Hoverable.kt

/*
 * 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

import androidx.compose.foundation.interaction.HoverInteraction
import androidx.compose.foundation.interaction.MutableInteractionSource
import androidx.compose.runtime.DisposableEffect
import androidx.compose.runtime.LaunchedEffect
import androidx.compose.runtime.getValue
import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.remember
import androidx.compose.runtime.setValue
import androidx.compose.ui.Modifier
import androidx.compose.ui.composed
import androidx.compose.ui.input.pointer.PointerEventType
import androidx.compose.ui.input.pointer.pointerInput
import androidx.compose.ui.platform.debugInspectorInfo
import kotlinx.coroutines.currentCoroutineContext
import kotlinx.coroutines.isActive

/**
 * Configure component to be hoverable via pointer enter/exit events.
 *
 * @sample androidx.compose.foundation.samples.HoverableSample
 *
 * @param interactionSource [MutableInteractionSource] that will be used to emit
 * [HoverInteraction.Enter] when this element is being hovered.
 * @param enabled Controls the enabled state. When `false`, hover events will be ignored.
 */
fun Modifier.hoverable(
    interactionSource: MutableInteractionSource,
    enabled: Boolean = true
): Modifier = composed(
    inspectorInfo = debugInspectorInfo {
        name = "hoverable"
        properties["interactionSource"] = interactionSource
        properties["enabled"] = enabled
    }
) {
    var hoverInteraction by remember { mutableStateOf<HoverInteraction.Enter?>(null) }

    suspend fun emitEnter() {
        if (hoverInteraction == null) {
            val interaction = HoverInteraction.Enter()
            interactionSource.emit(interaction)
            hoverInteraction = interaction
        }
    }

    suspend fun emitExit() {
        hoverInteraction?.let { oldValue ->
            val interaction = HoverInteraction.Exit(oldValue)
            interactionSource.emit(interaction)
            hoverInteraction = null
        }
    }

    fun tryEmitExit() {
        hoverInteraction?.let { oldValue ->
            val interaction = HoverInteraction.Exit(oldValue)
            interactionSource.tryEmit(interaction)
            hoverInteraction = null
        }
    }

    DisposableEffect(interactionSource) {
        onDispose { tryEmitExit() }
    }
    LaunchedEffect(enabled) {
        if (!enabled) {
            emitExit()
        }
    }

    if (enabled) {
        Modifier
// TODO(b/202505231):
//  because we only react to input events, and not on layout changes, we can have a situation when
//  Composable is under the cursor, but not hovered. To fix that, we have two ways:
//  a. Trigger Enter/Exit on any layout change, inside Owner
//  b. Manually react on layout changes via Modifier.onGloballyPosition, and check something like
//  LocalPointerPosition.current
            .pointerInput(interactionSource) {
                val currentContext = currentCoroutineContext()
                while (currentContext.isActive) {
                    val event = awaitPointerEventScope { awaitPointerEvent() }
                    when (event.type) {
                        PointerEventType.Enter -> emitEnter()
                        PointerEventType.Exit -> emitExit()
                    }
                }
            }
    } else {
        Modifier
    }
}