car: alerts from hosted apps show on the car screen

Waze asks whether a reported hazard is still there with an alert, and
Gearslip dropped every one (#54). An alert now shows as a card across
the top of any screen, with its buttons and a bar for the time left.

gearslip/src/main/java/app/seb3thehacker/gearslip/car/CarAlerts.kt

@@ -0,0 +1,203 @@
+package app.seb3thehacker.gearslip.car
+
+import androidx.annotation.MainThread
+import androidx.car.app.model.Action
+import androidx.car.app.model.Alert
+import androidx.car.app.model.AlertCallback
+import androidx.compose.animation.core.Animatable
+import androidx.compose.animation.core.LinearEasing
+import androidx.compose.animation.core.tween
+import androidx.compose.foundation.background
+import androidx.compose.foundation.layout.Arrangement
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.Row
+import androidx.compose.foundation.layout.Spacer
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.height
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.layout.size
+import androidx.compose.foundation.layout.width
+import androidx.compose.foundation.layout.widthIn
+import androidx.compose.foundation.shape.CircleShape
+import androidx.compose.foundation.shape.RoundedCornerShape
+import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.filled.Close
+import androidx.compose.material3.Icon
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Surface
+import androidx.compose.material3.Text
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.LaunchedEffect
+import androidx.compose.runtime.collectAsState
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.remember
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.draw.clip
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.res.stringResource
+import androidx.compose.ui.semantics.LiveRegionMode
+import androidx.compose.ui.semantics.liveRegion
+import androidx.compose.ui.semantics.semantics
+import androidx.compose.ui.text.font.FontWeight
+import androidx.compose.ui.text.style.TextOverflow
+import androidx.compose.ui.unit.dp
+import app.seb3thehacker.gearslip.GearslipLog
+import app.seb3thehacker.gearslip.R
+import app.seb3thehacker.gearslip.car.theme.GsColors
+import app.seb3thehacker.gearslip.car.theme.GsIconBox
+import app.seb3thehacker.gearslip.host.cancel
+import app.seb3thehacker.gearslip.host.click
+import app.seb3thehacker.gearslip.host.color
+import app.seb3thehacker.gearslip.host.dismissed
+import app.seb3thehacker.gearslip.host.text
+import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.StateFlow
+import kotlinx.coroutines.flow.asStateFlow
+
+/**
+ * The one alert on the car screen, from whichever hosted app sent it: Waze asking whether a
+ * hazard is still there, say. As in Android Auto, a newer alert replaces the one showing, and it
+ * shows over any screen, since a question about the road matters while music is up too.
+ */
+@MainThread
+internal object CarAlerts {
+    class Shown(val owner: Any, val alert: Alert)
+
+    private val current = MutableStateFlow<Shown?>(null)
+    val shown: StateFlow<Shown?> = current.asStateFlow()
+
+    fun show(owner: Any, alert: Alert) {
+        val old = current.value
+        current.value = Shown(owner, alert)
+        GearslipLog.i("host: alert ${alert.id} \"${alert.title.text()}\" with ${alert.actions.size} buttons")
+        if (old != null && !(old.owner === owner && old.alert.id == alert.id)) old.alert.callbackDelegate.dismissed()
+    }
+
+    /** The app took its alert down; a no-op unless that alert is the one showing. */
+    fun dismiss(owner: Any, id: Int) {
+        val shown = current.value ?: return
+        if (shown.owner !== owner || shown.alert.id != id) return
+        current.value = null
+        shown.alert.callbackDelegate.dismissed()
+    }
+
+    /** The driver tapped one of its buttons: the app gets the tap, and the alert goes. */
+    fun tapped(shown: Shown, action: Action) {
+        action.onClickDelegate.click("alert button")
+        if (current.value !== shown) return
+        current.value = null
+        shown.alert.callbackDelegate.dismissed()
+    }
+
+    fun cancelled(shown: Shown, reason: Int) {
+        if (current.value !== shown) return
+        current.value = null
+        shown.alert.callbackDelegate.cancel(reason)
+    }
+
+    /** The app disconnected: its alert goes with it, and there is no one left to tell. */
+    fun clear(owner: Any) {
+        if (current.value?.owner === owner) current.value = null
+    }
+}
+
+@Composable
+internal fun CarAlertOverlay(modifier: Modifier = Modifier) {
+    val current by CarAlerts.shown.collectAsState()
+    val shown = current ?: return
