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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 2021 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.grid

import androidx.compose.foundation.lazy.layout.LazyLayoutKeyIndexMap
import androidx.compose.ui.unit.Constraints

/**
 * Abstracts away subcomposition and span calculation from the measuring logic of entire lines.
 */
internal abstract class LazyGridMeasuredLineProvider(
    private val isVertical: Boolean,
    private val slots: LazyGridSlots,
    private val gridItemsCount: Int,
    private val spaceBetweenLines: Int,
    private val measuredItemProvider: LazyGridMeasuredItemProvider,
    private val spanLayoutProvider: LazyGridSpanLayoutProvider
) {
    // The constraints for cross axis size. The main axis is not restricted.
    internal fun childConstraints(startSlot: Int, span: Int): Constraints {
        val crossAxisSize = if (span == 1) {
            slots.sizes[startSlot]
        } else {
            val endSlot = startSlot + span - 1
            slots.positions[endSlot] + slots.sizes[endSlot] - slots.positions[startSlot]
        }.coerceAtLeast(0)
        return if (isVertical) {
            Constraints.fixedWidth(crossAxisSize)
        } else {
            Constraints.fixedHeight(crossAxisSize)
        }
    }

    fun spanOf(index: Int): Int = spanLayoutProvider.spanOf(index, spanLayoutProvider.slotsPerLine)

    /**
     * Used to subcompose items on lines of lazy grids. Composed placeables will be measured
     * with the correct constraints and wrapped into [LazyGridMeasuredLine].
     */
    fun getAndMeasure(lineIndex: Int): LazyGridMeasuredLine {
        val lineConfiguration = spanLayoutProvider.getLineConfiguration(lineIndex)
        val lineItemsCount = lineConfiguration.spans.size

        // we add space between lines as an extra spacing for all lines apart from the last one
        // so the lazy grid measuring logic will take it into account.
        val mainAxisSpacing = if (lineItemsCount == 0 ||
            lineConfiguration.firstItemIndex + lineItemsCount == gridItemsCount
        ) {
            0
        } else {
            spaceBetweenLines
        }

        var startSlot = 0
        val items = Array(lineItemsCount) {
            val span = lineConfiguration.spans[it].currentLineSpan
            val constraints = childConstraints(startSlot, span)
            measuredItemProvider.getAndMeasure(
                index = lineConfiguration.firstItemIndex + it,
                constraints = constraints,
                lane = startSlot,
                span = span,
                mainAxisSpacing = mainAxisSpacing
            ).also { startSlot += span }
        }
        return createLine(
            lineIndex,
            items,
            lineConfiguration.spans,
            mainAxisSpacing
        )
    }

    /**
     * Contains the mapping between the key and the index. It could contain not all the items of
     * the list as an optimization.
     */
    val keyIndexMap: LazyLayoutKeyIndexMap get() = measuredItemProvider.keyIndexMap

    abstract fun createLine(
        index: Int,
        items: Array,
        spans: List,
        mainAxisSpacing: Int
    ): LazyGridMeasuredLine
}