Added Bithday Validator

lib/animina/ birthday_validator.ex

@@ -0,0 +1,102 @@
+defmodule Animina.BirthdayValidator do
+  @moduledoc """
+  A module to validate a birthday in the format dd.mm.yy.
+  """
+
+  @doc """
+  Validates a birthday string in the format dd.mm.yy.
+
+  ## Examples
+
+      iex> BirthdayValidator.validate_birthday("15.08.95")
+      {:ok, ~D[1995-08-15]}
+
+      iex> BirthdayValidator.validate_birthday("32.01.21")
+      {:error, "Invalid day for the given month."}
+
+      iex> BirthdayValidator.validate_birthday("29.02.21")
+      {:error, "Invalid day for the given month."}
+
+      iex> BirthdayValidator.validate_birthday("15.08.30")
+      {:error, "Birthday cannot be in the future."}
+
+      iex> BirthdayValidator.validate_birthday("15.08.2005")
+      {:ok, ~D[2005-08-15]}
+
+      iex> BirthdayValidator.validate_birthday("15.08.2010")
+      {:error, "Birthday must be more than 18 years ago."}
+  """
+  def validate_birthday(birthday) do
+    with {:ok, date_parts} <- parse_birthday(birthday),
+         {:ok, date} <- validate_date(date_parts),
+         :ok <- check_not_future(date),
+         :ok <- check_age(date) do
+      {:ok, date}
+    else
+      {:error, reason} -> {:error, reason}
+    end
+  end
+
+  defp parse_birthday(birthday) do
+    case String.split(birthday, ".") do
+      [day, month, year] ->
+        case {Integer.parse(day), Integer.parse(month), Integer.parse(year)} do
+          {{day_int, ""}, {month_int, ""}, {year_int, ""}} ->
+            {:ok, {day_int, month_int, adjust_year(year_int, String.length(year))}}
+
+          _ ->
+            {:error, "Invalid format. Must be dd.mm.yy or dd.mm.yyyy."}
+        end
+
+      _ ->
+        {:error, "Invalid format. Must be dd.mm.yy or dd.mm.yyyy."}
+    end
+  end
+
+  defp adjust_year(year_int, 1), do: 2000 + year_int
+
+  defp adjust_year(year_int, 2) do
+    current_year = Date.utc_today().year
+    current_two_digits = rem(current_year, 100)
+
+    if year_int > current_two_digits do
+      1900 + year_int
+    else
+      2000 + year_int
+    end
+  end
+
+  defp adjust_year(year_int, 4), do: year_int
+
+  defp validate_date({day, month, year}) do
+    padded_day = String.pad_leading(Integer.to_string(day), 2, "0")
+    padded_month = String.pad_leading(Integer.to_string(month), 2, "0")
+
+    date_str = "#{year}-#{padded_month}-#{padded_day}"
+
+    case Date.from_iso8601(date_str) do
+      {:ok, date} -> {:ok, date}
+      {:error, _} -> {:error, "Invalid day for the given month."}
+    end
+  end
+
+  defp check_not_future(date) do
+    if Date.compare(date, Date.utc_today()) != :gt do
+      :ok
+    else
+      {:error, "Birthday cannot be in the future."}
+    end
+  end
+
+  defp check_age(date) do
+    # Calculate the threshold date (18 years ago)
+    # Approximate 18 years
+    age_threshold = Date.utc_today() |> Date.add(-18 * 365)
+
+    if Date.compare(date, age_threshold) != :gt do
+      :ok
+    else
+      {:error, "Birthday must be more than 18 years ago."}
+    end
+  end
+end

test/animina/birthday_validator_test.exs

@@ -0,0 +1,46 @@
+defmodule Animina.BirthdayValidatorTest do
+  use Animina.DataCase, async: true
+
+  alias Animina.BirthdayValidator
+
+  describe "Tests for the Birthday Validator" do
+    test "A valid birthday is returned as a date" do
+      assert {:ok, ~D[1995-08-15]} = BirthdayValidator.validate_birthday("15.08.95")
+    end
+
+    test "An invalid day for the given month returns an error" do
+      assert {:error, "Invalid day for the given month."} =
+               BirthdayValidator.validate_birthday("32.01.21")
+    end
+
+    test "A birthday in the future returns an error" do
+      assert {:error, "Birthday cannot be in the future."} =
+               BirthdayValidator.validate_birthday("15.08.2030")
+    end
+
+    test "A valid birthday with a 4 digit year is returned as a date" do
+      assert {:ok, ~D[2005-08-15]} = BirthdayValidator.validate_birthday("15.08.2005")
+    end
+
+    test "A Valid birthday with a 2 digit year returns a date" do
+      assert {:ok, ~D[2004-08-15]} = BirthdayValidator.validate_birthday("15.08.04")
+    end
+
+    test "A Valid birthday with a 1 digit year returns a date" do
+      assert {:ok, ~D[2004-08-15]} = BirthdayValidator.validate_birthday("15.08.4")
+    end
+
+    test "A Valid birthday with a 1 digit day returns a date" do
+      assert {:ok, ~D[2004-08-09]} = BirthdayValidator.validate_birthday("9.08.4")
+    end
+
+    test "A Valid birthday with a 1 digit month returns a date" do
+      assert {:ok, ~D[2004-08-09]} = BirthdayValidator.validate_birthday("09.8.04")
+    end
+
+    test "A birthday less than 18 years ago returns an error" do
+      assert {:error, "Birthday must be more than 18 years ago."} =
+               BirthdayValidator.validate_birthday("15.08.2010")
+    end
+  end
+end