vendor/github.com/apigee-labs/transicator/storage/comparator.go

/*
Copyright 2016 The Transicator Authors

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/
package storage

import (
	"fmt"
	"github.com/apigee-labs/transicator/common"
	"strings"
)

// Comparator names are persisted so should be consistent
const (
	EntryComparatorName    = "transicator-entries-v1"
	SequenceComparatorName = "transicator-sequence-v1"
)

var entryComparator = new(entryCmp)
var sequenceComparator = new(sequenceCmp)

type entryCmp struct {
}

/*
Compare tests the order of two keys in the "entries" collection. Keys are sorted
primarily in scope order, then by LSN, then by index within the LSN. This
allows searches to be linear for a given scope.
*/
func (c entryCmp) Compare(a, b []byte) int {
	aScope, aLsn, aIndex, err := keyToLsnAndOffset(a)
	if err != nil {
		panic(fmt.Sprintf("Error parsing database key: %s", err))
	}
	bScope, bLsn, bIndex, err := keyToLsnAndOffset(b)
	if err != nil {
		panic(fmt.Sprintf("Error parsing database key: %s", err))
	}

	scopeCmp := strings.Compare(aScope, bScope)
	if scopeCmp == 0 {
		if aLsn < bLsn {
			return -1
		} else if aLsn > bLsn {
			return 1
		}

		if aIndex < bIndex {
			return -1
		} else if aIndex > bIndex {
			return 1
		}
		return 0
	}
	return scopeCmp
}

/*
Name is part of the comparator interface.
*/
func (c entryCmp) Name() string {
	return EntryComparatorName
}

type sequenceCmp struct {
}

func (s sequenceCmp) Compare(a, b []byte) int {
	s1, err := common.ParseSequenceBytes(a)
	if err != nil {
		panic(fmt.Sprintf("Error parsing sequence: %s", err))
	}
	s2, err := common.ParseSequenceBytes(b)
	if err != nil {
		panic(fmt.Sprintf("Error parsing sequence: %s", err))
	}

	return s1.Compare(s2)
}

func (s sequenceCmp) Name() string {
	return SequenceComparatorName
}