I'm new to C#, and want to conform as much as possible to good design patterns. This code is the beginning of a Microservice, running as Asp.Net. It is based on a Microsoft tutorial doing similar work.

It has three functional components currently:

1. Converts a CSV file to JSON, for return via REST
2. A REST controller to test the conversion of the CSV to JSON return
3. A background service which monitors a directory looking for changed files. The file attributes (Path, Date, Checksum) are stored in a MongoDB database via a Repository.

Opinions/Recommendations regarding the design patterns welcomed.

The full code can be found at: https://github.com/BioComSoftware/unite-radimaging-source-n2m2.git

BONUS: Notice in FileSearchHostedService.cs, I instantiate the Repository objects explicitly. I think it would be more appropriate to have them as Dependency Injection - but I couldn't get it to work. Notice the commented-out lines that would have done this. My understanding is; I would need to do this with IScopedProcessingService - but I have no idea how to do this with this specific code.

[Startup.cs]

using unite.radimaging.source.n2m2.Data;
using unite.radimaging.source.n2m2.Repositories;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;
//using Microsoft.OpenApi.Models;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

namespace unite.radimaging.source.n2m2 {
    public class Startup {
        public Startup(IConfiguration configuration) {
            Configuration = configuration;
        }

        public IConfiguration Configuration { get; }

        // This method gets called by the runtime.
        // Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services) {

            services.AddControllers();

            services.AddScoped<IFoundFileContext, FoundFileContext>();
            services.AddScoped<IFoundFileRepository, FoundFileRepository>();
        }

        // This method gets called by the runtime.
        // Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env) {
            if (env.IsDevelopment()) {
                app.UseDeveloperExceptionPage();
            }
            app.UseExceptionHandler("/error");
            app.UseRouting();
            app.UseAuthorization();
            app.UseEndpoints(endpoints => { 
                endpoints.MapControllers(); 
            });
        }
    }
}

[FoundFileRepository.cs]

using unite.radimaging.source.n2m2.Data;
using unite.radimaging.source.n2m2.Entities;
using MongoDB.Driver;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

namespace unite.radimaging.source.n2m2.Repositories {
   public class FoundFileRepository : IFoundFileRepository {
       private readonly IFoundFileContext _context;
       public FoundFileRepository(IFoundFileContext context) {
           _context = context ?? throw new ArgumentNullException(nameof(context));
       }

       public async Task<IEnumerable<FoundFile>> GetFiles() {
       return await _context
           .FoundFiles
           .Find(p => true)
           .ToListAsync();
       }

       public async Task<FoundFile> GetFile(string id) {
           return await _context
                          .FoundFiles
                          .Find(p => p.Id == id)
                          .FirstOrDefaultAsync();
       }

       public async Task<FoundFile> GetFileByPath(string path) {
           return await _context
                          .FoundFiles
                          .Find(p => p.Path == path)
                          .FirstOrDefaultAsync();
       }

       public async Task<FoundFile> GetFileByChecksum(string checksum) {
           return await _context
                          .FoundFiles
                          .Find(p => p.Checksum == checksum)
                          .FirstOrDefaultAsync();
       }

       //public async Task<IEnumerable<FoundFile>> GetFileByMtime(string mtime) {
       //    FilterDefinition<FoundFile> filter = Builders<FoundFile>.Filter.ElemMatch<DateTime>(p => p.Mtime, mtime);

       //    return await _context
       //                    .FoundFiles
       //                    .Find(filter)
       //                    .ToListAsync();
       //}

       //public async Task<IEnumerable<FoundFile>> GetFileBySize(long size) {
       //    FilterDefinition<FoundFile> filter = Builders<FoundFile>.Filter.ElemMatch<long>(p => p.Size, size);

