feat: add splash window theming (#52)

Co-authored-by: V <vendicated@riseup.net>

src/renderer/themedSplash.ts

@@ -0,0 +1,46 @@
+/*
+ * SPDX-License-Identifier: GPL-3.0
+ * Vesktop, a desktop app aiming to give you a snappier Discord Experience
+ * Copyright (c) 2023 Vendicated and Vencord contributors
+ */
+
+import { Settings } from "./settings";
+
+function isValidColor(color: CSSStyleValue | undefined): color is CSSUnparsedValue & { [0]: string } {
+    return color instanceof CSSUnparsedValue && typeof color[0] === "string" && CSS.supports("color", color[0]);
+}
+
+function resolveColor(color: string) {
+    const span = document.createElement("span");
+    span.style.color = color;
+    span.style.display = "none";
+
+    document.body.append(span);
+    const rgbColor = getComputedStyle(span).color;
+    span.remove();
+
+    return rgbColor;
+}
+
+const updateSplashColors = () => {
+    const bodyStyles = document.body.computedStyleMap();
+
+    const color = bodyStyles.get("--text-normal");
+    const backgroundColor = bodyStyles.get("--background-primary");
+
+    if (isValidColor(color)) {
+        Settings.store.splashColor = resolveColor(color[0]);
+    }
+
+    if (isValidColor(backgroundColor)) {
+        Settings.store.splashBackground = resolveColor(backgroundColor[0]);
+    }
+};
+
+if (document.readyState === "complete") {
+    updateSplashColors();
+} else {
+    window.addEventListener("load", updateSplashColors);
+}
+
+window.addEventListener("beforeunload", updateSplashColors);