Notes/Services/FileNoteService.cs

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

        public FileNoteService(IConfiguration configuration)
        {
            defaultFileName = configuration["ContentFilePath"];

            CheckFile(defaultFileName);
        }

        public string Get(string? noteName)
        {
            CheckFile(noteName);

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

        public void Save(string content, string? noteName)
        {
            File.WriteAllText(GetFileName(noteName), content);
        }

        private void CheckFile(string noteName)
        {
            var fileName = GetFileName(noteName);

            // ensure initialized
            if (!File.Exists(fileName))
            {
                Save("Hi! Feel free to start typing. Everything will be saved soon after you are done typing.", fileName);
            }
        }

        private string GetFileName(string? noteName) => string.IsNullOrWhiteSpace(noteName) ? defaultFileName : noteName;
    }
}