package wal

import "encoding/binary"

type segmentHeader struct {
	CreatedAt       int64
	ArchivedAt      int64
	FirstSeqNum     int64
	LastSeqNum      int64 // FirstSeqNum - 1  if empty.
	LastTimestampMS int64 // 0 if empty.
	InsertAt        int64
}

func (h segmentHeader) WriteTo(b []byte) {
	vals := []int64{
		h.CreatedAt,
		h.ArchivedAt,
		h.FirstSeqNum,
		h.LastSeqNum,
		h.LastTimestampMS,
		h.InsertAt,
	}

	for _, val := range vals {
		binary.LittleEndian.PutUint64(b[0:8], uint64(val))
		b = b[8:]
	}
}

func (h *segmentHeader) ReadFrom(b []byte) {
	ptrs := []*int64{
		&h.CreatedAt,
		&h.ArchivedAt,
		&h.FirstSeqNum,
		&h.LastSeqNum,
		&h.LastTimestampMS,
		&h.InsertAt,
	}

	for _, ptr := range ptrs {
		*ptr = int64(binary.LittleEndian.Uint64(b[0:8]))
		b = b[8:]
	}
}