/* NetHack 3.6	ball.c	$NHDT-Date: 1557088406 2019/05/05 20:33:26 $  $NHDT-Branch: NetHack-3.6.2-beta01 $:$NHDT-Revision: 1.36 $ */
/* Copyright (c) Stichting Mathematisch Centrum, Amsterdam, 1985. */
/*-Copyright (c) David Cohrs, 2006. */
/* NetHack may be freely redistributed.  See license for details. */

/* Ball & Chain
 * =============================================================*/

#include "hack.h"

STATIC_DCL int NDECL(bc_order);
STATIC_DCL void NDECL(litter);

void
ballrelease(showmsg)
boolean showmsg;
{
    if (carried(uball)) {
        if (showmsg)
            pline("Startled, you drop the iron ball.");
        if (uwep == uball)
            setuwep((struct obj *) 0);
        if (uswapwep == uball)
            setuswapwep((struct obj *) 0);
        if (uquiver == uball)
            setuqwep((struct obj *) 0);
        /* [this used to test 'if (uwep != uball)' but that always passes
           after the setuwep() above] */
        freeinv(uball); /* remove from inventory but don't place on floor */
        encumber_msg();
    }
}

/* ball&chain might hit hero when falling through a trap door */
void
ballfall()
{
    boolean gets_hit;

    gets_hit = (((uball->ox != u.ux) || (uball->oy != u.uy))
                && ((uwep == uball) ? FALSE : (boolean) rn2(5)));
    ballrelease(TRUE);
    if (gets_hit) {
        int dmg = rn1(7, 25);

        pline_The("iron ball falls on your %s.", body_part(HEAD));
        if (uarmh) {
            if (is_metallic(uarmh)) {
                pline("Fortunately, you are wearing a hard helmet.");
                dmg = 3;
            } else if (flags.verbose)
                pline("%s does not protect you.", Yname2(uarmh));
        }
        losehp(Maybe_Half_Phys(dmg), "crunched in the head by an iron ball",
               NO_KILLER_PREFIX);
    }
}

/*
 *  To make this work, we have to mess with the hero's mind.  The rules for
 *  ball&chain are:
 *
 *      1. If the hero can see them, fine.
 *      2. If the hero can't see either, it isn't seen.
 *      3. If either is felt it is seen.
 *      4. If either is felt and moved, it disappears.
 *
 *  If the hero can see, then when a move is done, the ball and chain are
 *  first picked up, the positions under them are corrected, then they
 *  are moved after the hero moves.  Not too bad.
 *
 *  If the hero is blind, then she can "feel" the ball and/or chain at any
 *  time.  However, when the hero moves, the felt ball and/or chain become
 *  unfelt and whatever was felt "under" the ball&chain appears.  Pretty
 *  nifty, but it requires that the ball&chain "remember" what was under
 *  them --- i.e. they pick-up glyphs when they are felt and drop them when
 *  moved (and felt).  When swallowed, the ball&chain are pulled completely
 *  off of the dungeon, but are still on the object chain.  They are placed
 *  under the hero when she is expelled.
 */

/*
 * from you.h
 *      int u.bglyph            glyph under the ball
 *      int u.cglyph            glyph under the chain
 *      int u.bc_felt           mask for ball/chain being felt
 *      #define BC_BALL  0x01   bit mask in u.bc_felt for ball
 *      #define BC_CHAIN 0x02   bit mask in u.bc_felt for chain
 *      int u.bc_order          ball & chain order
 *
 * u.bc_felt is also manipulated in display.c and read.c, the others only
 * in this file.  None of these variables are valid unless the player is
 * Blind.
 */

/* values for u.bc_order */
#define BCPOS_DIFFER 0 /* ball & chain at different positions */
#define BCPOS_CHAIN 1  /* chain on top of ball */
#define BCPOS_BALL 2   /* ball on top of chain */

/*
 *  Place the ball & chain under the hero.  Make sure that the ball & chain
 *  variables are set (actually only needed when blind, but what the heck).
 *  It is assumed that when this is called, the ball and chain are NOT
 *  attached to the object list.
 *
 *  Should not be called while swallowed except on waterlevel.
 */
void
placebc()
{
    if (!uchain || !uball) {
        impossible("Where are your ball and chain?");
        return;
    }

