Define a new command depending on the biblatex style

Question

I was making a new document and I have the problem that I still don't know the style of bibliography that will be needed when I have to present it. It could be Vancouver style or APA style. I'm using biblatex because it seems me the most comfortable to use. However, if I use Vancouver style, I have citations like

According to person1 et al. (1) ...text...

Or, maybe, which is a bit more difficult

According to person1 et al. ^1 ...text...

which I could get just doing

According to \citeauthor{person1} \cite{person1} ...text...

According to \citeauthor{person1} \supercite{person1} ...text...

But if I change in biblatex style=apa with the same code above, I would get

According to person1 et al. (person1 et al. 2024) ...text...

Which is redundant and would be:

According to person1 et al. (2024) ...text...

I'd like to make a command that detects if style=vancouver or style=apa in biblatex options and executes a command if the first is true and another if the second is true

My idea was the following

\documentclass{article}
\usepackage[style=vancouver, backend=biber]{biblatex}
\usepackage{etoolbox}
\newif\ifvancouverstyle
\newif\ifapastyle
\ifcsstrequal{blx@bibstyle}{\string vancouver}{
    \vancouverstyletrue
}{
    \vancouverstylefalse
}
\ifcsstrequal{blx@bibstyle}{\string apa}{
    \apastyletrue
}{
    \apastylefalse
}
\newcommand{\detectstyle}{%
    \ifvancouverstyle
        % The action if the style is "vancouver"
        This is the Vancouver style.
    \fi
    \ifapastyle
        % The action if style is "apa"
        This is APA style.
    \fi
}
\begin{document}
\title{Hello}
\author{me}
\maketitle
\detectstyle
\end{document}

For now I don't have idea about how configure this new command or even it's possible get it. However, when I write \detectstyle, nothing is printed.

The arguments are missing for now. I would be very grateful if someone could help me with this.

Answer 1

For this particular use case you don't need a command to detect the citation style, you can just use \textcite.

\documentclass[british]{article}
\usepackage[T1]{fontenc}
\usepackage{babel}
\usepackage{csquotes}
\usepackage[backend=biber, style=apa]{biblatex}
\addbibresource{biblatex-examples.bib}
\begin{document}
Then \textcite{sigfridsson} showed
\printbibliography
\end{document}

With APA style you get

If you change the style=apa to style=vancouver, you get

---

If you're not happy with the output \texcite gives you with style=vancouver and you have to run certain code (e.g. the one from Biblatex \textcite using a superscript reference number) only when the (cite)style is vancouver, you can use \ifdefstring\blx@cbxfile{vancouver}{<true>}{<false>} (within \makeatletter...\makeatother).

\documentclass[british]{article}
\usepackage[T1]{fontenc}
\usepackage{babel}
\usepackage{csquotes}
\usepackage[backend=biber, style=vancouver]{biblatex}
\makeatletter
\ifdefstring\blx@cbxfile{vancouver}
  {\renewbibmacro*{textcite}{%
     \iffieldequals{namehash}{\cbx@lasthash}
       {\mkbibsuperscript{\supercitedelim}}
       {\cbx@tempa
        \ifnameundef{labelname}
          {\printfield[citetitle]{labeltitle}}
          {\printnames{labelname}}}%
     \ifnumequal{\value{citecount}}{1}
       {}
       {}%
     \mkbibsuperscript{\usebibmacro{cite}}%
     \savefield{namehash}{\cbx@lasthash}%
     \gdef\cbx@tempa{\addspace\multicitedelim}}%
\DeclareCiteCommand{\textcite}
      {\let\cbx@tempa=\empty
       \undef\cbx@lasthash
       \iffieldundef{prenote}
         {}
         {\BibliographyWarning{Ignoring prenote argument}}%
      \iffieldundef{postnote}
        {}
        {\BibliographyWarning{Ignoring postnote argument}}}
     {\usebibmacro{citeindex}%
      \usebibmacro{textcite}}
     {}
     {}}
  {}
\makeatother
\addbibresource{biblatex-examples.bib}
\begin{document}
Then \textcite{sigfridsson} showed
\printbibliography
\end{document}

With style=apa, this document will show the APA output from above.

Answer 2

Seems at the time of writing this answer there is no official interface for obtaining information about the style in use with biblatex. (But maybe the author of this answer overlooked that. Or things changed since this answer was written.) So, in order to get that, once more one needs to commit the crime of trying to resort to internals which might be subject to change.

---

Probably you can get what you need by comparing the replacement text/the expansion of the macro \blx@cbxfile via \ifcsstring:

\documentclass{article}
\usepackage[style=vancouver, backend=biber]{biblatex}
\usepackage{etoolbox}
\newif\ifvancouverstyle
\newif\ifapastyle
\ifcsstring{blx@cbxfile}{vancouver}{%
    \vancouverstyletrue
}{%
    \vancouverstylefalse
}
\ifcsstring{blx@cbxfile}{apa}{%
    \apastyletrue
}{%
    \apastylefalse
}
\newcommand{\detectstyle}{%
  \ifvancouverstyle
    % The action if the style is "vancouver"
    This is the Vancouver style.
  \fi
  \ifapastyle
    % The action if style is "apa"
    This is APA style.
  \fi
}
\begin{document}
\title{Hello}
\author{me}
\maketitle
\detectstyle
\end{document}

Alternatively expl3's \str_case:onF might be of interest:

\begin{filecontents}{\jobname.bib}
@article{person1,
  title = {Elaborate},
  author = {Person, One and Person, Two and Person, Three},
  date = {2024},
}
}
\end{filecontents}
\documentclass{article}
\usepackage[%
  style=vancouver, 
  % style=apa, 
  backend=biber,
  maxcitenames=2,
]{biblatex}
\addbibresource{\jobname.bib}
\ExplSyntaxOn
\cs_new:Npn \biblatexstylecases { \exp_args:Nc \str_case:onF {blx@cbxfile} }
\ExplSyntaxOff
\biblatexstylecases{%
  {vancouver}{\NewDocumentCommand{\MyCommand}{m}{\citeauthor{#1}\cite{#1}}}%
  {apa}{\NewDocumentCommand{\MyCommand}{m}{\cite{#1}}}%
}{%
  \message{^^JWarning: Style in use is not in cases list, thus \string\MyCommand\space not defined!^^J}%
}%
\begin{document}
\title{Hello}
\author{me}
\maketitle
According to \MyCommand{person1} ...text...
\printbibliography[heading=bibintoc]
\end{document}

---

Needless to say that I am not really fond of this way of approaching the matter as the "official" and better route to go for defining citing-commands is via \DeclareCiteCommand and \renewbibmacro and the like. That's also why I did not provide code for delivering an elaborate error message in case the style in use is not in the cases list. Moewe in the comments gave good reasons for sticking to the means for defining citing-commands provided by the package biblatex itself. In my examples I did not lay focus on how to define citing-commands properly. This can be learned from the biblatex manual. Instead, in my answer the focus is on how forking things depending on the style in use could be implemented because in a comment you said you think you "really need it".