From 25edb4ff1e0fbded63a4ce2b9de5159259974bb6 Mon Sep 17 00:00:00 2001
From: Johannes Millan <johannes.millan@gmail.com>
Date: Wed, 31 Dec 2025 11:45:52 +0100
Subject: [PATCH] perf(android): prewarm WebView during idle time to speed up
 startup

Load WebView native libraries during main thread idle time using
IdleHandler and WebSettings.getDefaultUserAgent(). This reduces
the 200-300ms freeze on first WebView creation.
---
 .../superproductivity/App.kt                  | 40 ++++++++++++++++---
 1 file changed, 35 insertions(+), 5 deletions(-)

diff --git a/android/app/src/main/java/com/superproductivity/superproductivity/App.kt b/android/app/src/main/java/com/superproductivity/superproductivity/App.kt
index bb9d9443a..540af3e9f 100644
--- a/android/app/src/main/java/com/superproductivity/superproductivity/App.kt
+++ b/android/app/src/main/java/com/superproductivity/superproductivity/App.kt
@@ -1,16 +1,15 @@
 package com.superproductivity.superproductivity
 
 import android.app.Application
+import android.os.Looper
+import android.os.MessageQueue
+import android.util.Log
+import android.webkit.WebSettings
 import com.superproductivity.superproductivity.app.AppLifecycleObserver
 import com.superproductivity.superproductivity.app.KeyValStore
 
 class App : Application() {
 
-    // NOTE using the web view like this causes all html5 inputs not to work
-//    val wv: WebView by lazy {
-//        WebHelper().instanceView(this)
-//    }
-
     val keyValStore: KeyValStore by lazy {
         KeyValStore(this)
     }
@@ -20,5 +19,36 @@ class App : Application() {
 
         // Initialize AppLifecycleObserver at app startup
         AppLifecycleObserver.getInstance()
+
+        // Prewarm WebView by loading native libraries during idle time
+        prewarmWebView()
+    }
+
+    /**
+     * Prewarms the WebView's Chromium engine by triggering native library loading
+     * during main thread idle time. This reduces the 200-300ms freeze that occurs
+     * on first WebView creation.
+     *
+     * Uses WebSettings.getDefaultUserAgent() as recommended by the Chromium team -
+     * it loads WebView libraries without side effects.
+     */
+    private fun prewarmWebView() {
+        try {
+            Looper.getMainLooper().queue.addIdleHandler(object : MessageQueue.IdleHandler {
+                override fun queueIdle(): Boolean {
+                    try {
+                        val startTime = System.currentTimeMillis()
+                        WebSettings.getDefaultUserAgent(this@App)
+                        val duration = System.currentTimeMillis() - startTime
+                        Log.d("SP-WebView", "WebView prewarmed in ${duration}ms")
+                    } catch (e: Exception) {
+                        Log.w("SP-WebView", "WebView prewarm failed: ${e.message}")
+                    }
+                    return false // Remove handler after execution
+                }
+            })
+        } catch (e: Exception) {
+            Log.w("SP-WebView", "Failed to schedule WebView prewarm: ${e.message}")
+        }
     }
 }