\begin{align} \delta_1 &\rightarrow x_2\geq c, ~x_3\geq d, ~x_1 = a\\ \delta_2 &\rightarrow x_2\geq c, ~0\leq x_3 \leq d, ~x_1 = bx_3\\ \delta_3 &\rightarrow x_2\leq c, ~x_1 = 0 \end{align}
You are in one of the regions so $$\delta_1+\delta_2 +\delta_3=1$$, and all the implications are standard big-M representable such as $$x_2-c\geq -M(1-\delta_1), -M(1-\delta_1) \leq x_1-a\leq M(1-\delta_1)$$ etc. By exloiting structure and linearity in some terms this can be reduced and simplified, but this is the basic model.