package wal

import (
	"time"

	"git.crumpington.com/public/jldb/lib/errs"
)

type walIterator struct {
	// getSeg should return a segment given its ID, or return nil.
	getSeg func(id int64) (*segment, error)
	seg    *segment // Our current segment.
	it     Iterator // Our current segment iterator.
	seqNum int64
	err    error
}

func newWALIterator(
	getSeg func(id int64) (*segment, error),
	seg *segment,
	fromSeqNum int64,
) (
	*walIterator,
	error,
) {
	segIter, err := seg.Iterator(fromSeqNum)
	if err != nil {
		return nil, err
	}

	return &walIterator{
		getSeg: getSeg,
		seg:    seg,
		it:     segIter,
		seqNum: fromSeqNum,
	}, nil
}

func (it *walIterator) Next(timeout time.Duration) bool {
	if it.err != nil {
		return false
	}

	if it.it.Next(timeout) {
		it.seqNum++
		return true
	}

	it.err = it.it.Error()
	if !errs.EOFArchived.Is(it.err) {
		return false
	}

	it.it.Close()

	id := it.seg.ID + 1
	it.seg, it.err = it.getSeg(id)

	if it.err != nil {
		return false
	}

	if it.seg == nil {
		it.err = errs.NotFound // Could be not-found, or closed.
		return false
	}

	it.it, it.err = it.seg.Iterator(it.seqNum)
	if it.err != nil {
		return false
	}

	return it.Next(timeout)
}

func (it *walIterator) Record() Record {
	return it.it.Record()
}

func (it *walIterator) Error() error {
	return it.err
}

func (it *walIterator) Close() {
	if it.it != nil {
		it.it.Close()
	}
	it.it = nil
}