Platform Lift

// =====================================================================
//  Platform Lift
//  skimi3d script library
//  https://grid.skimi3d.com/scripts/platform-lift
//
//  Sit on it and it takes you up. Stand up at the top and it comes back
//  down on its own, ready for the next person.
//
//  Two floors, no shaft, no doors, no call buttons. It is the simplest
//  thing that will actually carry somebody, and simple is the reason it
//  works: most home-made lifts fail because the avatar was standing on
//  the platform rather than sitting on it.
//
//  Plain LSL.
// =====================================================================


// ---------------------------------------------------------------------
//  Settings
// ---------------------------------------------------------------------

// How far up it goes, in metres.
float TRAVEL = 6.0;

// How long the trip takes, in seconds, each way.
float TIME = 5.0;

// Where the rider sits, measured from the middle of the platform. Never
// exactly zero: that is how you say there is no seat at all.
vector SIT_POSITION = <0.0, 0.0, 0.6>;

// What the right-click menu says.
string MENU_TEXT = "Ride up";

// A left click sits somebody straight down, with no menu.
integer CLICK_TO_RIDE = TRUE;

// Come back down by itself once the rider has stepped off at the top,
// and how many seconds to wait first.
integer RETURN_WHEN_EMPTY = TRUE;
float   RETURN_AFTER = 8.0;


// ---------------------------------------------------------------------
//  Everything below here is the machinery
// ---------------------------------------------------------------------

integer gUp     = FALSE;    // is it at the top?
integer gMoving = FALSE;
integer gJob    = 0;        // 0 nothing, 1 arriving, 2 waiting to come down
key     gRider  = NULL_KEY;


ride(integer up)
{
    // Both of these make keyframed motion do nothing at all, silently.
    if (llGetStatus(STATUS_PHYSICS))
    {
        llOwnerSay("I cannot move: I am physical, and keyframed motion only works on things that are not. Turn Physical off in the build tool.");
        return;
    }
    if (llGetAttached())
    {
        llOwnerSay("I cannot move while I am worn.");
        return;
    }

    float far = TRAVEL;
    if (!up) far = -TRAVEL;

    // One step, straight up or straight down. Keyframed motion is what
    // carries the rider: the platform and whoever is sitting on it move
    // as one thing, which llSetPos would not manage.
    llSetKeyframedMotion([<0.0, 0.0, far>, ZERO_ROTATION, TIME],
                         [KFM_MODE, KFM_FORWARD]);

    gMoving = TRUE;
    gUp     = up;
    gJob    = 1;
    llSetTimerEvent(TIME);
}


seat()
{
    llSitTarget(SIT_POSITION, ZERO_ROTATION);
    llSetSitText(MENU_TEXT);

    if (CLICK_TO_RIDE)  llSetClickAction(CLICK_ACTION_SIT);
    if (!CLICK_TO_RIDE) llSetClickAction(CLICK_ACTION_TOUCH);
}


default
{
    state_entry()
    {
        seat();

        // Wherever it is standing now counts as the bottom. Put it at
        // the bottom before you drop the script in.
        gUp     = FALSE;
        gMoving = FALSE;
        gJob    = 0;
        gRider  = NULL_KEY;
        llSetTimerEvent(0.0);
    }

    changed(integer what)
    {
        if (!(what & CHANGED_LINK)) return;

        key who = llAvatarOnSitTarget();

        if (who)
        {
            gRider = who;

            // Somebody got on at the bottom, so up we go. Somebody
            // getting on at the top is riding back down.
            if (!gMoving) ride(!gUp);
            return;
        }

        // The rider stepped off.
        if (gRider)
        {
            gRider = NULL_KEY;

            if (RETURN_WHEN_EMPTY && gUp && !gMoving)
            {
                gJob = 2;
                llSetTimerEvent(RETURN_AFTER);
            }
        }
    }

    timer()
    {
        if (gJob == 1)
        {
            // Arrived.
            gMoving = FALSE;
            gJob    = 0;
            llSetTimerEvent(0.0);

            // Nobody got off, because nobody was ever on: an empty trip
            // up should still come back down.
            if (RETURN_WHEN_EMPTY && gUp && !gRider)
            {
                gJob = 2;
                llSetTimerEvent(RETURN_AFTER);
            }
            return;
        }

        if (gJob == 2)
        {
            gJob = 0;
            llSetTimerEvent(0.0);

            // Somebody stepped on while it was waiting. Leave it where
            // it is; their sitting down will have already sent it.
            if (gRider) return;
            if (!gUp) return;

            ride(FALSE);
        }
    }

    on_rez(integer start)
    {
        // A rezzed copy is standing at its new bottom, whatever it was
        // doing when it was taken.
        llResetScript();
    }
}