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libraries/architecture/src/main/kotlin/io/element/android/libraries/architecture/appyx/FaderOrSliderTransitionHandler.kt

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+/*
+ * Copyright (c) 2026 Element Creations Ltd.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial.
+ * Please see LICENSE files in the repository root for full details.
+ */
+
+package io.element.android.libraries.architecture.appyx
+
+import androidx.compose.animation.core.Spring
+import androidx.compose.animation.core.Transition
+import androidx.compose.animation.core.spring
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.Modifier
+import com.bumble.appyx.core.navigation.transition.ModifierTransitionHandler
+import com.bumble.appyx.core.navigation.transition.TransitionDescriptor
+import com.bumble.appyx.navmodel.backstack.BackStack
+import com.bumble.appyx.navmodel.backstack.operation.NewRoot
+import com.bumble.appyx.navmodel.backstack.operation.Replace
+import com.bumble.appyx.navmodel.backstack.transitionhandler.rememberBackstackFader
+import com.bumble.appyx.navmodel.backstack.transitionhandler.rememberBackstackSlider
+
+/**
+ * A TransitionHandler that uses fade transition when the operation is Replace or NewRoot,
+ * and slide transition for all other cases.
+ */
+private class FaderOrSliderTransitionHandler<NavTarget>(
+    private val slider: ModifierTransitionHandler<NavTarget, BackStack.State>,
+    private val fader: ModifierTransitionHandler<NavTarget, BackStack.State>,
+) : ModifierTransitionHandler<NavTarget, BackStack.State>() {
+    override fun createModifier(
+        modifier: Modifier,
+        transition: Transition<BackStack.State>,
+        descriptor: TransitionDescriptor<NavTarget, BackStack.State>
+    ): Modifier {
+        val operation = descriptor.operation
+        val useFader = operation is Replace || operation is NewRoot
+        val handler = if (useFader) fader else slider
+        return handler.createModifier(modifier, transition, descriptor)
+    }
+}
+
+@Composable
+fun <NavTarget> rememberFaderOrSliderTransitionHandler(): ModifierTransitionHandler<NavTarget, BackStack.State> {
+    val slider = rememberBackstackSlider<NavTarget>(
+        transitionSpec = { spring(stiffness = Spring.StiffnessMediumLow) },
+    )
+    val fader = rememberBackstackFader<NavTarget>(
+        transitionSpec = { spring(stiffness = Spring.StiffnessMediumLow) },
+    )
+    return rememberDelegateTransitionHandler {
+        FaderOrSliderTransitionHandler(slider, fader)
+    }
+}