Notes/Services/FileNoteService.cs

namespace BinaryDad.Notes.Services
{
    public class FileNoteService : INoteService
    {
        private readonly string folderPath;

        private static readonly string defaultFolderPath = "notes";

        public FileNoteService(IConfiguration configuration)
        {
            folderPath = configuration["FileNoteService:ContentFolder"];

            if (string.IsNullOrWhiteSpace(folderPath))
            {
                folderPath = defaultFolderPath;
            }
        }

        public string GetNote(string noteName)
        {
            CheckFile(noteName);

            return File.ReadAllText(GetFilePath(noteName));
        }

        public ICollection<string> GetNoteNames()
        {
            return Directory.GetFiles(folderPath)
                .Select(f => Path.GetFileName(f))
                .ToList();
        }

        public void SaveNote(string content, string noteName)
        {
            File.WriteAllText(GetFilePath(noteName), content);
        }

        public void DeleteNote(string noteName)
        {
            var filePath = GetFilePath(noteName);

            File.Delete(filePath);
        }

        private void CheckFile(string noteName)
        {
            var filePath = GetFilePath(noteName);

            // ensure initialized
            if (!File.Exists(filePath))
            {
                Directory.CreateDirectory(folderPath);

                SaveNote("Hi! Feel free to start typing. Everything will be saved soon after you are done typing.", noteName);
            }
        }

        private string GetFilePath(string noteName)
        {
            noteName = noteName.Trim().ToLower();

            return Path.Combine(folderPath, noteName);
        }
    }
}