mamba-cpp: fix default paths

pkgs/by-name/ma/mamba-cpp/package.nix

@@ -4,6 +4,7 @@
   cmake,
   lib,
   libmamba,
+  makeWrapper,
   msgpack-c,
   nlohmann_json,
   python3,
@@ -14,12 +15,19 @@
   versionCheckHook,
   yaml-cpp,
   zstd,
+  # runtime options
+  defaultEnvPath ? "~/.mamba/envs",
+  defaultPkgPath ? "~/.mamba/pkgs",
+  defaultRootPath ? "~/.mamba",
 }:
 stdenv.mkDerivation {
   pname = "mamba-cpp";
   inherit (libmamba) version src;
 
-  nativeBuildInputs = [ cmake ];
+  nativeBuildInputs = [
+    cmake
+    makeWrapper
+  ];
 
   buildInputs = [
     bzip2
@@ -43,6 +51,13 @@ stdenv.mkDerivation {
 
   nativeInstallCheckInputs = [ versionCheckHook ];
 
+  postInstall = ''
+    wrapProgram $out/bin/mamba \
+      --set-default CONDA_ENVS_PATH '${defaultEnvPath}' \
+      --set-default CONDA_PKGS_DIRS '${defaultPkgPath}' \
+      --set-default MAMBA_ROOT_PREFIX '${defaultRootPath}'
+  '';
+
   __structuredAttrs = true;
   strictDeps = true;