improve Duck.ai fragment transitions (#6331)

Task/Issue URL:
https://app.asana.com/1/137249556945/project/1208671518894266/task/1210696192460180?focus=true

### Description
Improves transitions in and out of the Duck.ai screen.

### Steps to test this PR

- [x] Stress test opening/closing of the Duck.ai screen and verify that
the animations always play smoothly and end up in the right state.
- [x] Disable tab swiping with
https://www.jsonblob.com/api/1389979353823240192 and try again.

Author: LukasPaczos

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

@@ -45,6 +45,10 @@ import androidx.webkit.ServiceWorkerControllerCompat
 import androidx.webkit.WebViewFeature
 import com.duckduckgo.anvil.annotations.InjectWith
 import com.duckduckgo.app.browser.BrowserViewModel.Command
+import com.duckduckgo.app.browser.animations.slideAndFadeInFromLeft
+import com.duckduckgo.app.browser.animations.slideAndFadeInFromRight
+import com.duckduckgo.app.browser.animations.slideAndFadeOutToLeft
+import com.duckduckgo.app.browser.animations.slideAndFadeOutToRight
 import com.duckduckgo.app.browser.databinding.ActivityBrowserBinding
 import com.duckduckgo.app.browser.databinding.IncludeExperimentalOmnibarToolbarMockupBinding
 import com.duckduckgo.app.browser.databinding.IncludeExperimentalOmnibarToolbarMockupBottomBinding
@@ -777,13 +781,11 @@ open class BrowserActivity : DuckDuckGoActivity() {
         isDuckChatVisible = false
         val fragment = duckAiFragment
         if (fragment?.isVisible == true) {
-            val transaction = supportFragmentManager.beginTransaction()
-            transaction.setCustomAnimations(
-                com.duckduckgo.mobile.android.R.anim.slide_from_right,
-                com.duckduckgo.mobile.android.R.anim.slide_to_right,
-            )
-            transaction.hide(fragment)
-            transaction.commit()
+            animateDuckAiFragmentOut {
+                val transaction = supportFragmentManager.beginTransaction()
+                transaction.hide(fragment)
+                transaction.commit()
+            }
         }
     }
 
@@ -803,6 +805,7 @@ open class BrowserActivity : DuckDuckGoActivity() {
     }
 
     private fun launchNewDuckChat(duckChatUrl: String?) {
+        val wasFragmentVisible = duckAiFragment?.isVisible ?: false
         val fragment = DuckChatWebViewFragment().apply {
             duckChatUrl?.let {
                 arguments = Bundle().apply {
@@ -813,22 +816,41 @@ open class BrowserActivity : DuckDuckGoActivity() {
 
         duckAiFragment = fragment
         val transaction = supportFragmentManager.beginTransaction()
-        transaction.setCustomAnimations(
-            com.duckduckgo.mobile.android.R.anim.slide_from_right,
-            com.duckduckgo.mobile.android.R.anim.slide_to_right,
-        )
         transaction.replace(binding.duckAiFragmentContainer.id, fragment)
         transaction.commit()
+
+        if (!wasFragmentVisible) {
+            // If the fragment was already visible but needs to be force-reloaded, we don't want to animate it in again.
+            animateDuckAiFragmentIn()
+        }
     }
 
     private fun restoreDuckChat(fragment: DuckChatWebViewFragment) {
+        if (fragment.isVisible) {
+            return
+        }
+
         val transaction = supportFragmentManager.beginTransaction()
-        transaction.setCustomAnimations(
-            com.duckduckgo.mobile.android.R.anim.slide_from_right,
-            com.duckduckgo.mobile.android.R.anim.slide_to_right,
-        )
         transaction.show(fragment)
         transaction.commit()
+
+        animateDuckAiFragmentIn()
+    }
+
+    private fun animateDuckAiFragmentIn() {
+        val duckAiContainer = binding.duckAiFragmentContainer
+        val browserContainer = if (swipingTabsFeature.isEnabled) binding.tabPager else binding.fragmentContainer
+
+        duckAiContainer.slideAndFadeInFromRight()
+        browserContainer.slideAndFadeOutToLeft()
+    }
+
+    private fun animateDuckAiFragmentOut(onComplete: () -> Unit) {
+        val duckAiContainer = binding.duckAiFragmentContainer
+        val browserContainer = if (swipingTabsFeature.isEnabled) binding.tabPager else binding.fragmentContainer
+
+        duckAiContainer.slideAndFadeOutToRight(onComplete)
+        browserContainer.slideAndFadeInFromLeft()
     }
 
     private fun configureOnBackPressedListener() {

app/src/main/java/com/duckduckgo/app/browser/animations/ViewTransitionAnimations.kt

@@ -0,0 +1,74 @@
+/*
+ * Copyright (c) 2025 DuckDuckGo
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.duckduckgo.app.browser.animations
+
+import android.view.View
+import androidx.interpolator.view.animation.FastOutSlowInInterpolator
+
+private const val ANIMATION_DURATION = 300L
+private const val SLIDE_OFFSET_RATIO = 0.33f
+
+fun View.slideAndFadeInFromLeft(onComplete: (() -> Unit)? = null) = startSlideAndFadeAnimation(
+    translationXFrom = -width.toFloat() * SLIDE_OFFSET_RATIO,
+    translationXTo = 0f,
+    alphaFrom = 0f,
+    alphaTo = 1.0f,
+    onComplete = onComplete,
+)
+
+fun View.slideAndFadeOutToLeft(onComplete: (() -> Unit)? = null) = startSlideAndFadeAnimation(
+    translationXFrom = 0f,
+    translationXTo = -width.toFloat() * SLIDE_OFFSET_RATIO,
+    alphaFrom = 1f,
+    alphaTo = 0f,
+    onComplete = onComplete,
+)
+
+fun View.slideAndFadeInFromRight(onComplete: (() -> Unit)? = null) = startSlideAndFadeAnimation(
+    translationXFrom = width.toFloat() * SLIDE_OFFSET_RATIO,
+    translationXTo = 0f,
+    alphaFrom = 0f,
+    alphaTo = 1.0f,
+    onComplete = onComplete,
+)
+
+fun View.slideAndFadeOutToRight(onComplete: (() -> Unit)? = null) = startSlideAndFadeAnimation(
+    translationXFrom = 0f,
+    translationXTo = width.toFloat() * SLIDE_OFFSET_RATIO,
+    alphaFrom = 1f,
+    alphaTo = 0.0f,
+    onComplete = onComplete,
+)
+
+private fun View.startSlideAndFadeAnimation(
+    translationXFrom: Float,
+    translationXTo: Float,
+    alphaFrom: Float,
+    alphaTo: Float,
+    onComplete: (() -> Unit)? = null,
+) {
+    translationX = translationXFrom
+    alpha = alphaFrom
+
+    animate()
+        .translationX(translationXTo)
+        .alpha(alphaTo)
+        .setDuration(ANIMATION_DURATION)
+        .setInterpolator(FastOutSlowInInterpolator())
+        .apply { onComplete?.let { withEndAction(it) } }
+        .start()
+}