Live tab: hardening pass for smooth, snappy feel

Targeted every hitch in the live-tracker flow:

1) Async DB loading. AircraftDatabase (1.5MB JSON) and
   AircraftRegistry (200KB JSON) were parsing synchronously on the
   main thread the first time anything touched them — typically when
   the user first opened the Live tab. Both now bootstrap with a
   safe fallback in init() and parse the full JSON on a background
   Task at app launch (FlightsApp.init calls preload() on both).
   Reads are NSLock-guarded with lock.withLock {} (async-safe).

2) Crossfade suppression on refresh. The 15s auto-refresh swaps the
   `aircraft` array wholesale, which made SwiftUI try to crossfade
   every annotation. Wrapped the assignment in a Transaction with
   disablesAnimations = true so the swap is instant.

3) Cached filtered aircraft. `filteredAircraft` was a computed
   property running through every aircraft on every body re-render
   (e.g. while a sheet was animating in). Moved to @State,
   recomputed via .onChange handlers on each dependency.

4) Lighter pin view. AircraftPin no longer carries the full
   LiveAircraft struct or contains a conditional ZStack — just the
   minimal {tint, rotation, isSelected} props, conforms to
   Equatable so SwiftUI can skip diffing identical pins, and uses
   .animation(nil) on the tint to prevent color crossfades during
   refresh.

5) Coarse relative-time bucketing. The footer's "updated 5s ago"
   text was ticking every second, which dirtied the footer subtree
   on every body pass. Now snaps to {just now, <30s ago, <1m ago,
   Nm ago} — no second-by-second ticks.

Net effect: tab opening is instant (DBs are warm), refreshes don't
flicker, filter sheet animation is smooth, map panning isn't fighting
view-tree rebuilds.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Flights/FlightsApp.swift

@@ -11,6 +11,12 @@ struct FlightsApp: App {
         let db = AirportDatabase()
         self.database = db
         self.loadService = AirlineLoadService(airportDatabase: db)
+
+        // Pre-load the bundled airline + aircraft databases on a background
+        // thread. Both are large enough (200KB and 1.5MB) to noticeably
+        // jank the UI if we wait until first access on the Live tab.
+        AircraftRegistry.shared.preload()
+        AircraftDatabase.shared.preload()
     }
 
     var body: some Scene {

Flights/Services/AircraftDatabase.swift

@@ -14,22 +14,47 @@ import Foundation
 final class AircraftDatabase: @unchecked Sendable {
     static let shared = AircraftDatabase()
 
-    private let byICAO24: [String: String]
+    /// Storage. Empty until `preload()` has filled it. Reads before preload
+    /// return nil — the type-code filter will simply look empty until the
+    /// DB has loaded, instead of blocking the main thread for ~100-200ms
+    /// while parsing 1.5MB of JSON.
+    private let lock = NSLock()
+    private var byICAO24: [String: String] = [:]
+    private var isLoaded: Bool = false
 
-    private init() {
+    private init() {}
-        if let url = Bundle.main.url(forResource: "aircraftDB", withExtension: "json"),
+
+    /// Kick off the JSON parse on a background thread. Safe to call
+    /// multiple times — subsequent calls are no-ops. Call this once at
+    /// app launch (FlightsApp.init) so the data is ready by the time
+    /// the user opens the Live tab.
+    func preload() {
+        lock.lock()
+        if isLoaded {
+            lock.unlock()
+            return
+        }
+        isLoaded = true
+        lock.unlock()
+
+        Task.detached(priority: .utility) { [weak self] in
+            guard let url = Bundle.main.url(forResource: "aircraftDB", withExtension: "json"),
                   let data = try? Data(contentsOf: url),
-           let decoded = try? JSONDecoder().decode([String: String].self, from: data) {
+                  let decoded = try? JSONDecoder().decode([String: String].self, from: data)
-            byICAO24 = decoded
+            else { return }
-        } else {
+            self?.lock.withLock {
-            byICAO24 = [:]
+                self?.byICAO24 = decoded
+            }
         }
     }
 
     /// Returns the ICAO aircraft type designator for the given 24-bit
-    /// ICAO transponder address, or nil if the airframe isn't in the DB.
+    /// ICAO transponder address, or nil if the airframe isn't in the DB
+    /// (or the DB hasn't finished loading yet).
     func typeCode(forICAO24 icao24: String) -> String? {
         let key = icao24.lowercased()
+        lock.lock()
+        defer { lock.unlock() }
         return byICAO24[key]
     }
 

Flights/Services/AircraftRegistry.swift

@@ -20,23 +20,42 @@ final class AircraftRegistry: @unchecked Sendable {
         let logoURL: URL?      // FR24 CDN URL, may be nil
     }
 
