Clown Beatdown

Imagine a clown standing in front of you, taunting the crowd. Hidden in the clown's pockets are secrets — strings that only become visible once the clown is knocked out. There are primarily two actions you can take: hitting the clown or adding secrets to the clown's pockets. Hitting the clown reduces its stamina by one, bringing it closer to being knocked out. Adding a secret stores an encrypted string that no one can read until it's revealed. You can only rob the clown of a secret if you contributed to knocking it out, i.e., you hit the clown at least once in the current round. This collaborative challenge is the heart of the Clown Beatdown game, and it's all powered by the ClownBeatdown smart contract. Let's dive into the inner workings of the contract and uncover how each part fuels this game.

The contract can be found in the contracts/src/ClownBeatdown.sol file of the starter repo.

State variables

initialClownStamina and clownStamina

Think of stamina as the clown's durability. initialClownStamina is the clown's starting strength, and clownStamina tracks how much remains as players hit it.

secrets, secretsCount, and secretIndex

These are the hidden values at the heart of the game. secrets is a mapping of sbytes (shielded bytes) — encrypted strings stored on-chain that remain hidden until revealed. secretsCount tracks how many secrets have been added. secretIndex is a suint256 (shielded integer) that determines which secret will be revealed when the clown is robbed. Because secretIndex is shielded, no one can predict which secret will be returned.

round

A counter that increments with each new round/reset, ensuring every round has a fresh clown to beat down.

hitsPerRound

A mapping that records every player's contribution to the current round, ensuring only participants can rob the clown's secret.

Functions

addSecret (string _secret)

This function allows anyone to add a secret to the clown's pool. Since addSecret converts a plain string into sbytes (shielded bytes) and stores it in the secrets mapping, it performs a shielded write — the secret's contents are encrypted on-chain and invisible to observers.

What happens:

• Converts the input string to sbytes and stores it in the secrets mapping

• Increments secretsCount

• Re-picks a random secretIndex using _randomIndex()

hit ( )

This function allows a player to hit the clown, reducing its stamina and bringing it one step closer to being knocked out:

What happens:

• Checks if the clown is still standing (clownStamina > 0)

• If it is, decrements clownStamina by 1

• Increases the player who called hit()'s contribution in the current round (hitsPerRound[round][playerAddress]) by 1

• Emits the Hit event to update all participants.

rob ( )

This function allows contributors to the current round to steal a randomly selected secret from the clown. Since this is a view function that reveals an sbytes value, calling this function constitutes a signed read.

What happens:

• Requires the clown to be knocked out (requireDown modifier)

• Ensures the function caller contributed to knocking out the clown for this round (onlyContributor modifier)

• Returns the secret at the shielded secretIndex position, decrypted from sbytes to bytes.

reset ( )

This function resets the clown for a new round of gameplay:

What happens:

• Requires the clown to be knocked out (requireDown modifier)

• Restores clownStamina to initialClownStamina

• Picks a new random secretIndex

• Increments the round counter

• Emits the Reset event.

Modifiers

Modifiers enforce the rules of the game:

requireDown

Ensures that rob() and reset() can only be called if the clown's stamina has reached zero.

requireStanding

Ensures that hit() can only be called while the clown still has stamina remaining.

onlyContributor

Restricts access to rob(), and hence the secret being revealed, only to players who contributed at least one hit in the current round.