Tufte style table of contents in article class

Question

I want to create a tufte-book style ToC, very similar to how Gonzalo Medina made something in this request: Pretty Table of Contents

So far this is what I got:

\documentclass[letterpaper]{article}
\usepackage{geometry}
\usepackage{xcolor}
\usepackage{amsmath}
\usepackage[some]{background}
\usepackage{lipsum}
\usepackage{tikz}
\usetikzlibrary{shadows}

\definecolor{col2}{HTML}{80B2FF}

\DeclareFixedFont{\bigsf}{T1}{phv}{b}{n}{1.5cm}

\backgroundsetup{
scale=1,
angle=0,
opacity=1,
contents={\begin{tikzpicture}[remember picture,overlay]
 \path [fill=col2] (-0.5\paperwidth,5) rectangle (0.5\paperwidth,10);  
\end{tikzpicture}}
}
\begin{document}
\begin{titlepage}
\BgThispage
\newgeometry{left=1cm,right=4cm}
\vspace*{2cm}
\noindent
\textcolor{white}{\bigsf Reader analyse}   \begin{tikzpicture}[overlay]
    \def\nodeshadowed[#1]#2;{\node[scale=6,above,#1]{#2};\node[scale=6,
        above,#1,yscale=-1,scope fading=south,opacity=0.3]{#2};}
    \nodeshadowed [at={(4.5,-.5  )},yslant=-.08]
        {\Huge \textcolor{blue}{R}};
  \end{tikzpicture}
\vspace*{2.5cm}\par
\noindent
\begin{minipage}{0.35\linewidth}
    \begin{flushright}
I wish the chapter numbers were here
    \end{flushright}
\end{minipage} \hspace{15pt}
%
\begin{minipage}{0.02\linewidth}
    \textcolor{col2}{\rule{1pt}{300pt}}
\end{minipage} \hspace{-10pt}
%
\begin{minipage}{0.6\linewidth}
\vspace{5pt}
I wish the chapter titles were here
\end{minipage}
\end{titlepage}
\restoregeometry
\lipsum[1-2]
\end{document}

Any way of achieving the same effect as the example below, but instead in article class:

\documentclass{tufte-book}
\usepackage{lmodern}
\usepackage{tikzpagenodes}
\usetikzlibrary{calc}

\newcounter{chapmark}
\setcounter{tocdepth}{1}

\colorlet{mycolor}{BrickRed}

\titlecontents{chapter}%
  [0em]
  {\vspace{1.5\baselineskip}\begin{fullwidth}\LARGE\rmfamily\itshape}
  {\hspace*{0em}\thecontentslabel}
  {\hspace*{0em}\llap{%
    \parbox[b]{40pt}{%
      \fontsize{25}{30}\sffamily\bfseries\color{mycolor}%
      \hfill\thecontentspage%
      }\hspace{20pt}%
    }%
  }
  {\rmfamily\upshape\qquad}
  [\end{fullwidth}]

\titlecontents{section}
  [0em]
  {\vspace{0\baselineskip}\begin{fullwidth}\Large\rmfamily\itshape}
  {\hspace*{0em}\contentslabel{2em}}
  {\llap{\parbox[b]{40pt}{\hfill\thecontentspage}\hspace{20pt}}\hspace*{0em}}
  {\rmfamily\upshape\qquad}
  [\end{fullwidth}]

\titlecontents{subsection}
  [0em]
  {\vspace{-.15\baselineskip}\begin{fullwidth}\large\rmfamily\itshape}
  {\hspace*{0em}\contentslabel{4em}}
  {\llap{\parbox[b]{40pt}{\hfill\small\thecontentspage}\hspace{20pt}}\hspace*{0em}}
  {\rmfamily\upshape}
  [\end{fullwidth}] 

\newcommand\StartMark{%
\addtocontents{toc}{\protect\label{st\thechapmark}%
\par\protect\begin{tikzpicture}[overlay,remember picture,baseline]   
  \protect\node [anchor=base] (s\thechapmark) {};%
  \ifnum\getpagerefnumber{st\thechapmark}=\getpagerefnumber{en\thechapmark}   
  \else
    \protect\draw[mycolor,line width=3pt] 
      let \protect\p3= (s\thechapmark),%
            \protect\p4 = (current page text area.south) in %
      ( $ (0em,\protect\y3) + (-20pt,-5ex) $ ) -- 
      ( $ (0em,\protect\y4) + (-20pt,-5pt) $ );
  \fi
\protect\end{tikzpicture}\par}%
}

\newcommand\EndMark{%
\addtocontents{toc}{\protect\label{en\thechapmark}%
\par\protect\begin{tikzpicture}[overlay,remember picture,baseline]   
  \protect\node [anchor=base] (e\thechapmark) {};
  \ifnum\getpagerefnumber{st\thechapmark}=\getpagerefnumber{en\thechapmark} 
    \protect\draw[mycolor,line width=3pt] 
    let \protect\p1= (s\thechapmark), 
          \protect\p2=(e\thechapmark) in %
    ( $ (0em,\protect\y1) + (-20pt,-5ex) $ ) -- 
    ( $ (0em,\protect\y2) + (-20pt,2ex) $ );
  \else%
  \protect\draw[mycolor,line width=3pt] 
  let \protect\p1= (e\thechapmark), 
        \protect\p2=(current page text area.north) in 
  ( $ (0em,\protect\y2) + (-20pt,5pt) $ ) -- 
  ( $ (0em,\protect\y1) + (-20pt,2ex) $ );
  \fi
\protect\end{tikzpicture}\par}%
\stepcounter{chapmark}%
}

