From 8d9c0abe736194b664af8fcc5b6ca71c22f1d5b5 Mon Sep 17 00:00:00 2001
From: Michalis Kargakis <kargakis@protonmail.com>
Date: Wed, 20 Dec 2023 12:51:52 +0100
Subject: [PATCH] feat: calculate fees for multiple redemptions at once

This is going to be useful for both `redeemMany` and
eventually `redeemAuto` in the pool contract as these
functions already support redemption of multiple TCO2s
within a single transaction.

We can even get rid of `calculateRedemptionFees` altogether
since I don't forsee it being used in the Toucan pools
but this can be done in a follow-up if needed.
---
 src/FeeCalculator.sol                       | 36 +++++++++++++++++++++
 src/interfaces/IRedemptionFeeCalculator.sol | 10 ++++++
 2 files changed, 46 insertions(+)

diff --git a/src/FeeCalculator.sol b/src/FeeCalculator.sol
index 5f279df..5069596 100644
--- a/src/FeeCalculator.sol
+++ b/src/FeeCalculator.sol
@@ -197,6 +197,42 @@ contract FeeCalculator is IDepositFeeCalculator, IRedemptionFeeCalculator, Ownab
         return distributeFeeAmongShares(totalFee);
     }
 
+    /// @notice Calculates the redemption fees across multiple TCO2s for a given amount.
+    /// @param tco2s The addresses of the TCO2 tokens.
+    /// @param pool The address of the pool.
+    /// @param amounts The amounts to be redeemed per TCO2.
+    /// @return recipients The addresses of the fee recipients.
+    /// @return feesDenominatedInPoolTokens The amount of fees each recipient should receive.
+    function calculateRedemptionFeesMany(address[] calldata tco2s, address pool, uint256[] calldata amounts)
+        external
+        view
+        override
+        returns (address[] memory recipients, uint256[] memory feesDenominatedInPoolTokens)
+    {
+        uint256 tco2Len = tco2s.length;
+        require(tco2Len == amounts.length, "Length mismatch");
+
+        uint256 totalFee = 0;
+        uint256 totalPoolSupply = getTotalSupply(pool);
+
+        for (uint256 i = 0; i < tco2Len; ++i) {
+            uint256 redemptionAmount = amounts[i];
+            require(redemptionAmount > 0, "amount must be > 0");
+            uint256 tco2Balance = getTokenBalance(pool, tco2s[i]);
+            uint256 feeAmount = getRedemptionFee(redemptionAmount, tco2Balance, totalPoolSupply);
+            require(feeAmount <= redemptionAmount, "Fee must be lower or equal to redemption amount");
+            totalFee += feeAmount;
+            // Update total pool supply to account for the tokens to be burnt
+            // so the next iteration charges fees using the intermediate
+            // pool supply.
+            totalPoolSupply = totalPoolSupply - redemptionAmount + feeAmount;
+        }
+
+        require(totalFee > 0, "Fee must be greater than 0");
+
+        return distributeFeeAmongShares(totalFee);
+    }
+
     /// @notice Gets the balance of the TCO2 token in a given pool.
     /// @param pool The address of the pool.
     /// @param tco2 The address of the TCO2 token.
diff --git a/src/interfaces/IRedemptionFeeCalculator.sol b/src/interfaces/IRedemptionFeeCalculator.sol
index a0185f2..5280f76 100644
--- a/src/interfaces/IRedemptionFeeCalculator.sol
+++ b/src/interfaces/IRedemptionFeeCalculator.sol
@@ -18,4 +18,14 @@ interface IRedemptionFeeCalculator {
     function calculateRedemptionFees(address tco2, address pool, uint256 depositAmount)
         external
         returns (address[] memory recipients, uint256[] memory feesDenominatedInPoolTokens);
+
+    /// @notice Calculates the redemption fees across multiple TCO2s for a given amount.
+    /// @param tco2s The addresses of the TCO2 tokens.
+    /// @param pool The address of the pool.
+    /// @param amounts The amounts to be redeemed per TCO2.
+    /// @return recipients The addresses of the fee recipients.
+    /// @return feesDenominatedInPoolTokens The amount of fees each recipient should receive.
+    function calculateRedemptionFeesMany(address[] calldata tco2s, address pool, uint256[] calldata amounts)
+        external
+        returns (address[] memory recipients, uint256[] memory feesDenominatedInPoolTokens);
 }