+    val alert = shown.alert
+    val timed = alert.durationMillis in 1 until Alert.DURATION_SHOW_INDEFINITELY
+    // What's left of the alert's time, drawn as the bar along its foot.
+    val left = remember(shown) { Animatable(1f) }
+    LaunchedEffect(shown) {
+        if (!timed) return@LaunchedEffect
+        left.animateTo(0f, tween(alert.durationMillis.coerceAtMost(Int.MAX_VALUE.toLong()).toInt(), easing = LinearEasing))
+        CarAlerts.cancelled(shown, AlertCallback.REASON_TIMEOUT)
+    }
+    val scheme = MaterialTheme.colorScheme
+    val dark = scheme.surface.luminanceIsDark()
+    Surface(
+        modifier
+            .padding(horizontal = 24.dp, vertical = 16.dp)
+            .widthIn(max = 640.dp)
+            .fillMaxWidth()
+            .semantics { liveRegion = LiveRegionMode.Polite },
+        shape = RoundedCornerShape(24.dp),
+        color = scheme.surfaceContainerHigh,
+        shadowElevation = 8.dp,
+    ) {
+        Column {
+            Row(Modifier.padding(start = 20.dp, end = 12.dp, top = 16.dp), verticalAlignment = Alignment.CenterVertically) {
+                if (alert.icon != null) {
+                    CarGlyph(alert.icon, Modifier.size(40.dp))
+                    Spacer(Modifier.width(16.dp))
+                }
+                Column(Modifier.weight(1f)) {
+                    Text(
+                        alert.title.text(),
+                        style = MaterialTheme.typography.titleLarge,
+                        fontWeight = FontWeight.Bold,
+                        maxLines = 2,
+                        overflow = TextOverflow.Ellipsis,
+                    )
+                    alert.subtitle?.text()?.takeIf { it.isNotEmpty() }?.let {
+                        Text(
+                            it,
+                            style = MaterialTheme.typography.titleMedium,
+                            color = scheme.onSurfaceVariant,
+                            maxLines = 2,
+                            overflow = TextOverflow.Ellipsis,
+                        )
+                    }
+                }
+                // With no timer and no buttons, nothing else would ever take it away.
+                if (!timed || alert.actions.isEmpty()) {
+                    GsIconBox(
+                        onClick = { CarAlerts.cancelled(shown, AlertCallback.REASON_USER_ACTION) },
+                        modifier = Modifier.size(56.dp),
+                        colors = GsColors(Color.Transparent, scheme.onSurface),
+                        shape = CircleShape,
+                    ) {
+                        Icon(Icons.Filled.Close, contentDescription = stringResource(R.string.close))
+                    }
+                }
+            }
+            if (alert.actions.isNotEmpty()) {
+                Row(
+                    Modifier.fillMaxWidth().padding(horizontal = 20.dp, vertical = 16.dp),
+                    horizontalArrangement = Arrangement.spacedBy(12.dp),
+                ) {
+                    alert.actions.take(2).forEach { action ->
+                        val custom = action.backgroundColor?.type?.let { it != androidx.car.app.model.CarColor.TYPE_DEFAULT } == true
+                        GsIconBox(
+                            onClick = { CarAlerts.tapped(shown, action) },
+                            modifier = Modifier.weight(1f).height(64.dp),
+                            colors = GsColors(
+                                action.backgroundColor.color(dark, scheme.surfaceContainerHighest),
+                                if (custom) Color.White else scheme.onSurface,
+                            ),
+                            enabled = action.isEnabled,
+                        ) {
+                            Row(verticalAlignment = Alignment.CenterVertically) {
+                                if (action.icon != null) {
+                                    CarGlyph(action.icon, Modifier.size(28.dp))
+                                    Spacer(Modifier.width(8.dp))
+                                }
+                                Text(action.title.text(), style = MaterialTheme.typography.titleMedium, maxLines = 1, overflow = TextOverflow.Ellipsis)
+                            }
+                        }
+                    }
+                }
+            } else {
+                Spacer(Modifier.height(16.dp))
+            }
+            if (timed) {
+                Box(Modifier.fillMaxWidth().height(4.dp).background(scheme.surfaceContainerHighest)) {
+                    Box(Modifier.fillMaxWidth(left.value).height(4.dp).clip(RoundedCornerShape(2.dp)).background(scheme.primary))
+                }
+            }
+        }
+    }
+}

