xref: /compose/ui/ui/src/commonMain/kotlin/androidx/compose/ui/focus/FocusTraversal.kt

/*
 * 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.focus

import androidx.compose.ui.ComposeUiFlags
import androidx.compose.ui.ExperimentalComposeUiApi
import androidx.compose.ui.focus.FocusDirection.Companion.Down
import androidx.compose.ui.focus.FocusDirection.Companion.Enter
import androidx.compose.ui.focus.FocusDirection.Companion.Exit
import androidx.compose.ui.focus.FocusDirection.Companion.Left
import androidx.compose.ui.focus.FocusDirection.Companion.Next
import androidx.compose.ui.focus.FocusDirection.Companion.Previous
import androidx.compose.ui.focus.FocusDirection.Companion.Right
import androidx.compose.ui.focus.FocusDirection.Companion.Up
import androidx.compose.ui.focus.FocusRequester.Companion.Cancel
import androidx.compose.ui.focus.FocusRequester.Companion.Default
import androidx.compose.ui.focus.FocusRequester.Companion.Redirect
import androidx.compose.ui.focus.FocusStateImpl.Active
import androidx.compose.ui.focus.FocusStateImpl.ActiveParent
import androidx.compose.ui.focus.FocusStateImpl.Captured
import androidx.compose.ui.focus.FocusStateImpl.Inactive
import androidx.compose.ui.geometry.Rect
import androidx.compose.ui.layout.findRootCoordinates
import androidx.compose.ui.node.Nodes
import androidx.compose.ui.node.requireOwner
import androidx.compose.ui.node.visitAncestors
import androidx.compose.ui.node.visitChildren
import androidx.compose.ui.unit.LayoutDirection
import androidx.compose.ui.unit.LayoutDirection.Ltr
import androidx.compose.ui.unit.LayoutDirection.Rtl

/**
 * Search up the component tree for any parent/parents that have specified a custom focus order.
 * Allowing parents higher up the hierarchy to overwrite the focus order specified by their
 * children.
 *
 * @param focusDirection the focus direction passed to [FocusManager.moveFocus] that triggered this
 *   focus search.
 * @param layoutDirection the current system [LayoutDirection].
 */
internal fun FocusTargetNode.customFocusSearch(
    focusDirection: FocusDirection,
    layoutDirection: LayoutDirection
): FocusRequester {
    val focusProperties = fetchFocusProperties()
    return when (focusDirection) {
        Next -> focusProperties.next
        Previous -> focusProperties.previous
        Up -> focusProperties.up
        Down -> focusProperties.down
        Left ->
            when (layoutDirection) {
                Ltr -> focusProperties.start
                Rtl -> focusProperties.end
            }.takeUnless { it === Default } ?: focusProperties.left
        Right ->
            when (layoutDirection) {
                Ltr -> focusProperties.end
                Rtl -> focusProperties.start
            }.takeUnless { it === Default } ?: focusProperties.right
        // TODO(b/183746982): add focus order API for "In" and "Out".
        //  Developers can to specify a custom "In" to specify which child should be visited when
        //  the user presses dPad center. (They can also redirect the "In" to some other item).
        //  Developers can specify a custom "Out" to specify which composable should take focus
        //  when the user presses the back button.
        Enter,
        Exit -> {
            val scope = CancelIndicatingFocusBoundaryScope(focusDirection)
            with(focusProperties) {
                val focusTransactionManager = focusTransactionManager
                val generationBefore = focusTransactionManager?.generation ?: 0
                val focusOwner = requireOwner().focusOwner
                val activeNodeBefore = focusOwner.activeFocusTargetNode
                if (focusDirection == Enter) {
                    scope.onEnter()
                } else {
                    scope.onExit()
                }
                val generationAfter = focusTransactionManager?.generation ?: 0
                if (scope.isCanceled) {
                    Cancel
                } else if (
                    generationBefore != generationAfter ||
                        (@OptIn(ExperimentalComposeUiApi::class)
                        ComposeUiFlags.isTrackFocusEnabled &&
                            activeNodeBefore !== focusOwner.activeFocusTargetNode)
                ) {
                    Redirect
                } else {
                    Default
                }
            }
        }
        else -> error("invalid FocusDirection")
    }
}

/**
 * Moves focus based on the requested focus direction.
 *
 * @param focusDirection The requested direction to move focus.
 * @param layoutDirection Whether the layout is RTL or LTR.
 * @param previouslyFocusedRect The bounds of the previously focused item.
 * @param onFound This lambda is invoked if focus search finds the next focus node.
 * @return if no focus node is found, we return false. If we receive a cancel, we return null
 *   otherwise we return the result of [onFound].
 */
internal fun FocusTargetNode.focusSearch(
    focusDirection: FocusDirection,
    layoutDirection: LayoutDirection,
    previouslyFocusedRect: Rect?,
    onFound: (FocusTargetNode) -> Boolean
): Boolean? {
    return when (focusDirection) {
        Next,
        Previous -> oneDimensionalFocusSearch(focusDirection, onFound)
        Left,
        Right,
        Up,
        Down -> twoDimensionalFocusSearch(focusDirection, previouslyFocusedRect, onFound)
        Enter -> {
            // we search among the children of the active item.
            val direction =
                when (layoutDirection) {
                    Rtl -> Left
                    Ltr -> Right
                }
            findActiveFocusNode()
                ?.twoDimensionalFocusSearch(direction, previouslyFocusedRect, onFound)
        }
        Exit ->
            findActiveFocusNode()?.findNonDeactivatedParent().let {
                if (it == null || it == this) false else onFound.invoke(it)
            }
        else -> error("Focus search invoked with invalid FocusDirection $focusDirection")
    }
}

/**
 * Returns the bounding box of the focus layout area in the root or [Rect.Zero] if the FocusModifier
 * has not had a layout.
 */
internal fun FocusTargetNode.focusRect(): Rect =
    coordinator?.let { it.findRootCoordinates().localBoundingBoxOf(it, clipBounds = false) }
        ?: Rect.Zero

/** Whether this node should be considered when searching for the next item during a traversal. */
internal val FocusTargetNode.isEligibleForFocusSearch: Boolean
    get() = coordinator?.layoutNode?.isPlaced == true && coordinator?.layoutNode?.isAttached == true

internal val FocusTargetNode.activeChild: FocusTargetNode?
    get() {
        if (!node.isAttached) return null
        visitChildren(Nodes.FocusTarget) {
            if (!it.node.isAttached) return@visitChildren
            when (it.focusState) {
                Active,
                ActiveParent,
                Captured -> return it
                Inactive -> return@visitChildren
            }
        }
        return null
    }

internal fun FocusTargetNode.findActiveFocusNode(): FocusTargetNode? {
    if (@OptIn(ExperimentalComposeUiApi::class) ComposeUiFlags.isTrackFocusEnabled) {
        val activeNode = requireOwner().focusOwner.activeFocusTargetNode
        return if (activeNode != null && activeNode.isAttached) activeNode else null
    } else {
        when (focusState) {
            Active,
            Captured -> return this
            ActiveParent -> {
                visitChildren(Nodes.FocusTarget) { node ->
                    node.findActiveFocusNode()?.let {
                        return it
                    }
                }
                return null
            }
            Inactive -> return null
        }
    }
}

@Suppress("ModifierFactoryExtensionFunction", "ModifierFactoryReturnType")
private fun FocusTargetNode.findNonDeactivatedParent(): FocusTargetNode? {
    visitAncestors(Nodes.FocusTarget) { if (it.fetchFocusProperties().canFocus) return it }
    return null
}