InvestmentTrackerApp/Shared/WatchSnapshotCache.swift

import Foundation

/// On-watch cache of the last snapshot received from the iPhone.
///
/// The watch app writes it; the complication extension reads it. They are
/// separate processes, so the App Group container is what lets them share —
/// with a fallback to the process defaults so the app still shows data even if
/// the App Group entitlement is not in place yet.
enum WatchSnapshotCache {

    private static var sharedDefaults: UserDefaults? {
        UserDefaults(suiteName: WatchPortfolioSnapshot.appGroupIdentifier)
    }

    static func save(_ snapshot: WatchPortfolioSnapshot) {
        guard let data = snapshot.encoded() else { return }
        let key = WatchPortfolioSnapshot.payloadKey
        sharedDefaults?.set(data, forKey: key)
        UserDefaults.standard.set(data, forKey: key)
    }

    static func load() -> WatchPortfolioSnapshot? {
        let key = WatchPortfolioSnapshot.payloadKey
        let data = sharedDefaults?.data(forKey: key) ?? UserDefaults.standard.data(forKey: key)
        guard let data else { return nil }
        return WatchPortfolioSnapshot.decoded(from: data)
    }
}