Completed modpack flake

flake.nix

@@ -11,5 +11,8 @@
     inputs.nix-modpack (system: {
       packUrl = "https://git.bulthuis.dev/Jan/Modpack/raw/branch/main/pack.toml";
       server = inputs.nix-minecraft.legacyPackages.${system}.neoForgeServers.neoforge-21_1_172;
+      clientGameVersion = "1.21.1";
+      clientLoaderUid = "net.neoforged";
+      clientLoaderVersion = "21.1.172";
     });
 }

nix-modpack/lib/default.nix

@@ -19,11 +19,65 @@ let
 
           buildInfo = builder pkgs.system;
         in
-        lib.trace buildInfo {
+        rec {
+          default = server;
           server = pkgs.writeShellScriptBin "minecraft-server" ''
             ${lib.getExe pkgs.jre} -jar ${bootstrap} -g -s server ${buildInfo.packUrl}
-            # ${buildInfo.server}/bin/minecraft-server
+            ${buildInfo.server}/bin/minecraft-server
           '';
+          client = pkgs.stdenvNoCC.mkDerivation {
+            name = "minecraft-client";
+
+            dontUnpack = true;
+
+            mmcpack = ''
+              {
+                "components": [
+                  {
+                    "important": true,
+                    "uid": "net.minecraft",
+                    "version": "${buildInfo.clientGameVersion}"
+                  },
+                  {
+                    "uid": "${buildInfo.clientLoaderUid}",
+                    "version": "${buildInfo.clientLoaderVersion}"
+                  }
+                ],
+                "formatVersion": 1
+              }
+            '';
+
+            instancecfg = pkgs.writeText "instance.cfg" ''
+              [General]
+              ConfigVersion=1.2
+              InstanceType=OneSix
+              OverrideCommands=true
+              PreLaunchCommand=\"$INST_JAVA\" -jar packwiz-installer-bootstrap.jar ${buildInfo.packUrl}
+            '';
+
+            buildPhase = ''
+              # Remove env-vars
+              rm env-vars
+
+              # Add the mmc-pack
+              echo  $mmcpack > ./mmc-pack.json
+
+              # Add the instance-cfg
+              cp $instancecfg ./instance.cfg
+
+              # Add the bootstrap jar
+              mkdir ./minecraft
+              cp ${bootstrap} ./minecraft/packwiz-installer-bootstrap.jar
+
+              # Zip everything together
+              ${pkgs.zip}/bin/zip -r modpack.zip ./*
+            '';
+
+            installPhase = ''
+              mkdir $out
+              mv modpack.zip $out/
+            '';
+          };
         };
 
       overlay = final: prev: mkPackages prev;