Line break in nomencl for nomgroup

Question

I use nomencl for creating the nomenclature of my thesis.
The thesis consists of three chapters and I prefer to have a separate list for each of them.
I currently achieve this with the code in my minimal working example.
Unfortunately, the names of the chapters are quite long. Therefore they do not fit in one line.

How can I have the chapter name continue in the next line?
How can I have it aligned in such a way that the second line does not start from the beginning (below "Chapter ...") but below the name of the chapter after the dash ("A quite long title ...").

\documentclass[a4paper,12pt]{book}
\usepackage[british,ngerman]{babel}
\usepackage{longtable} % longtable lets you have tables that span multiple pages

\usepackage{nomencl}
\makenomenclature
\renewcommand{\nomname}{List of Symbols}
\renewcommand{\nompreamble}{just some symbols}

\usepackage{etoolbox}
\renewcommand\nomgroup[1]{%
\item[\bfseries
\ifstrequal{#1}{A}{Common}{%
\ifstrequal{#1}{B}{Chapter 2 - A quite long title, a quite long title, a quite long title, a quite long title, a quite long title}{%
\ifstrequal{#1}{C}{Chapter 3 - A quite long title, a quite long title, a quite long title, a quite long title, a quite long title}{}}}%
]}

\begin{document}
\tableofcontents
\nomenclature[A,  1]{$\gamma$}{text} 
\nomenclature[A,  2]{$B$}{text}
\nomenclature[B,  1]{$\beta$}{text}
\nomenclature[B,  2]{$S$}{text}
\nomenclature[C,  1]{$\alpha$}{text}
\nomenclature[C,  2]{$\beta$}{text}
\printnomenclature[2cm]
\end{document}enter code here

Answer 1

I was able to solve the problem with "parbox":

   \usepackage{etoolbox}
   \renewcommand\nomgroup[1]{%
   \item[\bfseries
   \ifstrequal{#1}{A}{Common}{%
   \ifstrequal{#1}{B}{{\parbox[t]{16cm}{Chapter 2 - A quite long title, a quite long title, a quite long title, a quite long title, a quite long title}}}{%
   \ifstrequal{#1}{C}{{\parbox[t]{16cm}{Chapter 3 - A quite long title, a quite long title, a quite long title, a quite long title, a quite long title}}}{}}}%
   ]}

Answer 2

Your idea of \parbox is good, but I suggest several improvements, first of all to avoid guessing the width.

\documentclass[a4paper,12pt]{book}
\usepackage[british,ngerman]{babel}

\usepackage{nomencl}
\usepackage{xparse}

\makenomenclature
\renewcommand{\nomname}{List of Symbols}
\renewcommand{\nompreamble}{just some symbols}

\newcommand{\nomA}{Common}
\newcommand{\nomB}{%
  \parbox[t]{\textwidth}{%
    Chapter 2 - A quite long title, a quite long title, a quite long title,
    a quite long title, a quite long title%
  }\kern-\labelsep
}
\newcommand{\nomC}{%
  \parbox[t]{\textwidth}{%
    Chapter 3 - A quite long title, a quite long title, a quite long title,
    a quite long title, a quite long title%
  }\kern-\labelsep
}
% this is easier than a long list of nested \ifstrequal calls and more easily scalable
\ExplSyntaxOn
\NewDocumentCommand{\nomgroupmake}{m}
 {
  \str_case:nnF { #1 }
   {
    {A}{\nomA}
    {B}{\nomB}
    {C}{\nomC}
   }
   {\ERROR}
 }
\ExplSyntaxOff

\renewcommand\nomgroup[1]{\item[\bfseries\nomgroupmake{#1}]}

\begin{document}

Some text to make the nomenclature appear
\nomenclature[A,1]{$\gamma$}{text} 
\nomenclature[A,2]{$B$}{text}
\nomenclature[B,1]{$\beta$}{text}
\nomenclature[B,2]{$S$}{text}
\nomenclature[C,1]{$\alpha$}{text}
\nomenclature[C,2]{$\beta$}{text}

\printnomenclature[2cm]

\end{document}