additional logic for burning reserve in exchange of native; initial draft

Signed-off-by: Uncle Fatso <uncle.fatso@ghostchain.io>

src/mocks/Reserve.sol

@@ -5,7 +5,9 @@ import "@openzeppelin-contracts/token/ERC20/extensions/ERC20Permit.sol";
 
 contract Reserve is ERC20Permit {
     address private immutable _owner;
+    uint256 public accumulatedDonation;
     uint256 public conversionRate;
+    uint256 public donationRate;
     error OnlyOwner();
 
     constructor(
@@ -30,9 +32,14 @@ contract Reserve is ERC20Permit {
         conversionRate = rate;
     }
 
+    function changeReminder(uint256 reminder) external {
+        if (msg.sender != _owner) revert OnlyOwner();
+        donationRate = reminder;
+    }
+
     function withdraw(address payable receiver) external {
         if (msg.sender != _owner) revert OnlyOwner();
-        (bool sent,) = receiver.call{ value: address(this).balance }("");
+        (bool sent,) = receiver.call{ value: accumulatedDonation }("");
         require(sent, "Failed to send Ether");
     }
 
@@ -42,10 +49,27 @@ contract Reserve is ERC20Permit {
     }
 
     function mint(address account) external payable {
+        uint256 donation = msg.value * donationRate / 1e5;
+        accumulatedDonation += donation;
         _innerMint(account, msg.value);
     }
 
+    function burn(uint256 amount) external payable {
+        (bool sent,) = msg.sender.call{ value: estimateAmount(amount) }("");
+        require(sent, "Failed to send Ether");
+        _innerBurn(msg.sender, amount);
+    }
+
+    function estimateAmount(uint256 amount) public view returns (uint256) {
+        uint256 valueDiff = address(this).balance - accumulatedDonation;
+        return amount * valueDiff / totalSupply();
+    }
+
     function _innerMint(address who, uint256 amount) internal {
         _mint(who, amount * conversionRate);
     }
+
+    function _innerBurn(address who, uint256 amount) internal {
+        _burn(who, amount);
+    }
 }