Add project files.

FreedomFighter/HighScores.cs

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+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Text.Json;
+
+namespace FreedomFighter;
+
+public record HighScoreEntry(string Name, int Score);
+
+/// <summary>High score table; JSON replaces the original Highscore.dat record file.</summary>
+public class HighScores
+{
+    const string FileName = "highscore.json";
+    public HighScoreEntry[] List = new HighScoreEntry[10];
+
+    public void Load()
+    {
+        if (File.Exists(FileName))
+        {
+            try
+            {
+                var loaded = JsonSerializer.Deserialize<HighScoreEntry[]>(File.ReadAllText(FileName));
+                if (loaded is { Length: 10 }) { List = loaded; return; }
+            }
+            catch { /* fall through to defaults */ }
+        }
+        for (int i = 0; i < 10; i++)
+            List[i] = new HighScoreEntry("Nameless", 0);
+        Save();
+    }
+
+    public void Save() => File.WriteAllText(FileName, JsonSerializer.Serialize(List));
+
+    public bool Qualifies(int score) => score > List[9].Score;
+
+    public void Add(int num, string name, int score)
+    {
+        for (int i = 9; i >= num + 1; i--)
+            List[i] = List[i - 1];
+        List[num] = new HighScoreEntry(name, score);
+    }
+
+    /// <summary>Port of EnterHighScoreList: insert from the bottom up.</summary>
+    public void Enter(string name, int score)
+    {
+        for (int i = 8; i >= 0; i--)
+        {
+            if (score <= List[i].Score)
+            {
+                Add(i + 1, name, score);
+                break;
+            }
+            if (i == 0)
+            {
+                Add(i, name, score);
+                break;
+            }
+        }
+        Save();
+    }
+}