Automated Lottery Closure: Ticket Purchase Validation

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Hey guys! Let's dive into a critical aspect of the Starklotto platform: ensuring smooth and reliable ticket purchases. This article breaks down the implementation of automatic lottery state validation, a crucial feature to prevent issues when a lottery closes during or immediately after a ticket purchase. We'll cover both the contract and frontend modifications needed to achieve this. This enhancement ensures a better user experience and maintains the integrity of the lottery system.

The Problem: Lottery Closure Timing

Imagine this: you're pumped to buy lottery tickets, you hit that "Buy" button right as the clock hits zero. But the lottery closes during your transaction! Currently, the system doesn't automatically handle this. This means the lottery might not transition to an "inactive" state, and the user interface (UI) might not reflect the actual lottery status. This can lead to confusion and potential problems for users. Our goal? To fix this. We need to ensure that the lottery state is always accurate and that the UI reflects this state in real-time. This is crucial for maintaining a positive user experience and the overall reliability of the platform.

To solve this, we're implementing two key validations: one within the contract itself (the brains of the operation) and another on the frontend (what the user sees and interacts with).

1. Contract Validation (Cairo)

This is where the core logic resides. We'll modify the BuyTicket function in the Lottery.cairo contract. This ensures that when a ticket purchase is successful, the contract automatically checks if the lottery has reached its end. If the remaining blocks are zero, the lottery's state is instantly changed to inactive within the same transaction. This is super important for the following reasons:

  • Consistency: The contract always reflects the correct lottery state. Always. No exceptions.
  • Automation: The process is seamless. Users don't have to worry about manually refreshing or checking the status.
  • Efficiency: The entire process happens within the transaction. No extra steps for the user.

2. Frontend Validation (TypeScript/React)

This is all about the user experience! We'll modify the buy-tickets page in our frontend to refresh the lottery state after a successful purchase. If the lottery has closed, the UI will update to reflect this, providing an informative message and disabling the purchase options. Think of it as a built-in notification system that keeps the user informed.

Here is what the frontend will provide:

  • Real-time Updates: The UI dynamically reflects the current lottery status.
  • User-Friendly Messages: Clear and concise messages guide the user.
  • Intuitive Interface: The interface adapts to the lottery's state, disabling purchase options when necessary.

Detailed Implementation: A Deep Dive

Now, let's dig into the specifics of how these validations will be implemented.

Part 1: Cairo Contract Modification

We're making changes in the BuyTicket function located in packages/snfoundry/contracts/src/Lottery.cairo. The core idea is to add a check at the end of the purchase process. Here's how it will work:

  1. Purchase Complete: After a ticket purchase is successfully executed (after ticket creation and event emission).
  2. Check Remaining Blocks: The contract will call an internal function GetBlocksRemaining(drawId) to calculate remaining blocks.
  3. Zero Blocks? If GetBlocksRemaining(drawId) == 0, then the lottery has ended.
  4. Close the Lottery: Execute SetDrawInactive(drawId). This changes the isActive flag to false. This means no more ticket purchases for this draw. This will also emit a DrawClosed event.

Important Considerations:

  • Order Matters: The state change must happen after the purchase is successful. The user gets their ticket, and then we close the lottery if necessary.
  • No Reversion: The transaction should not revert (fail) if the blocks reach zero. The ticket purchase is still valid; we just need to update the state.
  • Efficiency: The validation should be fast and efficient to avoid excessive gas costs.
  • Multiple Purchases: The system must work correctly for both single and multiple ticket purchases.

Key Contract Functions:

  • GetBlocksRemaining(drawId: u64): This function calculates and returns the remaining blocks. If the current block is greater than or equal to the end block, it returns 0 (lottery is over). Otherwise, it returns the difference between the end block and the current block.
  • SetDrawInactive(drawId: u64): This function is responsible for changing the lottery's state to inactive. It updates the draws.entry(drawId).isActive flag to false. It also emits a DrawClosed event to signal that the lottery has closed. This is critical for tracking and auditing.

Security Validations: We must ensure the integrity of the system. Important security validations include:

  • Draw Existence: Verify that the draw exists before modifying its state.
  • Active State: Ensure that SetDrawInactive is only called if the draw is actually active, preventing any unexpected changes.
  • Ticket Integrity: Maintain the integrity of all ticket records, ensuring no data loss or corruption.
  • Event Integrity: Existing events, such as TicketPurchased and BulkTicketPurchase, should not be affected by this new logic.

Part 2: Frontend Modification

The frontend changes will happen in the buy-tickets page located in packages/nextjs/app/dapp/buy-tickets/page.tsx. The primary change will be in the handleConfirmPurchase function, which handles the ticket purchase process. Here's the flow:

  1. Purchase Execution: The user clicks the "Buy" button, and the purchase is initiated.
  2. State Refresh: After a successful purchase, we'll call refetchDrawActiveBlocks() to refresh the lottery state from the contract. This ensures we have the latest information.
  3. State Check: The frontend checks the new value of isDrawActive (or isDrawActiveBlocks) to see if the lottery is still active.
  4. UI Update: If the lottery is inactive (isDrawActive === false), the UI will be updated:
    • Show an informative message to the user (e.g., "The lottery has closed!").
    • Disable the purchase button.
    • Optionally, change the countdown banner's appearance (e.g., change the color or style).

