defmodule EnvGuard do
  @external_resource "README.md"

  @moduledoc "README.md"
             |> File.read!()
             |> String.split("<!-- MDOC -->")
             |> Enum.fetch!(1)
  alias EnvGuard.Cast
  alias EnvGuard.Constraints
  alias EnvGuard.Env

  @type constraint :: EnvGuard.Types.constraint()
  @type type :: EnvGuard.Types.type()

  @spec test_var(String.t(), type, [constraint]) ::
          {:ok, any()} | {:error, atom()} | {:error, atom(), String.t()}
  def test_var(name, type, constraints) do
    with {:ok, value} <- Env.fetch(name),
         {:ok, value} <- Cast.cast(value, type),
         {:ok, value} <- Constraints.check_constraints(value, type, constraints) do
      {:ok, value}
    else
      {:error, :constraint_violation, err} ->
        {:error, :constraint_violation, err}

      {:error, :cast_fail, err} ->
        {:error, :invalid_type, err}

      {:error, :env_var_not_set} ->
        {:error, :env_var_not_set}
    end
  end
end