// SPDX-License-Identifier: MIT
// Copyright (c) 2026 Incoprea
// Sliding eight-tile puzzle
// Not compiled or tested in-world
// Setup: Owner-touch to generate a puzzle by valid random moves from a solved board. Enter the number of a tile next to the underscore.
// Stop / restore: Stop responding and the listener closes after 90 seconds, or remove/disable the script. Owner-touch restarts the exercise.
// Notes: Owner-only local exercise; no prizes, visitor records, network service, or persistent scores. The scramble is always reachable from the solved state. A random walk can occasionally finish near or at solved; restart for another scramble.
// License: see LICENSE in this distribution.
// Original Incoprea. MIT. Not compiled or tested in-world.
integer channel;
integer handle;
close()
{
    if(handle)llListenRemove(handle);
    handle=0;
    llSetTimerEvent(0.0);
}
ask(string prompt)
{
    if(!handle)
    {
        channel=-1000-(integer)llFrand(1000000.0);
        handle=llListen(channel,"",llGetOwner(),"");
    }
    llTextBox(llGetOwner(),prompt,channel);
    llSetTimerEvent(90.0);
}
integer digit(string text,integer min,integer max)
{
    if(llStringLength(text)!=1)return -1;
    integer n=llSubStringIndex("0123456789",text);
    if(n<min||n>max)return -1;
    return n;
}
list board;
integer blank;
string view()
{
    return llDumpList2String(llList2List(board,0,2)," ")+"\n"+llDumpList2String(llList2List(board,3,5)," ")+"\n"+llDumpList2String(llList2List(board,6,8)," ");
}
integer adjacent(integer p)
{
    return llAbs(p/3-blank/3)+llAbs(p%3-blank%3)==1;
}
move(integer p)
{
    string value=llList2String(board,p);
    board=llListReplaceList(board,[value],blank,blank);
    board=llListReplaceList(board,["_"],p,p);
    blank=p;
}
start()
{
    board=["1","2","3","4","5","6","7","8","_"];
    blank=8;
    integer i;
    for(i=0;i<100;++i)
    {
        integer p=(integer)llFrand(9.0);
        if(adjacent(p))move(p);
    }
    ask(view()+"\nEnter adjacent tile 1-8.");
}
answer(string s)
{
    if(digit(s,1,8)<0)
    {
        ask(view()+"\nEnter a tile number 1-8.");
        return;
    }
    integer p=llListFindList(board,[s]);
    if(p<0||!adjacent(p))
    {
        ask(view()+"\nChoose a tile beside the blank.");
        return;
    }
    move(p);
    if(llDumpList2String(board,"")=="12345678_")
    {
        close();
        llOwnerSay("Puzzle solved.");
        return;
    }
    ask(view()+"\nSlide another tile.");
}
default
{
    touch_start(integer count)
    {
        if(llDetectedKey(0)!=llGetOwner())return;
        close();
        start();
    }
    listen(integer ch,string name,key id,string message)
    {
        if(!handle||ch!=channel||id!=llGetOwner())return;
        answer(llStringTrim(message,STRING_TRIM));
    }
    timer()
    {
        close();
        llOwnerSay("Exercise paused. Touch to restart.");
    }
    changed(integer change)
    {
        if(change&CHANGED_OWNER)llResetScript();
    }
}