defmodule EnvGuard.Macros do
  @moduledoc """
  Macros for declaring environment variables in `runtime.exs`.

  Import these into your config to fetch, cast, and validate environment
  variables in a single expression:

      import Config
      require EnvGuard.Macros
      import EnvGuard.Macros

      if config_env() == :prod do
        secret_key_base = required("SECRET_KEY_BASE", :string, min_length: 64)
        phx_server = optional("PHX_SERVER", :boolean, false)
      end

  See `EnvGuard.Types` for the supported types and constraints.
  """

  @doc """
  Fetches a required environment variable, casting it to `type` and checking
  `constraints`.

  Returns the cast value. Raises a `RuntimeError` if the variable is not set,
  cannot be cast to `type`, or violates one of the `constraints`.

  ## Examples

      secret_key_base = required("SECRET_KEY_BASE", :string, min_length: 64)
      pool_size = required("POOL_SIZE", :integer, min: 1, max: 100)

  """
  defmacro required(env_name, type, constraints \\ []) do
    quote do
      case EnvGuard.test_var(unquote(env_name), unquote(type), unquote(constraints)) do
        {:ok, value} ->
          value

        {:error, :env_var_not_set} ->
          raise "Environment variable #{unquote(env_name)} is not set"

        {:error, :invalid_type, err} ->
          raise "Environment variable #{unquote(env_name)} is not of type #{inspect(unquote(type))}. #{err}"

        {:error, :constraint_violation, err} ->
          raise "Environment variable #{unquote(env_name)} does not meet constraints. #{err}"
      end
    end
  end

  @doc """
  Fetches an optional environment variable, falling back to `default`.

  When the variable is set, it is cast to `type` and checked against
  `constraints`, and the cast value is returned. When it is not set — or it is
  set but fails casting or a constraint — `default` is returned instead. In the
  failure cases a warning is logged via `Logger` before falling back.

  ## Examples

      phx_server = optional("PHX_SERVER", :boolean, false)
      log_level = optional("LOG_LEVEL", {:enum, ["debug", "info", "warning"]}, "info")

  """
  defmacro optional(env_name, type, default, constraints \\ []) do
    quote do
      case EnvGuard.test_var(unquote(env_name), unquote(type), unquote(constraints)) do
        {:ok, value} ->
          value

        {:error, :env_var_not_set} ->
          unquote(default)

        {:error, :invalid_type, err} ->
          require Logger

          Logger.warning(
            "Environment variable #{unquote(env_name)} is set but not of type #{inspect(unquote(type))}. #{err} Falling back to default."
          )

          unquote(default)

        {:error, :constraint_violation, err} ->
          require Logger

          Logger.warning(
            "Environment variable #{unquote(env_name)} is set but does not meet constraints. #{err} Falling back to default."
          )

          unquote(default)
      end
    end
  end
end