package dns

import "fmt"

type RData interface {
	Type() uint16
	Pack(p *packer) error
	Unpack(u *unpacker, length uint16) error
	String() string
}

type RR struct {
	Name  Name
	Type  uint16
	Class uint16
	TTL   uint32
	Data  RData
}

func unpackRR(u *unpacker) (RR, error) {
	var rr RR
	var err error
	rr.Name, err = u.readName()
	if err != nil {
		return rr, err
	}
	rr.Type, err = u.readUint16()
	if err != nil {
		return rr, err
	}
	rr.Class, err = u.readUint16()
	if err != nil {
		return rr, err
	}
	rr.TTL, err = u.readUint32()
	if err != nil {
		return rr, err
	}
	rdlength, err := u.readUint16()
	if err != nil {
		return rr, err
	}

	rdStart := u.off
	if u.off+int(rdlength) > len(u.buf) {
		return rr, fmt.Errorf("dns: short rdata")
	}

	switch rr.Type {
	case TypeA:
		rr.Data = &A{}
	case TypeNS:
		rr.Data = &NS{}
	case TypeCNAME:
		rr.Data = &CNAME{}
	case TypeSOA:
		rr.Data = &SOA{}
	case TypePTR:
		rr.Data = &PTR{}
	case TypeMX:
		rr.Data = &MX{}
	case TypeTXT:
		rr.Data = &TXT{}
	case TypeAAAA:
		rr.Data = &AAAA{}
	case TypeOPT:
		opt := &OPT{
			UDPSize: rr.Class,
		}
		opt.ExtRCode = uint8(rr.TTL >> 24)
		opt.Version = uint8(rr.TTL >> 16)
		// https://datatracker.ietf.org/doc/html/rfc3225
		// https://datatracker.ietf.org/doc/html/rfc4035
		opt.DO = rr.TTL&0x8000 != 0
		opt.Z = uint16(rr.TTL & 0x7FFF)
		rr.Data = opt
	default:
		rr.Data = &Unknown{RRType: rr.Type}
	}

	if err := rr.Data.Unpack(u, rdlength); err != nil {
		return rr, err
	}
	if u.off != rdStart+int(rdlength) {
		return rr, fmt.Errorf("dns: rdata length mismatch")
	}
	return rr, nil
}

func (rr *RR) pack(p *packer) error {
	if err := p.writeName(rr.Name); err != nil {
		return err
	}
	p.writeUint16(rr.Type)
	p.writeUint16(rr.Class)
	p.writeUint32(rr.TTL)

	rdlenOff := len(p.buf)
	p.buf = append(p.buf, 0, 0)
	rdStart := len(p.buf)

	if err := rr.Data.Pack(p); err != nil {
		return err
	}

	rdlen := uint16(len(p.buf) - rdStart)
	p.buf[rdlenOff] = byte(rdlen >> 8)
	p.buf[rdlenOff+1] = byte(rdlen)
	return nil
}