ReadViewSDK/Sources/RDReaderView/EPUBCore/RDEPUBSafeArea.swift

import UIKit

/// Device-level safe area lookup modeled after GKNavigationBarSwift.
/// Reads the real safe area from the key window so correct values are
/// available even before a view has been laid out in the hierarchy.
/// Must be called on the main thread.
public enum RDEPUBSafeArea {

    /// Minimum text margins applied when the device safe area on an edge is
    /// smaller (e.g. no notch / no home indicator). These are aesthetic
    /// paddings, not approximations of the safe area itself.
    public static let minimumVerticalTextMargin: CGFloat = 20

    public static let minimumHorizontalTextMargin: CGFloat = 16

    public static func keyWindow() -> UIWindow? {
        let scenes = UIApplication.shared.connectedScenes
            .compactMap { $0 as? UIWindowScene }
        if let window = scenes
            .filter({ $0.activationState == .foregroundActive })
            .flatMap({ $0.windows })
            .first(where: { $0.isKeyWindow }) {
            return window
        }
        if let window = scenes
            .flatMap({ $0.windows })
            .first(where: { $0.isKeyWindow }) {
            return window
        }
        return UIApplication.shared.delegate?.window ?? nil
    }

    public static func insets() -> UIEdgeInsets {
        if let window = keyWindow() {
            return window.safeAreaInsets
        }
        // No key window yet (early launch): create a detached window to read
        // the device safe area, same fallback as GKNavigationBarSwift.
        let window = UIWindow(frame: UIScreen.main.bounds)
        if window.safeAreaInsets.bottom <= 0 {
            window.rootViewController = UIViewController()
        }
        return window.safeAreaInsets
    }

    /// Prefers insets measured from a view already installed in the hierarchy;
    /// falls back to the key-window insets when the view is not laid out yet
    /// and reports .zero.
    public static func resolve(_ measuredInsets: UIEdgeInsets?) -> UIEdgeInsets {
        if let measuredInsets, measuredInsets != .zero {
            return measuredInsets
        }
        return insets()
    }

    /// Default reflowable content insets derived from the live device safe
    /// area instead of hard-coded heights.
    public static func defaultReflowableContentInsets() -> UIEdgeInsets {
        let safe = insets()
        return UIEdgeInsets(
            top: max(safe.top, minimumVerticalTextMargin),
            left: max(safe.left, minimumHorizontalTextMargin),
            bottom: max(safe.bottom, minimumVerticalTextMargin),
            right: max(safe.right, minimumHorizontalTextMargin)
        )
    }
}