// Example of input documents
// {
//    "_id" : ObjectId("59c52b3cb602cb6397c2ec9d"),
//    "Timestamp" : NumberLong(1505860144116),
//    "Value" : 14,
//    "Date" : ISODate("2017-09-19T22:29:04.116Z")
// }

public class Program
{
    private const string MapJs = @"function mapF() {
    const key = this.Date.getFullYear();
    const valuePerYear = { total: 1};

    emit(key, valuePerYear);
}; ";

    private const string ReduceJS = @"function reduceF(year, values) {
    let sum = 0;
    values.forEach(v => {
        sum += v.total;
    });
    return {total: NumberInt(sum)};
}";

    public static void Main()
    {
        string mongoConnectionString = "my-connection-string";
        MongoUrl mongoUrl = MongoUrl.Create(mongoConnectionString);
        MongoClient client = new MongoClient(mongoConnectionString);
        IMongoDatabase db = client.GetDatabase("ny_database_name");
        IMongoCollection<BsonDocument> collection = db.GetCollection<BsonDocument>("DocInput");
        BsonJavaScript map = new BsonJavaScript(MapJs);
        BsonJavaScript reduce = new BsonJavaScript(ReduceJS);
        FilterDefinitionBuilder<BsonDocument> filterBuilder = new FilterDefinitionBuilder<BsonDocument>();
        FilterDefinition<BsonDocument> filter = filterBuilder.Empty;
        MapReduceOptions<BsonDocument, BsonDocument> options = new MapReduceOptions<BsonDocument, BsonDocument>
        {
            Filter = filter,
            MaxTime = TimeSpan.FromMinutes(1),
            OutputOptions = MapReduceOutputOptions.Reduce("Result", nonAtomic: true),
            Verbose = true
        };
        try
        {
            collection.MapReduce(map, reduce, options).ToList();
        }
        catch (Exception ex)
        {
            Console.WriteLine($"Exception occurred {ex.Message}");
        }
    }
}