[MM] Provides a non-null GestureContext during STL transitions

/*

 * Copyright (C) 2025 The Android Open Source Project

 *

 * 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.android.compose.animation.scene.mechanics

import com.android.compose.animation.scene.ContentScope

import com.android.compose.animation.scene.SceneTransitionLayout

import com.android.mechanics.GestureContext

import com.android.mechanics.spec.InputDirection

/**

 * Provides a [GestureContext] retrieving gesture details from the current [SceneTransitionLayout]

 * transition, using default values as a fallback if the transition's own gesture context isn't

 * available.

 */

fun ContentScope.gestureContextOrDefault(

    defaultDragOffset: Float = 0f,

    defaultDirection: InputDirection = InputDirection.Max,

): GestureContext {

    return object : GestureContext {

        override val direction: InputDirection

            get() = gestureContext?.direction ?: defaultDirection

        override val dragOffset: Float

            get() = gestureContext?.dragOffset ?: defaultDragOffset

        private val gestureContext

            get() = layoutState.currentTransition?.gestureContext

    }

}