Rollover vault

spot-contracts/contracts/_utils/BondHelpers.sol

@@ -2,6 +2,7 @@
 pragma solidity ^0.8.18;
 
 import { SafeCastUpgradeable } from "@openzeppelin/contracts-upgradeable/utils/math/SafeCastUpgradeable.sol";
+import { MathUpgradeable } from "@openzeppelin/contracts-upgradeable/utils/math/MathUpgradeable.sol";
 
 import { IERC20Upgradeable } from "@openzeppelin/contracts-upgradeable/token/ERC20/IERC20Upgradeable.sol";
 import { IBondController } from "../_interfaces/buttonwood/IBondController.sol";
@@ -66,6 +67,9 @@ library TrancheHelpers {
  *
  */
 library BondHelpers {
+    using SafeCastUpgradeable for uint256;
+    using MathUpgradeable for uint256;
+
     // Replicating value used here:
     // https://github.com/buttonwood-protocol/tranche/blob/main/contracts/BondController.sol
     uint256 private constant TRANCHE_RATIO_GRANULARITY = 1000;
@@ -92,7 +96,7 @@ library BondHelpers {
     /// @return The tranche data.
     function getTrancheData(IBondController b) internal view returns (TrancheData memory) {
         TrancheData memory td;
-        td.trancheCount = SafeCastUpgradeable.toUint8(b.trancheCount());
+        td.trancheCount = b.trancheCount().toUint8();
         td.tranches = new ITranche[](td.trancheCount);
         td.trancheRatios = new uint256[](td.trancheCount);
         // Max tranches per bond < 2**8 - 1
@@ -191,27 +195,39 @@ library BondHelpers {
         return (td, collateralBalances, trancheSupplies);
     }
 
-    /// @notice Given a bond, retrieves the collateral redeemable for
-    ///         each tranche held by the given address.
+    /// @notice For a given bond and user address, computes the maximum number of each of the bond's tranches
+    ///         the user is able to redeem before the bond's maturity. These tranche amounts necessarily match the bond's tranche ratios.
     /// @param b The address of the bond contract.
     /// @param u The address to check balance for.
-    /// @return The tranche data and an array of collateral balances.
-    function getTrancheCollateralBalances(IBondController b, address u)
+    /// @return The tranche data and an array of tranche token balances.
+    function computeRedeemableTrancheAmounts(IBondController b, address u)
         internal
         view
         returns (TrancheData memory, uint256[] memory)
     {
-        TrancheData memory td;
-        uint256[] memory collateralBalances;
-        uint256[] memory trancheSupplies;
+        TrancheData memory td = getTrancheData(b);
+        uint256[] memory redeemableAmts = new uint256[](td.trancheCount);
+
+        // Calculate how many underlying assets could be redeemed from each tranche balance,
+        // assuming other tranches are not an issue, and record the smallest amount.
+        uint256 minUnderlyingOut = type(uint256).max;
+        uint8 i;
+        for (i = 0; i < td.trancheCount; i++) {
+            uint256 d = td.tranches[i].balanceOf(u).mulDiv(TRANCHE_RATIO_GRANULARITY, td.trancheRatios[i]);
+            if (d < minUnderlyingOut) {
+                minUnderlyingOut = d;
+            }
 
-        (td, collateralBalances, trancheSupplies) = getTrancheCollateralizations(b);
+            // if one of the balances is zero, we return
+            if (minUnderlyingOut == 0) {
+                return (td, redeemableAmts);
+            }
+        }
 
-        uint256[] memory balances = new uint256[](td.trancheCount);
-        for (uint8 i = 0; i < td.trancheCount; i++) {
-            balances[i] = (td.tranches[i].balanceOf(u) * collateralBalances[i]) / trancheSupplies[i];
+        for (i = 0; i < td.trancheCount; i++) {
+            redeemableAmts[i] = td.trancheRatios[i].mulDiv(minUnderlyingOut, TRANCHE_RATIO_GRANULARITY);
         }
 
-        return (td, balances);
+        return (td, redeemableAmts);
     }
 }

spot-contracts/contracts/test/BondHelpersTester.sol

@@ -33,14 +33,6 @@ contract BondHelpersTester {
         return b.previewDeposit(collateralAmount);
     }
 
-    function getTrancheCollateralBalances(IBondController b, address u)
-        public
-        view
-        returns (TrancheData memory, uint256[] memory)
-    {
-        return b.getTrancheCollateralBalances(u);
-    }
-
     function getTrancheCollateralizations(IBondController b)
         public
         view
@@ -57,4 +49,12 @@ contract BondHelpersTester {
         TrancheData memory td = b.getTrancheData();
         return td.getTrancheIndex(t);
     }
+
+    function computeRedeemableTrancheAmounts(IBondController b, address u)
+        public
+        view
+        returns (TrancheData memory td, uint256[] memory)
+    {
+        return b.computeRedeemableTrancheAmounts(u);
+    }
 }