breaking a line at very defined points

Question

I'm trying to create a macro for generating a title page for manuals. In the simplest case the title should look like

{\huge
\textbf{\productname{} \manualtitle{}}
}

But I would like to have the following rules applied for line-breaks:

1. If the whole title fits into one line, do not break it.
2. If manualtitle fits into one line but not together with productname, break between the two.
3. If manualtitle is longer than the line, break after productname and break manualtitle automatically but without hyphens.

I know how to get parts of it to work manually using \newline and the hyphenrules and sloppypar environments, but I can't find a solution that fulfills all three requirements.

Minimal example as requested:

\documentclass[a4paper, 12pt]{report}

\usepackage[paper=a4paper,
            left=25mm,
            right=25mm,
            top=25mm,
            bottom=25mm,
            showframe]{geometry}

\usepackage[english]{babel}

\setlength\parindent{0pt}

\newcommand{\product}{PRODUCT}
\newcommand{\manualtitle}{User Manual}

\newcommand{\printtitle}{
  \vspace{2em}

  {\huge
    \textbf{\product{} \manualtitle{}}
  }
}

\begin{document}

\printtitle

\renewcommand{\manualtitle}{More Important User Manual}
\printtitle

\renewcommand{\manualtitle}{Even Way More Important User Manual}
\printtitle

\end{document}

Desired output:

Answer 1

This is a possible solution:

\documentclass[a4paper, 12pt]{report}

\usepackage[paper=a4paper,
            left=25mm,
            right=25mm,
            top=25mm,
            bottom=25mm,
            showframe]{geometry}

\usepackage[english]{babel}

\setlength\parindent{0pt}

\newcommand{\product}{PRODUCT}
\newcommand{\manualtitle}{User Manual}

\newcommand{\printtitle}{%
  \par
  \vspace*{2em}%
  \par\begingroup\raggedright
  \huge\bfseries
  \sbox0{\let\\\relax\product{} \manualtitle}%
  \ifdim\wd0>\linewidth
    \product\\
    \manualtitle
    \par
  \else
    \box0
  \fi
  \endgroup
}

\begin{document}

\printtitle

\renewcommand{\manualtitle}{More Important User Manual}
\printtitle

\renewcommand{\manualtitle}{Even Way More Important User Manual}
\printtitle

\renewcommand{\manualtitle}{Even Way More Important \\ User Manual}
\printtitle

\end{document}