    (void) flooreffects(uchain, u.ux, u.uy, ""); /* chain might rust */

    if (carried(uball)) { /* the ball is carried */
        u.bc_order = BCPOS_DIFFER;
    } else {
        /* ball might rust -- already checked when carried */
        (void) flooreffects(uball, u.ux, u.uy, "");
        place_object(uball, u.ux, u.uy);
        u.bc_order = BCPOS_CHAIN;
    }

    place_object(uchain, u.ux, u.uy);

    u.bglyph = u.cglyph = levl[u.ux][u.uy].glyph; /* pick up glyph */

    newsym(u.ux, u.uy);
}

void
unplacebc()
{
    if (u.uswallow) {
        if (Is_waterlevel(&u.uz)) {
            /* we need to proceed with the removal from the floor
             * so that movebubbles() processing will disregard it as
             * intended. Ignore all the vision stuff.
             */
            if (!carried(uball))
                obj_extract_self(uball);
            obj_extract_self(uchain);
        }
        /* ball&chain not unplaced while swallowed */
        return;
    }

    if (!carried(uball)) {
        obj_extract_self(uball);
        if (Blind && (u.bc_felt & BC_BALL)) /* drop glyph */
            levl[uball->ox][uball->oy].glyph = u.bglyph;

        newsym(uball->ox, uball->oy);
    }
    obj_extract_self(uchain);
    if (Blind && (u.bc_felt & BC_CHAIN)) /* drop glyph */
        levl[uchain->ox][uchain->oy].glyph = u.cglyph;

    newsym(uchain->ox, uchain->oy);
    u.bc_felt = 0; /* feel nothing */
}

/*
 *  Return the stacking of the hero's ball & chain.  This assumes that the
 *  hero is being punished.
 */
STATIC_OVL int
bc_order()
{
    struct obj *obj;

    if (uchain->ox != uball->ox || uchain->oy != uball->oy || carried(uball)
        || u.uswallow)
        return BCPOS_DIFFER;

    for (obj = level.objects[uball->ox][uball->oy]; obj;
         obj = obj->nexthere) {
        if (obj == uchain)
            return BCPOS_CHAIN;
        if (obj == uball)
            return BCPOS_BALL;
    }
    impossible("bc_order:  ball&chain not in same location!");
    return BCPOS_DIFFER;
}

/*
 *  set_bc()
 *
 *  The hero is either about to go blind or already blind and just punished.
 *  Set up the ball and chain variables so that the ball and chain are "felt".
 */
void
set_bc(already_blind)
int already_blind;
{
    int ball_on_floor = !carried(uball);

    u.bc_order = bc_order(); /* get the order */
    u.bc_felt = ball_on_floor ? BC_BALL | BC_CHAIN : BC_CHAIN; /* felt */

    if (already_blind || u.uswallow) {
        u.cglyph = u.bglyph = levl[u.ux][u.uy].glyph;
        return;
    }

    /*
     *  Since we can still see, remove the ball&chain and get the glyph that
     *  would be beneath them.  Then put the ball&chain back.  This is pretty
     *  disgusting, but it will work.
     */
    remove_object(uchain);
    if (ball_on_floor)
        remove_object(uball);

    newsym(uchain->ox, uchain->oy);
    u.cglyph = levl[uchain->ox][uchain->oy].glyph;

    if (u.bc_order == BCPOS_DIFFER) { /* different locations */
        place_object(uchain, uchain->ox, uchain->oy);
        newsym(uchain->ox, uchain->oy);
        if (ball_on_floor) {
            newsym(uball->ox, uball->oy); /* see under ball */
            u.bglyph = levl[uball->ox][uball->oy].glyph;
            place_object(uball, uball->ox, uball->oy);
            newsym(uball->ox, uball->oy); /* restore ball */
        }
    } else {
        u.bglyph = u.cglyph;
        if (u.bc_order == BCPOS_CHAIN) {
            place_object(uball, uball->ox, uball->oy);
            place_object(uchain, uchain->ox, uchain->oy);
        } else {
            place_object(uchain, uchain->ox, uchain->oy);
            place_object(uball, uball->ox, uball->oy);
        }
        newsym(uball->ox, uball->oy);
    }
}

