feat: implement maximum holders before launch safeguard

contracts/src/tokens/interface.cairo

@@ -35,6 +35,12 @@ trait IUnruggableMemecoin<TState> {
     // ************************************
     // * Additional functions
     // ************************************
+
+    /// Checks whether token has launched
+    ///
+    /// # Returns 
+    ///     bool: whether token has launched
+    fn launched(self: @TState) -> bool;
     fn launch_memecoin(ref self: TState);
 }
 
@@ -61,5 +67,10 @@ trait IUnruggableMemecoinSnake<TState> {
 
 #[starknet::interface]
 trait IUnruggableAdditional<TState> {
+    /// Checks whether token has launched
+    ///
+    /// # Returns 
+    ///     bool: whether token has launched
+    fn launched(self: @TState) -> bool;
     fn launch_memecoin(ref self: TState);
 }

contracts/src/tokens/memecoin.cairo

@@ -40,6 +40,8 @@ mod UnruggableMemecoin {
     #[storage]
     struct Storage {
         marker_v_0: (),
+        launched: bool,
+        pre_launch_holders_count: u8,
         // Components.
         #[substorage(v0)]
         ownable: OwnableComponent::Storage,
@@ -56,6 +58,10 @@ mod UnruggableMemecoin {
         ERC20Event: ERC20Component::Event
     }
 
+    mod Errors {
+        const MAX_HOLDERS_REACHED: felt252 = 'memecoin: max holders reached';
+    }
+
 
     /// Constructor called once when the contract is deployed.
     /// # Arguments
@@ -80,7 +86,7 @@ mod UnruggableMemecoin {
         self.ownable.initializer(owner);
 
         // Mint initial supply to the initial recipient.
-        self.erc20._mint(initial_recipient, initial_supply);
+        self._mint(initial_recipient, initial_supply);
     }
 
     //
@@ -91,11 +97,18 @@ mod UnruggableMemecoin {
         // ************************************
         // * UnruggableMemecoin functions
         // ************************************
+
+        fn launched(self: @ContractState) -> bool {
+            self.launched.read()
+        }
+
         fn launch_memecoin(ref self: ContractState) {
             // Checks: Only the owner can launch the memecoin.
             self.ownable.assert_only_owner();
-        // Effects.
+            // Effects.
 
+            // Launch the coin
+            self.launched.write(true);
         // Interactions.
         }
     }
@@ -171,12 +184,60 @@ mod UnruggableMemecoin {
     //
     #[generate_trait]
     impl UnruggableMemecoinInternalImpl of UnruggableMemecoinInternalTrait {
+        /// Internal function to enforce pre launch holder limit
+        ///
+        /// Note that when transfers are done, between addresses that already
+        /// hold tokens, we do not increment the number of holders. it only
+        /// gets incremented when the recipient that hold no tokens
+        ///
+        /// # Arguments
+        /// * `recipient` - The recipient of the tokens being transferred.
+        #[inline(always)]
+        fn _enforce_holders_limit(ref self: ContractState, recipient: ContractAddress) {
+            // enforce max number of holders before launch
+
+            if !self.launched.read() && self.balance_of(recipient) == 0 {
+                let current_holders_count = self.pre_launch_holders_count.read();
+                assert(
+                    current_holders_count < MAX_HOLDERS_BEFORE_LAUNCH, Errors::MAX_HOLDERS_REACHED
+                );
+
+                self.pre_launch_holders_count.write(current_holders_count + 1);
+            }
+        }
+
+
+        /// Internal function to mint tokens
+        ///
+        /// Before minting, a check is done to ensure that 
+        /// only `MAX_HOLDERS_BEFORE_LAUNCH` addresses can hold 
+        /// tokens if token hasn't launched 
+        ///
+        /// # Arguments
+        /// * `recipient` - The recipient of the tokens.
+        /// * `amount` - The amount of tokens to be minted.
+        fn _mint(ref self: ContractState, recipient: ContractAddress, amount: u256) {
+            self._enforce_holders_limit(recipient);
+            self.erc20._mint(recipient, amount);
+        }
+
+        /// Internal function to transfer tokens
+        ///
+        /// Before transferring, a check is done to ensure that 
+        /// only `MAX_HOLDERS_BEFORE_LAUNCH` addresses can hold 
+        /// tokens if token hasn't launched 
+        ///
+        /// # Arguments
+        /// * `sender` - The sender or owner of the tokens.
+        /// * `recipient` - The recipient of the tokens.
+        /// * `amount` - The amount of tokens to be transferred.
         fn _transfer(
             ref self: ContractState,
             sender: ContractAddress,
             recipient: ContractAddress,
             amount: u256
         ) {
+            self._enforce_holders_limit(recipient);
             self.erc20._transfer(sender, recipient, amount);
         }
     }

contracts/tests/test_unruggable_memecoin.cairo

@@ -312,6 +312,8 @@ mod memecoin_entrypoints {
 
         start_prank(CheatTarget::One(memecoin.contract_address), owner);
         memecoin.launch_memecoin();
+
+        assert(memecoin.launched(), 'Coin not launched');
     //TODO
     }
 
