package kafka

import (
	"encoding/binary"
	"errors"
	"math"
)

type packetDecoder struct {
	raw []byte
	off int
}

func (pd *packetDecoder) avail() int {
	return len(pd.raw) - pd.off
}

func (pd *packetDecoder) getInt16() (int16, error) {
	if pd.avail() < 2 {
		return -1, errors.New("kafka getInt16: not enough data")
	}
	tmp := int16(binary.BigEndian.Uint16(pd.raw[pd.off:]))
	pd.off += 2
	return tmp, nil
}

func (pd *packetDecoder) getInt32() (int32, error) {
	if pd.avail() < 4 {
		return -1, errors.New("kafka getInt32: not enough data")
	}
	tmp := int32(binary.BigEndian.Uint32(pd.raw[pd.off:]))
	pd.off += 4
	return tmp, nil
}

func (pd *packetDecoder) getArrayCount() (int, error) {
	if pd.avail() < 4 {
		return -1, errors.New("kafka getArrayCount: not enough data")
	}
	tmp := int(binary.BigEndian.Uint32(pd.raw[pd.off:]))
	pd.off += 4
	if tmp > pd.avail() || tmp > 2*math.MaxUint16 {
		return -1, errors.New("kafka getArrayCount: unreasonably long array")
	}
	return tmp, nil
}

func (pd *packetDecoder) getError() (kafkaError, error) {
	val, err := pd.getInt16()
	return kafkaError(val), err
}

func (pd *packetDecoder) getString() (*string, error) {
	tmp, err := pd.getInt16()

	if err != nil {
		return nil, err
	}

	n := int(tmp)

	switch {
	case n < -1:
		return nil, errors.New("kafka getString: invalid negative length")
	case n == -1:
		return nil, nil
	case n == 0:
		return new(string), nil
	case n > pd.avail():
		return nil, errors.New("kafka getString: not enough data")
	default:
		tmp := new(string)
		*tmp = string(pd.raw[pd.off : pd.off+n])
		return tmp, nil
	}
}