First commit

chapter3/user_extraction.ex

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+defmodule UserData do
+  defp extract_login(%{"login" => login}), do: {:ok, login}
+  defp extract_login(_), do: {:error, "login missing"}
+
+  defp extract_password(%{"password" => password}), do: {:ok, password}
+  defp extract_password(_), do: {:error, "password mising"}
+
+  defp extract_email(%{"email" => email}), do: {:ok, email}
+  defp extract_email(_), do: {:error, "email missing"}
+
+  def extract_user_case(user) do
+    case extract_login(user) do
+      {:error, reason} ->
+        {:error, reason}
+
+      {:ok, login} ->
+        case extract_email(user) do
+          {:error, reason} ->
+            {:error, reason}
+
+          {:ok, email} ->
+            case extract_password(user) do
+              {:error, reason} ->
+                {:error, reason}
+
+              {:ok, password} ->
+                %{login: login, email: email, password: password}
+            end
+        end
+    end
+  end
+
+  def extract_user_with(user) do
+    with {:ok, login} <- extract_login(user),
+         {:ok, email} <- extract_email(user),
+         {:ok, password} <- extract_password(user) do
+      {:ok, %{login: login, email: email, password: password}}
+    end
+  end
+end