fix: fix up IBC amount input (#1281)

Fixes #1271.

- Use empty input with placeholder instead of default 0 value
- Check for max decimal places allowed by selected asset

apps/namadillo/src/App/Transfer/TransferSource.tsx

@@ -27,6 +27,17 @@ export type TransferSourceProps = {
   onChangeShielded?: (isShielded: boolean) => void;
 };
 
+const amountMaxDecimalPlaces = (asset?: Asset): number | undefined => {
+  if (typeof asset !== "undefined") {
+    for (const { denom, exponent } of asset.denom_units) {
+      if (denom === asset.display) {
+        return exponent;
+      }
+    }
+  }
+  return undefined;
+};
+
 export const TransferSource = ({
   chain,
   asset,
@@ -91,8 +102,10 @@ export const TransferSource = ({
             "[&_input]:!border-0 [&_input]:px-0"
           )}
           disabled={!chain || !asset}
-          value={amount || new BigNumber(0)}
-          onChange={(e) => onChangeAmount && onChangeAmount(e.target.value)}
+          value={amount}
+          onChange={(e) => onChangeAmount?.(e.target.value)}
+          placeholder="Amount"
+          maxDecimalPlaces={amountMaxDecimalPlaces(asset)}
         />
       </div>
       {asset && availableAmount && (

apps/namadillo/src/App/Transfer/__tests__/TransferSource.test.tsx

@@ -59,7 +59,7 @@ describe("Component: TransferSource", () => {
     const assetControl = getEmptyAsset();
     fireEvent.click(assetControl);
     expect(openAssetSelectorMock).not.toHaveBeenCalled();
-    const amountInput = screen.getByDisplayValue("0");
+    const amountInput = screen.getByPlaceholderText("Amount");
     expect(amountInput).toBeDisabled();
   });