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qry.go
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qry.go
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// SPDX-FileCopyrightText: 2021 The margaret Authors
//
// SPDX-License-Identifier: MIT
package roaring
import (
"context"
"fmt"
"strings"
"go.cryptoscope.co/luigi"
"go.cryptoscope.co/margaret"
)
type query struct {
log *sublog
nextSeq, lt int64
limit int
live bool
reverse bool
seqWrap bool
}
func (qry *query) Gt(s int64) error {
if qry.nextSeq > margaret.SeqEmpty {
return fmt.Errorf("lower bound already set")
}
qry.nextSeq = s + 1
return nil
}
func (qry *query) Gte(s int64) error {
if qry.nextSeq > margaret.SeqEmpty {
return fmt.Errorf("lower bound already set")
}
qry.nextSeq = s
return nil
}
func (qry *query) Lt(s int64) error {
if qry.lt != margaret.SeqEmpty {
return fmt.Errorf("upper bound already set")
}
qry.lt = s
return nil
}
func (qry *query) Lte(s int64) error {
if qry.lt != margaret.SeqEmpty {
return fmt.Errorf("upper bound already set")
}
qry.lt = s + 1
return nil
}
func (qry *query) Limit(n int) error {
qry.limit = n
return nil
}
func (qry *query) Live(live bool) error {
qry.live = live
return nil
}
func (qry *query) SeqWrap(wrap bool) error {
qry.seqWrap = wrap
return nil
}
func (qry *query) Reverse(rev bool) error {
qry.reverse = rev
if rev {
qry.nextSeq = qry.log.seq.Seq() - 1
}
return nil
}
func (qry *query) Next(ctx context.Context) (interface{}, error) {
qry.log.mlog.l.Lock()
if qry.limit == 0 {
qry.log.mlog.l.Unlock()
return nil, luigi.EOS{}
}
qry.limit--
if qry.nextSeq == margaret.SeqEmpty {
if qry.reverse {
qry.log.mlog.l.Unlock()
return nil, luigi.EOS{}
}
qry.nextSeq = 0
}
if qry.lt != margaret.SeqEmpty {
if qry.nextSeq >= qry.lt {
qry.log.mlog.l.Unlock()
return nil, luigi.EOS{}
}
}
var v interface{}
seqVal, err := qry.log.bmap.Select(uint64(qry.nextSeq))
v = int64(seqVal)
if err != nil {
if !strings.Contains(err.Error(), " is not less than the cardinality:") {
qry.log.mlog.l.Unlock()
return nil, fmt.Errorf("roaringfiles/qry: error in read transaction (%T): %w", err, err)
}
// key not found, so we reached the end
// abort if not a live query, else wait until it's written
if !qry.live {
qry.log.mlog.l.Unlock()
return nil, luigi.EOS{}
}
return qry.livequery(ctx)
}
if qry.seqWrap {
v = margaret.WrapWithSeq(v, qry.nextSeq)
if qry.reverse {
qry.nextSeq--
} else {
qry.nextSeq++
}
qry.log.mlog.l.Unlock()
return v, nil
}
if qry.reverse {
qry.nextSeq--
} else {
qry.nextSeq++
}
qry.log.mlog.l.Unlock()
return v, nil
}
func (qry *query) livequery(ctx context.Context) (interface{}, error) {
thisNextSeq := qry.nextSeq
qry.log.mlog.l.Unlock()
var (
v interface{}
err error
)
select {
case <-qry.log.seq.WaitFor(uint64(thisNextSeq)):
v, err = qry.log.Get(thisNextSeq)
if !qry.seqWrap { // simpler to have two +1's here then a defer
qry.nextSeq++
}
case <-ctx.Done():
err = fmt.Errorf("cancelled while waiting for value to be written: %w", ctx.Err())
}
if err != nil {
return nil, fmt.Errorf("livequery failed to retreive value: %w", err)
}
if qry.seqWrap {
v = margaret.WrapWithSeq(v, qry.nextSeq)
qry.nextSeq++
return v, nil
}
return v, err
}