fix(bridge-ui): fix use max logic

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

@@ -445,44 +445,67 @@
   }
 
   async function useFullAmount() {
-    if (isETH($token)) {
-      try {
-        const feeData = await fetchFeeData();
-        const gasEstimate = await $activeBridge.estimateGas({
-          amount: BigNumber.from(1),
-          signer: $signer,
-          tokenAddress: await getAddressForToken(
-            $token,
-            $srcChain,
-            $destChain,
-            $signer,
-          ),
-          srcChainId: $srcChain.id,
-          destChainId: $destChain.id,
-          tokenVaultAddress: tokenVaults[$srcChain.id],
-          processingFeeInWei: getProcessingFee(),
-          memo: memo,
-          to: showTo && to ? to : await $signer.getAddress(),
-        });
-
-        const requiredGas = gasEstimate.mul(feeData.gasPrice);
-        const userBalance = await $signer.getBalance('latest');
-        const processingFee = getProcessingFee();
-        let balanceAvailableForTx = userBalance.sub(requiredGas);
-
-        if (processingFee) {
-          balanceAvailableForTx = balanceAvailableForTx.sub(processingFee);
-        }
+    try {
+      const feeData = await fetchFeeData();
+      const processingFeeInWei = getProcessingFee();
+
+      const bridgeAddress = chains[$srcChain.id].bridgeAddress; // for ETH
+      const tokenVaultAddress = tokenVaults[$srcChain.id]; // for ERC20
 
-        amount = ethers.utils.formatEther(balanceAvailableForTx);
-      } catch (error) {
-        console.error(error);
+      const toAddress = showTo && to ? to : await $signer.getAddress();
 
-        // 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.toString();
+      // For ETH this function returns '0x00'
+      const tokenAddress = await getAddressForToken(
+        $token,
+        $srcChain,
+        $destChain,
+        $signer,
+      );
+
+      // Whatever amount just to get an estimation
+      const bnAmount = BigNumber.from(1);
+
+      // TODO: different arguments depending on the type of bridge
+      const gasEstimate = await $activeBridge.estimateGas({
+        memo,
+        tokenAddress,
+        bridgeAddress,
+        tokenVaultAddress,
+        processingFeeInWei,
+        to: toAddress,
+        signer: $signer,
+        amount: bnAmount,
+        srcChainId: $srcChain.id,
+        destChainId: $destChain.id,
+      });
+
+      const requiredGas = gasEstimate.mul(feeData.gasPrice);
+
+      // We might have decimals. BigNumber can't take strings
+      // with decimals. E.g. BigNumber.from('1.0') will throw an error.
+      // We can get a BigNumber by parsing, passing the right amount
+      // of decimals: ethers.utils.parseUnits('1.0', decimals)
+      const userBalance = ethers.utils.parseUnits(
+        tokenBalance,
+        $token.decimals || 18, // defaults to 18 decimals
+      );
+
+      // Let's start with substracting the estimated required gas to bridge
+      let balanceAvailableForTx = userBalance.sub(requiredGas);
+
+      // Following we substract the currently selected processing fee
+      const processingFee = getProcessingFee();
+      if (processingFee) {
+        balanceAvailableForTx = balanceAvailableForTx.sub(processingFee);
       }
-    } else {
+
+      // We convert back to user readable string: `1.0`
+      amount = ethers.utils.formatUnits(balanceAvailableForTx, $token.decimals);
+    } catch (error) {
+      console.error(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.toString();
     }
   }