import Foundation

/// Local IPv4 address discovery — which networks is this Mac actually on?
/// Used by the install join gate (mesh membership evidence) and the phone-setup QR
/// (advertising this Mac's bridge endpoints to a scanning phone).
public enum LocalNetwork {
    /// Every IPv4 address bound to a local interface, loopback excluded.
    public static func ipv4Addresses() -> [String] {
        var addrs: UnsafeMutablePointer<ifaddrs>?
        guard getifaddrs(&addrs) == 0 else { return [] }
        defer { freeifaddrs(addrs) }
        var out: [String] = []
        var cursor = addrs
        while let ifa = cursor?.pointee {
            defer { cursor = ifa.ifa_next }
            guard let sa = ifa.ifa_addr, sa.pointee.sa_family == sa_family_t(AF_INET) else { continue }
            var addr = sockaddr_in()
            memcpy(&addr, sa, MemoryLayout<sockaddr_in>.size)
            var ip = [CChar](repeating: 0, count: Int(INET_ADDRSTRLEN))
            var sin = addr.sin_addr
            inet_ntop(AF_INET, &sin, &ip, socklen_t(INET_ADDRSTRLEN))
            let s = String(cString: ip)
            if s != "127.0.0.1" { out.append(s) }
        }
        return out
    }

    /// This Mac's mesh (10.9.0.x) address, when the tunnel is configured.
    public static func meshAddress() -> String? {
        ipv4Addresses().first { $0.hasPrefix("10.9.0.") }
    }

    /// This Mac's best non-mesh private address (the LAN leg), if any.
    public static func lanAddress() -> String? {
        let v4 = ipv4Addresses().filter { !$0.hasPrefix("10.9.0.") }
        // Prefer the home LAN subnet, then any RFC1918 address.
        return v4.first { $0.hasPrefix("10.0.0.") }
            ?? v4.first { $0.hasPrefix("192.168.") || $0.hasPrefix("10.") || $0.hasPrefix("172.") }
    }
}