3 files changed, 59 insertions, 42 deletions

diff --git a/frontend/src/api/model.js b/frontend/src/api/model.js
index eb7ad9c5..2f9fad37 100644
--- a/frontend/src/api/model.js
+++ b/frontend/src/api/model.js
@@ -1,15 +1,16 @@
-export class ApiError {
+// @flow
+export type ApiError = {
   message: string;
   details: ApiErrorDetail[];
 }
 
-export class ApiErrorDetail {
+export type ApiErrorDetail = {
   message: string;
 }
 
 export type ApiGameState = "LOBBY" | "PLAYING";
 
-export class ApiLobby {
+export type ApiLobby = {
   id: number;
   name: string;
   owner: ApiPlayer;
@@ -20,7 +21,7 @@ export class ApiLobby {
 
 export type ApiWonderSidePickMethod = "EACH_RANDOM" | "ALL_A" | "ALL_B" | "SAME_RANDOM_FOR_ALL";
 
-export class ApiSettings {
+export type ApiSettings = {
   randomSeedForTests: number;
   timeLimitInSeconds: number;
   wonderSidePickMethod: ApiWonderSidePickMethod;
@@ -32,26 +33,28 @@ export class ApiSettings {
   wonPointsPerVictoryPerAge: Map<number, number>;
 }
 
-export class ApiPlayer {
+export type ApiPlayer = {
   username: string;
   displayName: string;
   index: number;
   ready: boolean;
 }
 
-export class ApiTable {}
+export type ApiTable = {}
 
-export class ApiHandCard {}
+export type ApiAction = {}
 
-export class ApiCard {}
+export type ApiHandCard = {}
 
-export class ApiPreparedCard {}
+export type ApiCard = {}
 
-export class ApiPlayerTurnInfo {
+export type ApiPreparedCard = {}
+
+export type ApiPlayerTurnInfo = {
   playerIndex: number;
   table: ApiTable;
   currentAge: number;
-  action: Action;
+  action: ApiAction;
   hand: ApiHandCard[];
   neighbourGuildCards: ApiCard[];
   message: string;
@@ -61,15 +64,15 @@ export type ApiMoveType = "PLAY" | "PLAY_FREE" | "UPGRADE_WONDER" | "DISCARD" |
 export type ApiProvider = "LEFT_NEIGHBOUR" | "RIGHT_NEIGHBOUR";
 export type ApiResourceType = "WOOD" | "STONE" | "ORE" | "CLAY" | "GLASS" | "PAPYRUS" | "LOOM";
 
-export class ApiResources {
+export type ApiResources = {
   quantities: Map<ApiResourceType, number>;
 }
-export class ApiBoughtResources {
+export type ApiBoughtResources = {
   provider: ApiProvider;
   resources: ApiResources;
 }
 
-export class ApiPlayerMove {
+export type ApiPlayerMove = {
   type: ApiMoveType;
   cardName: string;
   boughtResources: ApiBoughtResources[];
diff --git a/frontend/src/api/sevenWondersApi.js b/frontend/src/api/sevenWondersApi.js
index 1004c81e..9a68ec66 100644
--- a/frontend/src/api/sevenWondersApi.js
+++ b/frontend/src/api/sevenWondersApi.js
@@ -1,5 +1,7 @@
-import { createJsonStompClient, JsonStompClient, Callback } from './websocket';
-import { ApiError, ApiLobby, ApiPlayer, ApiPlayerMove, ApiPlayerTurnInfo, ApiPreparedCard, ApiTable } from './model';
+// @flow
+import { createJsonStompClient } from './websocket';
+import type { JsonStompClient, SubscribeFn } from './websocket'
+import type { ApiError, ApiLobby, ApiPlayer, ApiPlayerMove, ApiPlayerTurnInfo, ApiPreparedCard, ApiTable } from './model';
 
 const wsURL = '/seven-wonders-websocket';
 
@@ -10,32 +12,32 @@ export class SevenWondersSession {
     this.client = client;
   }
 
-  watchErrors(callback: Callback<ApiError>): void {
-    return this.client.subscribe('/user/queue/errors', callback);
+  watchErrors(): SubscribeFn<ApiError> {
+    return this.client.subscriber('/user/queue/errors');
   }
 
   chooseName(displayName: string): void {
     this.client.send('/app/chooseName', { playerName: displayName });
   }
 
-  watchNameChoice(callback: Callback<ApiPlayer>): void {
-    return this.client.subscribe('/user/queue/nameChoice', callback);
+  watchNameChoice(): SubscribeFn<ApiPlayer> {
+    return this.client.subscriber('/user/queue/nameChoice');
   }
 
