package resolver

import (
	"fmt"
	"net"

	"linum/internal/dns"
)

type Forwarder struct {
	upstream string
}

func NewForwarder(upstream string) *Forwarder {
	return &Forwarder{upstream: upstream}
}

func (f *Forwarder) Resolve(query *dns.Msg) (*dns.Msg, error) {
	query.Header.SetRD(true)

	wire, err := dns.Pack(query)
	if err != nil {
		return nil, fmt.Errorf("pack: %w", err)
	}

	conn, err := net.Dial("udp", f.upstream)
	if err != nil {
		return nil, fmt.Errorf("dial %s: %w", f.upstream, err)
	}
	defer conn.Close()

	if _, err := conn.Write(wire); err != nil {
		return nil, fmt.Errorf("write: %w", err)
	}

	buf := make([]byte, 4096)
	n, err := conn.Read(buf)
	if err != nil {
		return nil, fmt.Errorf("read: %w", err)
	}

	resp, err := dns.Unpack(buf[:n])
	if err != nil {
		return nil, fmt.Errorf("unpack response: $w", err)
	}
	return resp, nil
}