package layer
 
 import (
 	"fmt"
 	"io/ioutil"
 	"os"
 	"strings"
 )
 

 // setOS writes the "os" file to the layer filestore
 func (fm *fileMetadataTransaction) setOS(os string) error {

 	if os == "" {

 		return nil
 	}

 	return fm.ws.WriteFile("os", []byte(os), 0644)

 }
 

 // getOS reads the "os" file from the layer filestore
 func (fms *fileMetadataStore) getOS(layer ChainID) (string, error) {

 	contentBytes, err := ioutil.ReadFile(fms.getLayerFilename(layer, "os"))

 	if err != nil {

 		// For backwards compatibility, the os file may not exist. Default to "windows" if missing.

 		if os.IsNotExist(err) {
 			return "windows", nil
 		}
 		return "", err
 	}
 	content := strings.TrimSpace(string(contentBytes))
 
 	if content != "windows" && content != "linux" {

 		return "", fmt.Errorf("invalid operating system value: %s", content)

 	}
 

 	return content, nil

 }