// SPDX-License-Identifier: MIT
// Copyright (c) 2026 Incoprea
// Crank and piston study
// Not compiled or tested in-world
// Setup: Put in root with exactly one child named crank_marker and one piston. The illustration uses root-local XY; both should be small. Owner-touch starts/stops.
// Stop / restore: Owner-touch to stop and restore the captured starting pose before removing, resetting, or relinking.
// Notes: Use a small nonphysical rezzed build with clear space. Actual prim transforms change. Original poses live only in script memory. Do not change physical status or link topology during use. Uses a slider-crank relation with crank radius 0.2 m and connecting-rod length 0.6 m. No physics constraints or collisions are simulated.
// License: see LICENSE in this distribution.
// Original Incoprea. MIT. Not compiled or tested in-world.
integer crank;
integer piston;
list home;
integer active;
default
{
    state_entry()
    {
        integer i;
        integer hits;
        for(i=2;i<=llGetObjectPrimCount(llGetKey());++i)
        {
            string name=llGetLinkName(i);
            if(name=="crank_marker")
            {
                crank=i;
                ++hits;
            }
            if(name=="piston")
            {
                piston=i;
                ++hits;
            }
        }
        if(hits!=2||!crank||!piston)
        {
            crank=0;
            piston=0;
            return;
        }
        home=llGetLinkPrimitiveParams(crank,[PRIM_POS_LOCAL])+llGetLinkPrimitiveParams(piston,[PRIM_POS_LOCAL]);
    }
    touch_start(integer n)
    {
        if(llDetectedKey(0)!=llGetOwner()||llGetLinkNumber()>1||llGetStatus(STATUS_PHYSICS)||!crank||!piston)return;
        active=!active;
        if(active)
        {
            llResetTime();
            llSetTimerEvent(0.15);
        }
        else
        {
            llSetTimerEvent(0.0);
            llSetLinkPrimitiveParamsFast(crank,[PRIM_POS_LOCAL,llList2Vector(home,0)]);
            llSetLinkPrimitiveParamsFast(piston,[PRIM_POS_LOCAL,llList2Vector(home,1)]);
        }
    }
    timer()
    {
        if(llGetLinkNumber()>1||llGetStatus(STATUS_PHYSICS))
        {
            llSetTimerEvent(0.0);
            active=FALSE;
            return;
        }
        float a=llGetTime()*0.5;
        float y=0.2*llSin(a);
        float x=0.2*llCos(a);
        float slider=x+llSqrt(0.36-y*y);
        llSetLinkPrimitiveParamsFast(crank,[PRIM_POS_LOCAL,<x,y,0.5>]);
        llSetLinkPrimitiveParamsFast(piston,[PRIM_POS_LOCAL,<slider,0.0,0.5>]);
    }
    changed(integer change)
    {
        if(change&CHANGED_LINK)
        {
            llSetTimerEvent(0.0);
            active=FALSE;
            crank=0;
            piston=0;
            llOwnerSay("Links changed; reposition and reset before reuse.");
        }
    }
}