package dorkbox.netUtil

import dorkbox.executor.Executor
import dorkbox.netUtil.dnsUtils.DefaultHostsFileResolver
import dorkbox.netUtil.dnsUtils.ResolveConf
import dorkbox.netUtil.dnsUtils.ResolvedAddressTypes
import java.io.BufferedWriter
import java.io.File
import java.io.FileWriter
import java.io.IOException
import java.net.Inet4Address
import java.net.Inet6Address
import java.net.InetAddress
import java.net.InetSocketAddress


object Dns {
    /**
     * Gets the version number.
     */
    const val version = "2.9.1"

    const val DEFAULT_SEARCH_DOMAIN = ""

    /**
     * @throws IOException if the DNS resolve.conf file cannot be read
     */
    fun setDNSServers(dnsServersString: String) {
        if (Common.OS_LINUX) {
            val dnsServers = dnsServersString.split(",")
            val dnsFile = File("/etc/resolvconf/resolv.conf.d/head")

            if (!dnsFile.canRead()) {
                throw IOException("Unable to initialize dns server file. Something is SERIOUSLY wrong")
            }

            BufferedWriter(FileWriter(dnsFile)).use {
                it.write("# File location: /etc/resolvconf/resolv.conf.d/head\n")
                it.write("# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)\n")

                dnsServers.forEach { dns ->
                    it.write("nameserver $dns\n")
                }

                it.flush();
            }

            Executor().command("resolvconf", "-u").startBlocking()
        } else {
            throw RuntimeException("NOT IMPL.")
        }
    }

    /**
     * Resolve the address of a hostname against the entries in a hosts file, depending on some address types.
     *
     * @param inetHost the hostname to resolve
     * @param resolvedAddressTypes the address types to resolve
     *
     * @return the first matching address or null
     */
    fun resolveFromHosts(inetHost: String, resolvedAddressTypes: ResolvedAddressTypes = ResolvedAddressTypes.IPV4_PREFERRED): InetAddress? {
        return DefaultHostsFileResolver.address(inetHost, resolvedAddressTypes)
    }

    /** Returns all name servers, including the default ones. */
    val nameServers: Map<String, List<InetSocketAddress>> by lazy {
        ResolveConf.getUnsortedNameServers()
    }

    /** Returns all default name servers. */
    val defaultNameServers: List<InetSocketAddress> by lazy {
        val defaultServers = nameServers[DEFAULT_SEARCH_DOMAIN]!!
        if (IPv6.isPreferred) {
            // prefer IPv6: return IPv6 first, then IPv4 (each in the order added)
            defaultServers.filter { it.address is Inet6Address } + defaultServers.filter { it.address is Inet4Address }
        } else if (IPv4.isPreferred) {
            // skip IPv6 addresses
            defaultServers.filter { it.address is Inet4Address }
        } else {
            // neither is specified, return in the order added
            defaultServers
        }
    }

    /**
     * Gets the threshold for the number of dots which must appear in a name before it is considered
     * absolute. The default is 1.
     */
    val numberDots: Int by lazy {
        if (Common.OS_WINDOWS) {
            1
        } else {
            // first try the default unix config path
            var tryParse = ResolveConf.tryParseResolvConfNDots("/etc/resolv.conf")
            if (!tryParse.first) {
                // then fallback to netware
                tryParse = ResolveConf.tryParseResolvConfNDots("sys:/etc/resolv.cfg")
            }
            tryParse.second
        }
    }
}


//TODO add domain TLD, etc util tools