gearslip/src/main/java/app/seb3thehacker/gearslip/car/CarUi.kt

@@ -325,6 +325,7 @@ fun CarUi() {
                             }
                         }
                         CarToastOverlay(Modifier.align(Alignment.BottomCenter).padding(bottom = homeInset))
+                        CarAlertOverlay(Modifier.align(Alignment.TopCenter))
                         CallPromptOverlay()
                         BluetoothPairOverlay()
                         PopupTimer()

gearslip/src/main/java/app/seb3thehacker/gearslip/host/CarAppConnection.kt

@@ -659,8 +659,16 @@ class CarAppConnection(private val context: Context) {
         }
 
         override fun sendLocation(location: Location?) = Unit
-        override fun showAlert(alert: Bundleable?) = Unit
+        override fun showAlert(alert: Bundleable?) {
-        override fun dismissAlert(alertId: Int) = Unit
+            val shown = runCatching { alert?.get() as? androidx.car.app.model.Alert }
+                .onFailure { GearslipLog.w("host: couldn't read an alert: ${it.message}") }
+                .getOrNull() ?: return
+            main.post { if (toastOwner === owner) app.seb3thehacker.gearslip.car.CarAlerts.show(owner, shown) }
+        }
+
+        override fun dismissAlert(alertId: Int) {
+            main.post { app.seb3thehacker.gearslip.car.CarAlerts.dismiss(owner, alertId) }
+        }
         override fun openMicrophone(request: Bundleable?): Bundleable? = null
     }
 
@@ -839,6 +847,7 @@ class CarAppConnection(private val context: Context) {
 
     private fun clearToasts() {
         CarToasts.clear(toastOwner)
+        app.seb3thehacker.gearslip.car.CarAlerts.clear(toastOwner)
         toastOwner = Any()
     }
 

gearslip/src/main/java/app/seb3thehacker/gearslip/host/CarModels.kt

@@ -306,6 +306,20 @@ fun OnContentRefreshDelegate?.refresh() {
         .onFailure { GearslipLog.w("host: could not request a refresh: ${it.message}") }
 }
 
+/** An alert left the screen without the app taking it down: timed out, or closed by the driver. */
+fun androidx.car.app.model.AlertCallbackDelegate?.cancel(reason: Int) {
+    val delegate = this ?: return
+    runCatching { delegate.sendCancel(reason, doneCallback("an alert cancel")) }
+        .onFailure { GearslipLog.w("host: could not cancel an alert: ${it.message}") }
+}
+
+/** An alert left the screen another way: a newer one replaced it, the app took it down, or a tap. */
+fun androidx.car.app.model.AlertCallbackDelegate?.dismissed() {
+    val delegate = this ?: return
+    runCatching { delegate.sendDismiss(doneCallback("an alert dismiss")) }
+        .onFailure { GearslipLog.w("host: could not dismiss an alert: ${it.message}") }
+}
+
 private fun doneCallback(label: String) = object : OnDoneCallback {
     // onSuccess is annotated nullable and onFailure isn't - the asymmetry is real.
     override fun onSuccess(response: Bundleable?) = Unit