reward: use address#send(), add events

Based on #15

README.md

@@ -32,6 +32,8 @@
 
 ### `MeasurementsAdded(string cid, uint roundIndex)`
 ### `RoundStart(uint roundIndex)`
+### `Transfer(address indexed to, uint256 amount)`
+### `TransferFailed(address indexed to, uint256 amount)`
 
 ## Structs
 

src/ImpactEvaluator.sol

@@ -19,6 +19,8 @@ contract ImpactEvaluator is AccessControl {
 
     event MeasurementsAdded(string cid, uint roundIndex);
     event RoundStart(uint roundIndex);
+    event Transfer(address indexed to, uint256 amount);
+    event TransferFailed(address indexed to, uint256 amount);
 
     bytes32 public constant EVALUATE_ROLE = keccak256("EVALUATE_ROLE");
 
@@ -99,7 +101,12 @@ contract ImpactEvaluator is AccessControl {
         for (uint i = 0; i < addresses.length; i++) {
             address payable addr = addresses[i];
             uint score = scores[i];
-            addr.transfer((score / 1000000000000000) * roundReward);
+            uint256 amount = (score / 1000000000000000) * roundReward;
+            if (addr.send(amount)) {
+                emit Transfer(addr, amount);
+            } else {
+                emit TransferFailed(addr, amount);
+            }
         }
     }
 

test/ImpactEvaluator.t.sol

@@ -7,6 +7,7 @@ import "../src/ImpactEvaluator.sol";
 contract ImpactEvaluatorTest is Test {
     event RoundStart(uint roundIndex);
     event MeasurementsAdded(string cid, uint roundIndex);
+    event Transfer(address indexed to, uint256 amount);
 
     function test_AdvanceRound() public {
         ImpactEvaluator impactEvaluator = new ImpactEvaluator(address(this));
@@ -93,6 +94,8 @@ contract ImpactEvaluatorTest is Test {
         uint[] memory scores = new uint[](1);
         scores[0] = 1000000000000000;
         vm.deal(payable(address(impactEvaluator)), 100);
+        vm.expectEmit(false, false, false, true);
+        emit Transfer(addresses[0], 100);
         impactEvaluator.setScores(0, addresses, scores, "1 task performed");
         assertEq(addresses[0].balance, 100);