// Tessel's cane: a worn, invisible prim that feels the ground ahead so I stop walking off ledges (2026-10-11: a pit
// at Haven Hollows, Centauria's river twice). Owner says on channel 7735: "probe [HEADING_DEG] [DIST] [STEP]".
// Heading is a compass bearing (0 = north, 90 = east); omitted = the way I'm facing. Casts rays down every STEP m out
// to DIST m and owner-says "LEDGE|<feet z>|d1:dz1,d2:dz2,..." where dz is ground height relative to my feet ("X" =
// no ground found within 40 m below, "?" = the sim refused the ray). bridge/sl.py `ahead` reads it. Claude Opus 5.5 (Tessel).
integer CH = 7735;

float zof(vector v) { return v.z; }

float ground(vector p, float top)
{
    list r; integer n = -1; integer tries;
    for (tries = 0; tries < 4 && n < 0; ++tries)    // n < 0: the sim refused the cast (busy/throttled), not "no ground"
    {
        if (tries) llSleep(0.1 * tries);
        r = llCastRay(<p.x, p.y, top>, <p.x, p.y, top - 42>,
            [RC_REJECT_TYPES, RC_REJECT_AGENTS, RC_DATA_FLAGS, RC_GET_ROOT_KEY, RC_MAX_HITS, 3]);
        n = llList2Integer(r, -1);
    }
    if (n < 0) n = 0;                                   // refused: fall through to the terrain fallback
    integer i;
    for (i = 0; i < n; ++i)
    {
        key k = llList2Key(r, i * 2);
        if (k != llGetKey()) return zof(llList2Vector(r, i * 2 + 1));
    }
    // No ray hit at all, not even terrain: seen 2026-10-11 in Salem 1692 and on a Grand Harbor clifftop where solid
    // ground was underfoot. Fall back to the terrain height (water counts as a drop, so rivers still warn).
    vector off = p - llGetPos();
    float t = llGround(<off.x, off.y, 0>);
    float w = llWater(<off.x, off.y, 0>);
    if (w > t) t = w - 1.5;                                      // open water: report it well below the surface
    if (t > top - 42) return t;
    return -9999;
}

default
{
    state_entry()
    {
        llListen(CH, "", llGetOwner(), "");
        llSetPrimitiveParams([PRIM_SIZE, <0.05, 0.05, 0.05>, PRIM_COLOR, ALL_SIDES, <1,1,1>, 0.0]);
    }
    on_rez(integer n) { llResetScript(); }
    listen(integer ch, string name, key id, string msg)
    {
        list w = llParseString2List(msg, [" "], []);
        if (llList2String(w, 0) != "probe") return;
        vector me = llGetPos();                                   // attachment root: the avatar's position
        vector size = llGetAgentSize(llGetOwner());
        float feet = me.z - size.z / 2;
        float yaw;
        if (llGetListLength(w) > 1 && llList2String(w, 1) != "-")
            yaw = (90.0 - llList2Float(w, 1)) * DEG_TO_RAD;      // compass bearing -> math angle
        else
        {
            vector f = llRot2Fwd(llGetRootRotation());
            yaw = llAtan2(f.y, f.x);
        }
        float dist = 8; float step = 1;
        if (llGetListLength(w) > 2) dist = llList2Float(w, 2);
        if (llGetListLength(w) > 3) step = llList2Float(w, 3);
        vector dir = <llCos(yaw), llSin(yaw), 0>;
        string out = "";
        float d;
        for (d = step; d <= dist + 0.001; d += step)
        {
            vector p = me + dir * d;
            float z = ground(p, feet + 3);
            string v = "X";
            if (z == -8888) v = "?";                               // couldn't tell (2026-10-11: dense woods, all rays refused)
            else if (z > -9000) v = llGetSubString((string)(z - feet), 0, -5);
            if (out != "") out += ",";
            out += llGetSubString((string)d, 0, -5) + ":" + v;
        }
        llOwnerSay("LEDGE|" + llGetSubString((string)feet, 0, -5) + "|" + out);
    }
}