feat: add fee calculator

Author: erictaylor

src/vms/common/fees/dimensions.ts

@@ -48,3 +48,15 @@ export const addDimensions = (...dimensions: Dimensions[]): Dimensions => {
   }
   return result;
 };
+
+export const dimensionsToGas = (
+  dimensions: Dimensions,
+  weights: Dimensions,
+): bigint => {
+  return BigInt(
+    dimensions[FeeDimensions.Bandwidth] * weights[FeeDimensions.Bandwidth] +
+      dimensions[FeeDimensions.DBRead] * weights[FeeDimensions.DBRead] +
+      dimensions[FeeDimensions.DBWrite] * weights[FeeDimensions.DBWrite] +
+      dimensions[FeeDimensions.Compute] * weights[FeeDimensions.Compute],
+  );
+};

src/vms/pvm/txs/fee/calculator.test.ts

@@ -0,0 +1,44 @@
+import { hexToBuffer, unpackWithManager } from '../../../../utils';
+import { calculateFee } from './calculator';
+import {
+  TEST_DYNAMIC_PRICE,
+  TEST_DYNAMIC_WEIGHTS,
+  TEST_TRANSACTIONS,
+  TEST_UNSUPPORTED_TRANSACTIONS,
+} from './fixtures/transactions';
+
+const txHexToPVMTransaction = (txHex: string) => {
+  const txBytes = hexToBuffer(txHex);
+
+  // console.log('txBytes length:', txBytes.length, '=== expected bandwidth');
+
+  return unpackWithManager('PVM', txBytes);
+};
+
+describe('Calculator', () => {
+  describe('calculateFee', () => {
+    test.each(TEST_TRANSACTIONS)(
+      'calculates the fee for $name',
+      ({ txHex, expectedDynamicFee }) => {
+        const result = calculateFee(
+          txHexToPVMTransaction(txHex),
+          TEST_DYNAMIC_WEIGHTS,
+          TEST_DYNAMIC_PRICE,
+        );
+
+        expect(result).toBe(expectedDynamicFee);
+      },
+    );
+
+    test.each(TEST_UNSUPPORTED_TRANSACTIONS)(
+      'unsupported tx - $name',
+      ({ txHex }) => {
+        const tx = txHexToPVMTransaction(txHex);
+
+        expect(() => {
+          calculateFee(tx, TEST_DYNAMIC_WEIGHTS, TEST_DYNAMIC_PRICE);
+        }).toThrow('Unsupported transaction type.');
+      },
+    );
+  });
+});

src/vms/pvm/txs/fee/calculator.ts

@@ -0,0 +1,24 @@
+import type { Transaction } from '../../../common';
+import {
+  dimensionsToGas,
+  type Dimensions,
+} from '../../../common/fees/dimensions';
+import { txComplexity } from './complexity';
+
+/**
+ * Calculates the minimum required fee, in nAVAX, that an unsigned
+ * transaction must pay for valid inclusion into a block.
+ */
+export const calculateFee = (
+  // TODO: Do we need this to be UnsignedTx?
+  // If so, we can use .getTx() to get the Transaction.
+  tx: Transaction,
+  weights: Dimensions,
+  price: bigint,
+): bigint => {
+  const complexity = txComplexity(tx);
+
+  const gas = dimensionsToGas(complexity, weights);
+
+  return gas * price;
+};