fix(input-selection): roundRobinSelection now ensures all change bundles meet minRequiredAda

Author: AngelCastilloB

Diff for: packages/input-selection/src/RoundRobinRandomImprove/change.ts

@@ -207,7 +207,22 @@ const pickExtraRandomUtxo = (
   return { utxoRemaining: newUtxoRemaining, utxoSelected: newUtxoSelected };
 };
 
-const coalesceChangeBundlesForMinCoinRequirement = (
+const mergeWithSmallestBundle = (values: Cardano.Value[], index: number): Cardano.Value[] => {
+  let result = [...values];
+  const toBeMerged = result.splice(index, 1)[0];
+
+  if (result.length === 0) return [toBeMerged];
+
+  const last = result.splice(-1, 1)[0];
+  const merged = coalesceValueQuantities([toBeMerged, last]);
+
+  result = [...result, merged];
+  result = orderBy(result, ({ coins }) => coins, 'desc');
+
+  return result;
+};
+
+export const coalesceChangeBundlesForMinCoinRequirement = (
   changeBundles: Cardano.Value[],
   computeMinimumCoinQuantity: ComputeMinimumCoinQuantity
 ): Cardano.Value[] | undefined => {
@@ -230,15 +245,22 @@ const coalesceChangeBundlesForMinCoinRequirement = (
     return value.coins >= computeMinimumCoinQuantity(stubTxOut);
   };
 
-  while (sortedBundles.length > 1 && !satisfiesMinCoinRequirement(sortedBundles[sortedBundles.length - 1])) {
-    const smallestBundle = sortedBundles.pop()!;
-    sortedBundles[sortedBundles.length - 1] = coalesceValueQuantities([
-      sortedBundles[sortedBundles.length - 1],
-      smallestBundle
-    ]);
-    // Re-sort because last bundle is not necessarily the smallest one after merging it
-    sortedBundles = orderBy(sortedBundles, ({ coins }) => coins, 'desc');
+  let allBundlesSatisfyMinCoin = false;
+
+  while (sortedBundles.length > 1 && !allBundlesSatisfyMinCoin) {
+    allBundlesSatisfyMinCoin = true;
+    for (let i = sortedBundles.length - 1; i >= 0; --i) {
+      const satisfies = satisfiesMinCoinRequirement(sortedBundles[i]);
+
+      allBundlesSatisfyMinCoin = allBundlesSatisfyMinCoin && satisfies;
+
+      if (!satisfies) {
+        sortedBundles = mergeWithSmallestBundle(sortedBundles, i);
+        break;
+      }
+    }
   }
+
   if (!satisfiesMinCoinRequirement(sortedBundles[0])) {
     // Coalesced all bundles to 1 and it's still less than min utxo value
     return undefined;

