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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 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.ui.focus

import androidx.compose.ui.ExperimentalComposeUiApi
import androidx.compose.ui.Modifier
import androidx.compose.ui.node.ModifierNodeElement
import androidx.compose.ui.platform.InspectorInfo

/**
 * Properties that are applied to [focusTarget] that is the first child of the
 * [FocusPropertiesModifierNode] that sets these properties.
 *
 * @see [focusProperties]
 */
interface FocusProperties {
    /**
     * When set to false, indicates that the [focusTarget] that this is applied to can no longer
     * take focus. If the [focusTarget] is currently focused, setting this property to false will
     * end up clearing focus.
     */
    var canFocus: Boolean

    /**
     * A custom item to be used when the user requests the focus to move to the "next" item.
     *
     * @sample androidx.compose.ui.samples.CustomFocusOrderSample
     */
    var next: FocusRequester
        get() = FocusRequester.Default
        set(_) {}

    /**
     * A custom item to be used when the user requests the focus to move to the "previous" item.
     *
     * @sample androidx.compose.ui.samples.CustomFocusOrderSample
     */
    var previous: FocusRequester
        get() = FocusRequester.Default
        set(_) {}

    /**
     *  A custom item to be used when the user moves focus "up".
     *
     *  @sample androidx.compose.ui.samples.CustomFocusOrderSample
     */
    var up: FocusRequester
        get() = FocusRequester.Default
        set(_) {}

    /**
     *  A custom item to be used when the user moves focus "down".
     *
     *  @sample androidx.compose.ui.samples.CustomFocusOrderSample
     */
    var down: FocusRequester
        get() = FocusRequester.Default
        set(_) {}

    /**
     * A custom item to be used when the user requests a focus moves to the "left" item.
     *
     * @sample androidx.compose.ui.samples.CustomFocusOrderSample
     */
    var left: FocusRequester
        get() = FocusRequester.Default
        set(_) {}

    /**
     * A custom item to be used when the user requests a focus moves to the "right" item.
     *
     * @sample androidx.compose.ui.samples.CustomFocusOrderSample
     */
    var right: FocusRequester
        get() = FocusRequester.Default
        set(_) {}

    /**
     * A custom item to be used when the user requests a focus moves to the "left" in LTR mode and
     * "right" in RTL mode.
     *
     * @sample androidx.compose.ui.samples.CustomFocusOrderSample
     */
    var start: FocusRequester
        get() = FocusRequester.Default
        set(_) {}

    /**
     * A custom item to be used when the user requests a focus moves to the "right" in LTR mode
     * and "left" in RTL mode.
     *
     * @sample androidx.compose.ui.samples.CustomFocusOrderSample
     */
    var end: FocusRequester
        get() = FocusRequester.Default
        set(_) {}

    /**
     * A custom item to be used when the user requests focus to move focus in
     * ([FocusDirection.Enter]). An automatic [Enter][FocusDirection.Enter]"
     * can be triggered when we move focus to a focus group that is not itself focusable. In this
     * case, users can use the  the focus direction that triggered the move in to determine the
     * next item to be focused on.
     *
     * When you set the [enter] property, provide a lambda that takes the FocusDirection that
     * triggered the enter as an input, and provides a [FocusRequester] as an output. You can
     * return a custom destination by providing a [FocusRequester] attached to that destination,
     * a [Cancel][FocusRequester.Cancel] to cancel the focus enter or
     * [Default][FocusRequester.Default] to use the default focus enter behavior.
     *
     * @sample androidx.compose.ui.samples.CustomFocusEnterSample
     */
    @Suppress("OPT_IN_MARKER_ON_WRONG_TARGET")
    @get:ExperimentalComposeUiApi
    @set:ExperimentalComposeUiApi
    @ExperimentalComposeUiApi
    var enter: (FocusDirection) -> FocusRequester
        get() = { FocusRequester.Default }
        set(_) {}

    /**
     * A custom item to be used when the user requests focus to move out ([FocusDirection.Exit]).
     * An automatic [Exit][FocusDirection.Exit] can be triggered when we move focus outside the edge
     * of a parent. In this case, users can use the  the focus direction that triggered the move out
     * to determine the next focus destination.
     *
     * When you set the [exit] property, provide a lambda that takes the FocusDirection that
     * triggered the exit as an input, and provides a [FocusRequester] as an output. You can
     * return a custom destination by providing a [FocusRequester] attached to that destination,
     * a [Cancel][FocusRequester.Cancel] to cancel the focus exit or
     * [Default][FocusRequester.Default] to use the default focus exit behavior.
     *
     * @sample androidx.compose.ui.samples.CustomFocusExitSample
     */
    @Suppress("OPT_IN_MARKER_ON_WRONG_TARGET")
    @get:ExperimentalComposeUiApi
    @set:ExperimentalComposeUiApi
    @ExperimentalComposeUiApi
    var exit: (FocusDirection) -> FocusRequester
        get() = { FocusRequester.Default }
        set(_) {}
}

internal class FocusPropertiesImpl : FocusProperties {
    override var canFocus: Boolean = true
    override var next: FocusRequester = FocusRequester.Default
    override var previous: FocusRequester = FocusRequester.Default
    override var up: FocusRequester = FocusRequester.Default
    override var down: FocusRequester = FocusRequester.Default
    override var left: FocusRequester = FocusRequester.Default
    override var right: FocusRequester = FocusRequester.Default
    override var start: FocusRequester = FocusRequester.Default
    override var end: FocusRequester = FocusRequester.Default
    @OptIn(ExperimentalComposeUiApi::class)
    override var enter: (FocusDirection) -> FocusRequester = { FocusRequester.Default }
    @OptIn(ExperimentalComposeUiApi::class)
    override var exit: (FocusDirection) -> FocusRequester = { FocusRequester.Default }
}

/**
 * This modifier allows you to specify properties that are accessible to [focusTarget]s further
 * down the modifier chain or on child layout nodes.
 *
 * @sample androidx.compose.ui.samples.FocusPropertiesSample
 */
fun Modifier.focusProperties(
    scope: FocusProperties.() -> Unit
): Modifier = this then FocusPropertiesElement(scope)

private data class FocusPropertiesElement(
    val scope: FocusPropertiesScope
) : ModifierNodeElement() {
    override fun create() = FocusPropertiesNode(scope)

    override fun update(node: FocusPropertiesNode) {
        node.focusPropertiesScope = scope
    }

    override fun InspectorInfo.inspectableProperties() {
        name = "focusProperties"
        properties["scope"] = scope
    }
}

private class FocusPropertiesNode(
    var focusPropertiesScope: FocusPropertiesScope,
) : FocusPropertiesModifierNode, Modifier.Node() {

    override fun applyFocusProperties(focusProperties: FocusProperties) {
        focusPropertiesScope.apply(focusProperties)
    }
}