AlertDialog.kt

/*
 * Copyright 2019 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.material

import androidx.compose.foundation.layout.Arrangement
import androidx.compose.foundation.layout.Box
import androidx.compose.foundation.layout.Column
import androidx.compose.foundation.layout.ColumnScope
import androidx.compose.foundation.layout.padding
import androidx.compose.runtime.Composable
import androidx.compose.runtime.CompositionLocalProvider
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.graphics.Color
import androidx.compose.ui.graphics.Shape
import androidx.compose.ui.layout.AlignmentLine
import androidx.compose.ui.layout.FirstBaseline
import androidx.compose.ui.layout.LastBaseline
import androidx.compose.ui.layout.Layout
import androidx.compose.ui.layout.Placeable
import androidx.compose.ui.layout.layoutId
import androidx.compose.ui.unit.Constraints
import androidx.compose.ui.unit.Dp
import androidx.compose.ui.unit.dp
import androidx.compose.ui.unit.sp
import androidx.compose.ui.util.fastForEachIndexed
import kotlin.math.max

@Composable
internal fun AlertDialogContent(
    buttons: @Composable () -> Unit,
    modifier: Modifier = Modifier,
    title: (@Composable () -> Unit)? = null,
    text: @Composable (() -> Unit)? = null,
    shape: Shape = MaterialTheme.shapes.medium,
    backgroundColor: Color = MaterialTheme.colors.surface,
    contentColor: Color = contentColorFor(backgroundColor),
) {
    Surface(
        modifier = modifier,
        shape = shape,
        color = backgroundColor,
        contentColor = contentColor
    ) {
        Column {
            AlertDialogBaselineLayout(
                title = title?.let {
                    @Composable {
                        CompositionLocalProvider(LocalContentAlpha provides ContentAlpha.high) {
                            val textStyle = MaterialTheme.typography.subtitle1
                            ProvideTextStyle(textStyle, title)
                        }
                    }
                },
                text = text?.let {
                    @Composable {
                        CompositionLocalProvider(
                            LocalContentAlpha provides ContentAlpha.medium
                        ) {
                            val textStyle = MaterialTheme.typography.body2
                            ProvideTextStyle(textStyle, text)
                        }
                    }
                }
            )
            buttons()
        }
    }
}

/**
 * Layout that will add spacing between the top of the layout and [title]'s first baseline, and
 * [title]'s last baseline and [text]'s first baseline.
 *
 * If [title] and/or [text] do not have any baselines, the spacing will just be applied from the
 * edge of their layouts instead as a best effort implementation.
 */
@Composable
internal fun ColumnScope.AlertDialogBaselineLayout(
    title: @Composable (() -> Unit)?,
    text: @Composable (() -> Unit)?
) {
    Layout(
        {
            title?.let { title ->
                Box(TitlePadding.layoutId("title").align(Alignment.Start)) {
                    title()
                }
            }
            text?.let { text ->
                Box(TextPadding.layoutId("text").align(Alignment.Start)) {
                    text()
                }
            }
        },
        Modifier.weight(1f, false)
    ) { measurables, constraints ->
        // Measure with loose constraints for height as we don't want the text to take up more
        // space than it needs
        val titlePlaceable = measurables.firstOrNull { it.layoutId == "title" }?.measure(
            constraints.copy(minHeight = 0)
        )
        val textPlaceable = measurables.firstOrNull { it.layoutId == "text" }?.measure(
            constraints.copy(minHeight = 0)
        )

        val layoutWidth = max(titlePlaceable?.width ?: 0, textPlaceable?.width ?: 0)

        val firstTitleBaseline = titlePlaceable?.get(FirstBaseline)?.let { baseline ->
            if (baseline == AlignmentLine.Unspecified) null else baseline
        } ?: 0
        val lastTitleBaseline = titlePlaceable?.get(LastBaseline)?.let { baseline ->
            if (baseline == AlignmentLine.Unspecified) null else baseline
        } ?: 0

        val titleOffset = TitleBaselineDistanceFromTop.roundToPx()

        // Place the title so that its first baseline is titleOffset from the top
        val titlePositionY = titleOffset - firstTitleBaseline

        val firstTextBaseline = textPlaceable?.get(FirstBaseline)?.let { baseline ->
            if (baseline == AlignmentLine.Unspecified) null else baseline
        } ?: 0

        val textOffset = if (titlePlaceable == null) {
            TextBaselineDistanceFromTop.roundToPx()
        } else {
            TextBaselineDistanceFromTitle.roundToPx()
        }

        // Combined height of title and spacing above
        val titleHeightWithSpacing = titlePlaceable?.let { it.height + titlePositionY } ?: 0

        // Align the bottom baseline of the text with the bottom baseline of the title, and then
        // add the offset
        val textPositionY = if (titlePlaceable == null) {
            // If there is no title, just place the text offset from the top of the dialog
            textOffset - firstTextBaseline
        } else {
            if (lastTitleBaseline == 0) {
                // If `title` has no baseline, just place the text's baseline textOffset from the
                // bottom of the title
                titleHeightWithSpacing - firstTextBaseline + textOffset
            } else {
                // Otherwise place the text's baseline textOffset from the title's last baseline
                (titlePositionY + lastTitleBaseline) - firstTextBaseline + textOffset
            }
        }

