fix(bridge): max amount button should deduct gas

packages/bridge-ui/src/components/form/BridgeForm.svelte

@@ -36,6 +36,7 @@
   import { MessageStatus } from "../../domain/message";
   import { Funnel } from "svelte-heros-v2";
   import FaucetModal from "../modals/FaucetModal.svelte";
+  import { fetchFeeData } from "@wagmi/core";
 
   let amount: string;
   let amountInput: HTMLInputElement;
@@ -177,13 +178,27 @@
     }
   }
 
+  async function checkUserHasEnoughBalance(gasEstimate: BigNumber) {
+    const feeData = await fetchFeeData();
+    const requiredGas = gasEstimate.mul(feeData.gasPrice);
+    const userBalance = await $signer.getBalance("latest");
+
+    let balanceAvailableForTx = userBalance;
+
+    if($token.symbol === ETH.symbol) {
+      balanceAvailableForTx = userBalance.sub(ethers.utils.parseEther(amount));
+    }
+
+    return balanceAvailableForTx.gte(requiredGas);
+  }
+
   async function bridge() {
     try {
       loading = true;
       if (requiresAllowance) throw Error("requires additional allowance");
 
       const amountInWei = ethers.utils.parseUnits(amount, $token.decimals);
-      const tx = await $activeBridge.Bridge({
+      const bridgeOpts = {
         amountInWei: amountInWei,
         signer: $signer,
         tokenAddress: await addrForToken(),
@@ -192,7 +207,20 @@
         tokenVaultAddress: $chainIdToTokenVaultAddress.get($fromChain.id),
         processingFeeInWei: getProcessingFee(),
         memo: memo,
+      };
+
+      const gasEstimate = await $activeBridge.EstimateGas({
+        ...bridgeOpts,
+        amountInWei: BigNumber.from(1),
       });
+      const doesUserHaveEnoughBalance = await checkUserHasEnoughBalance(gasEstimate)
+
+      if(!doesUserHaveEnoughBalance) {
+        errorToast("Insufficient ETH balance");
+        return;
+      }
+
+      const tx = await $activeBridge.Bridge(bridgeOpts);
 
       // tx.chainId is not set immediately but we need it later. set it
       // manually.
@@ -243,9 +271,42 @@
     }
   }
 
-  function useFullAmount() {
-    amount = tokenBalance;
-    amountInput.value = tokenBalance.toString();
+  async function useFullAmount() {
+    if($token.symbol === ETH.symbol) {
+    try {
+        const feeData = await fetchFeeData();
+        const gasEstimate = await $activeBridge.EstimateGas({
+          amountInWei: BigNumber.from(1),
+          signer: $signer,
+          tokenAddress: await addrForToken(),
+          fromChainId: $fromChain.id,
+          toChainId: $toChain.id,
+          tokenVaultAddress: $chainIdToTokenVaultAddress.get($fromChain.id),
+          processingFeeInWei: getProcessingFee(),
+          memo: memo,
+        });
+        const requiredGas = gasEstimate.mul(feeData.gasPrice);
+        const userBalance = await $signer.getBalance("latest");
+        const processingFee = getProcessingFee();
+        let balanceAvailableForTx = userBalance.sub(requiredGas);
+        if(processingFee) {
+          balanceAvailableForTx = balanceAvailableForTx.sub(processingFee);
+        }
+
+        amount = ethers.utils.formatEther(balanceAvailableForTx);
+        amountInput.value = ethers.utils.formatEther(balanceAvailableForTx);
+    } catch (error) {
+      console.log(error);
+
+      // In case of error default to using the full amount of ETH available.
+      // The user would still not be able to make the restriction and will have to manually set the amount.
+      amount = tokenBalance;
+      amountInput.value = tokenBalance.toString();
+    }
+    } else {
+      amount = tokenBalance;
+      amountInput.value = tokenBalance.toString();
+    }
   }
 
   function updateAmount(e: any) {

packages/bridge-ui/src/domain/bridge.ts

@@ -39,6 +39,7 @@ interface Bridge {
   RequiresAllowance(opts: ApproveOpts): Promise<boolean>;
   Approve(opts: ApproveOpts): Promise<Transaction>;
   Bridge(opts: BridgeOpts): Promise<Transaction>;
+  EstimateGas(opts: BridgeOpts): Promise<BigNumber>;
   Claim(opts: ClaimOpts): Promise<Transaction>;
 }
 

packages/bridge-ui/src/erc20/bridge.ts

@@ -20,6 +20,33 @@ class ERC20Bridge implements Bridge {
     this.prover = prover;
   }
 