/*
 *  move_bc()
 *
 *  Move the ball and chain.  This is called twice for every move.  The first
 *  time to pick up the ball and chain before the move, the second time to
 *  place the ball and chain after the move.  If the ball is carried, this
 *  function should never have BC_BALL as part of its control.
 *
 *  Should not be called while swallowed.
 */
void
move_bc(before, control, ballx, bally, chainx, chainy)
int before, control;
xchar ballx, bally, chainx, chainy; /* only matter !before */
{
    if (Blind) {
        /*
         *  The hero is blind.  Time to work hard.  The ball and chain that
         *  are attached to the hero are very special.  The hero knows that
         *  they are attached, so when they move, the hero knows that they
         *  aren't at the last position remembered.  This is complicated
         *  by the fact that the hero can "feel" the surrounding locations
         *  at any time, hence, making one or both of them show up again.
         *  So, we have to keep track of which is felt at any one time and
         *  act accordingly.
         */
        if (!before) {
            if ((control & BC_CHAIN) && (control & BC_BALL)) {
                /*
                 *  Both ball and chain moved.  If felt, drop glyph.
                 */
                if (u.bc_felt & BC_BALL)
                    levl[uball->ox][uball->oy].glyph = u.bglyph;
                if (u.bc_felt & BC_CHAIN)
                    levl[uchain->ox][uchain->oy].glyph = u.cglyph;
                u.bc_felt = 0;

                /* Pick up glyph at new location. */
                u.bglyph = levl[ballx][bally].glyph;
                u.cglyph = levl[chainx][chainy].glyph;

                movobj(uball, ballx, bally);
                movobj(uchain, chainx, chainy);
            } else if (control & BC_BALL) {
                if (u.bc_felt & BC_BALL) {
                    if (u.bc_order == BCPOS_DIFFER) { /* ball by itself */
                        levl[uball->ox][uball->oy].glyph = u.bglyph;
                    } else if (u.bc_order == BCPOS_BALL) {
                        if (u.bc_felt & BC_CHAIN) { /* know chain is there */
                            map_object(uchain, 0);
                        } else {
                            levl[uball->ox][uball->oy].glyph = u.bglyph;
                        }
                    }
                    u.bc_felt &= ~BC_BALL; /* no longer feel the ball */
                }

                /* Pick up glyph at new position. */
                u.bglyph = (ballx != chainx || bally != chainy)
                               ? levl[ballx][bally].glyph
                               : u.cglyph;

                movobj(uball, ballx, bally);
            } else if (control & BC_CHAIN) {
                if (u.bc_felt & BC_CHAIN) {
                    if (u.bc_order == BCPOS_DIFFER) {
                        levl[uchain->ox][uchain->oy].glyph = u.cglyph;
                    } else if (u.bc_order == BCPOS_CHAIN) {
                        if (u.bc_felt & BC_BALL) {
                            map_object(uball, 0);
                        } else {
                            levl[uchain->ox][uchain->oy].glyph = u.cglyph;
                        }
                    }
                    u.bc_felt &= ~BC_CHAIN;
                }
                /* Pick up glyph at new position. */
                u.cglyph = (ballx != chainx || bally != chainy)
                               ? levl[chainx][chainy].glyph
                               : u.bglyph;

                movobj(uchain, chainx, chainy);
            }

            u.bc_order = bc_order(); /* reset the order */
        }

    } else {
        /*
         *  The hero is not blind.  To make this work correctly, we need to
         *  pick up the ball and chain before the hero moves, then put them
         *  in their new positions after the hero moves.
         */
        if (before) {
            if (!control) {
                /*
                 * Neither ball nor chain is moving, so remember which was
                 * on top until !before.  Use the variable u.bc_order
                 * since it is only valid when blind.
                 */
                u.bc_order = bc_order();
            }

