// Copyright (C) 2014-2018 Goodrain Co., Ltd.
// RAINBOND, Application Management Platform

// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version. For any non-GPL usage of Rainbond,
// one or multiple Commercial Licenses authorized by Goodrain Co., Ltd.
// must be obtained first.

// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with this program. If not, see <http://www.gnu.org/licenses/>.

package etcd

import (
	"errors"

	v3 "github.com/coreos/etcd/clientv3"
	spb "github.com/coreos/etcd/mvcc/mvccpb"
	"golang.org/x/net/context"
)

var (
	ErrKeyExists      = errors.New("key already exists")
	ErrWaitMismatch   = errors.New("unexpected wait result")
	ErrTooManyClients = errors.New("too many clients")
	ErrNoWatcher      = errors.New("no watcher channel")
)

// deleteRevKey deletes a key by revision, returning false if key is missing
func deleteRevKey(ctx context.Context, kv v3.KV, key string, rev int64) (bool, error) {
	cmp := v3.Compare(v3.ModRevision(key), "=", rev)
	req := v3.OpDelete(key)
	txnresp, err := kv.Txn(ctx).If(cmp).Then(req).Commit()
	if err != nil {
		return false, err
	} else if !txnresp.Succeeded {
		return false, nil
	}
	return true, nil
}

//claimFirstKey 获取队列第一个key,并从队列删除
func claimFirstKey(ctx context.Context, kv v3.KV, kvs []*spb.KeyValue) (*spb.KeyValue, error) {
	for _, k := range kvs {
		ok, err := deleteRevKey(ctx, kv, string(k.Key), k.ModRevision)
		if err != nil {
			return nil, err
		} else if ok {
			return k, nil
		}
	}
	return nil, nil
}