Example 2 Let the function $f(x)$ satisfy the following conditions:
(i) If $x>y$, and $f(x)+x \geqslant w \geqslant f(y)+y$, then there exists a real number $z \in[y, x]$, such that $f(z)=$ $w-z$;
(ii) The equation $f(x)=0$ has at least one solution, and among the solutions of this equation, there is one solution that is not greater than all other solutions;
(iii) $f(0)=1$;
(iv) $f(-2003) \leqslant 2004$;
(v) $f(x) \cdot f(y)=f[x \cdot f(y)+y \cdot f(x)+x y]$.
Find the value of $f(-2003)$.