Moving helper functions from dex-react (#69)

* Moving assert form dex-react

* Added isNeverExpiresOrder function

src/const.ts

@@ -20,3 +20,6 @@ export const FEE_PERCENTAGE = (1 / FEE_DENOMINATOR) * 100 // syntatic sugar for
 
 // Amount for an order to be considered unlimited, from contract's point of view: https://github.com/gnosis/dex-contracts/blob/master/contracts/BatchExchange.sol#L35
 export const UNLIMITED_ORDER_AMOUNT = TWO.pow(new BN(128)).sub(ONE)
+
+// Batch ID of orders without expiration date set
+export const MAX_BATCH_ID = 2 ** 32 - 1

src/utils/index.ts

@@ -2,3 +2,4 @@ export * from './time'
 export * from './ethereum'
 export * from './format'
 export * from './orders'
+export * from './misc'

src/utils/misc.ts

@@ -0,0 +1,7 @@
+import { AssertionError } from 'assert'
+
+export function assert<T>(val: T, message: string): asserts val is NonNullable<T> {
+  if (!val) {
+    throw new AssertionError({ message })
+  }
+}

src/utils/time.ts

@@ -1,6 +1,19 @@
+import { MAX_BATCH_ID } from 'const'
+
 /**
  * Epoch in seconds
  */
 export function getEpoch(): number {
   return Math.floor(Date.now() / 1000)
 }
+
+/**
+ * Checks whether batchId is `never expires`
+ * Using the convention which the fronted creates orders with expiration date set
+ * to max uint32 when placing orders active indefinitely.
+ *
+ * @param batchId The expiration batch id to check
+ */
+export function isNeverExpiresOrder(batchId: number): boolean {
+  return MAX_BATCH_ID === batchId
+}