From b499627b384092127d11b325b3d6a39d8dc2c842 Mon Sep 17 00:00:00 2001
From: Ricardo Guilherme Schmidt <3esmit@gmail.com>
Date: Tue, 4 Jun 2019 07:12:03 -0300
Subject: [PATCH] Migration contract example

---
 .../communication/MessageTributeMigrated.sol  | 36 +++++++++++++++++++
 1 file changed, 36 insertions(+)
 create mode 100644 contracts/communication/MessageTributeMigrated.sol

diff --git a/contracts/communication/MessageTributeMigrated.sol b/contracts/communication/MessageTributeMigrated.sol
new file mode 100644
index 0000000..824dff8
--- /dev/null
+++ b/contracts/communication/MessageTributeMigrated.sol
@@ -0,0 +1,36 @@
+pragma solidity >=0.5.0 <0.6.0;
+import "./MessageTribute.sol";
+
+/**
+ * @notice Defines migration contract of MessageTribute
+ */
+contract MessageTributeMigrated is MessageTribute {
+    mapping(address => bool) private migrated;
+    MessageTribute public previousVersion;
+
+    /**
+     * @notice Defines the previous contract to load unset users
+     * @param _previousVersion Contract to read unset tributes
+     */
+    constructor(MessageTribute _previousVersion) public {
+        require(address(_previousVersion) != address(0), "Previous version not provided");
+        previousVersion = _previousVersion;
+    }
+    /**
+     * @notice Obtain required tribute to talk with `_of` from `previousVersion` if `_of` never set on this one
+     * @param _of Account to lookup
+     * @return value of tribute
+     */
+    function getTribute(address _of) external view
+        returns (uint256)
+    {
+        return migrated[_of] ? tributeCatalog[_of] : previousVersion.getTribute(_of);
+    }
+
+    function setTribute(address _of, uint256 _value) internal {
+        migrated[_of] = true;
+        super.setTribute(_of, _value);
+    }
+
+
+}
\ No newline at end of file