embed plugin loader directly into the launcher

PluginLoader/Data/SEPMPlugin.cs

@@ -0,0 +1,45 @@
+using System.IO.Compression;
+using ProtoBuf;
+
+namespace PluginLoader.Data;
+
+[ProtoContract]
+public class SEPMPlugin : SteamPlugin
+{
+    private const string NameFile = "name.txt";
+
+    private string dataFolder;
+
+    protected SEPMPlugin()
+    {
+    }
+
+    public override string Source => "SEPM";
+    protected override string HashFile => "sepm-plugin.txt";
+
+    protected override void CheckForUpdates()
+    {
+        dataFolder = Path.Combine(root, "sepm-plugin");
+
+        if (Directory.Exists(dataFolder))
+            base.CheckForUpdates();
+        else
+            Status = PluginStatus.PendingUpdate;
+    }
+
+    protected override void ApplyUpdate()
+    {
+        if (Directory.Exists(dataFolder))
+            Directory.Delete(dataFolder, true);
+
+        ZipFile.ExtractToDirectory(sourceFile, dataFolder);
+    }
+
+    protected override string GetAssemblyFile()
+    {
+        if (!Directory.Exists(dataFolder))
+            return null;
+        return Directory.EnumerateFiles(dataFolder, "*.dll")
+                        .Where(s => !s.Equals("0Harmony.dll", StringComparison.OrdinalIgnoreCase)).FirstOrDefault();
+    }
+}