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Higher level abstractions of the Compose UI primitives. This library is design system agnostic, providing the high-level building blocks for both application and design-system developers

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/*
 * Copyright 2022 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 androidx.compose.foundation.lazy

import androidx.compose.foundation.gestures.Orientation
import androidx.compose.foundation.lazy.layout.LazyLayoutBeyondBoundsModifierLocal
import androidx.compose.foundation.lazy.layout.LazyLayoutBeyondBoundsState
import androidx.compose.runtime.Composable
import androidx.compose.runtime.remember
import androidx.compose.ui.Modifier
import androidx.compose.ui.platform.LocalLayoutDirection

/**
 * This modifier is used to measure and place additional items when the lazyList receives a
 * request to layout items beyond the visible bounds.
 */
@Suppress("ComposableModifierFactory")
@Composable
internal fun Modifier.lazyListBeyondBoundsModifier(
    state: LazyListState,
    beyondBoundsItemCount: Int,
    reverseLayout: Boolean,
    orientation: Orientation
): Modifier {
    val layoutDirection = LocalLayoutDirection.current
    val beyondBoundsState = remember(state, beyondBoundsItemCount) {
        LazyListBeyondBoundsState(state, beyondBoundsItemCount)
    }
    val beyondBoundsInfo = state.beyondBoundsInfo
    return this then remember(
        beyondBoundsState,
        beyondBoundsInfo,
        reverseLayout,
        layoutDirection,
        orientation
    ) {
        LazyLayoutBeyondBoundsModifierLocal(
            beyondBoundsState,
            beyondBoundsInfo,
            reverseLayout,
            layoutDirection,
            orientation
        )
    }
}

internal class LazyListBeyondBoundsState(
    val state: LazyListState,
    val beyondBoundsItemCount: Int
) : LazyLayoutBeyondBoundsState {

    override fun remeasure() {
        state.remeasurement?.forceRemeasure()
    }

    override val itemCount: Int
        get() = state.layoutInfo.totalItemsCount
    override val hasVisibleItems: Boolean
        get() = state.layoutInfo.visibleItemsInfo.isNotEmpty()
    override val firstPlacedIndex: Int
        get() = maxOf(0, state.firstVisibleItemIndex - beyondBoundsItemCount)
    override val lastPlacedIndex: Int
        get() = minOf(
            itemCount - 1,
            state.layoutInfo.visibleItemsInfo.last().index + beyondBoundsItemCount
        )
}