Move theme/mode related preload code into it's own module

electron/preload/theme-mode.ts

@@ -0,0 +1,27 @@
+const { ipcRenderer } = require('electron')
+
+const getComputedTheme = () => window.matchMedia('(prefers-color-scheme: dark)').matches ? "dark" : "light"
+const mediaMatch = window.matchMedia('(prefers-color-scheme: dark)')
+let darkModeChangeListener = null
+
+export default {
+    set: (mode) => ipcRenderer.invoke('dark-mode:set', mode),
+    get: async () => {
+        const mode = await ipcRenderer.invoke('dark-mode:get')
+        return {
+            theme: mode,
+            computed: getComputedTheme(),
+        }
+    },
+    onChange: (callback) => {
+        darkModeChangeListener = (event) => {
+            callback(event.matches ? "dark" : "light")
+        }
+        mediaMatch.addEventListener('change', darkModeChangeListener)
+        return mediaMatch
+    },
+    removeListener() {
+        mediaMatch.removeEventListener('change', darkModeChangeListener)
+    },
+    initial: getComputedTheme(),
+}