Add a "load more" button instead of always inserting events in timelines

Changelog-Added: Add a "load more" button instead of always inserting events in timelines

damus/Util/EventHolder.swift

@@ -0,0 +1,95 @@
+//
+//  EventHolder.swift
+//  damus
+//
+//  Created by William Casarin on 2023-02-19.
+//
+
+import Foundation
+
+/// Used for holding back events until they're ready to be displayed
+class EventHolder: ObservableObject {
+    private var has_event: Set<String>
+    @Published var events: [NostrEvent]
+    @Published var incoming: [NostrEvent]
+    @Published var should_queue: Bool
+    
+    var queued: Int {
+        return incoming.count
+    }
+    
+    var has_incoming: Bool {
+        return queued > 0
+    }
+    
+    var all_events: [NostrEvent] {
+        events + incoming
+    }
+    
+    init() {
+        self.should_queue = false
+        self.events = []
+        self.incoming = []
+        self.has_event = Set()
+    }
+    
+    init(events: [NostrEvent], incoming: [NostrEvent]) {
+        self.should_queue = false
+        self.events = events
+        self.incoming = incoming
+        self.has_event = Set()
+    }
+    
+    func filter(_ isIncluded: (NostrEvent) -> Bool) {
+        self.events = self.events.filter(isIncluded)
+        self.incoming = self.incoming.filter(isIncluded)
+    }
+    
+    func insert(_ ev: NostrEvent) -> Bool {
+        if should_queue {
+            return insert_queued(ev)
+        } else {
+            return insert_immediate(ev)
+        }
+    }
+    
+    private func insert_immediate(_ ev: NostrEvent) -> Bool {
+        if has_event.contains(ev.id) {
+            return false
+        }
+        
+        has_event.insert(ev.id)
+        
+        if insert_uniq_sorted_event_created(events: &self.events, new_ev: ev) {
+            return true
+        }
+        
+        return false
+    }
+    
+    private func insert_queued(_ ev: NostrEvent) -> Bool {
+        if has_event.contains(ev.id) {
+            return false
+        }
+        
+        has_event.insert(ev.id)
+        
+        incoming.append(ev)
+        return true
+    }
+    
+    func flush() {
+        var changed = false
+        for event in incoming {
+            if insert_uniq_sorted_event_created(events: &events, new_ev: event) {
+                changed = true
+            }
+        }
+        
+        if changed {
+            self.objectWillChange.send()
+        }
+        
+        self.incoming = []
+    }
+}

damus/Util/InsertSort.swift

@@ -59,6 +59,13 @@ func insert_uniq_sorted_zap(zaps: inout [Zap], new_zap: Zap) -> Bool {
     return true
 }
 
+
+func insert_uniq_sorted_event_created(events: inout [NostrEvent], new_ev: NostrEvent) -> Bool {
+    return insert_uniq_sorted_event(events: &events, new_ev: new_ev) {
+        $0.created_at > $1.created_at
+    }
+}
+
 @discardableResult
 func insert_uniq_sorted_event(events: inout [NostrEvent], new_ev: NostrEvent, cmp: (NostrEvent, NostrEvent) -> Bool) -> Bool {
     var i: Int = 0