ux(chat): scroll to bottom on geohash open; add infinite scroll up with stable anchor; track window size per chat

bitchat/Views/ContentView.swift

@@ -80,6 +80,9 @@ struct ContentView: View {
     @State private var autocompleteDebounceTimer: Timer?
     @State private var showLocationChannelsSheet = false
     @State private var expandedMessageIDs: Set<String> = []
+    // Window sizes for rendering (infinite scroll up)
+    @State private var windowCountPublic: Int = 300
+    @State private var windowCountPrivate: [String: Int] = [:]
     
     // MARK: - Computed Properties
     
@@ -295,8 +298,12 @@ struct ContentView: View {
                         }
                     }()
                     
-                    // Implement windowing - show last 300 messages for performance
+                    // Implement windowing with adjustable window count per chat
-                    let windowedMessages = messages.suffix(300)
+                    let currentWindowCount: Int = {
+                        if let peer = privatePeer { return windowCountPrivate[peer] ?? 300 }
+                        return windowCountPublic
+                    }()
+                    let windowedMessages = messages.suffix(currentWindowCount)
 
                     // Build stable UI IDs with a context key to avoid ID collisions when switching channels
                     #if os(iOS)
@@ -413,6 +420,40 @@ struct ContentView: View {
                             if message.id == windowedMessages.last?.id {
                                 isAtBottom.wrappedValue = true
                             }
+                            // Infinite scroll up: when top row appears, increase window and preserve anchor
+                            if message.id == windowedMessages.first?.id, messages.count > windowedMessages.count {
+                                let step = 200
+                                #if os(iOS)
+                                let contextKey: String = {
+                                    switch locationManager.selectedChannel {
+                                    case .mesh: return "mesh"
+                                    case .location(let ch): return "geo:\(ch.geohash)"
+                                    }
+                                }()
+                                #else
+                                let contextKey: String = "mesh"
+                                #endif
+                                let preserveID = "\(contextKey)|\(message.id)"
+                                if let peer = privatePeer {
+                                    let current = windowCountPrivate[peer] ?? 300
+                                    let newCount = min(messages.count, current + step)
+                                    if newCount != current {
+                                        windowCountPrivate[peer] = newCount
+                                        DispatchQueue.main.async {
+                                            proxy.scrollTo(preserveID, anchor: .top)
+                                        }
+                                    }
+                                } else {
+                                    let current = windowCountPublic
+                                    let newCount = min(messages.count, current + step)
+                                    if newCount != current {
+                                        windowCountPublic = newCount
+                                        DispatchQueue.main.async {
+                                            proxy.scrollTo(preserveID, anchor: .top)
+                                        }
+                                    }
+                                }
+                            }
                         }
                         .onDisappear {
                             if message.id == windowedMessages.last?.id {
@@ -549,7 +590,8 @@ struct ContentView: View {
                         #else
                         let contextKey: String = "mesh"
                         #endif
-                        let target = viewModel.messages.suffix(300).last.map { "\(contextKey)|\($0.id)" }
+                        let count = windowCountPublic
+                        let target = viewModel.messages.suffix(count).last.map { "\(contextKey)|\($0.id)" }
                         DispatchQueue.main.async {
                             if let target = target { proxy.scrollTo(target, anchor: .bottom) }
                         }
@@ -568,7 +610,8 @@ struct ContentView: View {
                             #else
                             let contextKey: String = "mesh"
                             #endif
-                            let target = viewModel.messages.suffix(300).last.map { "\(contextKey)|\($0.id)" }
+                            let count = windowCountPublic
+                            let target = viewModel.messages.suffix(count).last.map { "\(contextKey)|\($0.id)" }
                             DispatchQueue.main.async {
                                 if let target = target { proxy.scrollTo(target, anchor: .bottom) }
                             }
@@ -594,7 +637,8 @@ struct ContentView: View {
                     if now.timeIntervalSince(lastScrollTime) > 0.5 {
                         lastScrollTime = now
                         let contextKey = "dm:\(peerID)"
-                        let target = messages.suffix(300).last.map { "\(contextKey)|\($0.id)" }
+                        let count = windowCountPrivate[peerID] ?? 300
+                        let target = messages.suffix(count).last.map { "\(contextKey)|\($0.id)" }
                         DispatchQueue.main.async {
                             if let target = target { proxy.scrollTo(target, anchor: .bottom) }
                         }
@@ -603,7 +647,8 @@ struct ContentView: View {
                         scrollThrottleTimer = Timer.scheduledTimer(withTimeInterval: 0.5, repeats: false) { _ in
                             lastScrollTime = Date()
                             let contextKey = "dm:\(peerID)"
-                            let target = messages.suffix(300).last.map { "\(contextKey)|\($0.id)" }
+                            let count = windowCountPrivate[peerID] ?? 300
+                            let target = messages.suffix(count).last.map { "\(contextKey)|\($0.id)" }
                             DispatchQueue.main.async {
                                 if let target = target { proxy.scrollTo(target, anchor: .bottom) }
                             }
@@ -613,19 +658,20 @@ struct ContentView: View {
             }
             #if os(iOS)
             .onChange(of: locationManager.selectedChannel) { newChannel in
-                // When switching to a new geohash channel, scroll to the top of that chat
+                // When switching to a new geohash channel, scroll to the bottom
                 guard privatePeer == nil else { return }
                 switch newChannel {
                 case .mesh:
                     break
                 case .location(let ch):
-                    // Compute the top item (first of the current window)
+                    // Reset window size
+                    windowCountPublic = 300
                     let contextKey = "geo:\(ch.geohash)"
-                    let top = viewModel.messages.suffix(300).first?.id
+                    let last = viewModel.messages.suffix(windowCountPublic).last?.id
-                    let target = top.map { "\(contextKey)|\($0)" }
+                    let target = last.map { "\(contextKey)|\($0)" }
-                    isAtBottom.wrappedValue = false
+                    isAtBottom.wrappedValue = true
                     DispatchQueue.main.async {
-                        if let target = target { proxy.scrollTo(target, anchor: .top) }
+                        if let target = target { proxy.scrollTo(target, anchor: .bottom) }
                     }
                 }
             }