feat: add configurable max hashtag limit filter for spam prevention

Adds a security setting to hide posts with more than X hashtags (t tags),
defaulting to 5. Applied at the feed filter level via FilterByListParams.match()
and Account.isAcceptable() to cover all feeds. Configurable in Security Filters
settings, with 0 to disable.

https://claude.ai/code/session_01NMVypgGSU9EjQA7hZ9uvjD

amethyst/src/main/java/com/vitorpamplona/amethyst/model/Account.kt

@@ -143,6 +143,7 @@ import com.vitorpamplona.quartz.nip01Core.relay.normalizer.NormalizedRelayUrl
 import com.vitorpamplona.quartz.nip01Core.signers.EventTemplate
 import com.vitorpamplona.quartz.nip01Core.signers.NostrSigner
 import com.vitorpamplona.quartz.nip01Core.signers.NostrSignerInternal
+import com.vitorpamplona.quartz.nip01Core.tags.hashtags.countHashtags
 import com.vitorpamplona.quartz.nip01Core.tags.hashtags.hashtags
 import com.vitorpamplona.quartz.nip01Core.tags.people.taggedUserIds
 import com.vitorpamplona.quartz.nip01Core.tags.references.references
@@ -450,6 +451,12 @@ class Account(
         }
     }
 
+    suspend fun updateMaxHashtagLimit(limit: Int) {
+        if (settings.updateMaxHashtagLimit(limit)) {
+            sendNewAppSpecificData()
+        }
+    }
+
     suspend fun changeReactionTypes(reactionSet: List<String>) {
         if (settings.changeReactionTypes(reactionSet)) {
             sendNewAppSpecificData()
@@ -2024,10 +2031,16 @@ class Account(
 
     fun isKnown(user: HexKey): Boolean = user in allFollows.flow.value.authors
 
+    private fun hasExcessiveHashtags(note: Note): Boolean {
+        val limit = settings.syncedSettings.security.maxHashtagLimit.value
+        return limit > 0 && (note.event?.countHashtags() ?: 0) > limit
+    }
+
     override fun isAcceptable(note: Note): Boolean {
         return note.author?.let { isAcceptable(it) } ?: true &&
             // if user hasn't hided this author
             isAcceptableDirect(note) &&
+            !hasExcessiveHashtags(note) &&
             (
                 (note.event !is RepostEvent && note.event !is GenericRepostEvent) ||
                     (

amethyst/src/main/java/com/vitorpamplona/amethyst/model/AccountSettings.kt

@@ -753,4 +753,12 @@ class AccountSettings(
         } else {
             false
         }
+
+    fun updateMaxHashtagLimit(limit: Int): Boolean =
+        if (syncedSettings.security.updateMaxHashtagLimit(limit)) {
+            saveAccountSettings()
+            true
+        } else {
+            false
+        }
 }

amethyst/src/main/java/com/vitorpamplona/amethyst/model/AccountSyncedSettings.kt

@@ -53,6 +53,7 @@ class AccountSyncedSettings(
             MutableStateFlow(internalSettings.security.showSensitiveContent),
             internalSettings.security.warnAboutPostsWithReports,
             MutableStateFlow(internalSettings.security.filterSpamFromStrangers),
+            MutableStateFlow(internalSettings.security.maxHashtagLimit),
         )
 
     fun toInternal(): AccountSyncedSettingsInternal =
@@ -74,6 +75,7 @@ class AccountSyncedSettings(
                     security.showSensitiveContent.value,
                     security.warnAboutPostsWithReports,
                     security.filterSpamFromStrangers.value,
+                    security.maxHashtagLimit.value,
                 ),
         )
 
@@ -120,6 +122,10 @@ class AccountSyncedSettings(
         if (security.warnAboutPostsWithReports != syncedSettingsInternal.security.warnAboutPostsWithReports) {
             security.warnAboutPostsWithReports = syncedSettingsInternal.security.warnAboutPostsWithReports
         }
+
+        if (security.maxHashtagLimit.value != syncedSettingsInternal.security.maxHashtagLimit) {
+            security.maxHashtagLimit.tryEmit(syncedSettingsInternal.security.maxHashtagLimit)
+        }
     }
 
