automatic solver for simple reverse geocaches

automatically finds the three 6 digit numbers and shows final coordinates at the start of cache description
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// ==UserScript==
// @name         automatic solver for simple reverse geocaches
// @namespace    http://hautio.net/gctools/
// @version      2026-03-03-0
// @description  automatically finds the three 6 digit numbers and shows final coordinates at the start of cache description
// @author       Kari Hautio <[email protected]>
// @match        https://www.geocaching.com/geocache/GC*
// @icon         https://www.google.com/s2/favicons?sz=64&domain=geocaching.com
// @grant        none
// @license      CC CY-NC-SA 4.0
// ==/UserScript==

(function() {
    'use strict';
    function getdigit(a,n) {
        return Math.floor((a % Math.pow(10,n)) / Math.pow(10,n-1));
    }
    function reverse(a,b,c) {
        var lat, lon;
        var aa=[];
        var bb=[];
        var cc=[];
        for (var i=0; i<6; i++) {
            aa[i] = getdigit(a,6-i);
            bb[i] = getdigit(b,6-i);
            cc[i] = getdigit(c,6-i);
        }
        if ((cc[1]+cc[4]) % 2 == 0) {
            lat = aa[2] * 10 + bb[4] + bb[1] * 0.1 + cc[3] * 0.01 +
                aa[0] * 0.001 + cc[4] * 0.0001 + aa[5] * 0.00001;
            lon = aa[1] * 100 + cc[0] * 10 + cc[5] + bb[3] * 0.1 +
                bb[0] * 0.01 + aa[4] * 0.001 + cc[1] * 0.0001 + bb[5] * 0.00001;
        } else {
            lat = bb[0] * 10 + aa[5] + aa[2] * 0.1 + cc[0] * 0.01 +
                cc[3] * 0.001 + cc[4] * 0.0001 + aa[0] * 0.00001;
            lon = bb[4] * 100 + cc[5] * 10 + aa[4] + aa[1] * 0.1 +
                bb[3] * 0.01 + bb[5] * 0.001 + cc[1] * 0.0001 + bb[1] * 0.00001;
        }
      switch(aa[3]) {
        case 1:
            return [lat,lon];
        case 2:
            return [-lat,lon];
        case 3:
            return [lat,-lon];
        case 4:
            return [-lat,-lon];
        default:
            return [NaN,NaN];
        }
    }

    function printcoords(n,e) {
        var nn = Math.abs(n);
        var ee = Math.abs(e);
        var nnd = Math.floor(nn);
        var eed = Math.floor(ee);
        var nnm = 60 * (nn-nnd);
        var eem = 60 * (ee-eed);
        return `${n>0?'N':'S'}${nnd} ${nnm.toFixed(3)} ${e>0?'E':'W'}${eed} ${eem.toFixed(3)}`;
    }

    function findNumbers() {
        var numbers = new Array(0);
        // first look into note for the numbers
        var container = document.getElementById("srOnlyCacheNote");
        if (container) {
          // console.log("check1:" + container.innerHTML);
          const text = container.innerHTML;
          numbers = text.match(/\d{6}/g); // matches numbers with 6 digits
        }
        // if not found from note then check description
        container = document.getElementById("ctl00_ContentBody_LongDescription");
        if (container && (!numbers || numbers.length != 3)) {
          if (container) {
            // console.log("check2:" + container.innerText);
            const text = container.innerText;
            numbers = text.match(/\d{6}/g); // matches numbers with 6 digits
          }
        }
        // if exaclt 3 numbers found reverse them (multiplies accepted to handle translations)
        if ((numbers.length >= 3) && ((numbers.length % 3) == 0)) {
            // console.log("reversing:" + numbers);
            var out = reverse(numbers[0], numbers[1], numbers[2]);
            var coordstr = printcoords(out[0],out[1]);
	    // Update solution to the front of the page
            container.innerHTML="<p>Wherigo numbers (<I>" + numbers[0] + " " + numbers[1] + " " + numbers[2] + "</I>) found and parsed from the page, final coordinates are:<br><B>" + coordstr + "</B></br>These have been copied to cliboard.</p>" + container.innerHTML;
            // Copy solution to clipboard
            navigator.clipboard.writeText(coordstr);
        }
    }

    // Run after page load
    window.addEventListener("load", findNumbers);
})();