// retoor <retoor@molodetz.nl>

import Foundation

enum DnsResolver {
    struct DnsResult {
        let hostname: String
        let addresses: [String]
        let error: String?
    }

    static func resolve(_ hostname: String) -> DnsResult {
        let hints = addrinfo(
            ai_flags: AI_ALL,
            ai_family: AF_UNSPEC,
            ai_socktype: SOCK_STREAM,
            ai_protocol: 0,
            ai_addrlen: 0,
            ai_canonname: nil,
            ai_addr: nil,
            ai_next: nil
        )

        var result: UnsafeMutablePointer<addrinfo>?
        let errorCode = getaddrinfo(hostname, nil, &hints, &result)

        if errorCode != 0 {
            let errorStr = String(cString: gai_strerror(errorCode))
            return DnsResult(hostname: hostname, addresses: [], error: errorStr)
        }

        var addresses: [String] = []
        var current = result
        while let addr = current {
            var hostBuffer = [CChar](repeating: 0, count: Int(NI_MAXHOST))
            let sa_len: socklen_t
            let sa: UnsafePointer<sockaddr>

            if addr.pointee.ai_family == AF_INET {
                sa_len = socklen_t(MemoryLayout<sockaddr_in>.size)
                sa = UnsafeRawPointer(addr.pointee.ai_addr).assumingMemoryBound(to: sockaddr.self)
            } else if addr.pointee.ai_family == AF_INET6 {
                sa_len = socklen_t(MemoryLayout<sockaddr_in6>.size)
                sa = UnsafeRawPointer(addr.pointee.ai_addr).assumingMemoryBound(to: sockaddr.self)
            } else {
                current = addr.pointee.ai_next
                continue
            }

            let gaiResult = getnameinfo(
                sa, sa_len,
                &hostBuffer, socklen_t(hostBuffer.count),
                nil, 0,
                NI_NUMERICHOST
            )
            if gaiResult == 0 {
                addresses.append(String(cString: hostBuffer))
            }
            current = addr.pointee.ai_next
        }

        freeaddrinfo(result)
        return DnsResult(hostname: hostname, addresses: addresses, error: nil)
    }
}