3 files changed, 81 insertions, 8 deletions

diff --git a/packages/preload/package.json b/packages/preload/package.json
index 5556c10..2ad215c 100644
--- a/packages/preload/package.json
+++ b/packages/preload/package.json
@@ -10,7 +10,9 @@
   },
   "dependencies": {
     "@sophie/shared": "workspace:*",
-    "electron": "^16.0.5"
+    "electron": "^16.0.5",
+    "mobx": "^6.3.10",
+    "mobx-state-tree": "^5.1.0"
   },
   "devDependencies": {
     "typescript": "^4.5.4",
diff --git a/packages/preload/src/SophieRendererImpl.ts b/packages/preload/src/SophieRendererImpl.ts
new file mode 100644
index 0000000..e03c89e
--- /dev/null
+++ b/packages/preload/src/SophieRendererImpl.ts
@@ -0,0 +1,74 @@
+import { ipcRenderer } from 'electron';
+import type { IJsonPatch } from 'mobx-state-tree';
+import {
+  MainToRendererIpcMessage,
+  RendererToMainIpcMessage,
+  sharedStore,
+  SharedStoreListener,
+  SharedStoreSnapshotIn,
+  SophieRenderer
+} from '@sophie/shared';
+
+export type MessageSender = (channel: RendererToMainIpcMessage, ...args: unknown[]) => void;
+
+export class SophieRendererImpl implements SophieRenderer {
+  readonly #send: MessageSender;
+
+  #listener: SharedStoreListener | null = null;
+
+  #snapshot: SharedStoreSnapshotIn | null = null;
+
+  constructor(send: MessageSender) {
+    this.#send = send;
+  }
+
+  sharedStoreSnapshotReceived(snapshot: unknown): void {
+    if (sharedStore.is(snapshot)) {
+      if (this.#listener === null) {
+        this.#snapshot = snapshot;
+      } else {
+        this.#listener.onSnapshot(snapshot);
+      }
+    } else {
+      console.error('Received invalid snapshot', snapshot);
+      this.#snapshot = null;
+    }
+  }
+
+  sharedStorePatchReceived(patch: unknown): void {
+    if (this.#listener !== null) {
+      // `mobx-state-tree` will validate the patch, so we can safely cast here.
+      this.#listener.onPatch(patch as IJsonPatch);
+    }
+  }
+
+  setSharedStoreListener(listener: SharedStoreListener): void {
+    this.#listener = listener;
+    if (this.#snapshot !== null) {
+      listener.onSnapshot(this.#snapshot);
+      this.#snapshot = null;
+    }
+    this.#send(RendererToMainIpcMessage.SharedStoreSnapshotRequest);
+  }
+
+  buttonClick(): void {
+    this.#send(RendererToMainIpcMessage.ButtonClick);
+  }
+}
+
+export function createSophieRenderer(): SophieRenderer {
+  const impl = new SophieRendererImpl(ipcRenderer.send);
+
+  ipcRenderer.on(MainToRendererIpcMessage.SharedStoreSnapshot, (_event, snapshot) => {
+    impl.sharedStoreSnapshotReceived(snapshot);
+  });
+
+  ipcRenderer.on(MainToRendererIpcMessage.SharedStorePatch, (_event, patch) => {
+    impl.sharedStorePatchReceived(patch);
+  });
+
+  return {
+    setSharedStoreListener: impl.setSharedStoreListener.bind(impl),
+    buttonClick: impl.buttonClick.bind(impl),
+  };
+}
diff --git a/packages/preload/src/index.ts b/packages/preload/src/index.ts
index 830901a..19d1285 100644
--- a/packages/preload/src/index.ts
+++ b/packages/preload/src/index.ts
@@ -1,10 +1,7 @@
-import { contextBridge, ipcRenderer } from 'electron';
-import { RendererIpcMessage, SophieRenderer } from '@sophie/shared';
+import { contextBridge } from 'electron';
 
-const sophieRenderer: SophieRenderer = {
-  buttonClicked() {
-    ipcRenderer.send(RendererIpcMessage.ButtonClicked);
-  }
-};
+import { createSophieRenderer } from './SophieRendererImpl';
+
+const sophieRenderer = createSophieRenderer();
 
 contextBridge.exposeInMainWorld('sophieRenderer', sophieRenderer);