feat: add rainfall_insurance contract

contracts/test/TestRainfallInsurance.sol

@@ -0,0 +1,117 @@
+// SPDX-License-Identifier: GPL-3.0
+pragma solidity ^0.8.12;
+import "../samples/HybridAccount.sol";
+
+contract RainfallInsurance {
+    struct Policy {
+        address policyholder;
+        uint256 premium;
+        uint256 payoutAmount;
+        uint256 triggerRainfall;
+        string city;
+        uint256 timestamp;
+        PolicyState state;
+    }
+
+    enum PolicyState {
+        Active,
+        Expired,
+        Claimed
+    }
+
+    struct Rainfall {
+        uint256 rainfallInMm;
+        uint256 updatedAt;
+    }
+
+    mapping(uint256 => Policy) public policies;
+    mapping(string => Rainfall) public currentRainfall;
+    uint256 public constant MULTIPLIER = 3;
+    address payable immutable helperAddr;
+
+    uint256 private nonce;
+
+    event PolicyCreated(uint256 indexed policyId, address indexed policyholder, string city, uint256 premium, uint256 payoutAmount);
+
+
+    constructor(address payable _helperAddr) {
+        helperAddr = _helperAddr;
+    }
+
+    function generatePolicyId(address policyHolder, string memory city) internal returns (uint256) {
+        nonce++;
+        return uint256(keccak256(abi.encodePacked(policyHolder, city, block.timestamp, nonce)));
+    }
+
+    function buyInsurance(
+        uint256 triggerRainfall,
+        string memory city
+    ) public payable returns (uint256){
+        require(msg.value > 0, "Premium must be greater than zero");
+        uint256 payoutAmount = msg.value * MULTIPLIER;
+        uint256 policyId = generatePolicyId(msg.sender, city);
+
+        policies[policyId] = Policy(
+            msg.sender,
+            msg.value,
+            payoutAmount,
+            triggerRainfall,
+            city,
+            block.timestamp,
+            PolicyState.Active
+        );
+
+        emit PolicyCreated(policyId, msg.sender, city, msg.value, payoutAmount);
+    }
+
+    function updateRainfall(
+        string memory city
+    ) internal returns (Rainfall storage) {
+        HybridAccount ha = HybridAccount(helperAddr);
+
+        bytes memory req = abi.encodeWithSignature(
+            "get_rainfall(string)",
+            city
+        );
+        bytes32 userKey = bytes32(abi.encode(msg.sender));
+        (uint32 error, bytes memory ret) = ha.CallOffchain(userKey, req);
+
+        if (error != 0) {
+            revert(string(ret));
+        }
+
+        uint256 rainfallInMm;
+        (rainfallInMm) = abi.decode(ret, (uint256));
+        currentRainfall[city] = Rainfall(rainfallInMm, block.timestamp);
+
+        return currentRainfall[city];
+    }
+
+    function checkAndPayout(uint256 policyId) public {
+        Policy storage policy = policies[policyId];
+        require(policy.state == PolicyState.Active, "Policy is not active");
+
+        if (policy.timestamp + 365 days < block.timestamp) {
+            policy.state = PolicyState.Expired;
+            revert("Policy expired");
+        }
+
+        Rainfall storage rainfall = currentRainfall[policy.city];
+
+        if (
+            rainfall.updatedAt == 0 ||
+            rainfall.updatedAt + 24 hours < block.timestamp
+        ) {
+            rainfall = updateRainfall(policy.city);
+        }
+
+
+        require(
+            rainfall.rainfallInMm <= policy.triggerRainfall,
+            "Trigger condition not met"
+        );
+
+        policy.state = PolicyState.Claimed;
+        payable(policy.policyholder).transfer(policy.payoutAmount);
+    }
+}