import Foundation
import HostRegistry

/// T-iOS-15 · Cold-start selection logic, kept pure for unit tests
/// (ColdStartPolicyTests): which root screen boots, and whether the session
/// list highlights "继续上次" for the active host.
enum ColdStartPolicy {
    enum RootRoute: Equatable {
        /// Host store not read yet.
        case loading
        /// No paired host → pairing is the only next step (plan §7 step 1).
        case pairing
        /// At least one paired host → the merged chooser/dashboard list.
        case sessions
    }

    static func initialRoute(pairedHostCount: Int) -> RootRoute {
        pairedHostCount == 0 ? .pairing : .sessions
    }

    /// The "继续上次" target for the list's highlight banner: the last
    /// server-adopted session persisted for the ACTIVE host (nil = no banner).
    /// Persistence side: `SessionActivityBridge` (adopted → set, exited →
    /// cleared), so a returned id was live when last seen.
    static func continueLastSessionId(
        activeHost: HostRegistry.Host?,
        store: any LastSessionStore
    ) -> UUID? {
        guard let activeHost else { return nil }
        return store.lastSessionId(host: activeHost.id)
    }
}