Diff for: packages/input-selection/test/change.test.ts

@@ -0,0 +1,105 @@
+import { Cardano } from '@cardano-sdk/core';
+import { coalesceChangeBundlesForMinCoinRequirement } from '../src/RoundRobinRandomImprove/change';
+
+const TOKEN1_ASSET_ID = Cardano.AssetId('5c677ba4dd295d9286e0e22786fea9ed735a6ae9c07e7a45ae4d95c84249530000');
+const TOKEN2_ASSET_ID = Cardano.AssetId('5c677ba4dd295d9286e0e22786fea9ed735a6ae9c07e7a45ae4d95c84249530001');
+const TOKEN3_ASSET_ID = Cardano.AssetId('5c677ba4dd295d9286e0e22786fea9ed735a6ae9c07e7a45ae4d95c84249530002');
+
+const MIN_ADA_COIN_VAL = 5_000_000n;
+const computeMinimumCoinQuantity = (utxo: Cardano.TxOut): bigint =>
+  MIN_ADA_COIN_VAL + (utxo.value.assets ? BigInt(utxo.value.assets.size) : 0n) * 5_000_000n;
+
+describe('coalesceChangeBundlesForMinCoinRequirement', () => {
+  it('given empty change bundle list, returns the empty list', async () => {
+    const changeBundles: Cardano.Value[] = [];
+    const result = coalesceChangeBundlesForMinCoinRequirement(changeBundles, computeMinimumCoinQuantity);
+
+    expect(result).toBeDefined();
+    expect(result?.length).toBe(0);
+  });
+
+  it('when given 3 bundles with valid min ADA coin, return the three original bundles', async () => {
+    const changeBundles: Cardano.Value[] = [{ coins: 5_000_000n }, { coins: 5_000_000n }, { coins: 5_000_000n }];
+    const result = coalesceChangeBundlesForMinCoinRequirement(changeBundles, computeMinimumCoinQuantity);
+
+    expect(result).toBeDefined();
+    expect(result?.length).toBe(3);
+
+    expect(result![0].coins).toBe(MIN_ADA_COIN_VAL);
+    expect(result![1].coins).toBe(MIN_ADA_COIN_VAL);
+    expect(result![2].coins).toBe(MIN_ADA_COIN_VAL);
+  });
+
+  it('when the last bundle has less than min ADA coin, coalesce it with the second last', async () => {
+    const changeBundles: Cardano.Value[] = [{ coins: 5_000_000n }, { coins: 5_000_000n }, { coins: 4_000_000n }];
+    const result = coalesceChangeBundlesForMinCoinRequirement(changeBundles, computeMinimumCoinQuantity);
+
+    expect(result).toBeDefined();
+    expect(result?.length).toBe(2);
+
+    expect(result![0].coins).toBe(9_000_000n);
+    expect(result![1].coins).toBe(5_000_000n);
+  });
+
+  it('when the middle bundle has less than min ADA coin, coalesce it with the last', async () => {
+    const changeBundles: Cardano.Value[] = [
+      { coins: 10_000_000n },
+      { assets: new Map([[TOKEN1_ASSET_ID, 2333n]]), coins: 7_000_000n },
+      { coins: 5_000_000n }
+    ];
+
+    const result = coalesceChangeBundlesForMinCoinRequirement(changeBundles, computeMinimumCoinQuantity);
+
+    expect(result).toBeDefined();
+    expect(result?.length).toBe(2);
+
+    expect(result![0].coins).toBe(12_000_000n);
+    expect(result![0].assets!.get(TOKEN1_ASSET_ID)).toBe(2333n);
+    expect(result![1].coins).toBe(10_000_000n);
+  });
+
+  it('when the first bundle has less than min ADA coin, coalesce it with the last', async () => {
+    const changeBundles: Cardano.Value[] = [
+      { assets: new Map([[TOKEN1_ASSET_ID, 2333n]]), coins: 7_000_000n },
+      { coins: 5_000_000n },
+      { coins: 5_000_000n }
+    ];
+
+    const result = coalesceChangeBundlesForMinCoinRequirement(changeBundles, computeMinimumCoinQuantity);
+
+    expect(result).toBeDefined();
+    expect(result?.length).toBe(2);
+
+    expect(result![0].coins).toBe(12_000_000n);
+    expect(result![0].assets!.get(TOKEN1_ASSET_ID)).toBe(2333n);
+    expect(result![1].coins).toBe(5_000_000n);
+  });
+
+  it('when the three bundle have less than min ADA coin, coalesce them together', async () => {
+    const changeBundles: Cardano.Value[] = [
+      { assets: new Map([[TOKEN1_ASSET_ID, 2333n]]), coins: 7_000_000n },
+      { assets: new Map([[TOKEN1_ASSET_ID, 2333n]]), coins: 7_000_000n },
+      { assets: new Map([[TOKEN1_ASSET_ID, 2333n]]), coins: 7_000_000n }
+    ];
+
+    const result = coalesceChangeBundlesForMinCoinRequirement(changeBundles, computeMinimumCoinQuantity);
+
+    expect(result).toBeDefined();
+    expect(result?.length).toBe(1);
+
+    expect(result![0].coins).toBe(21_000_000n);
+    expect(result![0].assets!.get(TOKEN1_ASSET_ID)).toBe(6999n);
+  });
+
+  it('when coalescing the three bundles do not reach the min ADA coin return undefined', async () => {
+    const changeBundles: Cardano.Value[] = [
+      { assets: new Map([[TOKEN1_ASSET_ID, 2333n]]), coins: 2_000_000n },
+      { assets: new Map([[TOKEN2_ASSET_ID, 2333n]]), coins: 2_000_000n },
+      { assets: new Map([[TOKEN3_ASSET_ID, 2333n]]), coins: 2_000_000n }
+    ];
+
+    const result = coalesceChangeBundlesForMinCoinRequirement(changeBundles, computeMinimumCoinQuantity);
+
+    expect(result).toBeUndefined();
+  });
+});