From 61946ff703c445be041953e0f3fca5b667764720 Mon Sep 17 00:00:00 2001
From: Eric Taylor <eric.taylor@avalabs.org>
Date: Mon, 23 Sep 2024 08:38:56 -0600
Subject: [PATCH] feat: breakout spend reducers filters

---
 .../spend-reducers/useSpendableLockedUTXOs.ts | 57 +++++++++++--------
 .../spend-reducers/useUnlockedUTXOs.ts        | 49 +++++++++-------
 2 files changed, 60 insertions(+), 46 deletions(-)

diff --git a/src/vms/pvm/etna-builder/spend-reducers/useSpendableLockedUTXOs.ts b/src/vms/pvm/etna-builder/spend-reducers/useSpendableLockedUTXOs.ts
index 5b59f08cb..da42cf8a9 100644
--- a/src/vms/pvm/etna-builder/spend-reducers/useSpendableLockedUTXOs.ts
+++ b/src/vms/pvm/etna-builder/spend-reducers/useSpendableLockedUTXOs.ts
@@ -17,7 +17,38 @@ import {
 } from '../../../../utils';
 import { verifySignaturesMatch } from '../../../utils/calculateSpend/utils';
 import { IncorrectStakeableLockOutError } from './errors';
-import type { SpendReducerFunction } from './types';
+import type { SpendReducerFunction, SpendReducerState } from './types';
+
+/**
+ * Is responsible for filtering out the usable UTXOs from the list of UTXOs.
+ *
+ * @internal - Only exported for testing.
+ */
+export const getUsableUTXOsFilter =
+  (state: SpendReducerState) =>
+  (utxo: Utxo): utxo is Utxo<StakeableLockOut<TransferOutput>> => {
+    // 1a. Ensure UTXO output is a StakeableLockOut.
+    if (!isStakeableLockOut(utxo.output)) {
+      return false;
+    }
+
+    // 1b. Ensure UTXO is stakeable.
+    if (!(state.spendOptions.minIssuanceTime < utxo.output.getLocktime())) {
+      return false;
+    }
+
+    // 1c. Ensure transferOut is a TransferOutput.
+    if (!isTransferOut(utxo.output.transferOut)) {
+      throw IncorrectStakeableLockOutError;
+    }
+
+    // 1d. Filter out UTXOs that aren't needed for staking.
+    if ((state.toStake.get(utxo.assetId.value()) ?? 0n) === 0n) {
+      return false;
+    }
+
+    return true;
+  };
 
 export const useSpendableLockedUTXOs: SpendReducerFunction = (
   state,
@@ -26,29 +57,7 @@ export const useSpendableLockedUTXOs: SpendReducerFunction = (
   // 1. Filter out the UTXOs that are not usable.
   const usableUTXOs: Utxo<StakeableLockOut<TransferOutput>>[] = state.utxos
     // Filter out non stakeable lockouts and lockouts that are not stakeable yet.
-    .filter((utxo): utxo is Utxo<StakeableLockOut<TransferOutput>> => {
-      // 1a. Ensure UTXO output is a StakeableLockOut.
-      if (!isStakeableLockOut(utxo.output)) {
-        return false;
-      }
-
-      // 1b. Ensure UTXO is stakeable.
-      if (!(state.spendOptions.minIssuanceTime < utxo.output.getLocktime())) {
-        return false;
-      }
-
-      // 1c. Ensure there are funds to stake.
-      if ((state.toStake.get(utxo.assetId.value()) ?? 0n) === 0n) {
-        return false;
-      }
-
-      // 1d. Ensure transferOut is a TransferOutput.
-      if (!isTransferOut(utxo.output.transferOut)) {
-        throw IncorrectStakeableLockOutError;
-      }
-
-      return true;
-    });
+    .filter(getUsableUTXOsFilter(state));
 
   // 2. Verify signatures match.
   const verifiedUsableUTXOs = verifySignaturesMatch(
diff --git a/src/vms/pvm/etna-builder/spend-reducers/useUnlockedUTXOs.ts b/src/vms/pvm/etna-builder/spend-reducers/useUnlockedUTXOs.ts
index 796c50d54..8b9c4be37 100644
--- a/src/vms/pvm/etna-builder/spend-reducers/useUnlockedUTXOs.ts
+++ b/src/vms/pvm/etna-builder/spend-reducers/useUnlockedUTXOs.ts
@@ -15,7 +15,32 @@ import {
 } from '../../../../utils';
 import { verifySignaturesMatch } from '../../../utils/calculateSpend/utils';
 import { IncorrectStakeableLockOutError } from './errors';
-import type { SpendReducerFunction } from './types';
+import type { SpendReducerFunction, SpendReducerState } from './types';
+
+/**
+ * Is responsible for filtering out the usable UTXOs from the list of UTXOs.
+ *
+ * @internal - Only exported for testing.
+ */
+export const getUsableUTXOsFilter =
+  (state: SpendReducerState) =>
+  (
+    utxo: Utxo,
+  ): utxo is Utxo<TransferOutput | StakeableLockOut<TransferOutput>> => {
+    if (isTransferOut(utxo.output)) {
+      return true;
+    }
+
+    if (isStakeableLockOut(utxo.output)) {
+      if (!isTransferOut(utxo.output.transferOut)) {
+        throw IncorrectStakeableLockOutError;
+      }
+
+      return utxo.output.getLocktime() < state.spendOptions.minIssuanceTime;
+    }
+
+    return false;
+  };
 
 export const useUnlockedUTXOs: SpendReducerFunction = (
   state,
@@ -26,27 +51,7 @@ export const useUnlockedUTXOs: SpendReducerFunction = (
   const usableUTXOs: Utxo<TransferOutput | StakeableLockOut<TransferOutput>>[] =
     state.utxos
       // Filter out non stakeable lockouts and lockouts that are not stakeable yet.
-      .filter(
-        (
-          utxo,
-        ): utxo is Utxo<TransferOutput | StakeableLockOut<TransferOutput>> => {
-          if (isTransferOut(utxo.output)) {
-            return true;
-          }
-
-          if (isStakeableLockOut(utxo.output)) {
-            if (!isTransferOut(utxo.output.transferOut)) {
-              throw IncorrectStakeableLockOutError;
-            }
-
-            return (
-              utxo.output.getLocktime() < state.spendOptions.minIssuanceTime
-            );
-          }
-
-          return false;
-        },
-      );
+      .filter(getUsableUTXOsFilter(state));
 
   // 2. Verify signatures match.
   const verifiedUsableUTXOs = verifySignaturesMatch(