feat: add NIP-40 expiration date to short note post screen

Allows users to add an expiration date to posts via NIP-40. The feature
follows the same pattern as content warning (toggle button in the bottom
action bar, expandable section in the post body) and uses the same
calendar/time picker UI as poll deadlines.

- ExpirationDateButton: timer icon toggles orange when active
- ExpirationDatePicker: date+time picker with "Expires in X" display
- ViewModel: wantsExpirationDate + expirationDate state, wired into
  both TextNoteEvent and PollEvent builders, loaded from drafts
- Strings: add_expiration_date, expiration_date_label, etc.

https://claude.ai/code/session_016QjmArr6zfM1Qx58iNrntA

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/note/creators/expiration/ExpirationDateButton.kt

@@ -0,0 +1,61 @@
+/*
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.amethyst.ui.note.creators.expiration
+
+import androidx.compose.foundation.layout.size
+import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.outlined.Timer
+import androidx.compose.material.icons.outlined.TimerOff
+import androidx.compose.material3.Icon
+import androidx.compose.material3.IconButton
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.unit.dp
+import com.vitorpamplona.amethyst.R
+import com.vitorpamplona.amethyst.ui.stringRes
+
+@Composable
+fun ExpirationDateButton(
+    isActive: Boolean,
+    onClick: () -> Unit,
+) {
+    IconButton(
+        onClick = { onClick() },
+    ) {
+        if (!isActive) {
+            Icon(
+                imageVector = Icons.Outlined.Timer,
+                contentDescription = stringRes(R.string.add_expiration_date),
+                modifier = Modifier.size(20.dp),
+                tint = MaterialTheme.colorScheme.onBackground,
+            )
+        } else {
+            Icon(
+                imageVector = Icons.Outlined.TimerOff,
+                contentDescription = stringRes(R.string.remove_expiration_date),
+                modifier = Modifier.size(20.dp),
+                tint = Color(0xFFFF6600),
+            )
+        }
+    }
+}

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/note/creators/expiration/ExpirationDatePicker.kt

