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: awsparamstore.go
    path of file: ./repos/go-cloud/runtimevar/awsparamstore
    
    the code of the file until where you have to start completion: // Copyright 2018 The Go Cloud Development Kit 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
//
//     https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required b
    
func (w *watcher) WatchVariable(ctx context.Context, prev driver.State) (driver.State, time.Duration) {
	lastVersion := int64(-1)
	if prev != nil {
		lastVersion = prev.(*state).version
	}
	var svc *ssm.SSM
	if !w.useV2 {
		svc = ssm.New(w.sess)
	}

	// GetParameter from S3 to get the current value and version.
	var newVersion int64
	var newVal []byte
	var newLastModified time.Time
	var rawGetV1 *ssm.GetParameterOutput
	var rawGetV2 *ssmv2.GetParameterOutput
	var err error
	if w.useV2 {
		newVersion, newVal, newLastModified, rawGetV2, err = getParameterV2(ctx, w.clientV2, w.name)
	} else {
		newVersion, newVal, newLastModified, rawGetV1, err = getParameter(svc, w.name)
	}
	if err != nil {
		return errorState(err, prev), w.wait
	}
	if newVersion == lastVersion {
		// Version hasn't changed, so no change; return nil.
		return nil, w.wait
	}

	// New value (or at least, new version). Decode it.
	val, err := w.decoder.Decode(ctx, newVal)
	if err != nil {
		return errorState(err, prev), w.wait
	}
	return &state{
		val:        val,
		rawGetV1:   rawGetV1,
		rawGetV2:   rawGetV2,
		updateTime: newLastModified,
		version:    newVersion,
	}, w.wait
}