using MongoDB.Bson;
using MongoDB.Bson.Serialization.Attributes;
using MongoDB.Driver;

var client = new MongoClient("mongodb://localhost:27017");
var db = client.GetDatabase("test");
var coll = db.GetCollection<MyDocument>("update_with_aggregation_pipeline");

var doc = new MyDocument();
var filter = Builders<MyDocument>.Filter.Eq(x => x.Id, doc.Id);

var pipelineError = new EmptyPipelineDefinition<MyDocument>()
    .Set(x => new MyDocument()
    {
        ValueObject = new()
        {
            Value = x.ValueObject == null ? 1 : x.ValueObject.Value + 1
        }
    });
var updateError = Builders<MyDocument>.Update.Pipeline(pipelineError);


await coll.UpdateOneAsync(filter, updateError, new() { IsUpsert = true });
await PrintDocumentAsync(coll, doc.Id);

await coll.UpdateOneAsync(filter, updateError, new() { IsUpsert = true });
await PrintDocumentAsync(coll, doc.Id);

await coll.UpdateOneAsync(filter, updateError, new() { IsUpsert = true });
await PrintDocumentAsync(coll, doc.Id);

async Task PrintDocumentAsync(IMongoCollection<MyDocument> coll, string id)
{
    var filter = Builders<MyDocument>.Filter.Eq(x => x.Id, id);
    var doc = await (await coll.FindAsync(filter)).SingleOrDefaultAsync();
    Console.WriteLine(doc.ValueObject?.Value);
}

class MyDocument
{
    [BsonRepresentation(MongoDB.Bson.BsonType.ObjectId)]
    public string Id { get; set; } = ObjectId.GenerateNewId().ToString();

    public MyValue ValueObject { get; set; }
}

class MyValue
{
    public int Value { get; set; }
}

// Doesn't work too
//var pipelineWithInitialization = new EmptyPipelineDefinition<MyDocument>()
//    .Set(x => new MyDocument()
//    {
//        ValueObject = x.ValueObject ?? new()
//    })
//    .Set(x => new MyDocument()
//    {
//        ValueObject = new()
//        {
//            Value = x.ValueObject.Value + 1
//        }
//    });
//var updateWithInitialization = Builders<MyDocument>.Update.Pipeline(pipelineWithInitialization);

// A pipeline with static values works
//var pipelineWorks = new EmptyPipelineDefinition<MyDocument>()
//    .Set(x => new MyDocument()
//    {
//        ValueObject = new()
//        {
//            Value = 123
//        }
//    });