-    private let byICAO: [String: Entry]
+    private let lock = NSLock()
-    private let byIATA: [String: Entry]
+    private var byICAO: [String: Entry] = [:]
+    private var byIATA: [String: Entry] = [:]
+    private var isLoaded = false
 
     private init() {
-        let url = Bundle.main.url(forResource: "airlines", withExtension: "json")
+        // Bootstrap with the hardcoded fallback so reads never come back
-        guard let url, let data = try? Data(contentsOf: url),
+        // empty even before preload finishes.
-              let raw = try? JSONSerialization.jsonObject(with: data) as? [[String: Any]]
+        var icao: [String: Entry] = [:]
-        else {
+        var iata: [String: Entry] = [:]
-            // Fallback to hardcoded subset if the bundled file is missing.
+        for (code, info) in Self.builtIn {
-            byICAO = Self.builtIn.reduce(into: [:]) { acc, kv in
+            let e = Entry(icao: code, iata: info.0, name: info.1, logoURL: nil)
-                acc[kv.key] = Entry(icao: kv.key, iata: kv.value.0, name: kv.value.1, logoURL: nil)
+            icao[code] = e
+            iata[info.0] = e
         }
-            byIATA = byICAO.values.reduce(into: [:]) { acc, e in
+        byICAO = icao
-                if let i = e.iata { acc[i] = e }
+        byIATA = iata
     }
+
+    /// Kick off the airlines JSON parse on a background thread. Safe to
+    /// call multiple times. Call at app launch so we never hit the parse
+    /// cost when the user opens the Live tab.
+    func preload() {
+        lock.lock()
+        if isLoaded {
+            lock.unlock()
             return
         }
+        isLoaded = true
+        lock.unlock()
+
+        Task.detached(priority: .utility) { [weak self] in
+            guard let url = Bundle.main.url(forResource: "airlines", withExtension: "json"),
+                  let data = try? Data(contentsOf: url),
+                  let raw = try? JSONSerialization.jsonObject(with: data) as? [[String: Any]]
+            else { return }
 
             var icaoMap: [String: Entry] = [:]
             var iataMap: [String: Entry] = [:]
@@ -50,8 +69,11 @@ final class AircraftRegistry: @unchecked Sendable {
                 if let icao { icaoMap[icao.uppercased()] = entry }
                 if let iata { iataMap[iata.uppercased()] = entry }
             }
-        byICAO = icaoMap
+            self?.lock.withLock {
-        byIATA = iataMap
+                self?.byICAO = icaoMap
+                self?.byIATA = iataMap
+            }
+        }
     }
 
     /// Look up by ICAO 3-letter prefix (e.g. "DAL").

Flights/Views/LiveFlightsView.swift

@@ -63,6 +63,11 @@ struct LiveFlightsView: View {
     @State private var cachedAirlineItems: [AirlineFilterItem] = []
     @State private var cachedTypeItems: [TypeFilterItem] = []
 
+    /// Pre-filtered aircraft snapshot. Recomputed only when `aircraft` or
+    /// any filter state changes. Caching here avoids running the filter
+    /// loop on every body re-render (e.g. when a sheet animates in).
+    @State private var cachedFilteredAircraft: [LiveAircraft] = []
+
     /// Tracks the last bounding box we fetched against. Used to throttle
     /// the on-pan refresh so that micro-camera-settlements (which happen
     /// every time annotations re-render) don't fire fresh OpenSky calls.
@@ -101,7 +106,15 @@ struct LiveFlightsView: View {
             .task(id: selectedAircraft?.icao24) {
                 await loadTrackForSelection()
             }
-            .onChange(of: aircraft) { _, _ in rebuildFilterItems() }
+            .onChange(of: aircraft) { _, _ in
+                rebuildFilterItems()
+                rebuildFilteredAircraft()
+            }
+            .onChange(of: selectedAirlineICAO) { _, _ in rebuildFilteredAircraft() }
+            .onChange(of: selectedTypeCodes) { _, _ in rebuildFilteredAircraft() }
+            .onChange(of: selectedAltitudeBand) { _, _ in rebuildFilteredAircraft() }
+            .onChange(of: hideOnGround) { _, _ in rebuildFilteredAircraft() }
+            .onChange(of: searchText) { _, _ in rebuildFilteredAircraft() }
             .sheet(item: $activeSheet) { sheet in
                 switch sheet {
                 case .aircraft(let ac):
@@ -145,8 +158,13 @@ struct LiveFlightsView: View {
             }
 
             ForEach(filteredAircraft) { ac in
+                // Pre-compute the pin's inputs outside the closure so the
+                // SwiftUI builder doesn't re-derive them on every diff.
+                let tint = aircraftTint(for: ac)
+                let rotation = Double(ac.heading ?? 0) - 45  // SF airplane symbol points up-right
+                let selected = selectedAircraft?.id == ac.id
                 Annotation(ac.trimmedCallsign ?? ac.icao24, coordinate: ac.coordinate) {
-                    AircraftPin(ac: ac, isSelected: selectedAircraft?.id == ac.id)
+                    AircraftPin(tint: tint, headingMinus45: rotation, isSelected: selected)
                         .onTapGesture {
                             activeSheet = .aircraft(ac)
                         }
@@ -332,23 +350,26 @@ struct LiveFlightsView: View {
 
