How to correctly set a fancy header and footer in a included pdf, which contains many pages? - header

Question

Last time I tried to add fancy header and footer in my document, but I'm not happy of it's result. How to correctly set a fancy header and footer in a included pdf, which contains many pages?
My goal, which I want achieve, is: If the number of page is odd, I want to have a header and the number of page on the left side of page, otherwise I want to have it on the right.
Here is my base code:
\documentclass[oneside, a4paper, 12pt]{article}
\usepackage[utf8]{inputenc}
\usepackage{polski}
\usepackage{pdfpages}
\usepackage{changepage}
\usepackage{fancyhdr}
\usepackage[right=2.7cm,left=3.5cm, top=2.7cm, bottom=2.5cm,includehead]{geometry}
\strictpagecheck
\begin{document}
%\setcounter{page}{18}
\includepdf[pages=-,pagecommand={
\ifoddpage
\pagestyle{fancy} \fancyhf{}
\fancyhead[L]{Test of left header}
\fancyfoot[L]{\thepage}
\else
\fancyhead[R]{Test of right footer}
\fancyfoot[R]{\thepage}
\fi}]{scenariusz_wersja_do_edycji.pdf}
\end{document}
I would be glad if somebody knows the solution, because i need it necessarily for the BA thesis!

Answer 1

If you use a twosideed documentclass, then you can let fancyhdr automatically place your header/page number on even/odd pages:
\documentclass[twoside, a4paper, 12pt]{article}
\usepackage[utf8]{inputenc}
\usepackage{polski}
\usepackage{pdfpages}
\usepackage{changepage}
\usepackage{fancyhdr}
\usepackage[right=2.7cm,left=3.5cm, top=2.7cm, bottom=2.5cm,includehead]{geometry}
\strictpagecheck
\setlength{\headheight}{15pt}
\fancypagestyle{mystyle}{%
\fancyhf{}
\fancyhead[LO,RE]{Some header}
\fancyfoot[LO,RE]{\thepage}
}
\begin{document}
%\setcounter{page}{18}
\includepdf[pages=-,pagecommand={
\thispagestyle{mystyle}
}]{example-image-duck}
\end{document}