            remove_object(uchain);
            newsym(uchain->ox, uchain->oy);
            if (!carried(uball)) {
                remove_object(uball);
                newsym(uball->ox, uball->oy);
            }
        } else {
            int on_floor = !carried(uball);

            if ((control & BC_CHAIN)
                || (!control && u.bc_order == BCPOS_CHAIN)) {
                /* If the chain moved or nothing moved & chain on top. */
                if (on_floor)
                    place_object(uball, ballx, bally);
                place_object(uchain, chainx, chainy); /* chain on top */
            } else {
                place_object(uchain, chainx, chainy);
                if (on_floor)
                    place_object(uball, ballx, bally);
                /* ball on top */
            }
            newsym(chainx, chainy);
            if (on_floor)
                newsym(ballx, bally);
        }
    }
}

/* return TRUE if the caller needs to place the ball and chain down again
 *
 *  Should not be called while swallowed.  Should be called before movement,
 *  because we might want to move the ball or chain to the hero's old
 * position.
 *
 * It is called if we are moving.  It is also called if we are teleporting
 * *if* the ball doesn't move and we thus must drag the chain.  It is not
 * called for ordinary teleportation.
 *
 * allow_drag is only used in the ugly special case where teleporting must
 * drag the chain, while an identical-looking movement must drag both the ball
 * and chain.
 */
boolean
drag_ball(x, y, bc_control, ballx, bally, chainx, chainy, cause_delay,
          allow_drag)
xchar x, y;
int *bc_control;
xchar *ballx, *bally, *chainx, *chainy;
boolean *cause_delay;
boolean allow_drag;
{
    struct trap *t = (struct trap *) 0;
    boolean already_in_rock;

    *ballx = uball->ox;
    *bally = uball->oy;
    *chainx = uchain->ox;
    *chainy = uchain->oy;
    *bc_control = 0;
    *cause_delay = FALSE;

    if (dist2(x, y, uchain->ox, uchain->oy) <= 2) { /* nothing moved */
        move_bc(1, *bc_control, *ballx, *bally, *chainx, *chainy);
        return TRUE;
    }

    /* only need to move the chain? */
    if (carried(uball) || distmin(x, y, uball->ox, uball->oy) <= 2) {
        xchar oldchainx = uchain->ox, oldchainy = uchain->oy;

        *bc_control = BC_CHAIN;
        move_bc(1, *bc_control, *ballx, *bally, *chainx, *chainy);
        if (carried(uball)) {
            /* move chain only if necessary */
            if (distmin(x, y, uchain->ox, uchain->oy) > 1) {
                *chainx = u.ux;
                *chainy = u.uy;
            }
            return TRUE;
        }
#define CHAIN_IN_MIDDLE(chx, chy) \
    (distmin(x, y, chx, chy) <= 1 \
     && distmin(chx, chy, uball->ox, uball->oy) <= 1)
#define IS_CHAIN_ROCK(x, y)      \
    (IS_ROCK(levl[x][y].typ)     \
     || (IS_DOOR(levl[x][y].typ) \
         && (levl[x][y].doormask & (D_CLOSED | D_LOCKED))))
/* Don't ever move the chain into solid rock.  If we have to, then instead
 * undo the move_bc() and jump to the drag ball code.  Note that this also
 * means the "cannot carry and drag" message will not appear, since unless we
 * moved at least two squares there is no possibility of the chain position
 * being in solid rock.
 */
#define SKIP_TO_DRAG                                               \
    {                                                              \
        *chainx = oldchainx;                                       \
        *chainy = oldchainy;                                       \
        move_bc(0, *bc_control, *ballx, *bally, *chainx, *chainy); \
        goto drag;                                                 \
    }
        if (IS_CHAIN_ROCK(u.ux, u.uy) || IS_CHAIN_ROCK(*chainx, *chainy)
            || IS_CHAIN_ROCK(uball->ox, uball->oy))
            already_in_rock = TRUE;
        else
            already_in_rock = FALSE;

        switch (dist2(x, y, uball->ox, uball->oy)) {
        /* two spaces diagonal from ball, move chain inbetween */
        case 8:
            *chainx = (uball->ox + x) / 2;
            *chainy = (uball->oy + y) / 2;
            if (IS_CHAIN_ROCK(*chainx, *chainy) && !already_in_rock)
                SKIP_TO_DRAG;
            break;

