Attribute merge strategy

lib/speck/validation_metadata/attribute.ex

@@ -19,38 +19,60 @@ defmodule Speck.ValidationMetadata.Attribute do
 
   @doc """
   Merge the values from metadata attributes into a given map.
+
+  ## Opts
+  - `:merge_strategy` - Determines whether a value in the params or attributes
+    takes priority when both are present. Defaults to `:param_priority`.
   """
-  @spec merge(attributes :: [t], params :: map) :: map
-  def merge(attributes, params) do
+  @spec merge(
+    attributes :: [t],
+    params :: map,
+    opts :: [merge_strategy: :param_priority | :attribute_priority]
+  ) :: map
+  def merge(attributes, params, opts \\ []) do
+    merge_strategy = Keyword.get(opts, :merge_strategy, :param_priority)
+
     Enum.reduce(attributes, params, fn {path, _status, value}, acc ->
-      merge(acc, path, value)
+      merge(acc, path, value, merge_strategy)
     end)
   end
 
-  defp merge(nil = _params, [path], value) do
+  defp merge(nil = _params, [path], value, _strategy) do
     %{path => value}
   end
 
-  defp merge(params, [path], value) when is_map(params) do
-    params
-    |> to_key_strings()
-    |> Map.put(path, value)
+  defp merge(nil = _params, [attribute | path], value, strategy)
+    when not is_integer(attribute) do
+      %{attribute => merge(%{}, path, value, strategy)}
+  end
+
+  defp merge(params, [path], value, strategy) when is_map(params) do
+    params_with_key_strings = to_key_strings(params)
+
+    skip_put =
+         strategy == :param_priority
+      && Map.has_key?(params_with_key_strings, path)
+
+    case skip_put do
+      true -> params_with_key_strings
+      _    -> Map.put(params_with_key_strings, path, value)
+    end
   end
 
-  defp merge(params, [index | path], value) when is_integer(index) do
+  defp merge(params, [index | path], value, strategy) when is_integer(index) do
     params2  = params || []
     item     = Enum.at(params2, index)
-    new_item = merge(item, path, value)
+    new_item = merge(item, path, value, strategy)
 
     case item do
       nil -> List.insert_at(params2, -1, new_item)
       _   -> List.replace_at(params2, index, new_item)
     end
   end
 
-  defp merge(params, [attribute | path], value) do
+  defp merge(params, [attribute | path], value, strategy) do
     params2 = to_key_strings(params)
-    Map.put(params2, attribute, merge(params2[attribute], path, value))
+    Map.put(params2, attribute, merge(params2[attribute], path, value, strategy))
   end
 
   defp to_key_strings(map) do

test/validation_metadata/attribute_test.exs

@@ -3,6 +3,57 @@ defmodule Speck.ValidationMetadata.Attribute.Test do
 
   alias Speck.ValidationMetadata.Attribute
 
+  test "merge adds nested maps that don't exist" do
+    attributes = [
+      {["state", "reported", "serial"], :present, "sn1234"}
+    ]
+
+    assert Attribute.merge(attributes, %{}) ==
+      %{"state" => %{"reported" => %{"serial" => "sn1234"}}}
+  end
+
+  describe "merge strategy" do
+    test "attribute priority" do
+      params = %{"name" => "Test Device"}
+
+      attributes = [
+        {["name"], :present, "My Device"}
+      ]
+
+      assert Attribute.merge(attributes, params, merge_strategy: :attribute_priority) ==
+        %{"name" => "My Device"}
+
+      params = %{"state" => %{"reported" => %{"name" => "Test Device"}}}
+
+      attributes = [
+        {["state", "reported", "name"], :present, "My Device"}
+      ]
+
+      assert Attribute.merge(attributes, params, merge_strategy: :attribute_priority) ==
+        %{"state" => %{"reported" => %{"name" => "My Device"}}}
+    end
+
+    test "param priority" do
+      params = %{"name" => "Test Device"}
+
+      attributes = [
+        {["name"], :present, "My Device"}
+      ]
+
+      assert Attribute.merge(attributes, params, merge_strategy: :param_priority) ==
+        %{"name" => "Test Device"}
+
+      params = %{"state" => %{"reported" => %{"name" => "Test Device"}}}
+
+      attributes = [
+        {["state", "reported", "name"], :present, "My Device"}
+      ]
+
+      assert Attribute.merge(attributes, params, merge_strategy: :param_priority) ==
+        %{"state" => %{"reported" => %{"name" => "Test Device"}}}
+    end
+  end
+
   describe "use case" do
     test "can merge unknown attributes back into a device shadow" do
       shadow_reported = %{