// Weathervane: every 10 s, turn the "vane ..." prims about the post so the fish's head points into the wind
// (where it blows from), easing toward it. Claude Opus 5.5 (Tessel), 2026-10-10.
list gLinks;     // link numbers of the vane parts
list gBase;      // their positions relative to the pivot axis, at heading 0 (head pointing +x)
list gRot;       // their rotations at heading 0
float gHeading;  // radians, current

init()
{
    gLinks = []; gBase = []; gRot = [];
    integer n = llGetNumberOfPrims();
    integer i;
    for (i = 2; i <= n; ++i)
    {
        if (llGetSubString(llGetLinkName(i), 0, 4) == "vane ")
        {
            list p = llGetLinkPrimitiveParams(i, [PRIM_POS_LOCAL, PRIM_ROT_LOCAL]);
            gLinks += i; gBase += llList2Vector(p, 0); gRot += llList2Rot(p, 1);
        }
    }
    gHeading = 0.0;
}

turn(float h)
{
    rotation r = llEuler2Rot(<0.0, 0.0, h>);  // about the post (root local z)
    list set;
    integer i;
    for (i = 0; i < llGetListLength(gLinks); ++i)
        set += [PRIM_LINK_TARGET, llList2Integer(gLinks, i),
                PRIM_POS_LOCAL, llList2Vector(gBase, i) * r, PRIM_ROT_LOCAL, llList2Rot(gRot, i) * r];
    llSetLinkPrimitiveParamsFast(LINK_THIS, set);
}

default
{
    state_entry() { init(); llSetTimerEvent(10.0); }
    on_rez(integer p) { llResetScript(); }
    timer()
    {
        vector w = llWind(ZERO_VECTOR);
        if (llVecMag(w) < 0.2) return;
        float want = llAtan2(-w.y, -w.x);            // into the wind
        float d = want - gHeading;
        while (d > PI) d -= TWO_PI;
        while (d < -PI) d += TWO_PI;
        gHeading += d * 0.5 + (llFrand(0.1) - 0.05);  // ease, with a little wobble
        turn(gHeading);
    }
}