       //    return await _context
       //                    .FoundFiles
       //                    .Find(filter)
       //                    .ToListAsync();
       //}

       public async Task CreateFile(FoundFile foundFile) {
           await _context.FoundFiles.InsertOneAsync(foundFile);
       }

       public async Task<bool> UpdateFile(FoundFile foundFile) {
           var updateResult = await _context.FoundFiles.ReplaceOneAsync(
               filter: g => g.Path == foundFile.Path, replacement: foundFile);
           return updateResult.IsAcknowledged && updateResult.ModifiedCount > 0;
       }

       public async Task<bool> DeleteFile(string path) {
           FilterDefinition<FoundFile> filter = Builders<FoundFile>.Filter.Eq(p => p.Path, path);

           DeleteResult deleteResult = await _context
                                               .FoundFiles
                                               .DeleteOneAsync(filter);

           return deleteResult.IsAcknowledged
               && deleteResult.DeletedCount > 0;
       }
   }
}

[FileSearchHostedService.cs]

using unite.radimaging.source.n2m2.Repositories;
using unite.radimaging.source.n2m2.Entities;
using unite.radimaging.source.n2m2.Data;
using Serilog;
using Microsoft.Extensions.Configuration;
using System;
using System.IO;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;

namespace unite.radimaging.source.n2m2.HostedServices {
    public class FileSearchHostedService : BackgroundService {
        private readonly IConfiguration _configuration;
        //private IFoundFileRepository _repository;

        public FileSearchHostedService(
            //IFoundFileRepository repository,
            IConfiguration configuration
            ) {
            //_repository = repository ?? throw new ArgumentNullException(nameof(repository));
            _configuration = configuration ?? throw new ArgumentNullException(nameof(configuration));
        }

        protected override async Task ExecuteAsync(CancellationToken cancellationToken) {
            Log.Information("FileSearchHostedService: File searching started.");

            cancellationToken.Register(() => Log.Information("Processing service stopped"));

            //string checksum;
            string _current_path;
            FileInfo _current_file;
            FoundFile _foundFile;
            FoundFile _existingFile;
            FoundFile _addFoundFile;
            FoundFileContext FoundfileContext = new FoundFileContext(_configuration); // Normal instantiation, in leiu of injection
            FoundFileRepository _repository = new FoundFileRepository(FoundfileContext);  // Normal instantiation, in leiu of injection

            while (!cancellationToken.IsCancellationRequested) {
                Log.Information("Searching files...");
                string dir = _configuration.GetValue<string>("FileSearchSettings:SearchDir");
                string[] files = Directory.GetFiles(dir);
                foreach (string filename in files) {
                    Log.Debug($"Parsing '{filename}'");

                    _current_file     = new FileInfo(filename);
                    _current_path = Path.GetFullPath(Path.Combine(_current_file.Directory.ToString(), _current_file.Name));

                    _foundFile = new FoundFile() {
                        Path = _current_path,
                        Size = _current_file.Length,
                        Mtime = _current_file.LastWriteTime,
                        Checksum = FileChecksum.getChecksum(filename)
                    };
                    Console.WriteLine("==========================");
                    _existingFile = await _repository.GetFileByPath (_current_path);
                    Console.WriteLine("past _repository.GetFileByPath");

                    try {
                        Console.WriteLine($"{_existingFile.Path} exists!!!");
                        Console.WriteLine($"     _existingFile.Checksum: {_existingFile.Checksum}");
                        Console.WriteLine($"     _existingFile.Length = {_existingFile.Size}");
                        Console.WriteLine($"     _existingFile.LastWriteTime = ({_existingFile.Mtime}");
                    }
                    catch {
                        Console.WriteLine($"Creating MongoDB for file {_foundFile.Path} ");
                        _addFoundFile = new FoundFile() {
                            Path = _foundFile.Path,
                            Size = _foundFile.Size,
                            Mtime = _foundFile.Mtime,
                            Checksum = _foundFile.Checksum
                        };
                        await _repository.CreateFile(_addFoundFile);
                    }
                }

                await Task.Delay(
                    _configuration.GetValue<int>("FileSearchSettings:Delay"),
                    cancellationToken
                    );
            }
        }
    }
}