@@ -330,3 +332,174 @@ mod memecoin_entrypoints {
         memecoin.launch_memecoin();
     }
 }
+
+
+mod memecoin_internals {
+    use UnruggableMemecoin::{
+        UnruggableMemecoinInternalImpl, SnakeEntrypoints, UnruggableEntrypoints,
+        MAX_HOLDERS_BEFORE_LAUNCH
+    };
+    use core::option::OptionTrait;
+    use snforge_std::{start_prank, CheatTarget};
+    use starknet::{ContractAddress, contract_address_const};
+    use unruggable::tokens::memecoin::UnruggableMemecoin;
+
+
+    #[test]
+    fn test__transfer() {
+        let owner = contract_address_const::<42>();
+        let recipient = contract_address_const::<43>();
+        let initial_supply = 1000.into();
+
+        // call contract constructor
+        let mut contract_state = UnruggableMemecoin::contract_state_for_testing();
+        UnruggableMemecoin::constructor(
+            ref contract_state, owner, owner, 'UnruggableMemecoin', 'UM', initial_supply
+        );
+
+        // Transfer 100 tokens to the recipient
+        UnruggableMemecoinInternalImpl::_transfer(ref contract_state, owner, recipient, 100);
+
+        // Check balance. Should be equal to initial supply - 100.
+        let owner_balance = SnakeEntrypoints::balance_of(@contract_state, owner);
+        assert(owner_balance == (initial_supply - 100), 'Invalid balance owner');
+
+        // Check recipient balance. Should be equal to 100.
+        let recipient_balance = SnakeEntrypoints::balance_of(@contract_state, recipient);
+        assert(recipient_balance == 100.into(), 'Invalid balance recipient');
+    }
+
+
+    #[test]
+    fn test__transfer_recipients_equal_holder_cap() {
+        let owner = contract_address_const::<42>();
+        let initial_supply = 1000.into();
+
+        // call contract constructor
+        let mut contract_state = UnruggableMemecoin::contract_state_for_testing();
+        UnruggableMemecoin::constructor(
+            ref contract_state, owner, owner, 'UnruggableMemecoin', 'UM', initial_supply
+        );
+
+        // index starts from 1 because owner has initial supply
+        let mut index = 1;
+        loop {
+            if index == MAX_HOLDERS_BEFORE_LAUNCH {
+                break;
+            }
+
+            // Transfer 1 token to the unique recipient
+            let unique_recipient: ContractAddress = (index.into() + 9999).try_into().unwrap();
+            UnruggableMemecoinInternalImpl::_transfer(
+                ref contract_state, owner, unique_recipient, 1
+            );
+
+            // Check recipient balance. Should be equal to 1.
+            let recipient_balance = SnakeEntrypoints::balance_of(@contract_state, unique_recipient);
+            assert(recipient_balance == 1.into(), 'Invalid balance recipient');
+
+            index += 1;
+        };
+    }
+
+
+    #[test]
+    fn test__transfer_existing_holders() {
+        /// pre launch holder number should not change when
+        /// transfer is done to recipient(s) who already have tokens
+
+        /// to test this, we are going to continously self transfer tokens
+        /// and ensure that we can transfer more than `MAX_HOLDERS_BEFORE_LAUNCH` times
+
+        let owner = contract_address_const::<42>();
+        let initial_supply = 1000.into();
+
+        // call contract constructor
+        let mut contract_state = UnruggableMemecoin::contract_state_for_testing();
+        UnruggableMemecoin::constructor(
+            ref contract_state, owner, owner, 'UnruggableMemecoin', 'UM', initial_supply
+        );
+
+        // index starts from 1 because owner has initial supply
+        let mut index = 1;
+        loop {
+            if index == MAX_HOLDERS_BEFORE_LAUNCH + 1 {
+                break;
+            }
+
+            // Self transfer tokens
+
+            UnruggableMemecoinInternalImpl::_transfer(
+                ref contract_state, owner, owner, initial_supply
+            );
+
+            index += 1;
+        };
+    }
+
+
+    #[test]
+    #[should_panic(expected: ('memecoin: max holders reached',))]
+    fn test__transfer_above_holder_cap() {
+        let owner = contract_address_const::<42>();
+        let initial_supply = 1000.into();
+
+        // call contract constructor
+        let mut contract_state = UnruggableMemecoin::contract_state_for_testing();
+        UnruggableMemecoin::constructor(
+            ref contract_state, owner, owner, 'UnruggableMemecoin', 'UM', initial_supply
+        );
+
+        // index starts from 1 because owner has initial supply
+        let mut index = 1;
+        loop {
+            if index == MAX_HOLDERS_BEFORE_LAUNCH + 1 {
+                break;
+            }
+
+            // Transfer 1 token to the unique recipient
+            let unique_recipient: ContractAddress = (index.into() + 9999).try_into().unwrap();
+            UnruggableMemecoinInternalImpl::_transfer(
+                ref contract_state, owner, unique_recipient, 1
+            );
+
+            index += 1;
+        };
+    }
+
+
+    #[test]
+    fn test__transfer_no_holder_cap_after_launch() {
+        let owner = contract_address_const::<42>();
+        let initial_supply = 1000.into();
+
+        // call contract constructor
+        let mut contract_state = UnruggableMemecoin::contract_state_for_testing();
+        UnruggableMemecoin::constructor(
+            ref contract_state, owner, owner, 'UnruggableMemecoin', 'UM', initial_supply
+        );
+
+        // set owner as caller to bypass owner restrictions
+        start_prank(CheatTarget::All, owner);
+
+        // launch memecoin
+        UnruggableEntrypoints::launch_memecoin(ref contract_state);
+
+        // index starts from 1 because owner has initial supply
+        let mut index = 1;
+        loop {
+            if index == MAX_HOLDERS_BEFORE_LAUNCH + 1 {
+                break;
+            }
+
+            // Transfer 1 token to the unique recipient
+            let unique_recipient: ContractAddress = (index.into() + 9999).try_into().unwrap();
+            UnruggableMemecoinInternalImpl::_transfer(
+                ref contract_state, owner, unique_recipient, 1
+            );
+
+            index += 1;
+        };
+    }
+}
+