system

type CmdRunner interface {
	// RunComplexCommand returns error as nil:
	//  - command runs and exits with a zero exit status
	// RunComplexCommand returns error:
	//  - command runs and exits with a non-zero exit status
	//  - command does not run
	RunComplexCommand(cmd Command) (stdout, stderr string, exitStatus int, err error)

	RunComplexCommandAsync(cmd Command) (Process, error)

	RunCommand(cmdName string, args ...string) (stdout, stderr string, exitStatus int, err error)

	RunCommandWithInput(input, cmdName string, args ...string) (stdout, stderr string, exitStatus int, err error)

	CommandExists(cmdName string) (exists bool)
}

type Command struct {
	Name           string
	Args           []string
	Env            map[string]string
	UseIsolatedEnv bool

	WorkingDir string

	Stdin io.Reader

	// Full stdout and stderr will be captured to memory
	// and returned in the Result unless custom Stdout/Stderr are specified.
	Stdout io.Writer
	Stderr io.Writer
}

type ExecError struct {
	Command string
	StdOut  string
	StdErr  string
}

type File interface {
	io.ReadWriteCloser
	ReadAt([]byte, int64) (int, error)
	Stat() (os.FileInfo, error)
	Name() string
}

type FileSystem interface {
	HomeDir(username string) (path string, err error)
	ExpandPath(path string) (expandedPath string, err error)

	// MkdirAll will not change existing dir permissions
	// if dir exists and has different permissions
	MkdirAll(path string, perm os.FileMode) error
	RemoveAll(fileOrDir string) error

	Chown(path, username string) error
	Chmod(path string, perm os.FileMode) error

	OpenFile(path string, flag int, perm os.FileMode) (File, error)

	WriteFileString(path, content string) error
	WriteFile(path string, content []byte) error
	ConvergeFileContents(path string, content []byte) (written bool, err error)

	ReadFileString(path string) (content string, err error)
	ReadFile(path string) (content []byte, err error)

	FileExists(path string) bool

	Rename(oldPath, newPath string) error

	// After Symlink file at newPath will be pointing to file at oldPath.
	// Symlink call will remove file at newPath if one exists
	// to make newPath a symlink to the file at oldPath.
	Symlink(oldPath, newPath string) error
	ReadLink(symlinkPath string) (targetPath string, err error)

	CopyFile(srcPath, dstPath string) error
	CopyDir(srcPath, dstPath string) error

	// Returns *unique* temporary file/dir with a custom prefix
	TempFile(prefix string) (file File, err error)
	TempDir(prefix string) (path string, err error)

	Glob(pattern string) (matches []string, err error)
	Walk(root string, walkFunc filepath.WalkFunc) error
}

type Process interface {
	// Wait is the only way to get back process result information.
	// It must not be called multiple times.
	Wait() <-chan Result

	// TerminateNicely can be called multiple times.
	// It must only be called after Wait().
	TerminateNicely(killGracePeriod time.Duration) error
}

type Result struct {
	// Full stdout and stderr are captured to memory
	Stdout string
	Stderr string

	ExitStatus int
	Error      error
}