move from article to book, improve headers

lecture.cls

@@ -1,5 +1,5 @@
 \ProvidesClass{lecture}
-\LoadClass[a4paper, titlepage]{article}
+\LoadClass[a4paper]{book}
 
 \RequirePackage[utf8]{inputenc}
 \RequirePackage[T1]{fontenc}
@@ -7,7 +7,6 @@
 \RequirePackage[german]{babel}
 \RequirePackage{amsmath, amssymb, amsthm}
 \RequirePackage{mdframed}
-\RequirePackage{fancyhdr}
 \RequirePackage{geometry}
 \RequirePackage{import}
 \RequirePackage{pdfpages}
@@ -17,7 +16,7 @@
 \RequirePackage[shortlabels]{enumitem}
 \RequirePackage{tikz}
 \RequirePackage{pgfplots}
-\RequirePackage[nobottomtitles]{titlesec}
+\RequirePackage[pagestyles, nobottomtitles]{titlesec}
 \RequirePackage{listings}
 \RequirePackage{mathtools}
 \RequirePackage{forloop}
@@ -25,7 +24,7 @@
 
 \usetikzlibrary{quotes, angles}
 
-\DeclareOption*{\PassOptionsToClass{\CurrentOption}{article}}
+%\DeclareOption*{\PassOptionsToClass{\CurrentOption}{article}}
 \DeclareOption{uebung}{
     \makeatletter
     \lhead{\@title}
@@ -34,14 +33,6 @@
 }
 \ProcessOptions\relax
 
-% PAGE GEOMETRY
-\geometry{
-    left=15mm,
-    right=40mm,
-    top=20mm,
-    bottom=20mm
-}
-
 % PARAGRAPH no indent but skip
 \setlength{\parskip}{3mm}
 \setlength{\parindent}{0mm}
@@ -67,7 +58,16 @@
 
 % HEADERS
 
-\pagestyle{fancy}
+%\newpagestyle{main}[\small]{
+%  \setheadrule{.55pt}%
+%  \sethead[\thepage]%  even-left
+%          []%                              even-center
+%          [\thechapter~\chaptertitle]%     even-right
+%          {\thesection~\sectiontitle}%     odd-left
+%          {}%                              odd-center
+%          {\thepage}%  odd-right
+%}
+%\pagestyle{main}
 
 \newcommand{\incfig}[1]{%
     \def\svgwidth{\columnwidth}
@@ -134,3 +134,6 @@
 \makeatletter \renewcommand\d[1]{\ensuremath{%
   \;\mathrm{d}#1\@ifnextchar\d{\!}{}}}
 \makeatother
+
+% remove page before chapters
+\let\cleardoublepage=\clearpage