Adds support for modernuo.json (#56)

Projects/Server/Configuration.cs

@@ -0,0 +1,73 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Text.Json;
+
+namespace Server
+{
+  public class Configuration
+  {
+    private static Configuration m_Configuration;
+
+    public static Configuration Instance => m_Configuration ??= ReadConfiguration();
+
+    public List<string> DataDirectories { get; } = new List<string>();
+
+    private static string FilePath => Path.Join(Core.BaseDirectory, "modernuo.json");
+
+    private static void PromptDataDirectories(Configuration config)
+    {
+      Console.WriteLine("Please enter the Ultima Online directory:");
+
+      string directory;
+      do
+      {
+        Console.Write("> ");
+        directory = Console.ReadLine();
+      } while (!Directory.Exists(directory));
+
+      config.DataDirectories.Add(directory);
+    }
+
+    private static Configuration ReadConfiguration()
+    {
+      Console.Write($"Reading configuration from {FilePath}...");
+      Configuration config;
+
+      if (File.Exists(FilePath))
+      {
+        using FileStream fs = new FileStream(FilePath, FileMode.Open, FileAccess.Read, FileShare.Read);
+        Span<byte> configBytes = stackalloc byte[(int)fs.Length];
+        fs.Read(configBytes);
+        config = JsonSerializer.Deserialize<Configuration>(Utility.UTF8WithEncoding.GetString(configBytes));
+        Console.WriteLine("done");
+      }
+      else
+      {
+        Console.WriteLine("not found.");
+        config = new Configuration();
+      }
+
+      // TODO: Extend with a config read verification function that can be extended.
+      if (config.DataDirectories.Count == 0)
+      {
+        PromptDataDirectories(config);
+        config.Flush();
+      }
+
+      return config;
+    }
+
+    public void Flush()
+    {
+      using FileStream fs = new FileStream(FilePath, FileMode.OpenOrCreate, FileAccess.Write, FileShare.Write);
+      string configJson = JsonSerializer.Serialize(this, new JsonSerializerOptions {WriteIndented = true});
+      Span<byte> data = stackalloc byte[Utility.UTF8WithEncoding.GetMaxByteCount(configJson.Length)];
+      int bytesWritten = Utility.UTF8WithEncoding.GetBytes(configJson, data);
+      fs.Write(data.Slice(0, bytesWritten));
+      Console.ForegroundColor = ConsoleColor.Green;
+      Console.WriteLine($"Configuration saved to {FilePath}");
+      Console.ResetColor();
+    }
+  }
+}