@@ -0,0 +1,195 @@
+/*
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.amethyst.ui.note.creators.expiration
+
+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.padding
+import androidx.compose.foundation.layout.size
+import androidx.compose.foundation.layout.width
+import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.outlined.Timer
+import androidx.compose.material3.DatePicker
+import androidx.compose.material3.DatePickerDialog
+import androidx.compose.material3.ExperimentalMaterial3Api
+import androidx.compose.material3.HorizontalDivider
+import androidx.compose.material3.Icon
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.OutlinedCard
+import androidx.compose.material3.SelectableDates
+import androidx.compose.material3.Text
+import androidx.compose.material3.TextButton
+import androidx.compose.material3.TimePicker
+import androidx.compose.material3.TimePickerDialog
+import androidx.compose.material3.rememberDatePickerState
+import androidx.compose.material3.rememberTimePickerState
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.setValue
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.platform.LocalContext
+import androidx.compose.ui.res.stringResource
+import androidx.compose.ui.text.font.FontWeight
+import androidx.compose.ui.unit.dp
+import androidx.compose.ui.unit.sp
+import com.vitorpamplona.amethyst.R
+import com.vitorpamplona.amethyst.ui.note.timeAheadNoDot
+import com.vitorpamplona.amethyst.ui.screen.loggedIn.home.ShortNotePostViewModel
+import com.vitorpamplona.amethyst.ui.stringRes
+import com.vitorpamplona.amethyst.ui.theme.DividerThickness
+import com.vitorpamplona.amethyst.ui.theme.placeholderText
+import com.vitorpamplona.quartz.utils.TimeUtils
+import java.time.Instant
+import java.time.ZoneId
+import java.time.ZoneOffset
+
+@OptIn(ExperimentalMaterial3Api::class)
+@Composable
+fun ExpirationDatePicker(model: ShortNotePostViewModel) {
+    var showDatePicker by remember { mutableStateOf(false) }
+    var showTimePicker by remember { mutableStateOf(false) }
+
+    val currentTime = Instant.ofEpochMilli(model.expirationDate * 1000).atZone(ZoneId.systemDefault()).toLocalDateTime()
+
+    val datePickerState =
+        rememberDatePickerState(
+            initialSelectedDateMillis = model.expirationDate * 1000,
+            yearRange = currentTime.year..2050,
+            selectableDates =
+                object : SelectableDates {
+                    override fun isSelectableDate(utcTimeMillis: Long): Boolean {
+                        return utcTimeMillis >= System.currentTimeMillis() - 86400000
+                    }
+                },
+        )
+
+    val timePickerState =
+        rememberTimePickerState(
+            initialHour = currentTime.hour,
+            initialMinute = currentTime.minute,
+            is24Hour = false,
+        )
+
+    val context = LocalContext.current
+
+    Column(Modifier.fillMaxWidth()) {
+        Row(
+            verticalAlignment = Alignment.CenterVertically,
+            modifier =
+                Modifier
+                    .fillMaxWidth()
+                    .padding(bottom = 10.dp),
+        ) {
+            Icon(
+                imageVector = Icons.Outlined.Timer,
+                contentDescription = stringRes(R.string.expiration_date_label),
+                modifier = Modifier.size(20.dp),
+                tint = Color(0xFFFF6600),
+            )
+
+            Text(
+                text = stringRes(R.string.expiration_date_label),
+                fontSize = 20.sp,
+                fontWeight = FontWeight.W500,
+                modifier = Modifier.padding(start = 10.dp),
+            )
+        }
+
+        HorizontalDivider(thickness = DividerThickness)
+
+        Text(
+            text = stringRes(R.string.expiration_date_explainer),
+            color = MaterialTheme.colorScheme.placeholderText,
+            modifier = Modifier.padding(vertical = 10.dp),
+        )
+
+        OutlinedCard(
+            onClick = { showDatePicker = true },
+            modifier = Modifier.fillMaxWidth(),
+        ) {
+            Row(
+                modifier = Modifier.padding(16.dp),
+                verticalAlignment = Alignment.CenterVertically,
+            ) {
+                Icon(Icons.Outlined.Timer, contentDescription = stringResource(R.string.expiration_date_select))
+                Spacer(Modifier.width(12.dp))
+
+                if (model.expirationDate < TimeUtils.oneMinuteFromNow()) {
+                    Text(stringRes(R.string.expiration_date_label) + " " + model.expirationDate, style = MaterialTheme.typography.bodyLarge)
+                } else {
+                    Text(
+                        text = stringRes(R.string.expiration_expires_in, timeAheadNoDot(model.expirationDate, context)),
+                        style = MaterialTheme.typography.bodyLarge,
+                    )
+                }
+            }
+        }
+    }
+
+    if (showDatePicker) {
+        DatePickerDialog(
+            onDismissRequest = { showDatePicker = false },
+            confirmButton = {
+                TextButton(onClick = {
+                    showDatePicker = false
+                    showTimePicker = true
+                }) { Text(stringResource(R.string.next)) }
+            },
+        ) {
+            DatePicker(state = datePickerState)
+        }
+    }
+
+    if (showTimePicker) {
+        TimePickerDialog(
+            title = {
+                Text(stringResource(R.string.expiration_time))
+            },
+            onDismissRequest = { showTimePicker = false },
+            confirmButton = {
+                TextButton(
+                    onClick = {
+                        val datetimeLocalTimeZone =
+                            datePickerState.selectedDateMillis?.let { localDayAtZeroHourMillis ->
+                                (localDayAtZeroHourMillis / 1000) +
+                                    (timePickerState.hour * TimeUtils.ONE_HOUR) +
+                                    (timePickerState.minute * TimeUtils.ONE_MINUTE)
+                            } ?: TimeUtils.oneDayAhead()
+
+                        val offset: ZoneOffset = ZoneId.systemDefault().rules.getOffset(Instant.now())
+
+                        model.expirationDate = datetimeLocalTimeZone - offset.totalSeconds
+
+                        showTimePicker = false
+                    },
+                ) { Text(stringResource(R.string.confirm)) }
+            },
+        ) {
+            TimePicker(state = timePickerState)
+        }
+    }
+}

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/home/ShortNotePostScreen.kt

@@ -78,6 +78,8 @@ import com.vitorpamplona.amethyst.ui.note.BaseUserPicture
 import com.vitorpamplona.amethyst.ui.note.NoteCompose
 import com.vitorpamplona.amethyst.ui.note.creators.contentWarning.ContentSensitivityExplainer
 import com.vitorpamplona.amethyst.ui.note.creators.contentWarning.MarkAsSensitiveButton
+import com.vitorpamplona.amethyst.ui.note.creators.expiration.ExpirationDateButton
+import com.vitorpamplona.amethyst.ui.note.creators.expiration.ExpirationDatePicker
 import com.vitorpamplona.amethyst.ui.note.creators.emojiSuggestions.ShowEmojiSuggestionList
 import com.vitorpamplona.amethyst.ui.note.creators.emojiSuggestions.WatchAndLoadMyEmojiList
 import com.vitorpamplona.amethyst.ui.note.creators.invoice.AddLnInvoiceButton
@@ -311,6 +313,15 @@ private fun NewPostScreenBody(
                     }
                 }
 
+                if (postViewModel.wantsExpirationDate) {
+                    Row(
+                        verticalAlignment = CenterVertically,
+                        modifier = Modifier.padding(vertical = Size5dp, horizontal = Size10dp),
+                    ) {
+                        ExpirationDatePicker(postViewModel)
+                    }
+                }
+
                 if (postViewModel.wantsToAddGeoHash) {
                     Row(
                         verticalAlignment = CenterVertically,
@@ -539,6 +550,10 @@ private fun BottomRowActions(postViewModel: ShortNotePostViewModel) {
             postViewModel.toggleMarkAsSensitive()
         }
 
+        ExpirationDateButton(postViewModel.wantsExpirationDate) {
+            postViewModel.toggleExpirationDate()
+        }
+
         AddGeoHashButton(postViewModel.wantsToAddGeoHash) {
             postViewModel.wantsToAddGeoHash = !postViewModel.wantsToAddGeoHash
         }

