Pull out ReadStorage and WriteStorage to avoid need for runtime

exceptions.

Addresses: rocicorp/replidraw#10

frontend/data.ts

@@ -19,7 +19,7 @@ import {
   keyPrefix as clientStatePrefix,
   selectShape,
 } from "../shared/client-state";
-import type Storage from "../shared/storage";
+import type { ReadStorage, WriteStorage } from "../shared/storage";
 import type { UserInfo } from "../shared/client-state";
 import { newID } from "../shared/id";
 
@@ -156,21 +156,15 @@ export function createData(rep: Replicache) {
   };
 }
 
-function readStorage(tx: ReadTransaction): Storage {
+function readStorage(tx: ReadTransaction): ReadStorage {
   return {
-    getObject: tx.get.bind(tx),
-    putObject: () => {
-      throw new Error("Cannot write inside ReadTransaction");
-    },
-    delObject: () => {
-      throw new Error("Cannot delete inside ReadTransaction");
-    },
+    getObject: (key: string) => tx.get(key),
   };
 }
 
-function writeStorage(tx: WriteTransaction): Storage {
+function writeStorage(tx: WriteTransaction): WriteStorage {
   return Object.assign(readStorage(tx), {
-    putObject: tx.put.bind(tx),
-    delObject: tx.del.bind(tx),
+    putObject: (key: string, value: JSONValue) => tx.put(key, value),
+    delObject: async (key: string) => void (await tx.del(key)),
   });
 }

shared/client-state.ts

@@ -1,6 +1,6 @@
 import * as t from "io-ts";
 import { must } from "../backend/decode";
-import Storage from "./storage";
+import { ReadStorage, WriteStorage } from "./storage";
 import { randInt } from "./rand";
 
 const colors = [
@@ -56,7 +56,7 @@ export type UserInfo = t.TypeOf<typeof userInfo>;
 export type ClientState = t.TypeOf<typeof clientState>;
 
 export async function initClientState(
-  storage: Storage,
+  storage: WriteStorage,
   { id, defaultUserInfo }: { id: string; defaultUserInfo: UserInfo }
 ): Promise<void> {
   if (await storage.getObject(key(id))) {
@@ -77,7 +77,7 @@ export async function initClientState(
 }
 
 export async function getClientState(
-  storage: Storage,
+  storage: ReadStorage,
   id: string
 ): Promise<ClientState> {
   const jv = await storage.getObject(key(id));
@@ -88,14 +88,14 @@ export async function getClientState(
 }
 
 export function putClientState(
-  storage: Storage,
+  storage: WriteStorage,
   { id, clientState }: { id: string; clientState: ClientState }
 ): Promise<void> {
   return storage.putObject(key(id), clientState);
 }
 
 export async function setCursor(
-  storage: Storage,
+  storage: WriteStorage,
   { id, x, y }: { id: string; x: number; y: number }
 ): Promise<void> {
   const clientState = await getClientState(storage, id);
@@ -105,7 +105,7 @@ export async function setCursor(
 }
 
 export async function overShape(
-  storage: Storage,
+  storage: WriteStorage,
   { clientID, shapeID }: { clientID: string; shapeID: string }
 ): Promise<void> {
   const client = await getClientState(storage, clientID);
@@ -114,7 +114,7 @@ export async function overShape(
 }
 
 export async function selectShape(
-  storage: Storage,
+  storage: WriteStorage,
   { clientID, shapeID }: { clientID: string; shapeID: string }
 ): Promise<void> {
   const client = await getClientState(storage, clientID);

shared/shape.ts

@@ -1,6 +1,6 @@
 import * as t from "io-ts";
 import { must } from "../backend/decode";
-import Storage from "./storage";
+import { ReadStorage, WriteStorage } from "./storage";
 
 export const shape = t.type({
   type: t.literal("rect"),
@@ -15,7 +15,7 @@ export const shape = t.type({
 export type Shape = t.TypeOf<typeof shape>;
 
 export async function getShape(
-  storage: Storage,
+  storage: ReadStorage,
   id: string
 ): Promise<Shape | null> {
   const jv = await storage.getObject(key(id));
@@ -26,18 +26,18 @@ export async function getShape(
 }
 
 export function putShape(
-  storage: Storage,
+  storage: WriteStorage,
   { id, shape }: { id: string; shape: Shape }
 ): Promise<void> {
   return storage.putObject(key(id), shape);
 }
 
-export function deleteShape(storage: Storage, id: string): Promise<void> {
+export function deleteShape(storage: WriteStorage, id: string): Promise<void> {
   return storage.delObject(key(id));
 }
 
 export async function moveShape(
-  storage: Storage,
+  storage: WriteStorage,
   { id, dx, dy }: { id: string; dx: number; dy: number }
 ): Promise<void> {
   const shape = await getShape(storage, id);

shared/storage.ts

@@ -3,8 +3,11 @@ import { JSONValue } from "replicache";
 /**
  * Interface required of underlying storage.
  */
-export default interface Storage {
+export interface ReadStorage {
   getObject(key: string): Promise<JSONValue | undefined>;
+}
+
+export interface WriteStorage extends ReadStorage {
   putObject(key: string, value: JSONValue): Promise<void>;
   delObject(key: string): Promise<void>;
 }