WP-0: SwiftPM scaffold, shared model, signed app bundle script

Sources/ShotdeckCore/Support/DubaiTime.swift

@@ -0,0 +1,40 @@
+import Foundation
+
+public enum DubaiTime {
+    private static let stampFormatter = LockedDateFormatter(dateFormat: "d MMM yyyy, HH:mm 'Dubai'")
+    private static let fileStampFormatter = LockedDateFormatter(dateFormat: "yyyyMMdd-HHmmss")
+
+    public static func stamp(_ date: Date) -> String {
+        stampFormatter.string(from: date)
+    }
+
+    public static func fileStamp(_ date: Date) -> String {
+        fileStampFormatter.string(from: date)
+    }
+}
+
+/// DateFormatter is not Sendable. This holder is the only shared mutable state
+/// around a formatter: every read is serialized by the lock, so concurrent
+/// calls (one per PDF page) cannot race.
+private final class LockedDateFormatter: @unchecked Sendable {
+    private let lock = NSLock()
+    private let formatter: DateFormatter
+
+    init(dateFormat: String) {
+        let formatter = DateFormatter()
+        formatter.calendar = Calendar(identifier: .gregorian)
+        formatter.locale = Locale(identifier: "en_GB")
+        guard let dubai = TimeZone(identifier: "Asia/Dubai") else {
+            preconditionFailure("The Asia/Dubai time zone is missing from this system.")
+        }
+        formatter.timeZone = dubai
+        formatter.dateFormat = dateFormat
+        self.formatter = formatter
+    }
+
+    func string(from date: Date) -> String {
+        lock.lock()
+        defer { lock.unlock() }
+        return formatter.string(from: date)
+    }
+}