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Compose UI primitives. This library contains the primitives that form the Compose UI Toolkit, such as drawing, measurement and layout.
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/*
 * Copyright 2020 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.ui.semantics

import androidx.compose.runtime.InternalComposeApi
import androidx.compose.runtime.identityHashCode
import androidx.compose.ui.Modifier
import androidx.compose.ui.internal.JvmDefaultWithCompatibility
import androidx.compose.ui.node.ModifierNodeElement
import androidx.compose.ui.node.SemanticsModifierNode
import androidx.compose.ui.platform.AtomicInt
import androidx.compose.ui.platform.InspectorInfo

private var lastIdentifier = AtomicInt(0)
internal fun generateSemanticsId() = lastIdentifier.addAndGet(1)

/**
 * A [Modifier.Element] that adds semantics key/value for use in testing,
 * accessibility, and similar use cases.
 */
@JvmDefaultWithCompatibility
interface SemanticsModifier : Modifier.Element {
    @Deprecated(
        message = "SemanticsModifier.id is now unused and has been set to a fixed value. " +
            "Retrieve the id from LayoutInfo instead.",
        replaceWith = ReplaceWith("")
    )
    val id: Int get() = -1

    /**
     * The SemanticsConfiguration holds substantive data, especially a list of key/value pairs
     * such as (label -> "buttonName").
     */
    val semanticsConfiguration: SemanticsConfiguration
}

internal class EmptySemanticsElement(private val node: EmptySemanticsModifier) :
    ModifierNodeElement() {
    override fun create() = node

    override fun update(node: EmptySemanticsModifier) {}

    override fun InspectorInfo.inspectableProperties() {
        // Nothing to inspect.
    }

    @OptIn(InternalComposeApi::class)
    private val arbitraryHashCode: Int = identityHashCode(this)
    override fun hashCode(): Int = arbitraryHashCode
    override fun equals(other: Any?) = (other === this)
}

internal class CoreSemanticsModifierNode(
    var mergeDescendants: Boolean,
    var isClearingSemantics: Boolean,
    var properties: SemanticsPropertyReceiver.() -> Unit
) : Modifier.Node(), SemanticsModifierNode {
    override val shouldClearDescendantSemantics: Boolean
        get() = isClearingSemantics
    override val shouldMergeDescendantSemantics: Boolean
        get() = mergeDescendants
    override fun SemanticsPropertyReceiver.applySemantics() {
        properties()
    }
}

internal class EmptySemanticsModifier : Modifier.Node(), SemanticsModifierNode {
    override fun SemanticsPropertyReceiver.applySemantics() {}
}

/**
 * Add semantics key/value pairs to the layout node, for use in testing, accessibility, etc.
 *
 * The provided lambda receiver scope provides "key = value"-style setters for any
 * [SemanticsPropertyKey]. Additionally, chaining multiple semantics modifiers is
 * also a supported style.
 *
 * The resulting semantics produce two [SemanticsNode] trees:
 *
 * The "unmerged tree" rooted at [SemanticsOwner.unmergedRootSemanticsNode] has one
 * [SemanticsNode] per layout node which has any [SemanticsModifier] on it.  This [SemanticsNode]
 * contains all the properties set in all the [SemanticsModifier]s on that node.
 *
 * The "merged tree" rooted at [SemanticsOwner.rootSemanticsNode] has equal-or-fewer nodes: it
 * simplifies the structure based on [mergeDescendants] and [clearAndSetSemantics].  For most
 * purposes (especially accessibility, or the testing of accessibility), the merged semantics
 * tree should be used.
 *
 * @param mergeDescendants Whether the semantic information provided by the owning component and
 * its descendants should be treated as one logical entity.
 * Most commonly set on screen-reader-focusable items such as buttons or form fields.
 * In the merged semantics tree, all descendant nodes (except those themselves marked
 * [mergeDescendants]) will disappear from the tree, and their properties will get merged
 * into the parent's configuration (using a merging algorithm that varies based on the type
 * of property -- for example, text properties will get concatenated, separated by commas).
 * In the unmerged semantics tree, the node is simply marked with
 * [SemanticsConfiguration.isMergingSemanticsOfDescendants].
 * @param properties properties to add to the semantics. [SemanticsPropertyReceiver] will be
 * provided in the scope to allow access for common properties and its values.
 */
fun Modifier.semantics(
    mergeDescendants: Boolean = false,
    properties: (SemanticsPropertyReceiver.() -> Unit)
): Modifier = this then AppendedSemanticsElement(
    mergeDescendants = mergeDescendants,
    properties = properties
)

