// Copyright 2015 PingCAP, Inc.
//
// 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,
// See the License for the specific language governing permissions and
// limitations under the License.

package kv

import "math"

// VersionProvider provides increasing IDs.
type VersionProvider interface {
	CurrentVersion() (Version, error)
}

// Version is the wrapper of KV's version.
type Version struct {
	Ver uint64
}

var (
	// MaxVersion is the maximum version, notice that it's not a valid version.
	MaxVersion = Version{Ver: math.MaxUint64}
	// MinVersion is the minimum version, it's not a valid version, too.
	MinVersion = Version{Ver: 0}
)

// NewVersion creates a new Version struct.
func NewVersion(v uint64) Version {
	return Version{
		Ver: v,
	}
}

// Cmp returns the comparison result of two versions.
// The result will be 0 if a==b, -1 if a < b, and +1 if a > b.
func (v Version) Cmp(another Version) int {
	if v.Ver > another.Ver {
		return 1
	} else if v.Ver < another.Ver {
		return -1
	}
	return 0
}