feat: add push notifications for reactions

Add a new notification channel for reactions (kind 7 events) so users
get notified when someone reacts to their posts. Follows the same
pattern as zap notifications with deduplication, time-window filtering,
and grouped summaries.

https://claude.ai/code/session_01J9rAA4oeFEfNcYD6GoJqqt

amethyst/src/main/java/com/vitorpamplona/amethyst/service/notifications/EventNotificationConsumer.kt

@@ -30,6 +30,7 @@ import com.vitorpamplona.amethyst.model.Account
 import com.vitorpamplona.amethyst.model.LocalCache
 import com.vitorpamplona.amethyst.model.Note
 import com.vitorpamplona.amethyst.service.notifications.NotificationUtils.sendDMNotification
+import com.vitorpamplona.amethyst.service.notifications.NotificationUtils.sendReactionNotification
 import com.vitorpamplona.amethyst.service.notifications.NotificationUtils.sendZapNotification
 import com.vitorpamplona.amethyst.ui.note.showAmount
 import com.vitorpamplona.amethyst.ui.stringRes
@@ -43,6 +44,7 @@ import com.vitorpamplona.quartz.nip17Dm.files.ChatMessageEncryptedFileHeaderEven
 import com.vitorpamplona.quartz.nip17Dm.messages.ChatMessageEvent
 import com.vitorpamplona.quartz.nip19Bech32.toNpub
 import com.vitorpamplona.quartz.nip21UriScheme.toNostrUri
+import com.vitorpamplona.quartz.nip25Reactions.ReactionEvent
 import com.vitorpamplona.quartz.nip57Zaps.LnZapEvent
 import com.vitorpamplona.quartz.nip57Zaps.LnZapRequestEvent
 import com.vitorpamplona.quartz.nip59Giftwrap.seals.SealedRumorEvent
@@ -106,6 +108,7 @@ class EventNotificationConsumer(
                 when (innerEvent) {
                     is PrivateDmEvent -> notify(innerEvent, account)
                     is LnZapEvent -> notify(innerEvent, account)
+                    is ReactionEvent -> notify(innerEvent, account)
                     is ChatMessageEvent -> notify(innerEvent, account)
                     is ChatMessageEncryptedFileHeaderEvent -> notify(innerEvent, account)
                 }
@@ -481,6 +484,78 @@ class EventNotificationConsumer(
         }
     }
 
+    private suspend fun notify(
+        event: ReactionEvent,
+        account: Account,
+    ) {
+        Log.d(TAG, "New Reaction to Notify")
+
+        // old event being re-broadcast
+        if (event.createdAt < TimeUtils.fifteenMinutesAgo()) return
+
+        // don't notify for own reactions
+        if (event.pubKey == account.signer.pubKey) return
+
+        // only notify if the reaction is for the current user
+        if (!event.isTaggedUser(account.signer.pubKey)) return
+
+        val reactedPostId = event.originalPost().firstOrNull() ?: return
+        val reactedNote = LocalCache.checkGetOrCreateNote(reactedPostId)
+
+        val author = LocalCache.getOrCreateUser(event.pubKey)
+        val user = author.toBestDisplayName()
+        val userPicture = author.profilePicture()
+
+        val reactionContent = event.content
+        val reactionSymbol =
+            when {
+                reactionContent == ReactionEvent.LIKE || reactionContent.isBlank() -> "\uD83E\uDD19"
+                reactionContent == ReactionEvent.DISLIKE -> "\uD83D\uDC4E"
+                else -> reactionContent
+            }
+
+        val title = "$reactionSymbol $user"
+
+        val reactedContent =
+            reactedNote
+                ?.event
+                ?.content
+                ?.split("\n")
+                ?.firstOrNull() ?: ""
+
+        val content =
+            if (reactedContent.isNotBlank()) {
+                stringRes(
+                    applicationContext,
+                    R.string.app_notification_reactions_channel_message_for,
+                    reactedContent,
+                )
+            } else {
+                stringRes(
+                    applicationContext,
+                    R.string.app_notification_reactions_channel_message,
+                    user,
+                )
+            }
+
+        val noteUri =
+            "notifications$ACCOUNT_QUERY_PARAM" +
+                account.signer.pubKey
+                    .hexToByteArray()
+                    .toNpub()
+
+        notificationManager()
+            .sendReactionNotification(
+                event.id,
+                content,
+                title,
+                event.createdAt,
+                userPicture,
+                noteUri,
+                applicationContext,
+            )
+    }
+
     fun notificationManager(): NotificationManager =
         ContextCompat.getSystemService(applicationContext, NotificationManager::class.java)
             as NotificationManager

amethyst/src/main/java/com/vitorpamplona/amethyst/service/notifications/NotificationUtils.kt