\setcounter{page}{123}% just for the example

\begin{document}

\tableofcontents

\StartMark
\chapter{Beginning to learn design with \LaTeX}
\section{This is a test section}
\section{This is a test section}
\section{This is a test section}
\section{This is a test section}
\section{This is a test section}
\EndMark

\StartMark
\chapter{Beginning to learn design with HTML}
\section{This is a test section}
\section{This is a test section}
\section{This is a test section}
\EndMark

\StartMark
\chapter{Beginning to learn design with \LaTeX\ again}
\section{This is a test section}
\section{This is a test section}
\section{This is a test section}
\section{This is a test section}
\section{This is a test section}
\section{This is a test section}
\section{This is a test section}
\section{This is a test section}
\section{This is a test section}
\EndMark

\StartMark
\chapter{Beginning to learn design with \LaTeX\ again}
\section{This is a test section}
\section{This is a test section}
\section{This is a test section}
\EndMark

\end{document}

Answer 1

Here's one possibility:

\documentclass[dvipsnames,svgnames,x11names]{article}
\usepackage{refcount}
\usepackage{titletoc}
\usepackage{tikzpagenodes}
\usetikzlibrary{calc}

\newcounter{chapmark}
%\setcounter{tocdepth}{1}

\colorlet{mycolor}{BrickRed}

\titlecontents{section}%
  [0em]
  {\vspace{1.5\baselineskip}\LARGE\rmfamily\itshape}
  {\hspace*{0em}\llap{\parbox[t]{40pt}{\hfill\color{mycolor}\thecontentspage}\hspace*{10pt}}}
  {\thecontentspage}
  {\rmfamily\upshape\qquad}

\titlecontents{subsection}%
  [0em]
  {\vspace{.3\baselineskip}\large\rmfamily\itshape}
  {\hspace*{0em}\llap{\parbox[t]{40pt}{\hfill\color{mycolor}\thecontentspage}\hspace*{10pt}}}
  {\thecontentspage}
  {\rmfamily\upshape\qquad}

\titlecontents{subsubsection}%
  [0em]
  {\vspace{.3\baselineskip}\normalsize\rmfamily\itshape}
  {\hspace*{0em}\llap{\parbox[t]{40pt}{\hfill\color{mycolor}\thecontentspage}\hspace*{10pt}}}
  {\thecontentspage}
  {\rmfamily\upshape\qquad}

\newcommand\StartMark{%
\addtocontents{toc}{\protect\label{st\thechapmark}%
\par\protect\begin{tikzpicture}[overlay,remember picture,baseline]   
  \protect\node [anchor=base] (s\thechapmark) {};%
  \ifnum\getpagerefnumber{st\thechapmark}=\getpagerefnumber{en\thechapmark}   
  \else
    \protect\draw[mycolor,line width=3pt] 
      let \protect\p3= (s\thechapmark),%
            \protect\p4 = (current page text area.south) in %
      ( $ (0em,\protect\y3) + (-20pt,-5ex) $ ) -- 
      ( $ (0em,\protect\y4) + (-20pt,5pt) $ );
  \fi
\protect\end{tikzpicture}\par}%
}

\newcommand\EndMark{%
\addtocontents{toc}{\protect\label{en\thechapmark}%
\par\protect\begin{tikzpicture}[overlay,remember picture,baseline]   
  \protect\node [anchor=base] (e\thechapmark) {};
  \ifnum\getpagerefnumber{st\thechapmark}=\getpagerefnumber{en\thechapmark} 
    \protect\draw[mycolor,line width=3pt] 
    let \protect\p1= (s\thechapmark), 
          \protect\p2=(e\thechapmark) in %
    ( $ (0em,\protect\y1) + (-20pt,-5ex) $ ) -- 
    ( $ (0em,\protect\y2) + (-20pt,2ex) $ );
  \else%
  \protect\draw[mycolor,line width=3pt] 
  let \protect\p1= (e\thechapmark), 
        \protect\p2=(current page text area.north) in 
  ( $ (0em,\protect\y2) + (-20pt,5pt) $ ) -- 
  ( $ (0em,\protect\y1) + (-20pt,2ex) $ );
  \fi
\protect\end{tikzpicture}\par}%
\stepcounter{chapmark}%
}

\setcounter{page}{123}% just for the example

\begin{document}

\tableofcontents

\StartMark
\section{A test section}
\subsection{This is a test subsection}
\subsubsection{This is a test subsubsection}
\subsubsection{This is another test subsubsection}
\subsection{This is a test subsection}
\subsection{This is a test subsection}
\subsection{This is a test subsection}
\EndMark


\StartMark
\section{Another test section}
\subsection{This is a test subsection}
\subsection{This is a test subsection}
\subsubsection{This is a test subsubsection}
\subsubsection{This is another test subsubsection}
\EndMark

\StartMark
\section{Yet another test section}
\subsection{This is a test subsection}
\subsection{This is a test subsection}
\subsubsection{This is a test subsubsection}
\subsubsection{This is another test subsubsection}
\subsection{This is a test subsection}
\subsubsection{This is a test subsubsection}
\subsubsection{This is another test subsubsection}
\subsection{This is a test subsection}
\subsubsection{This is a test subsubsection}
\subsubsection{This is another test subsubsection}
\subsection{This is a test subsection}
\subsubsection{This is a test subsubsection}
\subsubsection{This is another test subsubsection}
\EndMark

\end{document}