        /* player is distance 2/1 from ball; move chain to one of the
         * two spaces between
         *   @
         *   __
         *    0
         */
        case 5: {
            xchar tempx, tempy, tempx2, tempy2;

            /* find position closest to current position of chain */
            /* no effect if current position is already OK */
            if (abs(x - uball->ox) == 1) {
                tempx = x;
                tempx2 = uball->ox;
                tempy = tempy2 = (uball->oy + y) / 2;
            } else {
                tempx = tempx2 = (uball->ox + x) / 2;
                tempy = y;
                tempy2 = uball->oy;
            }
            if (IS_CHAIN_ROCK(tempx, tempy) && !IS_CHAIN_ROCK(tempx2, tempy2)
                && !already_in_rock) {
                if (allow_drag) {
                    /* Avoid pathological case *if* not teleporting:
                     *   0                          0_
                     *   _X  move northeast  ----->  X@
                     *    @
                     */
                    if (dist2(u.ux, u.uy, uball->ox, uball->oy) == 5
                        && dist2(x, y, tempx, tempy) == 1)
                        SKIP_TO_DRAG;
                    /* Avoid pathological case *if* not teleporting:
                     *    0                          0
                     *   _X  move east       ----->  X_
                     *    @                           @
                     */
                    if (dist2(u.ux, u.uy, uball->ox, uball->oy) == 4
                        && dist2(x, y, tempx, tempy) == 2)
                        SKIP_TO_DRAG;
                }
                *chainx = tempx2;
                *chainy = tempy2;
            } else if (!IS_CHAIN_ROCK(tempx, tempy)
                       && IS_CHAIN_ROCK(tempx2, tempy2) && !already_in_rock) {
                if (allow_drag) {
                    if (dist2(u.ux, u.uy, uball->ox, uball->oy) == 5
                        && dist2(x, y, tempx2, tempy2) == 1)
                        SKIP_TO_DRAG;
                    if (dist2(u.ux, u.uy, uball->ox, uball->oy) == 4
                        && dist2(x, y, tempx2, tempy2) == 2)
                        SKIP_TO_DRAG;
                }
                *chainx = tempx;
                *chainy = tempy;
            } else if (IS_CHAIN_ROCK(tempx, tempy)
                       && IS_CHAIN_ROCK(tempx2, tempy2) && !already_in_rock) {
                SKIP_TO_DRAG;
            } else if (dist2(tempx, tempy, uchain->ox, uchain->oy)
                           < dist2(tempx2, tempy2, uchain->ox, uchain->oy)
                       || ((dist2(tempx, tempy, uchain->ox, uchain->oy)
                            == dist2(tempx2, tempy2, uchain->ox, uchain->oy))
                           && rn2(2))) {
                *chainx = tempx;
                *chainy = tempy;
            } else {
                *chainx = tempx2;
                *chainy = tempy2;
            }
            break;
        }

        /* ball is two spaces horizontal or vertical from player; move*/
        /* chain inbetween *unless* current chain position is OK */
        case 4:
            if (CHAIN_IN_MIDDLE(uchain->ox, uchain->oy))
                break;
            *chainx = (x + uball->ox) / 2;
            *chainy = (y + uball->oy) / 2;
            if (IS_CHAIN_ROCK(*chainx, *chainy) && !already_in_rock)
                SKIP_TO_DRAG;
            break;

