package pdu

import (
	"encoding/binary"
	"fmt"
)

type (
	PDU interface {
		EncodeInto(*[]uint8)
		Encode() []uint8
		Decode([]uint8)
		// Size in bytes
		Size() uint32
	}

	PDU_HEADER struct {
		command_length  uint32
		command_id      uint32
		command_status  uint32
		sequence_number uint32
	}

	GENERIC_NACK struct {
		PDU_HEADER
	}
)

func (p *PDU_HEADER) Encode() ([]uint8, error) {
	buf := make([]uint8, 16)
	binary.BigEndian.PutUint32(buf[0:4], p.command_length)
	binary.BigEndian.PutUint32(buf[4:8], p.command_id)
	binary.BigEndian.PutUint32(buf[8:12], p.command_status)
	binary.BigEndian.PutUint32(buf[12:16], p.sequence_number)
	return buf, nil
}
func (p *PDU_HEADER) EncodeInto(buf *[]uint8) error {
	if buf == nil {
		return fmt.Errorf("cannot encode PDU_HEADER, buffer is nil")
	}
	if len(*buf) < 16 {
		return fmt.Errorf("cannot encode PDU_HEADER, buffer too small (%d, required 16)", len(*buf))
	}
	bufVal := *buf
	binary.BigEndian.PutUint32(bufVal[0:4], p.command_length)
	binary.BigEndian.PutUint32(bufVal[4:8], p.command_id)
	binary.BigEndian.PutUint32(bufVal[8:12], p.command_status)
	binary.BigEndian.PutUint32(bufVal[12:16], p.sequence_number)
	return nil
}
func (p *PDU_HEADER) Decode(data []uint8) error {
	if len(data) >= 4 {
		p.command_length = binary.BigEndian.Uint32(data[0:4])
	}
	if len(data) >= 8 {
		p.command_id = binary.BigEndian.Uint32(data[4:8])
	}
	if len(data) >= 12 {
		p.command_status = binary.BigEndian.Uint32(data[8:12])

	}
	if len(data) >= 16 {
		p.sequence_number = binary.BigEndian.Uint32(data[12:16])
	}
	return nil
}
func (p *PDU_HEADER) Size() uint32 {
	return 16
}