Use token array instead of map (#739)

This PR refactors the auction state to use a token array instead of a map so that it is trivial to check if a token listing was missed.

### Test Plan

New unit tests added

src/streamed/state.ts

@@ -82,7 +82,7 @@ const UNLIMITED_ORDER_AMOUNT = BigInt(2 ** 128) - BigInt(1)
  * JSON representation of the account state.
  */
 export interface AuctionStateJson {
-  tokens: { [key: string]: string };
+  tokens: string[];
   accounts: {
     [key: string]: {
       balances: { [key: string]: string };
@@ -106,7 +106,7 @@ export interface AuctionStateJson {
 export class AuctionState {
   private lastBlock = -1;
 
-  private readonly tokens: Map<TokenId, Address> = new Map();
+  private readonly tokens: Address[] = [];
   private readonly accounts: Map<Address, Account> = new Map();
   private lastSolution?: Event<BatchExchange, "SolutionSubmission">;
 
@@ -131,7 +131,7 @@ export class AuctionState {
     }
 
     return {
-      tokens: map2obj(this.tokens, addr => addr),
+      tokens: this.tokens.slice(0),
       accounts: map2obj(this.accounts, account => ({
         balances: map2obj(account.balances, balance => balance.toString()),
         pendingWithdrawals: map2obj(
@@ -361,15 +361,14 @@ export class AuctionState {
    * it was listed out of order.
    */
   private applyTokenListing({ id, token }: Event<BatchExchange, "TokenListing">): void {
-    const tokenId = parseInt(id)
     if (this.options.strict) {
       assert(
-        this.tokens.get(tokenId) === undefined,
-        `token ${tokenId} has already been listed`,
+        this.tokens.length === parseInt(id),
+        `token ${token} with ID ${id} added as token ${this.tokens.length}`,
       )
     }
 
-    this.tokens.set(parseInt(id), token)
+    this.tokens.push(token)
   }
 
   /**
@@ -482,9 +481,9 @@ export class AuctionState {
       )
       return token
     } else {
-      const tokenAddr = this.tokens.get(token)
-      assert(tokenAddr, `missing token ${token}`)
-      return tokenAddr as Address
+      const tokenAddr = this.tokens[token]
+      assert(tokenAddr !== undefined, `missing token ${token}`)
+      return tokenAddr
     }
   }
 

test/models/streamed/state.spec.ts

@@ -61,7 +61,32 @@ describe("Account State", () => {
       const state = auctionState()
       expect(() => state.applyEvents([
         event(2, "TokenListing", { id: "0", token: addr(1) }),
-        event(1, "TokenListing", { id: "0", token: addr(1) }),
+        event(1, "TokenListing", { id: "1", token: addr(1) }),
+      ])).to.throw()
+    })
+  })
+
+  describe("TokenListing", () => {
+    it("Adds a new token", () => {
+      const state = auctionState()
+      state.applyEvents([
+        event(1, "TokenListing", { id: "0", token: addr(0) }),
+      ])
+      expect(state.toJSON().tokens[0]).to.equal(addr(0))
+    })
+
+    it("Throws if the same token is listed twice", () => {
+      const state = auctionState()
+      expect(() => state.applyEvents([
+        event(1, "TokenListing", { id: "0", token: addr(0) }),
+        event(2, "TokenListing", { id: "0", token: addr(0) }),
+      ])).to.throw()
+    })
+
+    it("Throws if a token is skipped", () => {
+      const state = auctionState()
+      expect(() => state.applyEvents([
+        event(1, "TokenListing", { id: "1", token: addr(0) }),
       ])).to.throw()
     })
   })