// Implement SemanticsModifier to allow tooling to inspect the semantics configuration
internal data class AppendedSemanticsElement(
    val mergeDescendants: Boolean,
    val properties: (SemanticsPropertyReceiver.() -> Unit)
) : ModifierNodeElement(), SemanticsModifier {

    // This should only ever be called by layout inspector
    override val semanticsConfiguration: SemanticsConfiguration
        get() = SemanticsConfiguration().apply {
            isMergingSemanticsOfDescendants = mergeDescendants
            properties()
        }

    override fun create(): CoreSemanticsModifierNode {
        return CoreSemanticsModifierNode(
            mergeDescendants = mergeDescendants,
            isClearingSemantics = false,
            properties = properties
        )
    }

    override fun update(node: CoreSemanticsModifierNode) {
        node.mergeDescendants = mergeDescendants
        node.properties = properties
    }

    override fun InspectorInfo.inspectableProperties() {
        name = "semantics"
        properties["mergeDescendants"] = mergeDescendants
        addSemanticsPropertiesFrom(semanticsConfiguration)
    }
}

/**
 * Clears the semantics of all the descendant nodes and sets new semantics.
 *
 * In the merged semantics tree, this clears the semantic information provided
 * by the node's descendants (but not those of the layout node itself, if any) and sets
 * the provided semantics.  (In the unmerged tree, the semantics node is marked with
 * "[SemanticsConfiguration.isClearingSemantics]", but nothing is actually cleared.)
 *
 * Compose's default semantics provide baseline usability for screen-readers, but this can be
 * used to provide a more polished screen-reader experience: for example, clearing the
 * semantics of a group of tiny buttons, and setting equivalent actions on the card containing them.
 *
 * @param properties properties to add to the semantics. [SemanticsPropertyReceiver] will be
 * provided in the scope to allow access for common properties and its values.
 */
fun Modifier.clearAndSetSemantics(
    properties: (SemanticsPropertyReceiver.() -> Unit)
): Modifier = this then ClearAndSetSemanticsElement(properties)

// Implement SemanticsModifier to allow tooling to inspect the semantics configuration
internal data class ClearAndSetSemanticsElement(
    val properties: SemanticsPropertyReceiver.() -> Unit
) : ModifierNodeElement(), SemanticsModifier {

    // This should only ever be called by layout inspector
    override val semanticsConfiguration: SemanticsConfiguration
        get() = SemanticsConfiguration().apply {
            isMergingSemanticsOfDescendants = false
            isClearingSemantics = true
            properties()
        }

    override fun create(): CoreSemanticsModifierNode {
        return CoreSemanticsModifierNode(
            mergeDescendants = false,
            isClearingSemantics = true,
            properties = properties
        )
    }

    override fun update(node: CoreSemanticsModifierNode) {
        node.properties = properties
    }

    override fun InspectorInfo.inspectableProperties() {
        name = "clearAndSetSemantics"
        addSemanticsPropertiesFrom(semanticsConfiguration)
    }
}

private fun InspectorInfo.addSemanticsPropertiesFrom(
    semanticsConfiguration: SemanticsConfiguration
) {
    properties["properties"] = semanticsConfiguration.associate { (key, value) ->
        key.name to value
    }
}