Graphs of the Other Trigonometric Functions · Superchallenge problem

Build the function $y=a\csc(bx-c)+d$ (with $a>0$, $b>0$, $0\le c<2\pi$) whose period is $4\pi$, which has adjacent vertical asymptotes at $x=-\pi$ and $x=\pi$, whose upward U has minimum value $2$, and whose downward U has maximum value $-4$; the branch between $x=-\pi$ and $x=\pi$ is a downward U. Find $a$, $b$, $c$, $d$.