[Tex/LaTex] rotate table (90 degrees) and stretch to fill whole page

adjustboxrotatingtables

I'd like to rotate a table (90 degrees) and stretch it to fill whole page.

That's what I've got so far: 

\documentclass{book}

\usepackage{tabularx}
\usepackage{adjustbox}

\begin{document}

\pagestyle{empty}

\begin{adjustbox}{angle=90}
  \begin{tabularx}{\textheight}{|X|X|X|X|X|X|X|X|X|X|X|X|}
      1 & 2 & 3 & 4 & 5 & 6 & 7 & 8 & 9 & 10 & 11 & 12 \\
        \hline
        1 & 2 & 3 & 4 & 5 & 6 & 7 & 8 & 9 & 10 & 11 & 12 
  \end{tabularx}
\end{adjustbox}

\end{document}

I don't know how to stretch the height of the table therewith it fills the page (horizontally).

Is there any possibility to reduce the size of the font automatically if one text is wider than its cell?

edit:
I probably didn't express myself very well. The table should look like this:

Best Answer

Is it like this?

\documentclass{book}

\usepackage{tabularx}
\usepackage{adjustbox}
\usepackage{showframe}

\begin{document}

\pagestyle{empty}
\hfill
\begin{adjustbox}{angle=90}    
  \begin{tabularx}{\textheight}{|X|X|X|X|X|X|X|X|X|X|X|X|}
      1 & 2 & 3 & 4 & 5 & 6 & 7 & 8 & 9 & 10 & 11 & 12 \\
        \hline
        1 & 2 & 3 & 4 & 5 & 6 & 7 & 8 & 9 & 10 & 11 & 12
  \end{tabularx}%
\end{adjustbox}
\hfill
\null

\end{document}

enter image description here

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