Add Contribution contract

The contribution contract implements an ERC721 interface which
represents any contribution.
The contributions are non-fungible (as opposed to the Kredits tokens)
and can be not be transferred. The contract stores the history of any
contribution.
Contributions can be claimed which will issue the Kredits tokens to the
contributor.

This is an early implementation and misses some access control and
probably more things.

contracts/Contribution.sol

@@ -0,0 +1,92 @@
+pragma solidity ^0.4.18;
+
+import "zeppelin-solidity/contracts/token/ERC721/ERC721Token.sol";
+import './upgradeable/Upgradeable.sol';
+
+// ToDo: only load interfaces
+import './Token.sol';
+
+contract Contribution is Upgradeable, ERC721Token { 
+
+  struct Contribution {
+    address contributor;
+    uint amount;
+    bool issued;
+    uint proposalId;
+    string url;
+    uint256 claimAfterBlock;
+    bool exists;
+  }
+  string internal name_;
+  string internal symbol_;
+  
+  mapping(uint256 => string) contributionURIs;
+  
+  mapping(uint256 => address) contributionOwner;
+  mapping(address => uint256[]) ownedContributions;
+
+  mapping(uint256 => Contribution) public contributions;
+  uint256 public contributionsCount;
+
+  event ContributionAdded(uint256 id, address indexed contributor, uint256 amount);
+
+  function tokenContract() view public returns (Token) {
+    return Token(registry.getProxyFor('Token'));
+  }
+
+  function name() external view returns (string) {
+    return name_;
+  }
+
+  function symbol() external view returns (string) {
+    return symbol_;
+  }
+
+  function contributionURI(uint256 contributionId) public view returns (string) {
+    require(exists(contributionId));
+    return contributions[contributionId].url;
+  }
+
+  function ownerOf(uint256 contributionId) public view returns (address) {
+    require(exists(contributionId));
+    return contributions[contributionId].contributor;
+  }
+
+  function balanceOf(address contributor) public view returns (uint) {
+    return ownedContributions[contributor].length;
+  }
+
+  function add(uint256 amount, uint256 proposalId, address contributor, uint256 blocksToWait, string url) public {
+    uint contributionId = contributionsCount + 1;
+    var c = contributions[contributionId];
+    c.exists = true;
+    c.amount = amount;
+    c.issued = false;
+    c.proposalId = proposalId;
+    c.url = url;
+    c.contributor = contributor;
+    c.claimAfterBlock = block.number + blocksToWait;
+
+    contributionsCount++;
+   
+    contributionOwner[contributionId] = contributor;
+    ownedContributions[contributor].push(contributionId);
+
+    ContributionAdded(contributionId, contributor, amount);
+  }
+
+  function claim(uint256 contributionId) public {
+    var c = contributions[contributionId];
+    require(c.exists);
+    require(!c.issued);
+    require(block.number > c.claimAfterBlock);
+    tokenContract().mintFor(c.contributor, c.amount, contributionId);
+    c.issued = true;
+  }
+
+  function exists(uint256 contributionId) view public returns (bool) {
+    return contributions[contributionId].exists; 
+  }
+
+
+}

contracts/Token.sol

@@ -17,7 +17,7 @@ contract Token is Upgradeable, BasicToken {
     decimals = 18;
   }
 
-  function mintFor(address contributorAccount, uint256 amount, uint proposalId) onlyRegistryContractFor('Operator') public {
+  function mintFor(address contributorAccount, uint256 amount, uint proposalId) onlyRegistryContractFor('Contribution') public {
     totalSupply_ = totalSupply_.add(amount);
     balances[contributorAccount] = balances[contributorAccount].add(amount); 
 

migrations/1528988660_contribution.js

@@ -0,0 +1,13 @@
+var Registry = artifacts.require('./Registry.sol');
+var Contribution = artifacts.require('./Contribution.sol');
+
+module.exports = function(deployer) {
+  deployer.deploy(Contribution).then(function(contribution) {
+    console.log('Registry address: ', Registry.address);
+    console.log('Contribution address: ', Contribution.address);
+    Registry.deployed().then(function(registry) {
+      registry.addVersion('Contribution', Contribution.address);
+      registry.createProxy('Contribution', 1);
+    });
+  });
+};