Requirements

Let's refine the "Design a Calendar Application" problem. Imagine we are building a calendar service similar to Google Calendar, but focusing on the core domain model and the interactions between its components. This means we won't be dealing with distributed systems concerns like load balancing or database sharding directly (unless they affect our class design choices – e.g., a caching mechanism). The heart of the system revolves around users creating and managing events, inviting attendees, and handling notifications. Events can be one-time occurrences or recurring schedules. We need to handle time zones correctly and ensure that event conflicts are detected. The application should provide ways to view events based on different criteria (daily, weekly, monthly). We need to build a robust and extensible system that can handle future requirements like resource booking or integration with other services. This requires careful consideration of object-oriented principles, design patterns, and concurrency management. # Requirements ## Functional Requirements 1. **User Management:** * Create User: Ability to create a new user profile with essential information (name, email, time zone). * Get User: Ability to retrieve user details by ID. * Update User: Ability to update user details. 2. **Event Management:** * Create Event: Users can create events with a title, description, start time, end time, location, and attendees. * Update Event: Users can modify event details, including time, location, attendees, and description. * Delete Event: Users can delete events they own. * Get Event: Retrieve event details by ID. * List Events: Retrieve a list of events for a user within a specified time range (daily, weekly, monthly views). * Recurring Events: Support for creating events that repeat daily, weekly, monthly, or yearly, with options for specifying exceptions (e.g., skip a specific instance). 3. **Attendee Management:** * Invite Attendees: Event organizers can invite other users to events. * RSVP: Attendees can accept, decline, or tentatively accept event invitations. * Attendee Status: Display the RSVP status of each attendee for an event. 4. **Notifications:** * Event Reminders: Send reminders to attendees before the start of an event. * Event Updates: Notify attendees of any changes to an event (time, location, description). * Cancellation Notifications: Notify attendees when an event is canceled. 5. **Conflict Detection:** * Prevent Overlapping Events: Prevent users from scheduling overlapping events in their calendar. * Check Attendee Availability: Before confirming an event, check the availability of all attendees to identify potential conflicts. 6. **Time Zone Handling:** * Store User Time Zone: Store the time zone for each user. * Convert Time Zones: Automatically convert event times to the user's local time zone. ## Non-Functional Requirements 1. **Thread Safety:** The system should be thread-safe to handle concurrent requests from multiple users. Data structures must be protected against race conditions. Consider using appropriate synchronization mechanisms (locks, atomic variables) where necessary. 2. **Extensibility:** The system should be designed to easily accommodate new features and integrations, such as support for different notification channels (SMS, push notifications), resource booking, or integration with other calendar services. Use design patterns to promote loose coupling and open/closed principle. 3. **Modularity:** The codebase should be well-organized into modules with clear responsibilities and well-defined interfaces. This promotes maintainability and testability. 4. **Testability:** The system should be designed to be easily testable at both the unit and integration levels. Use dependency injection and mocking frameworks to isolate components for testing. 5. **Performance:** Operations such as retrieving events for a given time range should be efficient. Consider using appropriate data structures and indexing strategies to optimize performance, but avoid premature optimization. Caching strategies (e.g., a `Cache` interface) could be employed but should be designed with concurrency in mind. 6. **Maintainability:** Code should be well-documented and follow coding standards to ensure ease of maintenance and understanding. ## Core Entities 1. **User:** Represents a user of the calendar application. Attributes: userId (unique identifier), name, email, timeZone. Methods: `getEvents(startTime, endTime)`. 2. **Event:** Represents an event in the calendar. Attributes: eventId (unique identifier), title, description, startTime, endTime, location, organizer (User), list of attendees (User). Methods: `addAttendee(User)`, `removeAttendee(User)`, `updateTime(startTime, endTime)`. 3. **RecurringEvent:** Represents an event that repeats according to a specific schedule. Inherits from Event. Attributes: recurrenceRule (specifies the frequency and pattern of recurrence), exceptions (list of dates that should be excluded from the recurrence). Methods: `getNextOccurrences(startTime, endTime)`. Consider different recurrence rule implementations using the Strategy pattern. 4. **Attendee:** Represents a user's participation in an event. Attributes: user (User), event (Event), status (RSVP status: Accepted, Declined, Tentative). 5. **Notification:** Represents a notification to be sent to a user. Attributes: notificationId, user (User), event (Event), type (reminder, update, cancellation), sentTime. The actual sending of notifications could be handled by a separate component using an Observer pattern. 6. **Calendar:** Represents a user's calendar, containing a collection of events. Attributes: user (User), events (List of Events). The calendar could manage event conflicts. 7. **RecurrenceRule:** Interface for defining recurrence rules. Implementations could include DailyRecurrenceRule, WeeklyRecurrenceRule, MonthlyRecurrenceRule, YearlyRecurrenceRule. 8. **ConflictDetector:** A class responsible for detecting conflicts between events, considering the user's existing events and the availability of attendees.

Design a calendar Application (similar like Google Calendar)

Requirements

Think like an Architect

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