% pie chart generator

\newcounter{pieSlicePercentage}
\newcounter{pieCounterCurrent}
\newcounter{pieCounterNext}
\newcounter{pieCounterTotal}

\newcommand{\pieslice}[3]{
	\pgfmathparse{0.5*#1+0.5*#2}
	\let\midangle\pgfmathresult

	\setcounter{pieSlicePercentage}{\p*100/\thepieCounterTotal}

	% slice
	\draw[thick,fill=#3!\thepieSlicePercentage] (0,0) -- (#1:1) arc (#1:#2:1) -- cycle;
}

\newcommand{\pieslicelabel}[3]{
	\pgfmathparse{0.5*#1+0.5*#2}
	\let\midangle\pgfmathresult

	\setcounter{pieSlicePercentage}{\p*100/\thepieCounterTotal}

	% Outer label.
	\pgfmathparse{min((#2-#1-10)/110*(-0.3),0)}
	\let\temp\pgfmathresult
	\pgfmathparse{max(\temp,-0.5) + 1.55}
	\let\outerpos\pgfmathresult
	\node at (\midangle:\outerpos) {\textbf{#3}};

	% Inner label.
	\pgfmathparse{min((#2-#1-10)/110*(-0.3),0)}
	\let\temp\pgfmathresult
	\pgfmathparse{max(\temp,-0.5) + 0.8}
	\let\innerpos\pgfmathresult

	\node at (\midangle:\innerpos) {\thepieSlicePercentage \%};
}

\newcommand{\piechart}[3]{
	\setcounter{pieCounterCurrent}{0}
	\setcounter{pieCounterNext}{0}
	\setcounter{pieCounterTotal}{0}

	\begin{center}

		\begin{tikzpicture}[scale=#2]

			%% Get the total to turn the values into percentages.
			\foreach \p/\t in {#3} {
				\setcounter{pieCounterTotal}{\thepieCounterTotal+\p}
			}

			%% Draw the slices.
			\foreach \p/\t in {#3} {
				\setcounter{pieCounterCurrent}{\value{pieCounterNext}}
				\addtocounter{pieCounterNext}{\p}
				\pieslice{
					\thepieCounterCurrent/\thepieCounterTotal*360
				}{
					\thepieCounterNext/\thepieCounterTotal*360
				}{
					#1
				}
			}

			\setcounter{pieCounterCurrent}{0}
			\setcounter{pieCounterNext}{0}

			%% Write the labels.
			\foreach \p/\t in {#3}{
				\setcounter{pieCounterCurrent}{\value{pieCounterNext}}
				\addtocounter{pieCounterNext}{\p}
				\pieslicelabel{
					\thepieCounterCurrent/\thepieCounterTotal*360
				}{
					\thepieCounterNext/\thepieCounterTotal*360
				}{
					\t
				}
			}

		\end{tikzpicture}
	\end{center}
}