You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: store.go
    path of file: ./repos/learning/golang/practice/go-crontab/gopath/src/github.com/coreos/etcd/etcdserver/api/v2store
    
    the code of the file until where you have to start completion: // Copyright 2015 The etcd 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 b
    
func (s *store) CompareAndDelete(nodePath string, prevValue string, prevIndex uint64) (*Event, error) {
	var err *v2error.Error

	s.worldLock.Lock()
	defer s.worldLock.Unlock()

	defer func() {
		if err == nil {
			s.Stats.Inc(CompareAndDeleteSuccess)
			reportWriteSuccess(CompareAndDelete)
			return
		}

		s.Stats.Inc(CompareAndDeleteFail)
		reportWriteFailure(CompareAndDelete)
	}()

	nodePath = path.Clean(path.Join("/", nodePath))

	n, err := s.internalGet(nodePath)
	if err != nil { // if the node does not exist, return error
		return nil, err
	}
	if n.IsDir() { // can only compare and delete file
		return nil, v2error.NewError(v2error.EcodeNotFile, nodePath, s.CurrentIndex)
	}

	// If both of the prevValue and prevIndex are given, we will test both of them.
	// Command will be executed, only if both of the tests are successful.
	if ok, which := n.Compare(prevValue, prevIndex); !ok {
		cause := getCompareFailCause(n, which, prevValue, prevIndex)
		return nil, v2error.NewError(v2error.EcodeTestFailed, cause, s.CurrentIndex)
	}

	// update etcd index
	s.CurrentIndex++

	e := newEvent(CompareAndDelete, nodePath, s.CurrentIndex, n.CreatedIndex)
	e.EtcdIndex = s.CurrentIndex
	e.PrevNode = n.Repr(false, false, s.clock)

	callback := func(path string) { // notify function
		// notify the watchers with deleted set true
		s.WatcherHub.notifyWatchers(e, path, true)
	}

	err = n.Remove(false, false, callback)
	if err != nil {
		return nil, err
	}

	s.WatcherHub.notify(e)

	return e, nil
}