Frontend Tools and Hooks: We'll leverage these existing hooks and functions to make things smooth:

  • useDrawInfo({ drawId }): Provides the necessary data about the lottery, including isDrawActiveBlocks, refetchDrawActiveBlocks(), and blocksRemaining.
  • useBuyTickets({ drawId }): This hook handles the ticket purchase logic and provides access to buyTickets and isDrawActive. It also provides a function refetchBalance() that will be used to refresh the user balance.

Suggested UI Flow: The frontend logic will follow a simple sequence. After the purchase is complete, the UI will refresh the lottery data and update based on the latest status. For example:

  • After successful purchase:
    1. await buyTickets(...) // Execute the purchase.
    2. await refetchDrawActiveBlocks() // Refresh the draw state.
    3. await refetchBalance() // Refresh the user's balance.
    4. Use the updated state to control the UI. For instance, we can show a "Lottery Closed" message or disable the purchase button.

UI States:

  • Active Lottery: The standard state. The countdown timer is displayed, and the purchase button is enabled.
  • Closed Lottery:
    • Display a message like: "The lottery has closed! Your tickets have been registered and will participate in the draw." (or an equivalent message in other languages).
    • Disable the purchase button.
    • Potentially change the countdown banner's appearance.
    • Maybe offer a link to view the next lottery.

Suggested Message (example):

  • English: "The lottery has closed! Your tickets have been successfully registered and will participate in the draw. Check 'Claim' to see if your tickets are winners and withdraw your prize."
  • Spanish: "¡La lotería ha cerrado! Tus tickets han sido registrados exitosamente y participarán en el sorteo. Revisa 'Reclamar' para saber si tus billetes son ganadores y retirar el premio."

Technical Details: Code Snippets and Considerations

Let's break down the code modifications. This section has some pseudocode and implementation details that you might find useful.

Contract Code Snippet (Conceptual)

Here's a conceptual representation of how the BuyTicket function in the Lottery.cairo contract will look:

fn BuyTicket(ref self: ContractState, drawId: u64, numbers_array: Array<Array<u16>>, quantity: u8) {
    // ... Existing purchase logic: validations, ticket creation, event emission ...

    // NEW LOGIC AT THE END:
    let blocks_remaining = GetBlocksRemaining(drawId);
    if (blocks_remaining == 0) {
        SetDrawInactive(drawId);
    }
}

Frontend Code Snippet (Conceptual)

Here's a basic example of what the frontend code might look like within the handleConfirmPurchase function (in packages/nextjs/app/dapp/buy-tickets/page.tsx):

async function handleConfirmPurchase() {
    // 1. Execute the purchase
    const result = await buyTickets(...);

    if (result) {
        // 2. Refresh the draw state
        await refetchDrawActiveBlocks();

        // 3. Check if the lottery is closed
        // After refetch, `isDrawActiveBlocks` will be updated. Use this value.
        if (!isDrawActiveBlocks) {
            // 4. Update the UI: show message, disable button, etc.
            toast.info("The lottery has closed! Your tickets will participate in the draw.");
        }
    }
}

Considerations for Implementation

  • Contract:
    • The SetDrawInactive function might have access restrictions. The code needs to be adjusted to allow internal calls from the BuyTicket function. Alternatively, you can duplicate the closure logic inside BuyTicket.
    • Remember that the event DrawClosed is important for traceability.
    • The added gas cost of validation should be minimal: a read and a conditional write.
  • Frontend:
    • The scaffolding (hooks and functions) already handles caching and revalidation.
    • There might be a small delay during the refetch process. Consider showing a brief loading indicator while the data is being updated.
    • The user should receive a clear and informative message that the purchase was successful, even if the lottery is closed.
    • Consider adding a link or a button to direct the user to the dashboard or the upcoming lotteries page.

Testing

Thorough testing is crucial! Here's how you can verify the implementation:

  • Contract Testing:
    • Create tests to simulate a ticket purchase when blocksRemaining is equal to zero.
    • Verify that the DrawClosed event is emitted correctly.
  • Frontend Testing:
    • Test the workflow with a lottery that's about to close.
    • Make sure the UI updates without requiring a manual refresh.

Conclusion: A Smoother Lottery Experience

By implementing automatic lottery state validation, we're significantly improving the user experience and ensuring that the Starklotto platform remains reliable. This feature will ensure that users are always informed of the lottery's status and that their ticket purchases are handled correctly, even when the lottery closes at the last second. This is just another step towards building a better and more user-friendly lottery platform for everyone involved. Let's build something great, guys!