Label Angle using tikz-euclide

Question

I am trying to recreate this diagram. I can get most of it except for the labelling of the top angle.

An MWE is below

\documentclass{article}
\usepackage{tikz}
\usepackage{tkz-euclide}
\usetkzobj{all}

\begin{document}
\begin{tikzpicture}[thick]

\coordinate (O) at (0,0); 
\coordinate (A) at (4,0); 
\coordinate (B) at (0,2); 
\draw (O)--(A)--(B)--cycle;

\node (a) at (1.4,2.1) {$90^{\circ}-\theta$}; 
\node (b) at (0.1,1.8){}; 
\path (a) edge [->,bend left=45,looseness=0.8] (b); 

\tkzLabelSegment[below=2pt](O,A){$b$}
\tkzLabelSegment[left=2pt](O,B){$a$}
\tkzLabelSegment[above right=2pt](A,B){$c$}
\tkzMarkRightAngle[size=0.3](A,O,B)

\tkzLabelAngle[pos = 1.0](O,A,B){$\theta$}

\end{tikzpicture}
\end{document}

Answer 1

One possible solution is based on using angle of nodes. 295 and 300 are my choices.

\path (a.295) edge [->,bend left=45,looseness=1] (b.300);