+  static async prepareTransaction(opts: BridgeOpts) {
+    const contract: Contract = new Contract(
+      opts.tokenVaultAddress,
+      TokenVault,
+      opts.signer
+    );
+
+    const owner = await opts.signer.getAddress();
+    const message = {
+      sender: owner,
+      srcChainId: opts.fromChainId,
+      destChainId: opts.toChainId,
+      owner: owner,
+      to: owner,
+      refundAddress: owner,
+      depositValue: opts.amountInWei,
+      callValue: 0,
+      processingFee: opts.processingFeeInWei ?? BigNumber.from(0),
+      gasLimit: opts.processingFeeInWei
+        ? BigNumber.from(100000)
+        : BigNumber.from(0),
+      memo: opts.memo ?? "",
+    };
+
+    return { contract, owner, message };
+  }
+
   private async spenderRequiresAllowance(
     tokenAddress: string,
     signer: Signer,
@@ -76,28 +103,7 @@ class ERC20Bridge implements Bridge {
       throw Error("token vault does not have required allowance");
     }
 
-    const contract: Contract = new Contract(
-      opts.tokenVaultAddress,
-      TokenVault,
-      opts.signer
-    );
-
-    const owner = await opts.signer.getAddress();
-    const message = {
-      sender: owner,
-      srcChainId: opts.fromChainId,
-      destChainId: opts.toChainId,
-      owner: owner,
-      to: owner,
-      refundAddress: owner,
-      depositValue: opts.amountInWei,
-      callValue: 0,
-      processingFee: opts.processingFeeInWei ?? BigNumber.from(0),
-      gasLimit: opts.processingFeeInWei
-        ? BigNumber.from(100000)
-        : BigNumber.from(0),
-      memo: opts.memo ?? "",
-    };
+    const { contract, owner, message } = await ERC20Bridge.prepareTransaction(opts);
 
     const tx = await contract.sendERC20(
       message.destChainId,
@@ -116,6 +122,27 @@ class ERC20Bridge implements Bridge {
     return tx;
   }
 
+  async EstimateGas(opts: BridgeOpts): Promise<BigNumber> {
+
+    const { contract, owner, message } = await ERC20Bridge.prepareTransaction(opts);
+
+    const gasEstimate = await contract.estimateGas.sendERC20(
+      message.destChainId,
+      owner,
+      opts.tokenAddress,
+      opts.amountInWei,
+      message.gasLimit,
+      message.processingFee,
+      message.refundAddress,
+      message.memo,
+      {
+        value: message.processingFee.add(message.callValue),
+      }
+    );
+
+    return gasEstimate;
+  }
+
   async Claim(opts: ClaimOpts): Promise<Transaction> {
     const contract: Contract = new Contract(
       opts.destBridgeAddress,

packages/bridge-ui/src/eth/bridge.ts

@@ -19,16 +19,7 @@ class ETHBridge implements BridgeInterface {
     this.prover = prover;
   }
 
-  RequiresAllowance(opts: ApproveOpts): Promise<boolean> {
-    return Promise.resolve(false);
-  }
-
-  // ETH does not need to be approved for transacting
-  Approve(opts: ApproveOpts): Promise<Transaction> {
-    return new Promise((resolve) => resolve({} as unknown as Transaction));
-  }
-
-  async Bridge(opts: BridgeOpts): Promise<Transaction> {
+  static async prepareTransaction(opts: BridgeOpts): Promise<{contract: Contract, message: any, owner: string}> {
     const contract: Contract = new Contract(
       opts.tokenVaultAddress,
       TokenVault,
@@ -52,6 +43,21 @@ class ETHBridge implements BridgeInterface {
       memo: opts.memo ?? "",
     };
 
+    return { contract, owner, message };
+  }
+
+  RequiresAllowance(opts: ApproveOpts): Promise<boolean> {
+    return Promise.resolve(false);
+  }
+
+  // ETH does not need to be approved for transacting
+  Approve(opts: ApproveOpts): Promise<Transaction> {
+    return new Promise((resolve) => resolve({} as unknown as Transaction));
+  }
+
+  async Bridge(opts: BridgeOpts): Promise<Transaction> {
+    const { contract, owner, message } = await ETHBridge.prepareTransaction(opts);
+
     const tx = await contract.sendEther(
       message.destChainId,
       owner,
@@ -69,6 +75,26 @@ class ETHBridge implements BridgeInterface {
     return tx;
   }
 
+  async EstimateGas(opts: BridgeOpts): Promise<BigNumber> {
+    const { contract, owner, message } = await ETHBridge.prepareTransaction(opts);
+
+    const gasEstimate = await contract.estimateGas.sendEther(
+      message.destChainId,
+      owner,
+      message.gasLimit,
+      message.processingFee,
+      message.refundAddress,
+      message.memo,
+      {
+        value: message.depositValue
+          .add(message.processingFee)
+          .add(message.callValue),
+      }
+    );
+
+    return gasEstimate;
+  }
+
   async Claim(opts: ClaimOpts): Promise<Transaction> {
     const contract: Contract = new Contract(
       opts.destBridgeAddress,