Creating a custom node shape with a variable number of anchors

Question

For the sake of training my self on PGF, I want to create such node shape having multiply ports with a selecting switch as shown below

This is my attempt to create this node for a particular number of anchors (3 inputs + 1 output) and initially it's satisfying

\documentclass[border=5pt]{standalone}
\usepackage{blindtext}
\usepackage{calc} 
\usepackage{ifthen}
\usepackage{tikz}
\usepackage{lipsum}
    \usetikzlibrary{calc,shapes,arrows,positioning,patterns,fit,shapes.arrows, fadings,arrows.meta}
    \usetikzlibrary{decorations.text}
        \usetikzlibrary{decorations.pathmorphing,calc,shadows.blur,shadings, , backgrounds}
        \usepackage{circuitikz}
    \pgfdeclarelayer{background layer}
    \pgfdeclarelayer{foreground layer}
    \pgfsetlayers{background,background layer,main,foreground layer}


\makeatletter
\pgfkeys{/tikz/ilength/.initial = 2cm}
\pgfkeys{/tikz/olength/.initial = 2cm}
\pgfkeys{/tikz/hspace/.initial = 1.5cm}
\pgfkeys{/tikz/port length ratio/.initial = 0.2}
\pgfkeys{/tikz/output len to output port ratio/.initial = 0.6}
\pgfkeys{/tikz/select/.initial = 1} %for multiswitch control
\newlength\portlen
\pgfdeclareshape{killer}{
    \anchor{center}{\pgfpointorigin}
    \anchor{middle}{\pgfpointorigin}
    \anchor{text}{\pgfpoint{-.5\wd\pgfnodeparttextbox}{-.5\ht\pgfnodeparttextbox}}
    %-------------------
    %----------------------
    \savedanchor\kcenter{\pgfpointorigin}
    \savedanchor\knorthwest{\pgfpoint{-0.5\pgfkeysvalueof{/tikz/hspace}}{0.5\pgfkeysvalueof{/tikz/ilength}}}%
    \savedanchor\ksouthwest{\pgfpoint{-0.5\pgfkeysvalueof{/tikz/hspace}}{-0.5\pgfkeysvalueof{/tikz/ilength}}}%
    \savedanchor\knortheast{\pgfpoint{0.5\pgfkeysvalueof{/tikz/hspace}}{0.5\pgfkeysvalueof{/tikz/olength}}}%
    \savedanchor\ksoutheast{\pgfpoint{0.5\pgfkeysvalueof{/tikz/hspace}}{-0.5\pgfkeysvalueof{/tikz/olength}}}%
    \anchor{north west}{\knorthwest}
    \anchor{south west}{\ksouthwest}

    \anchor{north east}{\knortheast}
    \anchor{south east}{\ksoutheast}
    \savedanchor\knorth{\pgfpoint{0cm}{0.25\pgfkeysvalueof{/tikz/ilength}+0.25\pgfkeysvalueof{/tikz/olength}}}%
    \savedanchor\ksouth{\pgfpoint{0cm}{-0.25\pgfkeysvalueof{/tikz/ilength}-0.25\pgfkeysvalueof{/tikz/olength}}}%
    \savedanchor\keast{\pgfpoint{0.5\pgfkeysvalueof{/tikz/hspace}}{0cm}}%
    \savedanchor\kwest{\pgfpoint{-0.5\pgfkeysvalueof{/tikz/hspace}}{0cm}}%
    \anchor{north}{\knorth}
    \anchor{north}{\knorth}
    \anchor{east}{\keast}
    \anchor{west}{\kwest}
%--------------------------

\savedanchor\porti{\pgfpoint{0.5*\pgfkeysvalueof{/tikz/hspace}}{
    0.5*\pgfkeysvalueof{/tikz/olength}*\pgfkeysvalueof{/tikz/output len to output port ratio} - 0*0.5*\pgfkeysvalueof{/tikz/olength}*\pgfkeysvalueof{/tikz/output len to output port ratio}}
    }%
\savedanchor\portii{\pgfpoint{0.5*\pgfkeysvalueof{/tikz/hspace}}{
    0.5*\pgfkeysvalueof{/tikz/olength}*\pgfkeysvalueof{/tikz/output len to output port ratio} - 1*0.5*\pgfkeysvalueof{/tikz/olength}*\pgfkeysvalueof{/tikz/output len to output port ratio}}
    }%
\savedanchor\portiii{\pgfpoint{0.5*\pgfkeysvalueof{/tikz/hspace}}{
    0.5*\pgfkeysvalueof{/tikz/olength}*\pgfkeysvalueof{/tikz/output len to output port ratio} - 2*0.5*\pgfkeysvalueof{/tikz/olength}*\pgfkeysvalueof{/tikz/output len to output port ratio}}
    }%

\savedanchor\inp{\pgfpoint{-0.5*\pgfkeysvalueof{/tikz/hspace}}{0cm}
    }%
\anchor{port 1}{\porti}
\anchor{port 2}{\portii}
\anchor{port 3}{\portiii}
\anchor{input}{\inp}

\backgroundpath{%
        %
        \pgfpathmoveto{\knorthwest}%
        \pgfpathlineto{\ksouthwest}%
        \pgfpathlineto{\ksoutheast}%
        \pgfpathlineto{\knortheast}%
        \pgfpathclose%
        %----------------
    }
\foregroundpath{
        \pgfmathsetlength{\portlen}{\pgfkeysvalueof{/tikz/hspace}0.5\pgfkeysvalueof{/tikz/port length ratio}}
        \pgfpathmoveto{\inp}
        \pgfpathlineto{\inp \advance \pgf@x by \portlen}
        \pgfsetarrows{{Stealth[width=1.5mm]}-}
        \pgfpathlineto{\pgfpoint{0.5\pgfkeysvalueof{/tikz/hspace}-\portlen}{
            0.5\pgfkeysvalueof{/tikz/olength}\pgfkeysvalueof{/tikz/output len to output port ratio} - (\pgfkeysvalueof{/tikz/select}-1)0.5\pgfkeysvalueof{/tikz/olength}\pgfkeysvalueof{/tikz/output len to output port ratio}
        }}
        \pgfusepath{stroke}
        \pgfsetarrows{-}
        \pgfpathmoveto{\porti}
        \pgfpathlineto{\porti \advance \pgf@x by -\portlen}
        \pgfpathmoveto{\portii}
        \pgfpathlineto{\portii \advance \pgf@x by -\portlen}
        \pgfpathmoveto{\portiii}
        \pgfpathlineto{\portiii \advance \pgf@x by -\portlen}
}}
\makeatother
\begin{document}
\begin{tikzpicture}
    \node [killer,draw=blue,scale=1, port length ratio=0.4,ilength=1.2cm] (A) {};
    \node [killer,draw=blue,fill=green,scale=1,select=3, port length ratio=0.4, left = of A] (B) {};
\end{tikzpicture}
\end{document}

However, I failed to draw anchor border for this node in spite of taking hours to read pgf manual to use the command \anchorborder{}, maybe I couldn't understand how it works. Anyway, bypassing my problem with anchor border, My next step is to control the number of input ports (anchor) by a key \pgfkeys{/tikz/number of input ports/.initial = 4} like that in logic gates. I know it's often requred to use commands like \csname ..... \endcsname and \expandafter which are confusing for me and besides I have already tried to use them but in vain.

Finally, any side suggestion to modify my code is welcomed except using predefined nodes.