import SwiftUI

/// T-iOS-15 · Privacy shade (security-critical, plan §7 T-iOS-15).
///
/// iOS writes the app-switcher snapshot to DISK the moment the scene reaches
/// `.background` — but the switcher is usually ENTERED at `.inactive`. The
/// shade therefore covers whenever `scenePhase != .active` (the exact rule;
/// `.inactive`-only would let the `.background` snapshot capture terminal
/// content — API keys, tokens, source — into the on-disk switcher image).
/// Restored on `.active`.
///
/// Pure mapping split from the view so the rule is unit-testable for all
/// three phases (PrivacyShadeTests).
enum PrivacyShadePolicy {
    static func isShadeVisible(for scenePhase: ScenePhase) -> Bool {
        scenePhase != .active
    }
}

/// Opaque cover rendered ABOVE the whole navigation tree (RootView ZStack) —
/// deliberately no animation: the snapshot moment must never race a fade.
///
/// Scope note (documented): sheets present in a separate presentation layer a
/// root overlay cannot cover — but no terminal bytes are ever rendered in a
/// sheet (pairing / plan-gate only), so the root-level shade covers every
/// surface that shows PTY content.
struct PrivacyShadeView: View {
    var body: some View {
        ZStack {
            Color(.systemBackground)
                .ignoresSafeArea()
            VStack(spacing: ShadeMetrics.spacing) {
                Image(systemName: "terminal.fill")
                    .font(.largeTitle)
                    .foregroundStyle(.secondary)
                Text("WebTerm")
                    .font(.headline)
                    .foregroundStyle(.secondary)
            }
        }
        .accessibilityHidden(true)
    }

    private enum ShadeMetrics {
        static let spacing: CGFloat = 12
    }
}