feat: leanback webview kiosk activity

app/src/main/AndroidManifest.xml

@@ -1,3 +1,33 @@
 <?xml version="1.0" encoding="utf-8"?>
 <manifest xmlns:android="http://schemas.android.com/apk/res/android">
+
+    <uses-permission android:name="android.permission.INTERNET" />
+
+    <!-- TV-only app: leanback required, touchscreen not -->
+    <uses-feature
+        android:name="android.software.leanback"
+        android:required="true" />
+    <uses-feature
+        android:name="android.hardware.touchscreen"
+        android:required="false" />
+
+    <application
+        android:allowBackup="false"
+        android:banner="@drawable/banner"
+        android:icon="@drawable/icon"
+        android:label="Grafana Kiosk"
+        android:usesCleartextTraffic="true"
+        android:theme="@android:style/Theme.NoTitleBar.Fullscreen">
+
+        <activity
+            android:name=".MainActivity"
+            android:exported="true"
+            android:screenOrientation="landscape"
+            android:configChanges="keyboard|keyboardHidden|navigation|screenSize|density">
+            <intent-filter>
+                <action android:name="android.intent.action.MAIN" />
+                <category android:name="android.intent.category.LEANBACK_LAUNCHER" />
+            </intent-filter>
+        </activity>
+    </application>
 </manifest>

app/src/main/java/cz/c3c/webviewkiosk/MainActivity.kt

@@ -0,0 +1,87 @@
+package cz.c3c.webviewkiosk
+
+import android.annotation.SuppressLint
+import android.app.Activity
+import android.os.Bundle
+import android.os.Handler
+import android.os.Looper
+import android.view.View
+import android.view.WindowManager
+import android.webkit.WebResourceError
+import android.webkit.WebResourceRequest
+import android.webkit.WebSettings
+import android.webkit.WebView
+import android.webkit.WebViewClient
+
+class MainActivity : Activity() {
+
+    companion object {
+        const val DASHBOARD_URL =
+            "https://grafana.c3c.cz/public-dashboards/381fe3e71e164eb99dd0b10e246a36e2"
+    }
+
+    private lateinit var webView: WebView
+    private val handler = Handler(Looper.getMainLooper())
+    private val backoff = BackoffPolicy(initialDelayMs = 2_000, maxDelayMs = 60_000)
+    private var lastLoadFailed = false
+
+    @SuppressLint("SetJavaScriptEnabled")
+    override fun onCreate(savedInstanceState: Bundle?) {
+        super.onCreate(savedInstanceState)
+        window.addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON)
+
+        webView = WebView(this)
+        webView.settings.apply {
+            javaScriptEnabled = true
+            domStorageEnabled = true
+            cacheMode = WebSettings.LOAD_DEFAULT
+            mediaPlaybackRequiresUserGesture = false
+        }
+        webView.webViewClient = object : WebViewClient() {
+            override fun onPageFinished(view: WebView, url: String) {
+                // onPageFinished also fires after a failed load (error page),
+                // so only treat a clean finish as recovery.
+                if (!lastLoadFailed) backoff.reset()
+                lastLoadFailed = false
+            }
+
+            override fun onReceivedError(
+                view: WebView,
+                request: WebResourceRequest,
+                error: WebResourceError,
+            ) {
+                // Subresource failures (one panel's query, a font) must not
+                // tear down the whole page; only main-frame failures retry.
+                if (!request.isForMainFrame) return
+                lastLoadFailed = true
+                handler.postDelayed(
+                    { view.loadUrl(DASHBOARD_URL) },
+                    backoff.nextDelayMs(),
+                )
+            }
+        }
+
+        setContentView(webView)
+        hideSystemUi()
+        webView.loadUrl(DASHBOARD_URL)
+    }
+
+    override fun onResume() {
+        super.onResume()
+        hideSystemUi()
+    }
+
+    private fun hideSystemUi() {
+        @Suppress("DEPRECATION") // WindowInsetsController needs API 30; minSdk is 26
+        window.decorView.systemUiVisibility =
+            View.SYSTEM_UI_FLAG_FULLSCREEN or
+            View.SYSTEM_UI_FLAG_HIDE_NAVIGATION or
+            View.SYSTEM_UI_FLAG_IMMERSIVE_STICKY
+    }
+
+    override fun onDestroy() {
+        handler.removeCallbacksAndMessages(null)
+        webView.destroy()
+        super.onDestroy()
+    }
+}