I'm trying to define a command which creates a part/chapter/section/subsection/... depending on the last defined part/chapter/section/subsection/...

It should look like this pseudo code:

```
global string currentSection;

function level(arg, sectioningArgs ...) { 
  switch(arg) {
    case '+' {
      switch(currentSection) {
        case 'none' {
          \part(sectioningArgs)
        }
        case 'part' {
          \chapter(sectioningArgs)
        }
        case 'chapter' {
          \section(sectioningArgs)
        }
        ...
      }
    }
    case '-' {
      ...
    }      
    case '0' {
      ...
    }
  }
}

```

(just imagine a 'break' after each case ...)

The usage should be like follows:

```
\documentclass[a4paper,12pt,oneside]{book}

\newcommand{\level}[<?>]{<?>}

\begin{document}
  \level{+}{A part}
  \level{+}{A chapter}
  \level{+}{A section}
  \level{0}{Another section}
  \level{-}{A chapter}
  \level{-}{A part}
\end{document}

```

Rationale: I often find myself changing subsections to sections and so on in subfiles I include in my main document --- this should automate the process.

Any help is greatly appreciated, thank you in advance.