move container generation to its own file

Signed-off-by: ahuston-0 <aliceghuston@gmail.com>

lib/container-utils.nix

@@ -0,0 +1,43 @@
+{ lib, ... }:
+
+{
+  # Given a attrset of images and a function which generates an image spec,
+  # generates a set of containers (although this could in theory be used for
+  # other things... I'd like to see people try)
+  #
+  # container set must be in the below format
+  # { container-name = {image = "image-uri"; scale = n;}; }
+  # where image-uri gets passed in to the container-spec function as a custom
+  # parameter, and scale is an integer that generates the containers
+  #
+  # container-spec must be a function which accepts two parameter (the
+  # container name and image name) and ideally returns an oci-compliant
+  # container.
+  #
+  # args:
+  # containers: an AttrSet which specifies the imageUri and scale of each
+  #   container
+  # container-spec: a function which produces an oci-compliant container spec
+  #
+  # type:
+  # AttrSet -> (String -> AttrSet -> AttrSet) -> AttrSet
+  createTemplatedContainers =
+    containers: container-spec:
+    builtins.listToAttrs (
+      lib.flatten (
+        lib.mapAttrsToList (
+          name: value:
+          (map (
+            num:
+            let
+              container-name = "${name}-${toString num}";
+            in
+            {
+              name = container-name;
+              value = container-spec container-name value.image;
+            }
+          ) (lib.lists.range 1 value.scale))
+        ) containers
+      )
+    );
+}