value} * * *`;
+	}
+	if (item.mode === 'everyDay') return `${randomSecond()} ${item.minute} ${item.hour} * * *`;
+	if (item.mode === 'everyWeek')
+		return `${randomSecond()} ${item.minute} ${item.hour} * * ${item.weekday}`;
+
+	if (item.mode === 'everyMonth')
+		return `${randomSecond()} ${item.minute} ${item.hour} ${item.dayOfMonth} * *`;
+
+	return item.cronExpression.trim();
+};