From c39dcb61649583c4f2c0ecfe033d69f26276f72f Mon Sep 17 00:00:00 2001
From: Jonatan Granqvist <jgranqvist@gmail.com>
Date: Sun, 8 Mar 2026 09:36:43 +0100
Subject: [PATCH] preload flutter

---
 apps/web/src/components/flutter-view.tsx   | 220 +++++++++++++--------
 apps/web/src/routes/_default.timelines.tsx |   6 +
 2 files changed, 142 insertions(+), 84 deletions(-)

diff --git a/apps/web/src/components/flutter-view.tsx b/apps/web/src/components/flutter-view.tsx
index af425e6..b72e9b4 100644
--- a/apps/web/src/components/flutter-view.tsx
+++ b/apps/web/src/components/flutter-view.tsx
@@ -28,6 +28,112 @@ declare global {
   }
 }
 
+// ---------------------------------------------------------------------------
+// Module-level singleton state
+// ---------------------------------------------------------------------------
+
+let flutterContainer: HTMLDivElement | null = null;
+let engineReady = false;
+let initPromise: Promise<void> | null = null;
+
+// Module-level refs so bridge closures always read latest values
+let currentStateRef: FlutterTimelineState | null = null;
+let currentOnEventRef: ((event: FlutterEvent) => void) | null = null;
+
+function ensureBridge() {
+  if (window.__zendegi__) return;
+  window.__zendegi__ = {
+    getState: () => JSON.stringify(currentStateRef),
+    onEvent: (json: string) => {
+      const event = JSON.parse(json) as FlutterEvent;
+      currentOnEventRef?.(event);
+    },
+  };
+}
+
+export function preloadFlutter() {
+  initFlutter();
+}
+
+function initFlutter(): Promise<void> {
+  if (initPromise) return initPromise;
+
+  initPromise = (async () => {
+    ensureBridge();
+    // Load flutter.js if not already loaded
+    if (!window._flutter) {
+      await new Promise<void>((resolve, reject) => {
+        if (document.querySelector('script[src="/flutter/flutter.js"]')) {
+          const timeout = setTimeout(() => {
+            clearInterval(interval);
+            reject(
+              new Error("Timed out waiting for flutter.js to initialize"),
+            );
+          }, 10_000);
+          const interval = setInterval(() => {
+            if (window._flutter) {
+              clearInterval(interval);
+              clearTimeout(timeout);
+              resolve();
+            }
+          }, 50);
+          return;
+        }
+        const script = document.createElement("script");
+        script.src = "/flutter/flutter.js";
+        script.defer = true;
+        script.onload = () => resolve();
+        script.onerror = () => reject(new Error("Failed to load flutter.js"));
+        document.head.appendChild(script);
+      });
+    }
+
+    // Fetch and set buildConfig so load() works (supports wasm)
+    if (!window._flutter!.buildConfig) {
+      const res = await fetch("/flutter/build_config.json");
+      if (!res.ok) {
+        throw new Error(`Failed to fetch build config: ${res.status}`);
+      }
+      window._flutter!.buildConfig = await res.json();
+    }
+
+    // Create the persistent container once
+    if (!flutterContainer) {
+      flutterContainer = document.createElement("div");
+      flutterContainer.style.width = "100%";
+      flutterContainer.style.height = "100%";
+    }
+
+    await window._flutter!.loader.load({
+      config: {
+        entrypointBaseUrl: "/flutter/",
+        assetBase: "/flutter/",
+      },
+      onEntrypointLoaded: async (engineInitializer) => {
+        const appRunner = await engineInitializer.initializeEngine({
+          hostElement: flutterContainer!,
+          assetBase: "/flutter/",
+        });
+        appRunner.runApp();
+      },
+    });
+
+    engineReady = true;
+  })().catch((error) => {
+    // Reset all module state so next mount retries
+    flutterContainer = null;
+    engineReady = false;
+    initPromise = null;
+    throw error;
+  });
+
+  return initPromise;
+}
+
+// ---------------------------------------------------------------------------
+// Component
+// ---------------------------------------------------------------------------
+
 type FlutterViewProps = {
   state: FlutterTimelineState;
   onEvent: (event: FlutterEvent) => void;
@@ -43,97 +149,43 @@ export function FlutterView({
 }: FlutterViewProps) {
   const containerRef = useRef<HTMLDivElement>(null);
   const [status, setStatus] = useState<"loading" | "ready" | "error">(
-    "loading"
+    engineReady ? "ready" : "loading",
   );
-  const stateRef = useRef(state);
-  stateRef.current = state;
 
-  const onEventRef = useRef(onEvent);
-  onEventRef.current = onEvent;
+  // Keep module-level refs in sync
+  currentStateRef = state;
+  currentOnEventRef = onEvent;
 
   useEffect(() => {
-    const container = containerRef.current;
-    if (!container) return;
+    const wrapper = containerRef.current;
+    if (!wrapper) return;
 
