Add Electron preload script to allow communication

Adds a channel to communicate between the main process & the renderer
process, so that the game can easily ship data back to the main process.

It uses the Electron contextBridge & ipcRenderer/ipcMain.

Connects those events to various save functions. Adds triggered events
on game save, game load, and imported game. Adds way for the Electron
app to ask for certain actions or data.

Hook handlers to disable automatic restore

Allows to temporarily disable restore when the game just did an import
or deleted a save game. Prevents looping screens.

electron/gameWindow.js

@@ -27,6 +27,7 @@ async function createWindow(killall) {
     backgroundColor: "#000000",
     webPreferences: {
       nativeWindowOpen: true,
+      preload: path.join(__dirname, 'preload.js'),
     },
   });
 

electron/preload.js

@@ -0,0 +1,38 @@
+/* eslint-disable @typescript-eslint/no-var-requires */
+const { ipcRenderer, contextBridge } = require('electron')
+const log = require("electron-log");
+
+contextBridge.exposeInMainWorld(
+  "electronBridge", {
+    send: (channel, data) => {
+      log.log("Send on channel " + channel)
+      // whitelist channels
+      let validChannels = [
+        "get-save-data-response",
+        "get-save-info-response",
+        "push-game-saved",
+        "push-game-ready",
+        "push-import-result",
+        "push-disable-restore",
+      ];
+      if (validChannels.includes(channel)) {
+          ipcRenderer.send(channel, data);
+      }
+    },
+    receive: (channel, func) => {
+      log.log("Receive on channel " + channel)
+      let validChannels = [
+        "get-save-data-request",
+        "get-save-info-request",
+        "push-save-request",
+        "trigger-save",
+        "trigger-game-export",
+        "trigger-scripts-export",
+      ];
+      if (validChannels.includes(channel)) {
+        // Deliberately strip event as it includes `sender`
+        ipcRenderer.on(channel, (event, ...args) => func(...args));
+      }
+    }
+  }
+);