        /* ball is one space diagonal from player.  Check for the
         * following special case:
         *   @
         *    _    moving southwest becomes  @_
         *   0                                0
         * (This will also catch teleporting that happens to resemble
         * this case, but oh well.)  Otherwise fall through.
         */
        case 2:
            if (dist2(x, y, uball->ox, uball->oy) == 2
                && dist2(x, y, uchain->ox, uchain->oy) == 4) {
                if (uchain->oy == y)
                    *chainx = uball->ox;
                else
                    *chainy = uball->oy;
                if (IS_CHAIN_ROCK(*chainx, *chainy) && !already_in_rock)
                    SKIP_TO_DRAG;
                break;
            }
        /* fall through */
        case 1:
        case 0:
            /* do nothing if possible */
            if (CHAIN_IN_MIDDLE(uchain->ox, uchain->oy))
                break;
            /* otherwise try to drag chain to player's old position */
            if (CHAIN_IN_MIDDLE(u.ux, u.uy)) {
                *chainx = u.ux;
                *chainy = u.uy;
                break;
            }
            /* otherwise use player's new position (they must have
               teleported, for this to happen) */
            *chainx = x;
            *chainy = y;
            break;

        default:
            impossible("bad chain movement");
            break;
        }
#undef SKIP_TO_DRAG
#undef CHAIN_IN_MIDDLE
        return TRUE;
    }

 drag:

    if (near_capacity() > SLT_ENCUMBER && dist2(x, y, u.ux, u.uy) <= 2) {
        You("cannot %sdrag the heavy iron ball.",
            invent ? "carry all that and also " : "");
        nomul(0);
        return FALSE;
    }

    if ((is_pool(uchain->ox, uchain->oy)
         /* water not mere continuation of previous water */
         && (levl[uchain->ox][uchain->oy].typ == POOL
             || !is_pool(uball->ox, uball->oy)
             || levl[uball->ox][uball->oy].typ == POOL))
        || ((t = t_at(uchain->ox, uchain->oy))
            && (is_pit(t->ttyp) || is_hole(t->ttyp)))) {
        if (Levitation) {
            You_feel("a tug from the iron ball.");
            if (t)
                t->tseen = 1;
        } else {
            struct monst *victim;

            You("are jerked back by the iron ball!");
            if ((victim = m_at(uchain->ox, uchain->oy)) != 0) {
                int tmp;
                int dieroll = rnd(20);

                tmp = -2 + Luck + find_mac(victim);
                tmp += omon_adj(victim, uball, TRUE);

                if (tmp >= dieroll)
                    (void) hmon(victim, uball, HMON_DRAGGED, dieroll);
                else
                    miss(xname(uball), victim);

            } /* now check again in case mon died */
            if (!m_at(uchain->ox, uchain->oy)) {
                u.ux = uchain->ox;
                u.uy = uchain->oy;
                newsym(u.ux0, u.uy0);
            }
            nomul(0);

            *bc_control = BC_BALL;
            move_bc(1, *bc_control, *ballx, *bally, *chainx, *chainy);
            *ballx = uchain->ox;
            *bally = uchain->oy;
            move_bc(0, *bc_control, *ballx, *bally, *chainx, *chainy);
            spoteffects(TRUE);
            return FALSE;
        }
    }

    *bc_control = BC_BALL | BC_CHAIN;

    move_bc(1, *bc_control, *ballx, *bally, *chainx, *chainy);
    if (dist2(x, y, u.ux, u.uy) > 2) {
        /* Awful case: we're still in range of the ball, so we thought we
         * could only move the chain, but it turned out that the target
         * square for the chain was rock, so we had to drag it instead.
         * But we can't drag it either, because we teleported and are more
         * than one square from our old position.  Revert to the teleport
         * behavior.
         */
        *ballx = *chainx = x;
        *bally = *chainy = y;
    } else {
        xchar newchainx = u.ux, newchainy = u.uy;

        /*
         * Generally, chain moves to hero's previous location and ball
         * moves to chain's previous location, except that we try to
         * keep the chain directly between the hero and the ball.  But,
         * take the simple approach if the hero's previous location or
         * the potential between location is inaccessible.
         */
        if (dist2(x, y, uchain->ox, uchain->oy) == 4
            && !IS_CHAIN_ROCK(newchainx, newchainy)) {
            newchainx = (x + uchain->ox) / 2;
            newchainy = (y + uchain->oy) / 2;
            if (IS_CHAIN_ROCK(newchainx, newchainy)) {
                /* don't let chain move to inaccessible location */
                newchainx = u.ux;
                newchainy = u.uy;
            }
        }

