new: add loading overlay for WebView widget while pages load

shared/src/iosMain/kotlin/bzh/ajaury/chombev/web/ui/PlatformWebView.ios.kt

@@ -1,25 +1,36 @@
 package bzh.ajaury.chombev.web.ui
 
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.remember
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.interop.UIKitView
 import kotlinx.cinterop.ExperimentalForeignApi
+import kotlinx.cinterop.ObjCSignatureOverride
 import platform.CoreGraphics.CGRectZero
+import platform.Foundation.NSError
 import platform.Foundation.NSURL
 import platform.Foundation.NSURLRequest
 import platform.UIKit.UIUserInterfaceStyle
 import platform.UIKit.UIUserInterfaceStyle.UIUserInterfaceStyleDark
 import platform.UIKit.UIUserInterfaceStyle.UIUserInterfaceStyleLight
+import platform.WebKit.WKNavigation
+import platform.WebKit.WKNavigationDelegateProtocol
 import platform.WebKit.WKWebView
 import platform.WebKit.WKWebViewConfiguration
+import platform.darwin.NSObject
 
 @OptIn(ExperimentalForeignApi::class)
 @Composable
 actual fun PlatformWebView(
     url: String,
     darkTheme: Boolean,
+    onLoadingStateChange: (Boolean) -> Unit,
     modifier: Modifier,
 ) {
+    // WKWebView holds its navigationDelegate weakly, so keep a strong reference across recompositions.
+    val navigationDelegate = remember { WebViewNavigationDelegate() }
+    navigationDelegate.onLoadingStateChange = onLoadingStateChange
+
     UIKitView(
         modifier = modifier,
         factory = {
@@ -27,6 +38,7 @@ actual fun PlatformWebView(
                 frame = CGRectZero.readValue(),
                 configuration = WKWebViewConfiguration(),
             ).apply {
+                navigationDelegate = navigationDelegate
                 setOverrideUserInterfaceStyle(darkTheme.toInterfaceStyle())
                 NSURL.URLWithString(url)?.let { nsUrl ->
                     loadRequest(NSURLRequest(uRL = nsUrl))
@@ -40,4 +52,48 @@ actual fun PlatformWebView(
     )
 }
 
+/**
+ * Forwards WKWebView load lifecycle events to [onLoadingStateChange] so the UI can show a loader
+ * while a page is loading and hide it once loading finishes (or fails).
+ */
+private class WebViewNavigationDelegate :
+    NSObject(),
+    WKNavigationDelegateProtocol {
+    var onLoadingStateChange: (Boolean) -> Unit = {}
+
+    override fun webView(
+        webView: WKWebView,
+        didStartProvisionalNavigation: WKNavigation?,
+    ) {
+        onLoadingStateChange(true)
+    }
+
+    // Shares the (WKWebView, WKNavigation?) Kotlin signature with didStartProvisionalNavigation above.
+    @ObjCSignatureOverride
+    override fun webView(
+        webView: WKWebView,
+        didFinishNavigation: WKNavigation?,
+    ) {
+        onLoadingStateChange(false)
+    }
+
+    override fun webView(
+        webView: WKWebView,
+        didFailNavigation: WKNavigation?,
+        withError: NSError,
+    ) {
+        onLoadingStateChange(false)
+    }
+
+    // Shares the (WKWebView, WKNavigation?, NSError) Kotlin signature with didFailNavigation above.
+    @ObjCSignatureOverride
+    override fun webView(
+        webView: WKWebView,
+        didFailProvisionalNavigation: WKNavigation?,
+        withError: NSError,
+    ) {
+        onLoadingStateChange(false)
+    }
+}
+
 private fun Boolean.toInterfaceStyle(): UIUserInterfaceStyle = if (this) UIUserInterfaceStyleDark else UIUserInterfaceStyleLight