     fun dontTranslateFromFilteredBySpokenLanguages(): Set<String> = languages.dontTranslateFrom.value - getLanguagesSpokenByUser()
@@ -204,6 +210,7 @@ class AccountSecurityPreferences(
     val showSensitiveContent: MutableStateFlow<Boolean?> = MutableStateFlow(null),
     var warnAboutPostsWithReports: Boolean = true,
     var filterSpamFromStrangers: MutableStateFlow<Boolean> = MutableStateFlow(true),
+    val maxHashtagLimit: MutableStateFlow<Int> = MutableStateFlow(5),
 ) {
     fun updateShowSensitiveContent(show: Boolean?): Boolean {
         if (showSensitiveContent.value != show) {
@@ -228,4 +235,12 @@ class AccountSecurityPreferences(
         } else {
             false
         }
+
+    fun updateMaxHashtagLimit(limit: Int): Boolean =
+        if (maxHashtagLimit.value != limit) {
+            maxHashtagLimit.update { limit }
+            true
+        } else {
+            false
+        }
 }

amethyst/src/main/java/com/vitorpamplona/amethyst/model/AccountSyncedSettingsInternal.kt

@@ -105,4 +105,5 @@ class AccountSecurityPreferencesInternal(
     val showSensitiveContent: Boolean? = null,
     var warnAboutPostsWithReports: Boolean = true,
     var filterSpamFromStrangers: Boolean = true,
+    val maxHashtagLimit: Int = 5,
 )

amethyst/src/main/java/com/vitorpamplona/amethyst/model/nip51Lists/HiddenUsersState.kt

@@ -52,6 +52,7 @@ class HiddenUsersState(
         muteList: List<MuteTag>,
         transientHiddenUsers: Set<String>,
         showSensitiveContent: Boolean?,
+        maxHashtagLimit: Int,
     ): LiveHiddenUsers {
         val hiddenUsers = blockList.mapNotNullTo(mutableSetOf()) { if (it is UserTag) it.pubKey else null } + muteList.mapNotNull { if (it is UserTag) it.pubKey else null }
         val hiddenWords = blockList.mapNotNullTo(mutableSetOf()) { if (it is WordTag) it.word else null } + muteList.mapNotNull { if (it is WordTag) it.word else null }
@@ -64,6 +65,7 @@ class HiddenUsersState(
             hiddenUsers = hiddenUsers,
             spammers = transientHiddenUsers,
             hiddenWords = hiddenWords,
+            maxHashtagLimit = maxHashtagLimit,
         )
     }
 
@@ -73,9 +75,10 @@ class HiddenUsersState(
             muteList,
             transientHiddenUsers,
             settings.syncedSettings.security.showSensitiveContent,
-        ) { blockList, muteList, transientHiddenUsers, showSensitiveContent ->
+            settings.syncedSettings.security.maxHashtagLimit,
+        ) { blockList, muteList, transientHiddenUsers, showSensitiveContent, maxHashtagLimit ->
             checkNotInMainThread()
-            emit(assembleLiveHiddenUsers(blockList, muteList, transientHiddenUsers, showSensitiveContent))
+            emit(assembleLiveHiddenUsers(blockList, muteList, transientHiddenUsers, showSensitiveContent, maxHashtagLimit))
         }.onStart {
             emit(
                 assembleLiveHiddenUsers(
@@ -83,6 +86,7 @@ class HiddenUsersState(
                     muteList.value,
                     transientHiddenUsers.value,
                     settings.syncedSettings.security.showSensitiveContent.value,
+                    settings.syncedSettings.security.maxHashtagLimit.value,
                 ),
             )
         }.flowOn(Dispatchers.IO)

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/dal/FilterByListParams.kt

@@ -29,6 +29,7 @@ import com.vitorpamplona.quartz.nip01Core.core.Address
 import com.vitorpamplona.quartz.nip01Core.core.Event
 import com.vitorpamplona.quartz.nip01Core.core.HexKey
 import com.vitorpamplona.quartz.nip01Core.relay.normalizer.NormalizedRelayUrl
+import com.vitorpamplona.quartz.nip01Core.tags.hashtags.countHashtags
 import com.vitorpamplona.quartz.nip51Lists.muteList.MuteListEvent
 import com.vitorpamplona.quartz.nip51Lists.peopleList.PeopleListEvent
 import com.vitorpamplona.quartz.utils.TimeUtils
@@ -43,6 +44,8 @@ class FilterByListParams(
 
     fun isNotInTheFuture(noteEvent: Event) = noteEvent.createdAt <= now
 
+    fun hasExcessiveHashtags(noteEvent: Event) = hiddenLists.maxHashtagLimit > 0 && noteEvent.countHashtags() > hiddenLists.maxHashtagLimit
+
     fun isEventInList(noteEvent: Event): Boolean {
         if (followLists == null) return false
 