        *ballx = uchain->ox;
        *bally = uchain->oy;
        *chainx = newchainx;
        *chainy = newchainy;
    }
#undef IS_CHAIN_ROCK
    *cause_delay = TRUE;
    return TRUE;
}

/*
 *  drop_ball()
 *
 *  The punished hero drops or throws her iron ball.  If the hero is
 *  blind, we must reset the order and glyph.  Check for side effects.
 *  This routine expects the ball to be already placed.
 *
 *  Should not be called while swallowed.
 */
void
drop_ball(x, y)
xchar x, y;
{
    if (Blind) {
        /* get the order */
        u.bc_order = bc_order();
        /* pick up glyph */
        u.bglyph = (u.bc_order) ? u.cglyph : levl[x][y].glyph;
    }

    if (x != u.ux || y != u.uy) {
        static const char *pullmsg = "The ball pulls you out of the %s!";
        struct trap *t;
        long side;

        if (u.utrap
            && u.utraptype != TT_INFLOOR && u.utraptype != TT_BURIEDBALL) {
            switch (u.utraptype) {
            case TT_PIT:
                pline(pullmsg, "pit");
                break;
            case TT_WEB:
                pline(pullmsg, "web");
                pline_The("web is destroyed!");
                deltrap(t_at(u.ux, u.uy));
                break;
            case TT_LAVA:
                pline(pullmsg, hliquid("lava"));
                break;
            case TT_BEARTRAP:
                side = rn2(3) ? LEFT_SIDE : RIGHT_SIDE;
                pline(pullmsg, "bear trap");
                set_wounded_legs(side, rn1(1000, 500));
                if (!u.usteed) {
                    Your("%s %s is severely damaged.",
                         (side == LEFT_SIDE) ? "left" : "right",
                         body_part(LEG));
                    losehp(Maybe_Half_Phys(2),
                           "leg damage from being pulled out of a bear trap",
                           KILLED_BY);
                }
                break;
            }
            reset_utrap(TRUE);
            fill_pit(u.ux, u.uy);
        }

        u.ux0 = u.ux;
        u.uy0 = u.uy;
        if (!Levitation && !MON_AT(x, y) && !u.utrap
            && (is_pool(x, y)
                || ((t = t_at(x, y))
                    && (is_pit(t->ttyp)
                        || is_hole(t->ttyp))))) {
            u.ux = x;
            u.uy = y;
        } else {
            u.ux = x - u.dx;
            u.uy = y - u.dy;
        }
        vision_full_recalc = 1; /* hero has moved, recalculate vision later */

        if (Blind) {
            /* drop glyph under the chain */
            if (u.bc_felt & BC_CHAIN)
                levl[uchain->ox][uchain->oy].glyph = u.cglyph;
            u.bc_felt = 0; /* feel nothing */
            /* pick up new glyph */
            u.cglyph = (u.bc_order) ? u.bglyph : levl[u.ux][u.uy].glyph;
        }
        movobj(uchain, u.ux, u.uy); /* has a newsym */
        if (Blind) {
            u.bc_order = bc_order();
        }
        newsym(u.ux0, u.uy0); /* clean up old position */
        if (u.ux0 != u.ux || u.uy0 != u.uy) {
            spoteffects(TRUE);
            sokoban_guilt();
        }
    }
}

/* ball&chain cause hero to randomly lose stuff from inventory */
STATIC_OVL void
litter()
{
    struct obj *otmp, *nextobj = 0;
    int capacity = weight_cap();

    for (otmp = invent; otmp; otmp = nextobj) {
        nextobj = otmp->nobj;
        if ((otmp != uball) && (rnd(capacity) <= (int) otmp->owt)) {
            if (canletgo(otmp, "")) {
                You("drop %s and %s %s down the stairs with you.",
                    yname(otmp), (otmp->quan == 1L) ? "it" : "they",
                    otense(otmp, "fall"));
                dropx(otmp);
                encumber_msg(); /* drop[xyz]() probably ought to to this... */
            }
        }
    }
}

void
drag_down()
{
    boolean forward;
    uchar dragchance = 3;

