feat(recurring-tasks): implement recurring tasks service with timezone support and notifications

- Added a new service for managing recurring tasks, allowing configuration of task schedules with timezone support.
- Introduced job queues for processing recurring tasks and handling task creation in bulk.
- Implemented notification system to alert users about newly created recurring tasks, including email and in-app notifications.
- Enhanced database schema with new tables for notifications and audit logs to track recurring task operations.
- Updated frontend components to support timezone selection and manage excluded dates for recurring tasks.
- Refactored existing code to integrate new features and improve overall task management experience.

worklenz-backend/src/utils/timezone-utils.ts

@@ -0,0 +1,156 @@
+import moment from "moment-timezone";
+import { IRecurringSchedule } from "../interfaces/recurring-tasks";
+
+export class TimezoneUtils {
+  /**
+   * Convert a date from one timezone to another
+   */
+  static convertTimezone(date: moment.Moment | Date | string, fromTz: string, toTz: string): moment.Moment {
+    return moment.tz(date, fromTz).tz(toTz);
+  }
+
+  /**
+   * Get the current time in a specific timezone
+   */
+  static nowInTimezone(timezone: string): moment.Moment {
+    return moment.tz(timezone);
+  }
+
+  /**
+   * Check if a recurring task should run based on timezone
+   */
+  static shouldRunInTimezone(schedule: IRecurringSchedule, timezone: string): boolean {
+    const now = this.nowInTimezone(timezone);
+    const scheduleTime = moment.tz(schedule.created_at, timezone);
+    
+    // Check if it's the right time of day (within a 1-hour window)
+    const hourDiff = Math.abs(now.hour() - scheduleTime.hour());
+    return hourDiff < 1;
+  }
+
+  /**
+   * Calculate next end date considering timezone
+   */
+  static calculateNextEndDateWithTimezone(
+    schedule: IRecurringSchedule, 
+    lastDate: moment.Moment | Date | string,
+    timezone: string
+  ): moment.Moment {
+    const lastMoment = moment.tz(lastDate, timezone);
+    
+    switch (schedule.schedule_type) {
+      case "daily":
+        return lastMoment.clone().add(1, "day");
+        
+      case "weekly":
+        if (schedule.days_of_week && schedule.days_of_week.length > 0) {
+          // Find next occurrence based on selected days
+          let nextDate = lastMoment.clone();
+          let daysChecked = 0;
+          
+          do {
+            nextDate.add(1, "day");
+            daysChecked++;
+            if (schedule.days_of_week.includes(nextDate.day())) {
+              return nextDate;
+            }
+          } while (daysChecked < 7);
+          
+          // If no valid day found, return next week's first selected day
+          const sortedDays = [...schedule.days_of_week].sort((a, b) => a - b);
+          nextDate = lastMoment.clone().add(1, "week").day(sortedDays[0]);
+          return nextDate;
+        }
+        return lastMoment.clone().add(1, "week");
+        
+      case "monthly":
+        if (schedule.date_of_month) {
+          // Specific date of month
+          let nextDate = lastMoment.clone().add(1, "month").date(schedule.date_of_month);
+          
+          // Handle months with fewer days
+          if (nextDate.date() !== schedule.date_of_month) {
+            nextDate = nextDate.endOf("month");
+          }
+          
+          return nextDate;
+        } else if (schedule.week_of_month && schedule.day_of_month !== undefined) {
+          // Nth occurrence of a day in month
+          const nextMonth = lastMoment.clone().add(1, "month").startOf("month");
+          const targetDay = schedule.day_of_month;
+          const targetWeek = schedule.week_of_month;
+          
+          // Find first occurrence of the target day
+          let firstOccurrence = nextMonth.clone();
+          while (firstOccurrence.day() !== targetDay) {
+            firstOccurrence.add(1, "day");
+          }
+          
+          // Calculate nth occurrence
+          if (targetWeek === 5) {
+            // Last occurrence
+            let lastOccurrence = firstOccurrence.clone();
+            let temp = firstOccurrence.clone().add(7, "days");
+            
+            while (temp.month() === nextMonth.month()) {
+              lastOccurrence = temp.clone();
+              temp.add(7, "days");
+            }
+            
+            return lastOccurrence;
+          } else {
+            // Specific week number
+            return firstOccurrence.add((targetWeek - 1) * 7, "days");
+          }
+        }
+        return lastMoment.clone().add(1, "month");
+        
+      case "every_x_days":
+        return lastMoment.clone().add(schedule.interval_days || 1, "days");
+        
+      case "every_x_weeks":
+        return lastMoment.clone().add(schedule.interval_weeks || 1, "weeks");
+        
+      case "every_x_months":
+        return lastMoment.clone().add(schedule.interval_months || 1, "months");
+        
+      default:
+        return lastMoment.clone().add(1, "day");
+    }
+  }
+
+  /**
+   * Get all timezones that should be processed in the current hour
+   */
+  static getActiveTimezones(): string[] {
+    const activeTimezones: string[] = [];
+    const allTimezones = moment.tz.names();
+    
+    for (const tz of allTimezones) {
+      const tzTime = moment.tz(tz);
+      // Check if it's 11:00 AM in this timezone (matching the cron schedule)
+      if (tzTime.hour() === 11) {
+        activeTimezones.push(tz);
+      }
+    }
+    
+    return activeTimezones;
+  }
+
+  /**
+   * Validate timezone string
+   */
+  static isValidTimezone(timezone: string): boolean {
+    return moment.tz.zone(timezone) !== null;
+  }
+
+  /**
+   * Get user's timezone or default to UTC
+   */
+  static getUserTimezone(userTimezone?: string): string {
+    if (userTimezone && this.isValidTimezone(userTimezone)) {
+      return userTimezone;
+    }
+    return "UTC";
+  }
+}