Add initial incomplete BlockStore implementation

src/stores/block_store.ts

@@ -0,0 +1,38 @@
+import * as _ from 'lodash';
+import * as Web3 from 'web3';
+import {BigNumber} from 'bignumber.js';
+import {BlockParamLiteral, InternalZeroExError} from '../types';
+import {Web3Wrapper} from '../web3_wrapper';
+
+/**
+ * Store for a current latest block number
+ */
+export class BlockStore {
+    private web3Wrapper?: Web3Wrapper;
+    private latestBlockNumber?: number;
+    constructor(web3Wrapper?: Web3Wrapper) {
+        this.web3Wrapper = web3Wrapper;
+        // TODO start a subscription
+    }
+    public getBlockNumberWithNConfirmations(numConfirmations: number): Web3.BlockParam {
+        let blockNumber;
+        if (numConfirmations === 0) {
+            blockNumber = BlockParamLiteral.Pending;
+        } else if (numConfirmations === 1) {
+            // HACK: We special-case `numConfirmations === 1` so that we can use this block store without actually
+            // setting `latestBlockNumber` when block number is latest (in order validation) whhich allows us to omit
+            // an async call in a constructor of `ExchangeTransferSimulator`
+            blockNumber = BlockParamLiteral.Latest;
+        } else {
+            if (_.isUndefined(this.latestBlockNumber)) {
+                throw new Error(InternalZeroExError.LatestBlockNumberNotSet);
+            }
+            // Latest block already has 1 confirmation
+            blockNumber = this.latestBlockNumber - numConfirmations + 1;
+        }
+        return blockNumber;
+    }
+    public setLatestBlock(latestBlockNumber: number): void {
+        this.latestBlockNumber = latestBlockNumber;
+    }
+}