import Foundation

/// Which ipx-web the app shows. Asked for on first launch; shaking the phone asks again.
/// `-ipx.server <url>` on the launch arguments overrides it for that run (UserDefaults' argument
/// domain), which is how a test points the app somewhere else.
enum Server {
    private static let key = "ipx.server"
    static let suggested = "https://ipodderx.sdf1.net"

    static var url: URL? {
        get { UserDefaults.standard.string(forKey: key).flatMap(normalise) }
        set { UserDefaults.standard.set(newValue?.absoluteString, forKey: key) }
    }

    /// What someone typed, as an address: a bare host gets https. Plain http is allowed only on
    /// your own network, which is all NSAllowsLocalNetworking lets through, so it is refused here
    /// rather than failing later and looking like the server is down.
    static func normalise(_ text: String) -> URL? {
        var s = text.trimmingCharacters(in: .whitespacesAndNewlines)
        if s.isEmpty { return nil }
        if !s.contains("://") { s = "https://" + s }
        guard let u = URL(string: s), let host = u.host, !host.isEmpty else { return nil }
        switch u.scheme {
        case "https": return u
        case "http": return isLocal(host) ? u : nil
        default: return nil
        }
    }

    static func isLocal(_ host: String) -> Bool {
        if host == "localhost" || host.hasSuffix(".local") { return true }
        let p = host.split(separator: ".").compactMap { Int($0) }
        guard p.count == 4 else { return false }
        return p[0] == 10 || p[0] == 127 || (p[0] == 192 && p[1] == 168)
            || (p[0] == 172 && (16...31).contains(p[1]))
    }

    /// A path the page sent (`/media/42`), against the server.
    static func resolve(_ path: String) -> URL? {
        guard let base = url else { return nil }
        return URL(string: path, relativeTo: base)?.absoluteURL
    }
}