Adds a new observable system to local cache.

app/src/main/java/com/vitorpamplona/amethyst/model/LocalCache.kt

@@ -26,6 +26,7 @@ import androidx.compose.runtime.Stable
 import com.vitorpamplona.amethyst.Amethyst
 import com.vitorpamplona.amethyst.commons.data.DeletionIndex
 import com.vitorpamplona.amethyst.commons.data.LargeCache
+import com.vitorpamplona.amethyst.model.observables.LatestByKindWithETag
 import com.vitorpamplona.amethyst.service.checkNotInMainThread
 import com.vitorpamplona.amethyst.service.relays.Relay
 import com.vitorpamplona.amethyst.ui.components.BundledInsert
@@ -142,6 +143,38 @@ object LocalCache {
 
     val deletionIndex = DeletionIndex()
 
+    val observablesByKindAndETag = ConcurrentHashMap<Int, ConcurrentHashMap<HexKey, LatestByKindWithETag>>(10)
+
+    fun observeETag(
+        kind: Int,
+        eventId: HexKey,
+        onCreate: () -> LatestByKindWithETag,
+    ): LatestByKindWithETag {
+        var eTagList = observablesByKindAndETag.get(kind)
+
+        if (eTagList == null) {
+            eTagList = ConcurrentHashMap<HexKey, LatestByKindWithETag>(1)
+            observablesByKindAndETag.put(kind, eTagList)
+        }
+
+        val value = eTagList.get(eventId)
+
+        return if (value != null) {
+            value
+        } else {
+            val newObject = onCreate()
+            val obj = eTagList.putIfAbsent(eventId, newObject) ?: newObject
+            obj
+        }
+    }
+
+    fun updateObservables(event: Event) {
+        val observablesOfKind = observablesByKindAndETag[event.kind()] ?: return
+        event.forEachTaggedEvent {
+            observablesOfKind[it]?.updateIfMatches(event)
+        }
+    }
+
     fun checkGetOrCreateUser(key: String): User? {
         // checkNotInMainThread()
 
@@ -2239,6 +2272,7 @@ object LocalCache {
     val live: LocalCacheLiveData = LocalCacheLiveData()
 
     private fun refreshObservers(newNote: Note) {
+        updateObservables(newNote.event as Event)
         live.invalidateData(newNote)
     }
 

app/src/main/java/com/vitorpamplona/amethyst/model/observables/LatestByKindWithETag.kt

@@ -0,0 +1,72 @@
+/**
+ * Copyright (c) 2024 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.model.observables
+
+import com.vitorpamplona.amethyst.model.LocalCache
+import com.vitorpamplona.amethyst.model.Note
+import com.vitorpamplona.quartz.events.Event
+import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.asStateFlow
+
+class LatestByKindWithETag(private val kind: Int, private val eTag: String) {
+    private val _latest = MutableStateFlow<Event?>(null)
+    val latest = _latest.asStateFlow()
+
+    fun updateIfMatches(event: Event) {
+        if (event.kind == kind && event.isTaggedEvent(eTag)) {
+            if (event.createdAt > (_latest.value?.createdAt ?: 0)) {
+                _latest.tryEmit(event)
+            }
+        }
+    }
+
+    fun canDelete(): Boolean {
+        return _latest.subscriptionCount.value == 0
+    }
+
+    suspend fun init() {
+        val latestNote =
+            LocalCache.notes.maxOrNullOf(
+                filter = { idHex: String, note: Note ->
+                    note.event?.let {
+                        it.kind() == kind && it.isTaggedEvent(eTag)
+                    } == true
+                },
+                comparator = { first: Note?, second: Note? ->
+                    println("Comparator $first $second")
+                    val firstEvent = first?.event
+                    val secondEvent = second?.event
+
+                    if (firstEvent == null && secondEvent == null) {
+                        0
+                    } else if (firstEvent == null) {
+                        1
+                    } else if (secondEvent == null) {
+                        -1
+                    } else {
+                        firstEvent.createdAt().compareTo(secondEvent.createdAt())
+                    }
+                },
+            )?.event as? Event
+
+        _latest.tryEmit(latestNote)
+    }
+}