        // Combined height of text and spacing above
        val textHeightWithSpacing = textPlaceable?.let {
            if (lastTitleBaseline == 0) {
                textPlaceable.height + textOffset - firstTextBaseline
            } else {
                textPlaceable.height + textOffset - firstTextBaseline -
                    ((titlePlaceable?.height ?: 0) - lastTitleBaseline)
            }
        } ?: 0

        val layoutHeight = titleHeightWithSpacing + textHeightWithSpacing

        layout(layoutWidth, layoutHeight) {
            titlePlaceable?.place(0, titlePositionY)
            textPlaceable?.place(0, textPositionY)
        }
    }
}

/**
 * Simple clone of FlowRow that arranges its children in a horizontal flow with limited
 * customization.
 */
@Composable
internal fun AlertDialogFlowRow(
    mainAxisSpacing: Dp,
    crossAxisSpacing: Dp,
    content: @Composable () -> Unit
) {
    Layout(content) { measurables, constraints ->
        val sequences = mutableListOf<List<Placeable>>()
        val crossAxisSizes = mutableListOf<Int>()
        val crossAxisPositions = mutableListOf<Int>()

        var mainAxisSpace = 0
        var crossAxisSpace = 0

        val currentSequence = mutableListOf<Placeable>()
        var currentMainAxisSize = 0
        var currentCrossAxisSize = 0

        val childConstraints = Constraints(maxWidth = constraints.maxWidth)

        // Return whether the placeable can be added to the current sequence.
        fun canAddToCurrentSequence(placeable: Placeable) =
            currentSequence.isEmpty() || currentMainAxisSize + mainAxisSpacing.roundToPx() +
                placeable.width <= constraints.maxWidth

        // Store current sequence information and start a new sequence.
        fun startNewSequence() {
            if (sequences.isNotEmpty()) {
                crossAxisSpace += crossAxisSpacing.roundToPx()
            }
            sequences += currentSequence.toList()
            crossAxisSizes += currentCrossAxisSize
            crossAxisPositions += crossAxisSpace

            crossAxisSpace += currentCrossAxisSize
            mainAxisSpace = max(mainAxisSpace, currentMainAxisSize)

            currentSequence.clear()
            currentMainAxisSize = 0
            currentCrossAxisSize = 0
        }

        for (measurable in measurables) {
            // Ask the child for its preferred size.
            val placeable = measurable.measure(childConstraints)

            // Start a new sequence if there is not enough space.
            if (!canAddToCurrentSequence(placeable)) startNewSequence()

            // Add the child to the current sequence.
            if (currentSequence.isNotEmpty()) {
                currentMainAxisSize += mainAxisSpacing.roundToPx()
            }
            currentSequence.add(placeable)
            currentMainAxisSize += placeable.width
            currentCrossAxisSize = max(currentCrossAxisSize, placeable.height)
        }

        if (currentSequence.isNotEmpty()) startNewSequence()

        val mainAxisLayoutSize = if (constraints.maxWidth != Constraints.Infinity) {
            constraints.maxWidth
        } else {
            max(mainAxisSpace, constraints.minWidth)
        }
        val crossAxisLayoutSize = max(crossAxisSpace, constraints.minHeight)

        val layoutWidth = mainAxisLayoutSize

        val layoutHeight = crossAxisLayoutSize

        layout(layoutWidth, layoutHeight) {
            sequences.fastForEachIndexed { i, placeables ->
                val childrenMainAxisSizes = IntArray(placeables.size) { j ->
                    placeables[j].width +
                        if (j < placeables.lastIndex) mainAxisSpacing.roundToPx() else 0
                }
                val arrangement = Arrangement.Bottom
                // TODO(soboleva): rtl support
                // Handle vertical direction
                val mainAxisPositions = IntArray(childrenMainAxisSizes.size) { 0 }
                with(arrangement) {
                    arrange(mainAxisLayoutSize, childrenMainAxisSizes, mainAxisPositions)
                }
                placeables.fastForEachIndexed { j, placeable ->
                    placeable.place(
                        x = mainAxisPositions[j],
                        y = crossAxisPositions[i]
                    )
                }
            }
        }
    }
}

private val TitlePadding = Modifier.padding(start = 24.dp, end = 24.dp)
private val TextPadding = Modifier.padding(start = 24.dp, end = 24.dp, bottom = 28.dp)
// Baseline distance from the first line of the title to the top of the dialog
private val TitleBaselineDistanceFromTop = 40.sp
// Baseline distance from the first line of the text to the last line of the title
private val TextBaselineDistanceFromTitle = 36.sp
// For dialogs with no title, baseline distance from the first line of the text to the top of the
// dialog
private val TextBaselineDistanceFromTop = 38.sp