pair.go

package cutedb

import "encoding/binary"
import "fmt"

// 2+2+30+90 = 127
const pairSize = 124
const maxKeyLength = 30
const maxValueLength = 93

type pairs struct {
	keyLen   uint16 // 2
	valueLen uint16 // 2
	key      string // 30
	value    string // 93
}

func (p *pairs) setKey(key string) {
	p.key = key
	p.keyLen = uint16(len(key))
}

func (p *pairs) setValue(value string) {
	p.value = value
	p.valueLen = uint16(len(value))
}

func (p *pairs) validate() error {
	if len(p.key) > maxKeyLength {
		return fmt.Errorf("key length should not be more than 30, currently it is %d ", len(p.key))
	}
	if len(p.value) > maxValueLength {
		return fmt.Errorf("value length should not be more than 93, currently it is %d", len(p.value))
	}
	return nil
}

func newPair(key string, value string) *pairs {
	pair := new(pairs)
	pair.setKey(key)
	pair.setValue(value)
	return pair
}

func convertPairsToBytes(pair *pairs) []byte {
	pairByte := make([]byte, pairSize)
	var pairOffset uint16
	pairOffset = 0
	copy(pairByte[pairOffset:], uint16ToBytes(pair.keyLen))
	pairOffset += 2
	copy(pairByte[pairOffset:], uint16ToBytes(pair.valueLen))
	pairOffset += 2
	keyByte := []byte(pair.key)
	copy(pairByte[pairOffset:], keyByte[:pair.keyLen])
	pairOffset += pair.keyLen
	valueByte := []byte(pair.value)
	copy(pairByte[pairOffset:], valueByte[:pair.valueLen])
	return pairByte
}

func convertBytesToPair(pairByte []byte) *pairs {
	pair := new(pairs)
	var pairOffset uint16
	pairOffset = 0
	//Read key length
	pair.keyLen = uint16FromBytes(pairByte[pairOffset:])
	pairOffset += 2
	//Read value length
	pair.valueLen = uint16FromBytes(pairByte[pairOffset:])
	pairOffset += 2
	pair.key = string(pairByte[pairOffset : pairOffset+pair.keyLen])
	pairOffset += pair.keyLen
	pair.value = string(pairByte[pairOffset : pairOffset+pair.valueLen])
	return pair
}

func uint16FromBytes(b []byte) uint16 {
	i := uint16(binary.LittleEndian.Uint64(b))
	return i
}

func uint16ToBytes(value uint16) []byte {
	b := make([]byte, 2)
	binary.LittleEndian.PutUint16(b, uint16(value))
	return b
}