CosmosDb stored procedure to generate the next number in a 7-digit non-repeating pseudo random sequence.

getNext.js

function getNext(name) {    
    var response = getContext().getResponse();

    var result = __.chain()
        .filter(function(doc) { return doc.id === name; })
        .value({}, updateCounter);

    if(!result.isAccepted) throw new Error("The call was not accepted");

    var next;
    var etag;

    function updateCounter(err, docs) {
        if (err) throw err;

        var settings = docs[0];        

        if(settings.current === 0) {
            next = settings.offset;                
        }
        else {
            next = (settings.a * (settings.current - settings.offset) + settings.c) % settings.m + settings.offset;
            if (next === settings.offset)
                throw new Error(name + " counter values exhausted");
        }        

        var doc = {
            id: settings.id,
            m: settings.m,
            a: settings.a,                
            c: settings.c,
            offset: settings.offset,
            current: next,
            issue: settings.issue + 1
        };
                     
        var result =__.replaceDocument(
            settings._self,
            doc,
            {
                indexAction: 'default',
                etag: settings._etag
            },
            setResponse);

        if(!result) throw new Error("The call was not accepted");        
    }

    function setResponse(err, doc) {
        if (err) throw err;
        response.setBody("" + next);
    }
}