feat: create transaction fee estimator

src/actions/estimateFee.ts

@@ -0,0 +1,37 @@
+import { Keypair, PublicKey } from '@solana/web3.js';
+import { Transaction } from '@metaplex-foundation/mpl-core';
+import BN from 'bn.js';
+import { Connection } from '../Connection';
+
+interface Params {
+  connection: Connection;
+  feePayer: PublicKey;
+  txs: Transaction[];
+  signers?: Keypair[];
+}
+
+type Lamports = BN;
+
+type EstimateFee = (params: Params) => Promise<Lamports>;
+
+export const estimateFee: EstimateFee = async (params) => {
+  const { connection, feePayer, txs, signers = [] } = params;
+
+  const {
+    blockhash,
+    feeCalculator: { lamportsPerSignature },
+  } = await connection.getRecentBlockhash();
+
+  const tx = Transaction.fromCombined(txs, {
+    feePayer,
+    recentBlockhash: blockhash,
+  });
+
+  if (signers.length) {
+    tx.partialSign(...signers);
+  }
+
+  const { numRequiredSignatures } = tx.compileMessage().header;
+
+  return new BN(numRequiredSignatures * lamportsPerSignature);
+};