@@ -45,8 +45,10 @@ import kotlinx.coroutines.withContext
 object NotificationUtils {
     private var dmChannel: NotificationChannel? = null
     private var zapChannel: NotificationChannel? = null
+    private var reactionChannel: NotificationChannel? = null
     private const val DM_GROUP_KEY = "com.vitorpamplona.amethyst.DM_NOTIFICATION"
     private const val ZAP_GROUP_KEY = "com.vitorpamplona.amethyst.ZAP_NOTIFICATION"
+    private const val REACTION_GROUP_KEY = "com.vitorpamplona.amethyst.REACTION_NOTIFICATION"
     const val REPLY_ACTION = "com.vitorpamplona.amethyst.REPLY_ACTION"
     const val MARK_READ_ACTION = "com.vitorpamplona.amethyst.MARK_READ_ACTION"
     const val KEY_REPLY_TEXT = "key_reply_text"
@@ -56,6 +58,7 @@ object NotificationUtils {
 
     private const val DM_SUMMARY_ID = 0x10000
     private const val ZAP_SUMMARY_ID = 0x20000
+    private const val REACTION_SUMMARY_ID = 0x30000
 
     fun getOrCreateDMChannel(applicationContext: Context): NotificationChannel {
         if (dmChannel != null) return dmChannel!!
@@ -99,6 +102,55 @@ object NotificationUtils {
         return zapChannel!!
     }
 
+    fun getOrCreateReactionChannel(applicationContext: Context): NotificationChannel {
+        if (reactionChannel != null) return reactionChannel!!
+
+        reactionChannel =
+            NotificationChannel(
+                stringRes(applicationContext, R.string.app_notification_reactions_channel_id),
+                stringRes(applicationContext, R.string.app_notification_reactions_channel_name),
+                NotificationManager.IMPORTANCE_DEFAULT,
+            ).apply {
+                description =
+                    stringRes(applicationContext, R.string.app_notification_reactions_channel_description)
+            }
+
+        val notificationManager: NotificationManager =
+            applicationContext.getSystemService(Context.NOTIFICATION_SERVICE) as NotificationManager
+
+        notificationManager.createNotificationChannel(reactionChannel!!)
+
+        return reactionChannel!!
+    }
+
+    suspend fun NotificationManager.sendReactionNotification(
+        id: String,
+        messageBody: String,
+        messageTitle: String,
+        time: Long,
+        pictureUrl: String?,
+        uri: String,
+        applicationContext: Context,
+    ) {
+        getOrCreateReactionChannel(applicationContext)
+        val channelId = stringRes(applicationContext, R.string.app_notification_reactions_channel_id)
+
+        sendNotification(
+            id = id,
+            messageBody = messageBody,
+            messageTitle = messageTitle,
+            time = time,
+            pictureUrl = pictureUrl,
+            uri = uri,
+            channelId = channelId,
+            notificationGroupKey = REACTION_GROUP_KEY,
+            category = NotificationCompat.CATEGORY_SOCIAL,
+            summaryId = REACTION_SUMMARY_ID,
+            summaryText = stringRes(applicationContext, R.string.app_notification_reactions_summary),
+            applicationContext = applicationContext,
+        )
+    }
+
     suspend fun NotificationManager.sendZapNotification(
         id: String,
         messageBody: String,

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

@@ -751,6 +751,13 @@
     <string name="app_notification_dms_summary">New messages</string>
     <string name="app_notification_zaps_summary">New zaps</string>
 
+    <string name="app_notification_reactions_channel_id" translatable="false">ReactionsID</string>
+    <string name="app_notification_reactions_channel_name">Reactions</string>
+    <string name="app_notification_reactions_channel_description">Notifies you when somebody reacts to your post</string>
+    <string name="app_notification_reactions_channel_message">%1$s reacted to your post</string>
+    <string name="app_notification_reactions_channel_message_for">for %1$s</string>
+    <string name="app_notification_reactions_summary">New reactions</string>
+
     <string name="reply_notify">Notify: </string>
 
     <string name="channel_list_join_conversation">Join Conversation</string>