Refactor burn native tokens method

contracts/sfc/SFC.sol

@@ -152,6 +152,7 @@ contract SFC is OwnableUpgradeable, UUPSUpgradeable, Version {
     // values
     error ZeroAmount();
     error ZeroRewards();
+    error ValueTooLarge();
 
     // pubkeys
     error PubkeyUsedByOtherValidator();
@@ -216,7 +217,7 @@ contract SFC is OwnableUpgradeable, UUPSUpgradeable, Version {
     );
     event ClaimedRewards(address indexed delegator, uint256 indexed toValidatorID, uint256 rewards);
     event RestakedRewards(address indexed delegator, uint256 indexed toValidatorID, uint256 rewards);
-    event BurntFTM(uint256 amount);
+    event BurntNativeTokens(uint256 amount);
     event UpdatedSlashingRefundRatio(uint256 indexed validatorID, uint256 refundRatio);
     event RefundedSlashedLegacyDelegation(address indexed delegator, uint256 indexed validatorID, uint256 amount);
     event AnnouncedRedirection(address indexed from, address indexed to);
@@ -459,9 +460,12 @@ contract SFC is OwnableUpgradeable, UUPSUpgradeable, Version {
         emit TreasuryFeesResolved(fees);
     }
 
-    /// burnFTM allows SFC to burn an arbitrary amount of FTM tokens.
-    function burnFTM(uint256 amount) external onlyOwner {
-        _burnFTM(amount);
+    /// Burn native tokens by sending them to the SFC contract.
+    function burnNativeTokens() external payable {
+        if (msg.value == 0) {
+            revert ZeroAmount();
+        }
+        _burnNativeTokens(msg.value);
     }
 
     /// Issue tokens to the issued tokens recipient as a counterparty to the burnt FTM tokens.
@@ -753,7 +757,7 @@ contract SFC is OwnableUpgradeable, UUPSUpgradeable, Version {
         if (!sent) {
             revert TransferFailed();
         }
-        _burnFTM(penalty);
+        _burnNativeTokens(penalty);
 
         emit Withdrawn(delegator, toValidatorID, wrID, amount - penalty, penalty);
     }
@@ -817,12 +821,16 @@ contract SFC is OwnableUpgradeable, UUPSUpgradeable, Version {
         return rewards;
     }
 
-    /// Burn FTM tokens.
+    /// Burn native tokens.
     /// The tokens are sent to the zero address.
-    function _burnFTM(uint256 amount) internal {
+    function _burnNativeTokens(uint256 amount) internal {
         if (amount != 0) {
+            if (amount > totalSupply) {
+                revert ValueTooLarge();
+            }
+            totalSupply -= amount;
             payable(address(0)).transfer(amount);
-            emit BurntFTM(amount);
+            emit BurntNativeTokens(amount);
         }
     }
 

test/SFC.ts

@@ -8,6 +8,7 @@ import { BlockchainNode, ValidatorMetrics } from './helpers/BlockchainNode';
 describe('SFC', () => {
   const fixture = async () => {
     const [owner, user] = await ethers.getSigners();
+    const totalSupply = ethers.parseEther('100');
     const sfc = await upgrades.deployProxy(await ethers.getContractFactory('UnitTestSFC'), {
       kind: 'uups',
       initializer: false,
@@ -24,7 +25,7 @@ describe('SFC', () => {
     const evmWriter: IEVMWriter = await ethers.deployContract('StubEvmWriter');
     const initializer: UnitTestNetworkInitializer = await ethers.deployContract('UnitTestNetworkInitializer');
 
-    await initializer.initializeAll(0, 0, sfc, nodeDriverAuth, nodeDriver, evmWriter, owner);
+    await initializer.initializeAll(0, totalSupply, sfc, nodeDriverAuth, nodeDriver, evmWriter, owner);
     const constants: UnitTestConstantsManager = await ethers.getContractAt(
       'UnitTestConstantsManager',
       await sfc.constsAddress(),
@@ -39,6 +40,7 @@ describe('SFC', () => {
       nodeDriver,
       nodeDriverAuth,
       constants,
+      totalSupply,
     };
   };
 
@@ -55,6 +57,32 @@ describe('SFC', () => {
     ).to.revertedWithCustomError(this.sfc, 'TransfersNotAllowed');
   });
 
+  describe('Burn native tokens', () => {
+    it('Should revert when no amount sent', async function () {
+      await expect(this.sfc.connect(this.user).burnNativeTokens()).to.be.revertedWithCustomError(
+        this.sfc,
+        'ZeroAmount',
+      );
+    });
+
+    it('Should revert when amount greater than total supply', async function () {
+      await expect(
+        this.sfc.connect(this.user).burnNativeTokens({ value: this.totalSupply + 1n }),
+      ).to.be.revertedWithCustomError(this.sfc, 'ValueTooLarge');
+    });
+
+    it('Should succeed and burn native tokens', async function () {
+      const amount = ethers.parseEther('1.5');
+      const totalSupply = await this.sfc.totalSupply();
+      const tx = await this.sfc.connect(this.user).burnNativeTokens({ value: amount });
+      await expect(tx).to.emit(this.sfc, 'BurntNativeTokens').withArgs(amount);
+      expect(await this.sfc.totalSupply()).to.equal(totalSupply - amount);
+      await expect(tx).to.changeEtherBalance(this.sfc, 0);
+      await expect(tx).to.changeEtherBalance(this.user, -amount);
+      await expect(tx).to.changeEtherBalance(ethers.ZeroAddress, amount);
+    });
+  });
+
   describe('Genesis validator', () => {
     beforeEach(async function () {
       const validator = ethers.Wallet.createRandom();