Added validation of moved funds sweep proposal

solidity/contracts/bridge/WalletProposalValidator.sol

@@ -104,6 +104,14 @@ contract WalletProposalValidator {
         uint256 movingFundsTxFee;
     }
 
+    /// @notice Helper structure representing a moved funds sweep proposal.
+    struct MovedFundsSweepProposal {
+        // 20-byte public key hash of the wallet.
+        bytes20 walletPubKeyHash;
+        // Proposed BTC fee for the entire transaction.
+        uint256 movedFundsSweepTxFee;
+    }
+
     /// @notice Helper structure representing a heartbeat proposal.
     struct HeartbeatProposal {
         // 20-byte public key hash of the target wallet.
@@ -662,6 +670,37 @@ contract WalletProposalValidator {
         return true;
     }
 
+    function validateMovedFundsSweepProposal(
+        MovedFundsSweepProposal calldata proposal
+    ) external view returns (bool) {
+        Wallets.Wallet memory wallet = bridge.wallets(
+            proposal.walletPubKeyHash
+        );
+
+        // Make sure the wallet is in Live or MovingFunds state.
+        require(
+            wallet.state == Wallets.WalletState.Live ||
+                wallet.state == Wallets.WalletState.MovingFunds,
+            "Source wallet is not in Live or MovingFunds state"
+        );
+
+        // Make sure the proposed fee is valid.
+        (, , , , , , , uint64 movedFundsSweepTxMaxTotalFee, , , ) = bridge
+            .movingFundsParameters();
+
+        require(
+            proposal.movedFundsSweepTxFee > 0,
+            "Proposed transaction fee cannot be zero"
+        );
+
+        require(
+            proposal.movedFundsSweepTxFee <= movedFundsSweepTxMaxTotalFee,
+            "Proposed transaction fee is too high"
+        );
+
+        return true;
+    }
+
     /// @notice View function encapsulating the main rules of a valid heartbeat
     ///         proposal. This function is meant to facilitate the off-chain
     ///         validation of the incoming proposals. Thanks to it, most