    /*
     *  Assume that the ball falls forward if:
     *
     *  a) the character is wielding it, or
     *  b) the character has both hands available to hold it (i.e. is
     *     not wielding any weapon), or
     *  c) (perhaps) it falls forward out of his non-weapon hand
     */
    forward = carried(uball) && (uwep == uball || !uwep || !rn2(3));

    if (carried(uball))
        You("lose your grip on the iron ball.");

    cls();  /* previous level is still displayed although you
               went down the stairs. Avoids bug C343-20 */

    if (forward) {
        if (rn2(6)) {
            pline_The("iron ball drags you downstairs!");
            losehp(Maybe_Half_Phys(rnd(6)),
                   "dragged downstairs by an iron ball", NO_KILLER_PREFIX);
            litter();
        }
    } else {
        if (rn2(2)) {
            pline_The("iron ball smacks into you!");
            losehp(Maybe_Half_Phys(rnd(20)), "iron ball collision",
                   KILLED_BY_AN);
            exercise(A_STR, FALSE);
            dragchance -= 2;
        }
        if ((int) dragchance >= rnd(6)) {
            pline_The("iron ball drags you downstairs!");
            losehp(Maybe_Half_Phys(rnd(3)),
                   "dragged downstairs by an iron ball", NO_KILLER_PREFIX);
            exercise(A_STR, FALSE);
            litter();
        }
    }
}

void
bc_sanity_check()
{
    int otyp;
    unsigned save_nameknown;
    const char *onam;

    if (Punished && (!uball || !uchain)) {
        impossible("Punished without %s%s%s?",
                   !uball ? "iron ball" : "",
                   (!uball && !uchain) ? " and " : "",
                   !uchain ? "attached chain" : "");
    } else if (!Punished && (uball || uchain)) {
        impossible("Attached %s%s%s without being Punished?",
                   uchain ? "chain" : "",
                   (uchain && uball) ? " and " : "",
                   uball ? "iron ball" : "");
    }
    /* ball is free when swallowed, changing levels, other times? */
    if (uball && (uball->otyp != HEAVY_IRON_BALL
                  || (uball->where != OBJ_FLOOR
                      && uball->where != OBJ_INVENT
                      && uball->where != OBJ_FREE)
                  || (uball->owornmask & W_BALL) == 0L
                  || (uball->owornmask & ~(W_BALL | W_WEAPON)) != 0L)) {
        otyp = uball->otyp;
        if (otyp < STRANGE_OBJECT || otyp >= NUM_OBJECTS
            || !OBJ_NAME(objects[otyp])) {
            onam = "glorkum";
        } else {
            save_nameknown = objects[otyp].oc_name_known;
            objects[otyp].oc_name_known = 1;
            onam = simple_typename(otyp);
            objects[otyp].oc_name_known = save_nameknown;
        }
        impossible("uball: type %d (%s), where %d, wornmask=0x%08lx",
                   otyp, onam, uball->where, uball->owornmask);
    }
    /* similar check to ball except can't be in inventory */
    if (uchain && (uchain->otyp != IRON_CHAIN
                   || (uchain->where != OBJ_FLOOR
                       && uchain->where != OBJ_FREE)
                   /* [could simplify this to owornmask != W_CHAIN] */
                   || (uchain->owornmask & W_CHAIN) == 0L
                   || (uchain->owornmask & ~W_CHAIN) != 0L)) {
        otyp = uchain->otyp;
        if (otyp < STRANGE_OBJECT || otyp >= NUM_OBJECTS
            || !OBJ_NAME(objects[otyp])) {
            onam = "glorkum";
        } else {
            save_nameknown = objects[otyp].oc_name_known;
            objects[otyp].oc_name_known = 1;
            onam = simple_typename(otyp);
            objects[otyp].oc_name_known = save_nameknown;
        }
        impossible("uchain: type %d (%s), where %d, wornmask=0x%08lx",
                   otyp, onam, uchain->where, uchain->owornmask);
    }
    /* [check bc_order too?] */
}

/*ball.c*/