-    let pollingInterval: ReturnType<typeof setInterval> | undefined;
-    let pollingTimeout: ReturnType<typeof setTimeout> | undefined;
-
-    window.__zendegi__ = {
-      getState: () => JSON.stringify(stateRef.current),
-      onEvent: (json: string) => {
-        const event = JSON.parse(json) as FlutterEvent;
-        onEventRef.current(event);
-      },
-    };
-
-    const init = async () => {
-      // Load flutter.js if not already loaded
-      if (!window._flutter) {
-        await new Promise<void>((resolve, reject) => {
-          if (document.querySelector('script[src="/flutter/flutter.js"]')) {
-            // Script tag exists but hasn't finished — wait for _flutter to appear
-            pollingTimeout = setTimeout(() => {
-              clearInterval(pollingInterval);
-              reject(
-                new Error("Timed out waiting for flutter.js to initialize")
-              );
-            }, 10_000);
-            pollingInterval = setInterval(() => {
-              if (window._flutter) {
-                clearInterval(pollingInterval);
-                clearTimeout(pollingTimeout);
-                resolve();
-              }
-            }, 50);
-            return;
-          }
-          const script = document.createElement("script");
-          script.src = "/flutter/flutter.js";
-          script.defer = true;
-          script.onload = () => resolve();
-          script.onerror = () => reject(new Error("Failed to load flutter.js"));
-          document.head.appendChild(script);
-        });
-      }
-
-      // Fetch and set buildConfig so load() works (supports wasm)
-      if (!window._flutter!.buildConfig) {
-        const res = await fetch("/flutter/build_config.json");
-        if (!res.ok) {
-          throw new Error(`Failed to fetch build config: ${res.status}`);
-        }
-        window._flutter!.buildConfig = await res.json();
-      }
-
-      try {
-        await window._flutter!.loader.load({
-          config: {
-            entrypointBaseUrl: "/flutter/",
-            assetBase: "/flutter/",
-          },
-          onEntrypointLoaded: async (engineInitializer) => {
-            const appRunner = await engineInitializer.initializeEngine({
-              hostElement: container,
-              assetBase: "/flutter/",
-            });
-            appRunner.runApp();
-            setStatus("ready");
-          },
-        });
-      } catch (error) {
-        throw new Error(
-          `Flutter engine initialization failed: ${error instanceof Error ? error.message : error}`
-        );
-      }
-    };
-
-    init().catch(() => setStatus("error"));
+    if (engineReady && flutterContainer) {
+      // Engine already running — reparent immediately, no loading flash
+      wrapper.appendChild(flutterContainer);
+      setStatus("ready");
+      // Push latest state so Flutter renders the correct timeline
+      window.__zendegi__?.updateState?.(JSON.stringify(currentStateRef));
+    } else {
+      // First mount — initialize engine
+      setStatus("loading");
+      initFlutter()
+        .then(() => {
+          // Guard: component may have unmounted while awaiting
+          if (!containerRef.current || !flutterContainer) return;
+          wrapper.appendChild(flutterContainer);
+          setStatus("ready");
+          // Push current state after engine is ready
+          window.__zendegi__?.updateState?.(JSON.stringify(currentStateRef));
+        })
+        .catch(() => setStatus("error"));
+    }
 
     return () => {
-      clearInterval(pollingInterval);
-      clearTimeout(pollingTimeout);
-      container.replaceChildren();
-      delete (window as Partial<Window>).__zendegi__;
+      // Detach but don't destroy the Flutter container
+      if (flutterContainer?.parentElement === wrapper) {
+        wrapper.removeChild(flutterContainer);
+      }
     };
   }, []);
 
diff --git a/apps/web/src/routes/_default.timelines.tsx b/apps/web/src/routes/_default.timelines.tsx
index cad0169..52b0748 100644
--- a/apps/web/src/routes/_default.timelines.tsx
+++ b/apps/web/src/routes/_default.timelines.tsx
@@ -1,6 +1,8 @@
+import { useEffect } from "react";
 import { createFileRoute, Link } from "@tanstack/react-router";
 import { useSuspenseQuery } from "@tanstack/react-query";
 import { timelinesQueryOptions } from "@/functions/get-timelines";
+import { preloadFlutter } from "@/components/flutter-view";
 
 export const Route = createFileRoute("/_default/timelines")({
   loader: async ({ context }) => {
@@ -11,6 +13,10 @@ export const Route = createFileRoute("/_default/timelines")({
 
 function RouteComponent() {
   const timelinesQuery = useSuspenseQuery(timelinesQueryOptions());
+
+  useEffect(() => {
+    preloadFlutter();
+  }, []);
   return (
     <section className="container mx-auto max-w-3xl px-4 py-2">
       <h1 className="text-4xl font-serif font-bold mb-6">Timelines</h1>