WIP

lib/drops/contract.ex

@@ -39,6 +39,7 @@ defmodule Drops.Contract do
       use Drops.Validator
 
       alias Drops.Types
+      alias Drops.Contract.Messages
 
       import Drops.Contract
       import Drops.Contract.Runtime
@@ -103,6 +104,12 @@ defmodule Drops.Contract do
         end
       end
 
+      def errors({:error, errors}) do
+        Messages.errors(errors)
+      end
+
+      def errors({:ok, _}), do: []
+
       def validate(data, keys) when is_list(keys) do
         Enum.map(keys, &validate(data, &1)) |> List.flatten()
       end

lib/drops/contract/messages.ex

@@ -0,0 +1,34 @@
+defmodule Drops.Contract.Messages do
+  @moduledoc false
+
+  defmodule Error do
+    alias __MODULE__
+
+    defstruct [:path, :text, :opts]
+
+    defimpl String.Chars, for: Error do
+      def to_string(%Error{text: text}) do
+        text
+      end
+    end
+  end
+
+  def errors(results) do
+    Enum.map(results, &error/1)
+  end
+
+  defp error({:error, {path, predicate, [arg, value] = args}}) do
+    %Error{
+      path: path,
+      text: text(predicate, arg, value),
+      opts: %{
+        predicate: predicate,
+        args: args
+      }
+    }
+  end
+
+  defp text(:type?, :integer, _value) do
+    "must be an integer"
+  end
+end

test/contract/messages_test.exs

@@ -0,0 +1,24 @@
+defmodule Drops.Contract.MessagesTest do
+  use Drops.ContractCase
+
+  describe "errors/1" do
+    contract do
+      schema do
+        %{
+          required(:name) => string(),
+          required(:age) => integer()
+        }
+      end
+    end
+
+    test "returns a list with error structs", %{contract: contract} do
+      result = contract.conform(%{name: "Jane Doe", age: "twenty"})
+
+      assert [error = %{path: path, opts: opts}] = contract.errors(result)
+
+      assert path == [:age]
+      assert opts == %{predicate: :type?, args: [:integer, "twenty"]}
+      assert to_string(error) == "must be an integer"
+    end
+  end
+end