/* vscreen.c - screen and keyboard for the c64 vim clone.
 *
 * The editor writes straight into the screen matrix at $0400 and colour ram at
 * $d800 rather than going through the kernal, and it selects the lower/upper
 * case character set at $1800 so that petscii $41-$5a draws as real lowercase.
 *
 * Everything here returns int, so the other compilation unit can call these
 * without declaring them (power c is K&R C).
 */

char *scr;                          /* screen matrix, $0400 */
char *colr;                         /* colour ram, $d800 */

/* petscii byte -> screen code */
s2v(p)
int p;
{
    if (p >= 0xc0) return p - 0x80;
    if (p >= 0xa0) return p - 0x40;
    if (p >= 0x60) return p - 0x20;
    if (p >= 0x40) return p - 0x40;
    return p;
}

/* raw screen code at row r, column c */
sraw(r, c, v)
int r, c, v;
{
    int i;

    if (r < 0) return 0;
    if (r > 24) return 0;
    if (c < 0) return 0;
    if (c > 39) return 0;
    i = r * 40 + c;
    scr[i] = v;
    colr[i] = 1;
    return 0;
}

/* one petscii character */
spc(r, c, p)
int r, c, p;
{
    sraw(r, c, s2v(p));
    return 0;
}

/* one petscii character, inverted: the cursor and the status row */
srpc(r, c, p)
int r, c, p;
{
    sraw(r, c, s2v(p) + 128);
    return 0;
}

/* a reversed space, for the cursor sitting past the end of a line */
sblk(r, c)
int r, c;
{
    sraw(r, c, 160);
    return 0;
}

/* a zero terminated petscii string */
sps(r, c, s)
int r, c;
char *s;
{
    while (*s) spc(r, c++, *s++);
    return 0;
}

/* n blanks from (r,c) */
sclr(r, c, n)
int r, c, n;
{
    while (n-- > 0) sraw(r, c++, 32);
    return 0;
}

/* take over the machine: black on blue, lower case, no blinking cursor */
sinit()
{
    int i;
    char *p;

    scr = (char *) 0x0400;
    colr = (char *) 0xd800;
    p = (char *) 0xd018;
    *p = 0x17;
    p = (char *) 0xd020;
    *p = 0;
    p = (char *) 0xd021;
    *p = 6;
    p = (char *) 0x00cc;
    *p = 0;
    p = (char *) 0x0091;            /* run/stop flag: drop whatever boot left */
    *p = 0;
    for (i = 0; i < 1000; i++) {
        scr[i] = 32;
        colr[i] = 1;
    }
    return 0;
}

/* give the machine back the way basic expects it */
sdone()
{
    int i;
    char *p;

    p = (char *) 0xd018;
    *p = 0x15;
    p = (char *) 0xd020;
    *p = 14;
    p = (char *) 0xd021;
    *p = 6;
    for (i = 0; i < 1000; i++) {
        scr[i] = 32;
        colr[i] = 1;
    }
    return 0;
}

/* ---------------------------------------------------------------- keyboard
 *
 * Keys come straight out of the kernal's keyboard buffer: $c6 says how many
 * are waiting and they queue from $0277. The kernal's own irq handler scans
 * the keyboard matrix and fills that buffer, so this gets each press as it
 * happens - and it also catches anything typed before the program started.
 *
 * Two obvious alternatives do not work: calling the kernal's GETIN through
 * sys() crashed the program, and the library's getchar() is line buffered - it
 * echoes through the screen editor and only hands characters over after RETURN.
 */

/* next key, or 0 if none is waiting */
skeyp()
{
    int n, k, i;
    char *cnt, *buf;

    cnt = (char *) 0x00c6;
    n = *cnt;
    n = n & 255;
    if (n == 0) return 0;
    buf = (char *) 0x0277;
    k = buf[0];
    k = k & 255;
    for (i = 1; i < n; i++) buf[i - 1] = buf[i];
    *cnt = (char) (n - 1);
    return k;
}

/* wait for a key */
skey()
{
    int k;

    for (;;) {
        k = skeyp();
        if (k != 0) return k;
    }
}