-  watchGames(callback: Callback<ApiLobby[]>): void {
-    return this.client.subscribe('/topic/games', callback);
+  watchGames(): SubscribeFn<ApiLobby[]> {
+    return this.client.subscriber('/topic/games');
   }
 
-  watchLobbyJoined(callback: Callback<Object>): void {
-    return this.client.subscribe('/user/queue/lobby/joined', callback);
+  watchLobbyJoined(): SubscribeFn<Object> {
+    return this.client.subscriber('/user/queue/lobby/joined');
   }
 
-  watchLobbyUpdated(currentGameId: number, callback: Callback<Object>): void {
-    return this.client.subscribe(`/topic/lobby/${currentGameId}/updated`, callback);
+  watchLobbyUpdated(currentGameId: number): SubscribeFn<Object> {
+    return this.client.subscriber(`/topic/lobby/${currentGameId}/updated`);
   }
 
-  watchGameStarted(currentGameId: number, callback: Callback<Object>): void {
-    return this.client.subscribe(`/topic/lobby/${currentGameId}/started`, callback);
+  watchGameStarted(currentGameId: number): SubscribeFn<Object> {
+    return this.client.subscriber(`/topic/lobby/${currentGameId}/started`);
   }
 
   createGame(gameName: string): void {
@@ -50,20 +52,20 @@ export class SevenWondersSession {
     this.client.send('/app/lobby/startGame');
   }
 
-  watchPlayerReady(currentGameId: number, callback: Callback<string>): void {
-    return this.client.subscribe(`/topic/game/${currentGameId}/playerReady`, callback);
+  watchPlayerReady(currentGameId: number): SubscribeFn<string> {
+    return this.client.subscriber(`/topic/game/${currentGameId}/playerReady`);
   }
 
-  watchTableUpdates(currentGameId: number, callback: Callback<ApiTable>): void {
-    return this.client.subscribe(`/topic/game/${currentGameId}/tableUpdates`, callback);
+  watchTableUpdates(currentGameId: number): SubscribeFn<ApiTable> {
+    return this.client.subscriber(`/topic/game/${currentGameId}/tableUpdates`);
   }
 
-  watchPreparedMove(currentGameId: number, callback: Callback<ApiPreparedCard>): void {
-    return this.client.subscribe(`/topic/game/${currentGameId}/prepared`, callback);
+  watchPreparedMove(currentGameId: number): SubscribeFn<ApiPreparedCard> {
+    return this.client.subscriber(`/topic/game/${currentGameId}/prepared`);
   }
 
-  watchTurnInfo(callback: Callback<ApiPlayerTurnInfo>): void {
-    return this.client.subscribe('/user/queue/game/turnInfo', callback);
+  watchTurnInfo(): SubscribeFn<ApiPlayerTurnInfo> {
+    return this.client.subscriber('/user/queue/game/turnInfo');
   }
 
   sayReady(): void {
diff --git a/frontend/src/api/websocket.js b/frontend/src/api/websocket.js
index d411587a..8a893a87 100644
--- a/frontend/src/api/websocket.js
+++ b/frontend/src/api/websocket.js
@@ -7,9 +7,9 @@ const DEFAULT_DEBUG_OPTIONS = {
   debug: process.env.NODE_ENV !== 'production',
 };
 
-export type Callback<T> = (value: T) => void;
-
-export type Callable = () => void;
+export type Callback<T> = (value?: T) => void;
+export type UnsubscribeFn = () => void;
+export type SubscribeFn<T> = (callback: Callback<T>) => UnsubscribeFn;
 
 export class JsonStompClient {
   client: Client;
@@ -24,16 +24,28 @@ export class JsonStompClient {
     });
   }
 
-  subscribe<T>(path: string, callback: Callback<T>): Callable {
+  subscribe<T>(path: string, callback: Callback<T>): UnsubscribeFn {
     const socketSubscription: Subscription = this.client.subscribe(path, (frame: Frame) => {
       // not all frames have a JSON body
-      const value = frame && frame.body && JSON.parse(frame.body);
+      const value: T = frame && JsonStompClient.parseBody(frame);
       callback(value);
     });
     return () => socketSubscription.unsubscribe();
   }
 
-  send(url: string, body: Object) {
+  static parseBody<T>(frame: Frame): T | void {
+    try {
+      return frame.body && JSON.parse(frame.body);
+    } catch (jsonParseError) {
+      throw new Error('Cannot parse websocket message as JSON: ' + jsonParseError.message);
+    }
+  }
+
+  subscriber<T>(path: string): SubscribeFn<T> {
+    return (callback: Callback<T>) => this.subscribe(path, callback);
+  }
+
+  send(url: string, body?: Object) {
     const strBody = body ? JSON.stringify(body) : '';
     this.client.send(url, strBody);
   }