Add support for building minecraft modpacks

lib/default.nix

@@ -0,0 +1,8 @@
+{ inputs, lib, pkgs, ... }:
+
+let
+  inherit (lib) makeExtensible foldr attrValues;
+  tlater-lib = makeExtensible (self:
+    let callLibs = file: import file { inherit self lib pkgs inputs; };
+    in { minecraft = callLibs ./minecraft.nix; });
+in tlater-lib.extend (self: super: foldr (a: b: a // b) { } (attrValues super))

lib/minecraft.nix

@@ -0,0 +1,30 @@
+{ lib, pkgs, ... }:
+
+{
+  # Make a modpack given its mod inputs.
+  #
+  # Mods should be attrsets in this format:
+  #   {
+  #     project = "";
+  #     id = "";
+  #     filename = "";
+  #     sha256 = "";
+  #   }
+  #
+  # This may be nice to read from a json ;)
+  #
+  mkModpack = { name, version, mods }:
+    pkgs.stdenv.mkDerivation {
+      inherit name version;
+      srcs = map pkgs.local.fetchFromCurseForge mods;
+
+      sourceRoot = "src/";
+      preUnpack = "mkdir -p src/";
+      unpackCmd = "cp $curSrc src/";
+
+      installPhase = ''
+        mkdir -p $out/mods/
+        cp * $out/mods
+      '';
+    };
+}