Add estimate fee function

utils/estimateFee.ts

@@ -0,0 +1,20 @@
+import { sign, XRPL_Account } from "xrpl-accountlib"
+import state from "../state"
+
+// Mutate tx object with network estimated fee value
+const estimateFee = async (tx: Record<string, unknown>, keypair: XRPL_Account): Promise<null | { base_fee: string, median_fee: string; minimum_fee: string; open_ledger_fee: string; }> => {
+  const copyTx = JSON.parse(JSON.stringify(tx))
+  delete copyTx['SigningPubKey']
+  const { signedTransaction } = sign(copyTx, keypair);
+  try {
+    const res = await state.client?.send({ command: 'fee', tx_blob: signedTransaction })
+    if (res && res.drops) {
+      return tx['Fee'] = res.drops.base_fee;
+    }
+    return null
+  } catch (err) {
+    throw Error('Cannot estimate fee')
+  }
+}
+
+export default estimateFee