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/home/ShortNotePostViewModel.kt

@@ -97,6 +97,7 @@ import com.vitorpamplona.quartz.nip36SensitiveContent.contentWarning
 import com.vitorpamplona.quartz.nip36SensitiveContent.contentWarningReason
 import com.vitorpamplona.quartz.nip36SensitiveContent.isSensitive
 import com.vitorpamplona.quartz.nip36SensitiveContent.isSensitiveOrNSFW
+import com.vitorpamplona.quartz.nip40Expiration.expiration
 import com.vitorpamplona.quartz.nip37Drafts.DraftWrapEvent
 import com.vitorpamplona.quartz.nip57Zaps.splits.ZapSplitSetup
 import com.vitorpamplona.quartz.nip57Zaps.splits.ZapSplitSetupLnAddress
@@ -239,6 +240,10 @@ open class ShortNotePostViewModel :
     var wantsToMarkAsSensitive by mutableStateOf(false)
     var contentWarningDescription by mutableStateOf("")
 
+    // Expiration Date (NIP-40)
+    var wantsExpirationDate by mutableStateOf(false)
+    var expirationDate by mutableLongStateOf(TimeUtils.oneDayAhead())
+
     // GeoHash
     var wantsToAddGeoHash by mutableStateOf(false)
     var location: StateFlow<LocationState.LocationResult>? = null
@@ -427,6 +432,10 @@ open class ShortNotePostViewModel :
         wantsToMarkAsSensitive = draftEvent.isSensitive()
         contentWarningDescription = draftEvent.contentWarningReason() ?: ""
 
+        val draftExpiration = draftEvent.tags.expiration()
+        wantsExpirationDate = draftExpiration != null
+        expirationDate = draftExpiration ?: TimeUtils.oneDayAhead()
+
         val geohash = draftEvent.getGeoHash()
         wantsToAddGeoHash = geohash != null
         if (geohash != null) {
@@ -507,6 +516,10 @@ open class ShortNotePostViewModel :
         wantsToMarkAsSensitive = draftEvent.isSensitive()
         contentWarningDescription = draftEvent.contentWarningReason() ?: ""
 
+        val draftExpiration = draftEvent.tags.expiration()
+        wantsExpirationDate = draftExpiration != null
+        expirationDate = draftExpiration ?: TimeUtils.oneDayAhead()
+
         val geohash = draftEvent.getGeoHash()
         wantsToAddGeoHash = geohash != null
         if (geohash != null) {
@@ -690,6 +703,7 @@ open class ShortNotePostViewModel :
         val usedAttachments = iMetaAttachments.filterIsIn(urls.toSet())
 
         val contentWarningReason = if (wantsToMarkAsSensitive) contentWarningDescription else null
+        val localExpirationDate = if (wantsExpirationDate) expirationDate else null
 
         return if (wantsPoll) {
             val options = pollOptions.map { it.value }
@@ -710,6 +724,7 @@ open class ShortNotePostViewModel :
                 localZapRaiserAmount?.let { zapraiser(it) }
                 zapReceiver?.let { zapSplits(it) }
                 contentWarningReason?.let { contentWarning(it) }
+                localExpirationDate?.let { expiration(it) }
 
                 emojis(emojis)
                 imetas(usedAttachments)
@@ -765,6 +780,7 @@ open class ShortNotePostViewModel :
                 localZapRaiserAmount?.let { zapraiser(it) }
                 zapReceiver?.let { zapSplits(it) }
                 contentWarningReason?.let { contentWarning(it) }
+                localExpirationDate?.let { expiration(it) }
 
                 emojis(emojis)
                 imetas(usedAttachments)
@@ -1237,5 +1253,13 @@ open class ShortNotePostViewModel :
         draftTag.newVersion()
     }
 
+    fun toggleExpirationDate() {
+        wantsExpirationDate = !wantsExpirationDate
+        if (wantsExpirationDate) {
+            expirationDate = TimeUtils.oneDayAhead()
+        }
+        draftTag.newVersion()
+    }
+
     override fun locationManager(): LocationState = Amethyst.instance.locationManager
 }

amethyst/src/main/res/values/strings.xml

@@ -1291,6 +1291,14 @@
 
     <string name="add_content_warning">Add content warning</string>
     <string name="remove_content_warning">Remove content warning</string>
+
+    <string name="add_expiration_date">Add expiration date</string>
+    <string name="remove_expiration_date">Remove expiration date</string>
+    <string name="expiration_date_label">Expiration Date</string>
+    <string name="expiration_date_explainer">Post will be hidden by clients after this date (NIP-40)</string>
+    <string name="expiration_date_select">Select expiration date and time</string>
+    <string name="expiration_expires_in">Expires in %1$s</string>
+    <string name="expiration_time">Expiration Time</string>
     <string name="show_npub_as_a_qr_code">Show npub as a QR code</string>
     <string name="show_nprofile_as_a_qr_code">Show nprofile as a QR code</string>