@@ -70,7 +73,8 @@ class FilterByListParams(
         comingFrom: List<NormalizedRelayUrl>,
     ) = ((isGlobal(comingFrom)) || isEventInList(noteEvent)) &&
         (isHiddenList || isNotHidden(noteEvent.pubKey)) &&
-        isNotInTheFuture(noteEvent)
+        isNotInTheFuture(noteEvent) &&
+        !hasExcessiveHashtags(noteEvent)
 
     fun match(
         address: Address?,

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

@@ -1152,6 +1152,8 @@ class AccountViewModel(
 
     fun updateShowSensitiveContent(show: Boolean?) = launchSigner { account.updateShowSensitiveContent(show) }
 
+    fun updateMaxHashtagLimit(limit: Int) = launchSigner { account.updateMaxHashtagLimit(limit) }
+
     fun changeReactionTypes(
         reactionSet: List<String>,
         onDone: () -> Unit,

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/settings/SecurityFiltersScreen.kt

@@ -58,6 +58,7 @@ import androidx.compose.ui.graphics.Color
 import androidx.compose.ui.text.font.FontWeight
 import androidx.compose.ui.text.input.ImeAction
 import androidx.compose.ui.text.input.KeyboardCapitalization
+import androidx.compose.ui.text.input.KeyboardType
 import androidx.compose.ui.text.style.TextAlign
 import androidx.compose.ui.unit.dp
 import androidx.lifecycle.Lifecycle
@@ -266,6 +267,34 @@ private fun HeaderOptions(accountViewModel: AccountViewModel) {
                 },
             )
         }
+
+        SettingsRow(
+            R.string.max_hashtag_limit_title,
+            R.string.max_hashtag_limit_explainer,
+        ) {
+            var maxHashtags by remember {
+                mutableStateOf(
+                    accountViewModel.account.settings.syncedSettings.security.maxHashtagLimit.value.let {
+                        if (it == 0) "" else it.toString()
+                    },
+                )
+            }
+
+            OutlinedTextField(
+                value = maxHashtags,
+                onValueChange = {
+                    maxHashtags = it
+                    accountViewModel.updateMaxHashtagLimit(it.toIntOrNull() ?: 0)
+                },
+                keyboardOptions =
+                    KeyboardOptions.Default.copy(
+                        keyboardType = KeyboardType.Number,
+                        imeAction = ImeAction.Done,
+                    ),
+                singleLine = true,
+                modifier = Modifier.padding(start = 8.dp),
+            )
+        }
     }
 }
 

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

@@ -834,6 +834,8 @@
     <string name="warn_when_posts_have_reports_from_your_follows_explainer">Shows a warning message when posts have 5 or more reports from your follows</string>
     <string name="show_sensitive_content_title">Show sensitive content</string>
     <string name="show_sensitive_content_explainer">Shows a warning message when the author of the post marked it as sensitive</string>
+    <string name="max_hashtag_limit_title">Max hashtags per post</string>
+    <string name="max_hashtag_limit_explainer">Hides posts with more hashtags than this limit. Set to 0 to disable</string>
 
     <string name="new_reaction_symbol">New Reaction Symbol</string>
     <string name="no_reaction_type_setup_long_press_to_change">No reaction types pre-selected for this user. Long press on the heart button to change</string>

commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/model/IAccount.kt

@@ -59,6 +59,7 @@ data class LiveHiddenUsers(
     val hiddenUsers: Set<String> = emptySet(),
     val spammers: Set<String> = emptySet(),
     val hiddenWords: Set<String> = emptySet(),
+    val maxHashtagLimit: Int = 5,
 ) {
     fun isUserHidden(userHex: String) = hiddenUsers.contains(userHex) || spammers.contains(userHex)
 }

quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/nip01Core/tags/hashtags/EventExt.kt

@@ -24,6 +24,8 @@ import com.vitorpamplona.quartz.nip01Core.core.Event
 
 fun Event.anyHashTag(onEach: (str: String) -> Boolean) = tags.anyHashTag(onEach)
 
+fun Event.countHashtags() = tags.countHashtags()
+
 fun Event.hasHashtags() = tags.hasHashtags()
 
 fun Event.hashtags() = tags.hashtags()