Merge pull request #2534 from vitorpamplona/claude/add-notification-filtering-RF0Td

Refactor notification pipeline to use cache observer pattern

commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/model/observables/NewEventMatchingFilter.kt

@@ -0,0 +1,50 @@
+/*
+ * 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.commons.model.observables
+
+import com.vitorpamplona.amethyst.commons.model.Note
+import com.vitorpamplona.quartz.nip01Core.core.Event
+import com.vitorpamplona.quartz.nip01Core.relay.filters.Filter
+
+/**
+ * Emits each new event that matches the given Nostr filter, one at a time.
+ *
+ * Unlike [EventListMatchingFilter] / [NoteListMatchingFilter], this does not
+ * accumulate a list — it simply calls [onNew] per matching event as it is
+ * inserted into the cache. Useful for reactive event-triggered pipelines
+ * (e.g. notifications) that need per-event delivery without list overhead.
+ */
+class NewEventMatchingFilter<T : Event>(
+    private val filter: Filter,
+    private val onNew: (T) -> Unit,
+) : Observable {
+    @Suppress("UNCHECKED_CAST")
+    override fun new(
+        event: Event,
+        note: Note,
+    ) {
+        if (filter.match(event)) {
+            onNew(event as T)
+        }
+    }
+
+    override fun remove(note: Note) {}
+}