Disable swipe to refresh on pages that define overscrollBehavior

- Added JavaScript interface to retrieve the css overscrollBehaviorY value

- Added switch on custom WebView to allow disabling swipe to refresh completely

- Minor fix for lastClampedY issue on pages where height <= window to detect whether we actually are clampedY at the top

app/src/main/java/com/duckduckgo/app/browser/BrowserTabFragment.kt

@@ -834,8 +834,17 @@ class BrowserTabFragment : Fragment(), FindListener, CoroutineScope, DaxDialogLi
             }
 
             it.setEnableSwipeRefreshCallback { enable ->
-                swipeRefreshContainer?.isEnabled = enable
+                try {
+                    activity?.runOnUiThread {
+                        swipeRefreshContainer?.isEnabled = enable
+                    }
+                } catch (e: Exception) {
+                    Timber.e("ERROR: ${Thread.currentThread().name} $e")
+                }
             }
+            it.addJavascriptInterface(BrowserWebViewClient.WebAppInterface { enable ->
+                it.setContentAllowsSwipeToRefresh(enable)
+            }, "ddg_swipe_handler");
 
             registerForContextMenu(it)
 

app/src/main/java/com/duckduckgo/app/browser/BrowserWebViewClient.kt

@@ -32,6 +32,7 @@ import kotlinx.coroutines.*
 import timber.log.Timber
 import java.net.URI
 
+
 class BrowserWebViewClient(
     private val requestRewriter: RequestRewriter,
     private val specialUrlDetector: SpecialUrlDetector,
@@ -137,6 +138,7 @@ class BrowserWebViewClient(
             val navigationList = webView.safeCopyBackForwardList() ?: return
             webViewClientListener?.navigationStateChanged(WebViewNavigationState(navigationList))
             flushCookies()
+            detectOverscrollBehavior(webView)
         } catch (e: Throwable) {
             GlobalScope.launch {
                 uncaughtExceptionRepository.recordUncaughtException(e, ON_PAGE_FINISHED)
@@ -145,6 +147,16 @@ class BrowserWebViewClient(
         }
     }
 
+    private fun detectOverscrollBehavior(webView: WebView) {
+        webView.loadUrl(
+            """
+                        javascript:(function() {
+                            ddg_swipe_handler.registerOverscrollBehavior(getComputedStyle(document.querySelector('body')).overscrollBehaviorY);
+                        })();
+                    """
+        )
+    }
+
     private fun flushCookies() {
         GlobalScope.launch(Dispatchers.IO) {
             cookieManager.flush()
@@ -242,4 +254,11 @@ class BrowserWebViewClient(
             it.requiresAuthentication(request)
         }
     }
+
+    class WebAppInterface internal constructor(private var enableSwipeRefresh: (Boolean) -> Unit) {
+        @JavascriptInterface
+        fun registerOverscrollBehavior(behavior: String) {
+            enableSwipeRefresh(behavior == "auto")
+        }
+    }
 }

app/src/main/java/com/duckduckgo/app/browser/DuckDuckGoWebView.kt

@@ -35,10 +35,12 @@ import androidx.core.view.ViewCompat
  * Originally based on https://github.com/takahirom/webview-in-coordinatorlayout for scrolling behaviour
  */
 class DuckDuckGoWebView : WebView, NestedScrollingChild {
-    private var lastClampedY: Boolean = false
+    private var lastClampedTopY: Boolean = false
+    private var contentAllowsSwipeToRefresh: Boolean = true
     private var enableSwipeRefreshCallback: ((Boolean) -> Unit)? = null
 
     private var lastY: Int = 0
+    private var lastDeltaY: Int = 0
     private val scrollOffset = IntArray(2)
     private val scrollConsumed = IntArray(2)
     private var nestedOffsetY: Int = 0
@@ -78,7 +80,7 @@ class DuckDuckGoWebView : WebView, NestedScrollingChild {
                 var deltaY = lastY - eventY
 
                 if (deltaY > 0) {
-                    lastClampedY = false
+                    lastClampedTopY = false
                 }
 
                 if (dispatchNestedPreScroll(0, deltaY, scrollConsumed, scrollOffset)) {
@@ -90,15 +92,18 @@ class DuckDuckGoWebView : WebView, NestedScrollingChild {
 
                 returnValue = super.onTouchEvent(event)
 
-                if (scrollY == 0 && lastClampedY) {
+                if (scrollY == 0 && lastClampedTopY) {
                     // we have reached the top and are clamped -> enable swipeRefresh (by default always disabled)
                     enableSwipeRefresh(true)
+
                     stopNestedScroll()
                 } else if (dispatchNestedScroll(0, scrollOffset[1], 0, deltaY, scrollOffset)) {
                     event.offsetLocation(0f, scrollOffset[1].toFloat())
                     nestedOffsetY += scrollOffset[1]
                     lastY -= scrollOffset[1]
                 }
+
+                lastDeltaY = deltaY
             }
 
             MotionEvent.ACTION_DOWN -> {
@@ -146,19 +151,27 @@ class DuckDuckGoWebView : WebView, NestedScrollingChild {
         nestedScrollHelper.dispatchNestedPreFling(velocityX, velocityY)
 
     override fun onOverScrolled(scrollX: Int, scrollY: Int, clampedX: Boolean, clampedY: Boolean) {
-        lastClampedY = clampedY
+        // taking into account lastDeltaY since we are only interested whether we clamped at the top
+        lastClampedTopY = clampedY && lastDeltaY <= 0
         enableSwipeRefresh(clampedY && scrollY == 0)
         super.onOverScrolled(scrollX, scrollY, clampedX, clampedY)
     }
 
     private fun enableSwipeRefresh(enable: Boolean) {
-        enableSwipeRefreshCallback?.invoke(enable)
+        enableSwipeRefreshCallback?.invoke(enable && contentAllowsSwipeToRefresh)
     }
 
     fun setEnableSwipeRefreshCallback(callback: (Boolean) -> Unit) {
         enableSwipeRefreshCallback = callback
     }
 
+    fun setContentAllowsSwipeToRefresh(allowed: Boolean) {
+        contentAllowsSwipeToRefresh = allowed
+        if (!allowed) {
+            enableSwipeRefresh(false)
+        }
+    }
+
     companion object {
 
         /*