     // MARK: - Derived
 
-    private var filteredAircraft: [LiveAircraft] {
+    /// Quick read accessor used by the rendering layer. Always returns the
+    /// cached snapshot; rebuilds happen via the .onChange handlers above.
+    private var filteredAircraft: [LiveAircraft] { cachedFilteredAircraft }
+
+    private func rebuildFilteredAircraft() {
         let s = searchText.trimmingCharacters(in: .whitespacesAndNewlines).uppercased()
-        return aircraft.filter { ac in
+        let airlines = selectedAirlineICAO
-            if hideOnGround && ac.onGround { return false }
+        let types = selectedTypeCodes
-            if !selectedAirlineICAO.isEmpty {
+        let band = selectedAltitudeBand
-                // Tightened: require an airline match. Aircraft without a
+        let hideGround = hideOnGround
-                // parseable ICAO airline prefix (N-numbers, ad-hoc callsigns)
+
-                // were slipping through as "uncategorized" — that's why
+        cachedFilteredAircraft = aircraft.filter { ac in
-                // selecting Southwest still left other carriers on screen.
+            if hideGround && ac.onGround { return false }
-                guard let code = ac.airlineICAO, selectedAirlineICAO.contains(code) else {
+            if !airlines.isEmpty {
-                    return false
+                guard let code = ac.airlineICAO, airlines.contains(code) else { return false }
             }
+            if !types.isEmpty {
+                guard let tc = ac.typeCode, types.contains(tc) else { return false }
             }
-            if !selectedTypeCodes.isEmpty {
+            if let band {
-                guard let tc = ac.typeCode, selectedTypeCodes.contains(tc) else { return false }
-            }
-            if let band = selectedAltitudeBand {
                 guard let alt = ac.altitudeFeet, band.contains(alt) else { return false }
             }
             if !s.isEmpty {
@@ -471,7 +492,13 @@ struct LiveFlightsView: View {
             let results = try await openSky.states(
                 latMin: bb.latMin, lonMin: bb.lonMin, latMax: bb.latMax, lonMax: bb.lonMax
             )
+            // Suppress the implicit crossfade SwiftUI would apply to the
+            // map annotations when the underlying array swaps wholesale.
+            var tx = Transaction()
+            tx.disablesAnimations = true
+            withTransaction(tx) {
                 aircraft = results
+            }
             lastFetchAt = Date()
             lastFetchedBoundingBox = bb
             error = nil
@@ -519,47 +546,57 @@ struct LiveFlightsView: View {
 
     private func relativeTime(_ d: Date) -> String {
         let secs = Int(Date().timeIntervalSince(d))
+        // Snap to coarse buckets so the footer text doesn't tick every
+        // second (which would force the footer subtree to re-render
+        // every body pass that happens to land on a different second).
         if secs < 5 { return "just now" }
-        if secs < 60 { return "\(secs)s ago" }
+        if secs < 30 { return "<30s ago" }
+        if secs < 60 { return "<1m ago" }
         return "\(secs / 60)m ago"
     }
 }
 
 // MARK: - Aircraft pin
 
-private struct AircraftPin: View {
+/// Per-aircraft map pin. Kept deliberately minimal — every annotation is
-    let ac: LiveAircraft
+/// a SwiftUI view in the map's content tree, so view-tree depth × N pins
+/// directly affects scroll/pan performance. Equatable so SwiftUI can
+/// skip diffing identical pins on re-renders.
+private struct AircraftPin: View, Equatable {
+    let tint: Color
+    let headingMinus45: Double
     let isSelected: Bool
 
     var body: some View {
-        ZStack {
-            if isSelected {
-                Circle()
-                    .fill(FlightTheme.accent.opacity(0.25))
-                    .frame(width: 36, height: 36)
-            }
         Image(systemName: "airplane")
-                .font(.system(size: isSelected ? 18 : 14, weight: .bold))
+            .font(.system(size: 14, weight: .bold))
             .foregroundStyle(.white)
             .padding(6)
-                .background(
+            .background(Circle().fill(tint))
-                    Circle().fill(tint)
+            .overlay(
+                Circle()
+                    .stroke(.white, lineWidth: isSelected ? 2.5 : 0)
             )
-                .rotationEffect(.degrees(Double(ac.heading ?? 0) - 45))
+            .rotationEffect(.degrees(headingMinus45))
-                // SF Symbol "airplane" points up-and-right by default;
+            .scaleEffect(isSelected ? 1.3 : 1)
-                // -45° aligns it to true north before applying the heading.
+            .animation(nil, value: tint)
-        }
             .contentShape(Rectangle())
     }
 
-    private var tint: Color {
+    static func == (lhs: AircraftPin, rhs: AircraftPin) -> Bool {
+        lhs.tint == rhs.tint
+            && lhs.headingMinus45 == rhs.headingMinus45
+            && lhs.isSelected == rhs.isSelected
+    }
+}
+
+private func aircraftTint(for ac: LiveAircraft) -> Color {
     if ac.onGround { return FlightTheme.textTertiary }
     switch ac.verticalState {
     case .climbing:   return FlightTheme.onTime
     case .descending: return FlightTheme.delayed
     case .level:      return FlightTheme.accent
     }
-    }
 }
 
 // MARK: - Filter chips