feat: skeleton for GsmConverter buyAsset

src/contracts/facilitators/gsm/GsmConverter.sol

@@ -0,0 +1,86 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.10;
+
+// import {VersionedInitializable} from '@aave/core-v3/contracts/protocol/libraries/aave-upgradeability/VersionedInitializable.sol';
+// import {IERC20} from '@aave/core-v3/contracts/dependencies/openzeppelin/contracts/IERC20.sol';
+import {GPv2SafeERC20} from '@aave/core-v3/contracts/dependencies/gnosis/contracts/GPv2SafeERC20.sol';
+// import {EIP712} from '@openzeppelin/contracts/utils/cryptography/EIP712.sol';
+// import {SignatureChecker} from '@openzeppelin/contracts/utils/cryptography/SignatureChecker.sol';
+// import {SafeCast} from '@openzeppelin/contracts/utils/math/SafeCast.sol';
+// import {AccessControl} from '@openzeppelin/contracts/access/AccessControl.sol';
+// import {IGhoFacilitator} from '../../gho/interfaces/IGhoFacilitator.sol';
+// import {IGhoToken} from '../../gho/interfaces/IGhoToken.sol';
+// import {IGsmPriceStrategy} from './priceStrategy/interfaces/IGsmPriceStrategy.sol';
+// import {IGsmFeeStrategy} from './feeStrategy/interfaces/IGsmFeeStrategy.sol';
+import {IGsm} from './interfaces/IGsm.sol';
+import {IRedemption} from './dependencies/circle/interfaces/IRedemption.sol';
+
+/**
+ * @title GsmConverter
+ * @author Aave
+ * @notice GHO Stability Module. It provides buy/sell facilities to go to/from an underlying asset to/from GHO.
+ * @dev To be covered by a proxy contract.
+ */
+contract GsmConverter {
+  using GPv2SafeERC20 for IERC20;
+
+  address public immutable GSM;
+  address public immutable GHO_TOKEN;
+  address public immutable REDEEMABLE_ASSET; // BUIDL token
+  address public immutable REDEEMED_ASSET; // USDC token
+  address public immutable REDEMPTION; // redeem BUIDL to USDC
+
+  event BuyAssetThroughRedemption(
+    address indexed originator,
+    address indexed receiver,
+    uint256 redemptionAssetAmount,
+    uint256 ghoSold
+  );
+
+  /**
+   * @dev Constructor
+   * @param ghoToken The address of the GHO token contract
+   * @param underlyingAsset The address of the collateral asset
+   * @param priceStrategy The address of the price strategy
+   */
+  constructor(address gsm, address redemption, address redeemableAsset, address redeemedAsset) {
+    require(gsm != address(0), 'ZERO_ADDRESS_NOT_VALID');
+    require(redemption != address(0), 'ZERO_ADDRESS_NOT_VALID');
+    require(redeemableAsset != address(0), 'ZERO_ADDRESS_NOT_VALID');
+    require(redeemedAsset != address(0), 'ZERO_ADDRESS_NOT_VALID');
+
+    GSM = gsm;
+    REDEMPTION = redemption;
+    REDEEMABLE_ASSET = redeemableAsset;
+    REDEEMED_ASSET = redeemedAsset;
+  }
+
+  // TODO:
+  // 1) implement buyAsset (sell GHO -> get USDC)
+  // - GHO transferFrom user to converter
+  // - call buyAsset on GSM, get the BUIDL
+  // - offramp BUIDL to USDC, send USDC to user
+  // - call redeem on offramp to get BUIDL
+  // - send USDC to user, safeTransfer
+
+  /**
+   * @dev
+   */
+  function buyAssetThroughRedemption(
+    uint256 minAmount,
+    address receiver
+  ) external returns (uint256, uint256) {
+    IGhoToken(IGSM(GSM).GHO_TOKEN()).transferFrom(msg.sender, address(this), minAmount);
+    (uint256 redemptionAssetAmount, uint256 ghoSold) = IGSM(GSM).buyAsset(minAmount, receiver);
+    IRedemption(REDEMPTION).redeem(redemptionAssetAmount);
+    IERC20(REDEEMED_ASSET).safeTransfer(receiver, redemptionAssetAmount);
+
+    emit BuyAssetThroughRedemption(msg.sender, receiver, redemptionAssetAmount, ghoSold);
+  }
+
+  // TODO:
+  // 2) implement sellAsset (sell USDC -> get GHO)
+  // - onramp USDC to BUIDL, get BUIDL - unknown how to onramp USDC to BUIDL currently
+  // - send BUIDL to GSM, get GHO from GSM
+  // - send GHO to user, safeTransfer
+}

src/contracts/facilitators/gsm/dependencies/circle/interfaces/IRedemption.sol

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+/**
+ * Copyright 2024 Circle Internet Financial, LTD. All rights reserved.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+pragma solidity ^0.8.16;
+
+/**
+ * @title IRedemption
+ */
+interface IRedemption {
+  /**
+   * @notice The asset being redeemed.
+   * @return The address of the asset token.
+   */
+  function asset() external view returns (address);
+
+  /**
+   * @notice The liquidity token that the asset is being redeemed for.
+   * @return The address of the liquidity token.
+   */
+  function liquidity() external view returns (address);
+
+  /**
+   * @notice Redeems an amount of asset for liquidity
+   * @param amount The amount of the asset token to redeem
+   */
+  function redeem(uint256 amount) external;
+}