Footnotes flushed left, same space on page

Question

I have to typeset quite complex footnotes:

• On each page the footnote text starts at the same indention for all footnotes there (doesn't have to be equal on all the pages)
• The footnote number should be flush left
• The paragraph of a footnote text should all be indented the same (justified like in TestD)
• There should not be huge space after the number, so I can't just reserve the space for three numbers for each footnote number.

Currently I'm using the following code, but that one is far from perfect:

\documentclass[fontsize=10pt,ngerman,paper=a4]{scrbook}

\newlength{\test}
\let\myfootnote\footnote
\renewcommand{\footnote}[1]{\myfootnote{\settowidth{\test}{\thefootnotemark}\hspace*{\test}#1}}
\deffootnote[.5em]{1.5em}{1.5em}{\makebox[.5em][l]{\thefootnotemark}}

\usepackage{blindtext}
\begin{document}
TestA
\footnote{TestfootnoteOne}
TestB
\footnote{Long Footnote: \blindtext}
TestC
\setcounter{footnote}{10}
\footnote{Two places}
TestD
\footnote{Long Footnote: \blindtext}
TestE
\setcounter{footnote}{123}
\footnote{Three places}
TestF
\footnote{Long Footnote: \blindtext}
\end{document}

Answer 1

You have to run this twice for it to work, since the first run is used to write to the aux file.

\documentclass[fontsize=10pt,ngerman,paper=a4]{scrbook}
\usepackage{everypage}
\usepackage{blindtext}

\newlength{\tempdima}
\newlength{\tempdimb}
\newcommand{\maxfootnotemark}{}
\newcommand{\ThisFootnotemark}{\thefootnotemark}

\makeatletter
\newcommand{\writepagehook}{%
  \ifx\maxfootnotemark\empty\relax%
  \else
    \begingroup
      \immediate\write\@auxout{%
        \string\MaxFootnotemark{\maxfootnotemark}{\thepage}%
      }%
    \endgroup
    \gdef\maxfootnotemark{}%
  \fi}

\newcommand{\usepagehook}{%
  \@ifundefined{MaxFootnotemark\thepage}{}%
  {\global\edef\ThisFootnotemark{\expandafter\csname MaxFootnotemark\thepage\endcsname}}%
}
\makeatother

\AtBeginDocument{\usepagehook}
\AddEverypageHook{\writepagehook\stepcounter{page}\usepagehook\addtocounter{page}{-1}}

\newcommand{\MaxFootnotemark}[2]% #1 = largest footnote mark, #2 = page
{\expandafter\gdef\csname MaxFootnotemark#2\endcsname{#1}}

\let\myfootnote=\footnote

\renewcommand{\footnote}[1]{\myfootnote{%
\settowidth{\tempdima}{\thefootnotemark}%
\settowidth{\tempdimb}{\maxfootnotemark}%
\ifdim\tempdima>\tempdimb\global\edef\maxfootnotemark{\thefootnotemark}\fi%
\settowidth{\tempdima}{\ThisFootnotemark}%
\setlength{\tempdimb}{\textwidth}%
\addtolength{\tempdimb}{-\tempdima}%
\hspace{\tempdima}\parbox[t]{\tempdimb}{#1}}}

\deffootnote[.5em]{1.5em}{1.5em}%
  {\makebox[.5em][l]{\rlap{\thefootnotemark}}}%

\begin{document}
TestA
\footnote{TestfootnoteOne}

\newpage
TestB
\footnote{Long Footnote: \blindtext}
TestC
\setcounter{footnote}{10}
\footnote{Two places}

\newpage
TestD
\footnote{Long Footnote: \blindtext}
TestE
\setcounter{footnote}{123}
\footnote{Three places}
TestF
\footnote{Long Footnote: \blindtext}

\end{document}