KTaNE Module Solver: Memory

/* Version 1.1
 * Implements the rules for the 'Memory' module
 * Warning: contains terse type syntax. cdecl might help.
 * Unless grabbed from user input, numbers are internally counted from 0, so ds0 refers to the handler for stage 1.
 * See <http://www.bombmanual.com/manual/1/html/index.html> for the rules. Subject of Memory.
 */

#include <stdio.h>
#include <ctype.h>

#define MAP(a, b, c, d) \
    ( ((int[4]){(a), (b), (c), (d)})[st->display - 1] )

struct state {
    int stage;
    int display;
    int positions[5];
    int labels[5];
};

int
get_num(char *prompt)
{
    int ret = 0;

    while(ret < '1' || ret > '4'){
        if(!isspace(ret))
            printf("%s >", prompt);

        ret = getchar();
    }

    return ret - '0';
}

static int
ds0(struct state *st)
{
    return MAP(2,2,3,4);
}

static int
ds1(struct state *st)
{
    if(st->display == 1)
        puts("Press Label 4");

    return MAP(0, st->positions[0], 1, st->positions[0]);
}

static int
ds2(struct state *st)
{
    if(st->display == 4)
        puts("Press Label 4");

    return MAP(st->labels[1], st->labels[0], 3, 0);
}


static int
ds3(struct state *st)
{
    return MAP(st->positions[0], 1, st->positions[1], st->positions[1]);
}

static int
ds4(struct state *st)
{
    printf("Press Label %i\n", st->labels[ MAP(0,1,3,2) ]);
    return 0;
}

int
main(void)
{
    struct state st = {0};
    static int (*stagefn[5])(struct state *) = { ds0, ds1, ds2, ds3, ds4 };

    while(st.stage < 5){
        st.display = get_num("Display?");
        st.positions[st.stage] = stagefn[st.stage](&st);

        if(st.positions[st.stage])
            printf("Press %i\n", st.positions[st.stage]);
        else
            st.positions[st.stage] = get_num("Position?");

        if(st.stage < 4)
            st.labels[st.stage] = get_num("Label?");

        st.stage++;
    }

    return 0;
}