Add gandalf shell

shells/gandalf.nix

@@ -0,0 +1,45 @@
+{ pkgs, inputs }: pkgs.devshell.mkShell {
+  name = "Gandalf";
+  imports = [ "${inputs.devshell}/extra/language/ruby.nix" ];
+  commands = [
+    {
+      name = "refresh-deps";
+      category = "general commands";
+      help = "Install dependencies";
+      command = ''
+        yarn install
+        bundle install
+        bundle pristine
+      '';
+    }
+    {
+      name = "mysql";
+      category = "general commands";
+      help = "Start mysql (in docker container)";
+      command = ''
+        docker run --name gandalf-db -p 3306:3306 --rm -v gandalf-db-data:/var/lib/mysql -e MYSQL_ROOT_PASSWORD=gandalf mariadb:latest
+      '';
+    }
+  ];
+  packages = with pkgs; [
+    imagemagick
+    libyaml
+    nodejs
+    yarn
+  ];
+  env = [
+    { name = "DATABASE_URL"; value = "mysql2://root:gandalf@127.0.0.1:3306/gandalf"; }
+    { name = "TEST_DATABASE_URL"; value = "mysql2://root:gandalf@127.0.0.1:3306/gandalf_test"; }
+  ];
+  serviceGroups.server.services = {
+    rails = {
+      name = "server";
+      command = "rails s -p 3000";
+    };
+    mysql.command = "mysql";
+  };
+  language.ruby = {
+    package = pkgs.ruby_3_0;
+    nativeDeps = [ pkgs.sqlite pkgs.libmysqlclient pkgs.zlib ];
+  };
+}