/*
   Copyright 2014 CoreOS, 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,
   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 wal

import (
	"fmt"
	"log"
	"os"
	"path"

	"github.com/coreos/etcd/pkg/types"
)

// WalVersion is an enum for versions of etcd logs.
type WalVersion string

const (
	WALUnknown  WalVersion = "Unknown WAL"
	WALNotExist WalVersion = "No WAL"
	WALv0_4     WalVersion = "0.4.x"
	WALv0_5     WalVersion = "0.5.x"
)

func DetectVersion(dirpath string) WalVersion {
	names, err := readDir(dirpath)
	if err != nil || len(names) == 0 {
		return WALNotExist
	}
	nameSet := types.NewUnsafeSet(names...)
	if nameSet.ContainsAll([]string{"snap", "wal"}) {
		// .../wal cannot be empty to exist.
		if Exist(path.Join(dirpath, "wal")) {
			return WALv0_5
		}
		return WALNotExist
	}
	if nameSet.ContainsAll([]string{"snapshot", "conf", "log"}) {
		return WALv0_4
	}

	return WALUnknown
}

func Exist(dirpath string) bool {
	names, err := readDir(dirpath)
	if err != nil {
		return false
	}
	return len(names) != 0
}

// searchIndex returns the last array index of names whose raft index section is
// equal to or smaller than the given index.
// The given names MUST be sorted.
func searchIndex(names []string, index uint64) (int, bool) {
	for i := len(names) - 1; i >= 0; i-- {
		name := names[i]
		_, curIndex, err := parseWalName(name)
		if err != nil {
			log.Panicf("parse correct name should never fail: %v", err)
		}
		if index >= curIndex {
			return i, true
		}
	}
	return -1, false
}

// names should have been sorted based on sequence number.
// isValidSeq checks whether seq increases continuously.
func isValidSeq(names []string) bool {
	var lastSeq uint64
	for _, name := range names {
		curSeq, _, err := parseWalName(name)
		if err != nil {
			log.Panicf("parse correct name should never fail: %v", err)
		}
		if lastSeq != 0 && lastSeq != curSeq-1 {
			return false
		}
		lastSeq = curSeq
	}
	return true
}

// readDir returns the filenames in wal directory.
func readDir(dirpath string) ([]string, error) {
	dir, err := os.Open(dirpath)
	if err != nil {
		return nil, err
	}
	defer dir.Close()
	names, err := dir.Readdirnames(-1)
	if err != nil {
		return nil, err
	}
	return names, nil
}

func checkWalNames(names []string) []string {
	wnames := make([]string, 0)
	for _, name := range names {
		if _, _, err := parseWalName(name); err != nil {
			log.Printf("wal: parse %s error: %v", name, err)
			continue
		}
		wnames = append(wnames, name)
	}
	return wnames
}

func parseWalName(str string) (seq, index uint64, err error) {
	var num int
	num, err = fmt.Sscanf(str, "%016x-%016x.wal", &seq, &index)
	if num != 2 && err == nil {
		err = fmt.Errorf("bad wal name: %s", str)
	}
	return
}

func walName(seq, index uint64) string {
	return fmt.Sprintf("%016x-%016x.wal", seq, index)
}

func max(a, b int64) int64 {
	if a > b {
		return a
	}
	return b
}