Update LendToAaveMigrator.sol

contracts/token/LendToAaveMigrator.sol

@@ -5,74 +5,84 @@ import {IERC20} from "../interfaces/IERC20.sol";
 import {SafeMath} from "../open-zeppelin/SafeMath.sol";
 import {VersionedInitializable} from "../utils/VersionedInitializable.sol";
 
-
 /**
-* @title LendToAaveMigrator
-* @notice This contract implements the migration from LEND to AAVE token
-* @author Aave 
-*/
+ * @title LendToAaveMigrator
+ * @notice Implements the migration from LEND to AAVE
+ * @dev Proxy-initialized via VersionedInitializable
+ */
 contract LendToAaveMigrator is VersionedInitializable {
-    using SafeMath for uint256;
+  using SafeMath for uint256;
+
+  IERC20 public immutable AAVE;
+  IERC20 public immutable LEND;
+  uint256 public immutable LEND_AAVE_RATIO;
+  uint256 public constant REVISION = 1;
+
+  uint256 public _totalLendMigrated;
+
+  /**
+   * @dev Emitted on every migration call
+   * @param sender Caller performing the migration
+   * @param amount Amount of LEND migrated (in LEND units)
+   * @param aaveOut Amount of AAVE sent (in AAVE units)
+   */
+  event LendMigrated(address indexed sender, uint256 indexed amount, uint256 indexed aaveOut);
 
-    IERC20 public immutable AAVE;
-    IERC20 public immutable LEND;
-    uint256 public immutable LEND_AAVE_RATIO;
-    uint256 public constant REVISION = 1;
-
-    uint256 public _totalLendMigrated;
+  /**
+   * @param aave The AAVE token address
+   * @param lend The LEND token address
+   * @param lendAaveRatio The exchange rate LEND:AAVE (e.g. 100 means 100 LEND -> 1 AAVE)
+   */
+  constructor(IERC20 aave, IERC20 lend, uint256 lendAaveRatio) public {
+    require(address(aave) != address(0), "AAVE_ZERO");
+    require(address(lend) != address(0), "LEND_ZERO");
+    require(lendAaveRatio > 0, "RATIO_ZERO");
+    AAVE = aave;
+    LEND = lend;
+    LEND_AAVE_RATIO = lendAaveRatio;
+  }
 
-    /**
-    * @dev emitted on migration
-    * @param sender the caller of the migration
-    * @param amount the amount being migrated
-    */
-    event LendMigrated(address indexed sender, uint256 indexed amount);
+  /**
+   * @dev Initializes the implementation (proxy pattern)
+   */
+  function initialize() public initializer {}
 
-    /**
-    * @param aave the address of the AAVE token
-    * @param lend the address of the LEND token
-    * @param lendAaveRatio the exchange rate between LEND and AAVE 
-     */
-    constructor(IERC20 aave, IERC20 lend, uint256 lendAaveRatio) public {
-        AAVE = aave;
-        LEND = lend;
-        LEND_AAVE_RATIO = lendAaveRatio;
-    }
+  /**
+   * @dev Returns true if migration has started (contract initialized via proxy)
+   */
+  function migrationStarted() external view returns (bool) {
+    return lastInitializedRevision != 0;
+  }
 
-    /**
-    * @dev initializes the implementation
-    */
-    function initialize() public initializer {
-    }
+  /**
+   * @dev Executes migration from LEND to AAVE
+   *      Caller must approve this contract to spend their LEND beforehand
+   * @param amount Amount of LEND to migrate
+   */
+  function migrateFromLEND(uint256 amount) external {
+    require(lastInitializedRevision != 0, "MIGRATION_NOT_STARTED");
+    require(amount > 0, "ZERO_AMOUNT");
 
-    /**
-    * @dev returns true if the migration started
-    */
-    function migrationStarted() external view returns(bool) {
-        return lastInitializedRevision != 0;
-    }
+    // Pull LEND from user
+    require(LEND.transferFrom(msg.sender, address(this), amount), "LEND_PULL_FAIL");
 
+    // Calculate AAVE out (integer division truncates dust by design)
+    uint256 aaveOut = amount.div(LEND_AAVE_RATIO);
+    require(aaveOut > 0, "INSUFFICIENT_FOR_1_AAVE");
 
-    /**
-    * @dev executes the migration from LEND to AAVE. Users need to give allowance to this contract to transfer LEND before executing
-    * this transaction.
-    * @param amount the amount of LEND to be migrated
-    */
-    function migrateFromLEND(uint256 amount) external {
-        require(lastInitializedRevision != 0, "MIGRATION_NOT_STARTED");
+    // Send AAVE to user
+    require(AAVE.transfer(msg.sender, aaveOut), "AAVE_SEND_FAIL");
 
-        _totalLendMigrated = _totalLendMigrated.add(amount);
-        LEND.transferFrom(msg.sender, address(this), amount);
-        AAVE.transfer(msg.sender, amount.div(LEND_AAVE_RATIO));
-        emit LendMigrated(msg.sender, amount);
-    }
+    // Bookkeeping
+    _totalLendMigrated = _totalLendMigrated.add(amount);
 
-    /**
-    * @dev returns the implementation revision
-    * @return the implementation revision
-    */
-    function getRevision() internal pure override returns (uint256) {
-        return REVISION;
-    }
+    emit LendMigrated(msg.sender, amount, aaveOut);
+  }
 
-}
+  /**
+   * @dev Implementation revision
+   */
+  function getRevision() internal pure override returns (uint256) {
+    return REVISION;
+  }
+}