#include "manual.h"
using namespace std;

void manual::decide(int *dx, int *dy) const
{
    struct keystroke {
        char c;
        int dx;   //horizontal difference
        int dy;   //vertical difference
    };
    static const keystroke a[] = {
        {'h',   -1,    0},   //left
        {'j',    0,    1},   //down
        {'k',    0,   -1},   //up
        {'l',    1,    0}    //right
    };
    static const size_t n = sizeof a / sizeof a[0];

    if (const char k = key()) {
        for (const keystroke *p = a; p < a + n; ++p) {
            if (k == p->c) {
                *dx = p->dx;
                *dy = p->dy;
                return;
            }
        }
        //Punish user who pressed an illegal key or tried to move off screen.
        punish();
    }
    //Arrive here if the user pressed no key, or pressed an illegal key.
    *dx = *dy = 0;
}