feat: add AutoIncrementing contract (#1023)

* feat: add AutoIncrementing contract

* feat: allow multiple counters per instance

* fix: some linting errors

* feat: use recommended implementaiton

* fix: remove .only in tests

* fix: PR notes

* fix: add note about incrementing counter

contracts/AutoIncrementing.sol

+pragma solidity ^0.4.24;
+
+
+/**
+ * @title AutoIncrementing
+ * @author Matt Condon (@shrugs)
+ * @dev Provides an auto-incrementing uint256 id acquired by the `Counter#nextId` getter.
+ * Use this for issuing ERC721Token ids or keeping track of request ids, anything you want, really.
+ *
+ * Include with `using AutoIncrementing for AutoIncrementing.Counter;`
+ * @notice Does not allow an Id of 0, which is popularly used to signify a null state in solidity.
+ * Does not protect from overflows, but if you have 2^256 ids, you have other problems.
+ * (But actually, it's generally impossible to increment a counter this many times, energy wise
+ * so it's not something you have to worry about.)
+ */
+library AutoIncrementing {
+
+  struct Counter {
+    uint256 prevId; // default: 0
+  }
+
+  function nextId(Counter storage _counter)
+    internal
+    returns (uint256)
+  {
+    _counter.prevId = _counter.prevId + 1;
+    return _counter.prevId;
+  }
+}

contracts/crowdsale/emission/AllowanceCrowdsale.sol

@@ -5,6 +5,8 @@ import "../../token/ERC20/ERC20.sol";
 import "../../token/ERC20/ERC20Basic.sol";
 import "../../token/ERC20/SafeERC20.sol";
 import "../../math/SafeMath.sol";
+
+
 /**
  * @title AllowanceCrowdsale
  * @dev Extension of Crowdsale where tokens are held by a wallet, which approves an allowance to the crowdsale.

contracts/mocks/AutoIncrementingImpl.sol

+pragma solidity ^0.4.24;
+
+import "../AutoIncrementing.sol";
+
+
+contract AutoIncrementingImpl {
+  using AutoIncrementing for AutoIncrementing.Counter;
+
+  uint256 public theId;
+
+  // use whatever key you want to track your counters
+  mapping(string => AutoIncrementing.Counter) private counters;
+
+  function doThing(string _key)
+    public
+    returns (uint256)
+  {
+    theId = counters[_key].nextId();
+    return theId;
+  }
+}

test/AutoIncrementing.test.js

+const { hashMessage } = require('./helpers/sign');
+
+const AutoIncrementing = artifacts.require('AutoIncrementingImpl');
+
+require('chai')
+  .use(require('chai-bignumber')(web3.BigNumber))
+  .should();
+
+const EXPECTED = [1, 2, 3, 4];
+const KEY1 = hashMessage('key1');
+const KEY2 = hashMessage('key2');
+
+contract('AutoIncrementing', function ([_, owner]) {
+  beforeEach(async function () {
+    this.mock = await AutoIncrementing.new({ from: owner });
+  });
+
+  context('custom key', async function () {
+    it('should return expected values', async function () {
+      for (let expectedId of EXPECTED) {
+        await this.mock.doThing(KEY1, { from: owner });
+        const actualId = await this.mock.theId();
+        actualId.should.be.bignumber.eq(expectedId);
+      }
+    });
+  });
+
+  context('parallel keys', async function () {
+    it('should return expected values for each counter', async function () {
+      for (let expectedId of EXPECTED) {
+        await this.mock.doThing(KEY1, { from: owner });
+        let actualId = await this.mock.theId();
+        actualId.should.be.bignumber.eq(expectedId);
+
+        await this.mock.doThing(KEY2, { from: owner });
+        actualId = await this.mock.theId();
+        actualId.should.be.bignumber.eq(expectedId);
+      }
+    });
+  });
+});