increment docs and add tests cases for transform with MFA

README.md

@@ -48,8 +48,9 @@ end
 - `{type, {:default, default}}` - Provides a default value if the field is missing or `nil`.
   - `{type, {:default, &some_fun/0}}` - The default values is retrieved from callinf `some_fun/0` if the field is missing.
   - `{type, {:default, {mod, fun}}}` - The default values is retrieved from callinf `mod.fun/0` if the field is missing.
-- `{type, {:transform, mapper}}` - Transforms the field value using the specified mapper function.
-  - `{type, {:transform, {mod, fun}}}` - Transforms the field value using the specified `mod.fun/1` function.
+- `{type, {:transform, mapper}}` - Transforms the field value using the specified mapper function. It can be a 1 or 2 arity function: when is a single arity the mapper function will only receive the defined field value, while with 2 arity will receive the current defined field value and the whole data as the second argument.
+  - `{type, {:transform, {mod, fun}}}` - Transforms the field value using the specified `mod.fun/1` function. Notice that `fun` can be a 2 arity so it can receive the whole data being validated, in case on dependent fields transformations.
+  - `{type, {:transform, {mod, fun, args}}}` - Transforms the field value using the specified MFA. Notice that `fun` will be at least a 2 arity one so it can receive the whole data being validated, in case on dependent fields transformations and the maximum arity allowed will be 2 + `length(args)`.
 - `{:either, {type1, type2}}` - Validates that the field is either of the two specified types.
 - `{:oneof, types}` - Validates that the field is one of the specified types.
 - `{:custom, callback}` - Validates that the field passes the custom validation function.

lib/peri.ex

@@ -675,14 +675,34 @@ defmodule Peri do
   defp validate_field(val, {type, {:transform, {mod, fun}}}, data)
        when is_atom(mod) and is_atom(fun) do
     with :ok <- validate_field(val, type, data) do
-      {:ok, apply(mod, fun, [val])}
+      cond do
+        function_exported?(mod, fun, 1) ->
+          {:ok, apply(mod, fun, [val])}
+
+        function_exported?(mod, fun, 2) ->
+          {:ok, apply(mod, fun, [val, maybe_get_root_data(data)])}
+
+        true ->
+          template = "expected %{mod} to export %{fun}/1 or %{fun}/2"
+          {:error, template, mod: mod, fun: fun}
+      end
     end
   end
 
   defp validate_field(val, {type, {:transform, {mod, fun, args}}}, data)
        when is_atom(mod) and is_atom(fun) and is_list(args) do
     with :ok <- validate_field(val, type, data) do
-      {:ok, apply(mod, fun, [val | args])}
+      cond do
+        function_exported?(mod, fun, length(args) + 2) ->
+          {:ok, apply(mod, fun, [val, maybe_get_root_data(data) | args])}
+
+        function_exported?(mod, fun, length(args) + 1) ->
+          {:ok, apply(mod, fun, [val | args])}
+
+        true ->
+          template = "expected %{mod} to export %{fun} with arity from %{base} to %{arity}"
+          {:error, template, mod: mod, fun: fun, arity: length(args), base: length(args) + 1}
+      end
     end
   end
 

test/peri_test.exs

@@ -1492,6 +1492,53 @@ defmodule PeriTest do
     end
   end
 
+  describe "transform with MFA" do
+    test "it should apply the mapper function without additional argument" do
+      s = {:string, {:transform, {String, :to_integer}}}
+      assert {:ok, 10} = Peri.validate(s, "10")
+    end
+
+    test "it should apply the mapper function without additional argument but with dependent field" do
+      s = %{id: {:string, {:transform, {__MODULE__, :integer_by_name}}}, name: :string}
+      data = %{id: "10", name: "john"}
+      assert {:ok, %{id: 20, name: "john"}} = Peri.validate(s, data)
+
+      data = %{id: "10", name: "maria"}
+      assert {:ok, %{id: 10, name: "maria"}} = Peri.validate(s, data)
+    end
+
+    test "it should apply mapper function with additional arguments" do
+      s = {:string, {:transform, {String, :split, [~r/\D/, [trim: true]]}}}
+      assert {:ok, ["10"]} = Peri.validate(s, "omw 10")
+    end
+
+    test "it should apply mapper function with additional arguments with dependent field" do
+      s = %{
+        id: {:string, {:transform, {__MODULE__, :integer_by_name, [[make_sense?: false]]}}},
+        name: :string
+      }
+
+      data = %{id: "10", name: "john"}
+      assert {:ok, %{id: 10, name: "john"}} = Peri.validate(s, data)
+    end
+  end
+
+  def integer_by_name(id, %{name: name}) do
+    if name != "john" do
+      String.to_integer(id)
+    else
+      String.to_integer(id) + 10
+    end
+  end
+
+  def integer_by_name(id, %{name: name}, make_sense?: sense) do
+    cond do
+      sense && name != "john" -> String.to_integer(id) - 10
+      not sense && name == "john" -> String.to_integer(id)
+      true -> 42
+    end
+  end
+
   defschema(:either_transform, %{
     value: {:either, {{:integer, {:transform, &double/1}}, {:string, {:transform, &upcase/1}}}}
   })