Implement Event capacity management and Waitlist functionality.

[codebestia]

Summary

This pull request introduces event capacity management and waitlist functionality to the ChainEvents contract. It allows event owners to set and update the maximum capacity for events, enforces capacity limits during registration, and enables users to join a waitlist when an event is full. Additionally, it provides mechanisms to automatically register users from the waitlist when spots become available.

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Key Changes

1. Event Capacity Management

• Added max_capacity to EventDetails struct to track the maximum number of attendees per event.
• Default capacity is set via DEFAULT_EVENT_MAX_CAPACITY.
• New function update_event_max_capacity allows event owners to update the capacity of their events (with checks for validity and event state).
• Emits EventCapacityUpdated event when capacity is changed.

2. Waitlist Functionality

• Waitlist storage: Added mappings for waitlist, waitlist_position, and joined_waitlist to track waitlisted users per event.
• New function join_event_waitlist: Allows users to join the waitlist if the event is full and they are not already registered or on the waitlist.
• Emits JoinEventWaitlist event when a user joins the waitlist.
• Automatic registration from waitlist: When a user unregisters from an event, the next user on the waitlist is automatically registered.

3. Registration Logic Updates

• Registration now checks max_capacity before allowing a user to register.
• Unregistration triggers waitlist processing to fill vacated spots.

4. Interface & Event Updates

• Updated IEvent interface to include new functions for capacity and waitlist management.
• New events: EventCapacityUpdated and JoinEventWaitlist for better indexer support and transparency.

5. Error Handling

• New error messages for capacity and waitlist-related conditions (e.g., EVENT_IS_FULL, ALREADY_JOINED_WAITLIST, etc.).

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Motivation

• Scalability: Enables event organizers to manage attendee limits efficiently.
• User Experience: Provides a fair mechanism for users to join popular events via a waitlist.
• Automation: Reduces manual intervention by automatically filling spots from the waitlist.

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Backward Compatibility

• Existing event creation and registration flows remain unchanged for events that do not reach capacity.
• New features are additive and do not break existing interfaces.

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Additional Notes

• All new functions are documented and emit relevant events for off-chain tracking.
• The waitlist is implemented as a FIFO queue per event.
• Only event owners can update event capacity, and only when the event is closed.

Related Issue

Closes #192

[codebestia]

GM @mubarak23
Please review the changes and provide feedback.

[mubarak23]

@codebestia i will review this PR tonight

[codebestia]

GM @mubarak23
Does this PR meet the requirements of the issue?

[mubarak23]

LFGM

[mubarak23]

@codebestia excellent work