# Copyright(c) 2015-2018 ACCESS CO., LTD. All rights reserved.

use Croma

defmodule Antikythera.Env do
  @moduledoc """
  Module to provide helpers to access environment variables defined by antikythera.

  ## Environments and deployments

  Antikythera instances and gears may run in the following two modes:

  - As a mix project, when invoked by running `iex` or `mix` command-line tool.
  - As an OTP release, which is generated by e.g. `antikythera_core.generate_release` task.

  In general there are multiple deployments per antikythera instance.
  To distingish the target deployment from code, antikythera defines the following environment variables:

  - At compile time (for metaprogramming):
    `ANTIKYTHERA_COMPILE_ENV` must be appropriately set; the value can be retrieved by `compile_env/0`.
  - At runtime:
    `ANTIKYTHERA_RUNTIME_ENV` must be appropriately set; the value can be retrieved by `runtime_env/0`.

  It is the responsibility of antikythera instance administrators to correctly set these environment variables
  when compiling/running antikythera and gears.
  Possible values returned by `compile_env/0` and `runtime_env/0` are:

  - names of deployments given by `:deployments` application config
  - `:local` (running an OTP release at local machine for testing purpose)
  - `:undefined`

  As an example, if you set `:dev` and `:prod` in `:deployments`, then you get:

      |                           | Mix.env() at compile-time              | Mix.env() at runtime    | compile_env(), runtime_env() |
      |---------------------------+----------------------------------------+-------------------------+------------------------------|
      | $ iex -S mix              | :dev  (toplevel), :prod (dependencies) | :dev                    | :undefined                   |
      | $ mix test                | :test (toplevel), :prod (dependencies) | :test                   | :undefined                   |
      | $ mix antikythera_local.* | :prod                                  | (:mix is not available) | :local                       |
      | :dev deployment           | :prod                                  | (:mix is not available) | :dev                         |
      | :prod deployment          | :prod                                  | (:mix is not available) | :prod                        |

  You can use these values to distinguish the current context from your code.
  """

  deployment_envs = Application.fetch_env!(:antikythera, :deployments) |> Keyword.keys()
  use Croma.SubtypeOfAtom, values: (deployment_envs ++ [:local, :undefined])
  alias Antikythera.{GearName, GearNameStr, Url}
  alias AntikytheraCore.Handler.CowboyRouting, as: Routing

  defmodule Mapping do
    Enum.each(deployment_envs, fn env ->
      env_str = Atom.to_string(env)
      def env_var_to_atom(unquote(env_str)), do: unquote(env)
    end)
    def env_var_to_atom("local"), do: :local
    def env_var_to_atom(_      ), do: :undefined

    Enum.each(deployment_envs, fn env ->
      def cloud?(unquote(env)), do: true
    end)
    def cloud?(_), do: false
  end

  defun no_listen?() :: boolean do
    case System.get_env() do
      %{"NO_LISTEN" => "true"}           -> true
      %{"TEST_MODE" => "blackbox_" <> _} -> true
      _otherwise                         -> false
    end
  end

  defun runtime_env()           :: t      , do: System.get_env("ANTIKYTHERA_RUNTIME_ENV") |> Mapping.env_var_to_atom()
  defun running_with_release?() :: boolean, do: runtime_env() != :undefined
  defun running_in_cloud?()     :: boolean, do: Mapping.cloud?(runtime_env())

  @compile_env            System.get_env("ANTIKYTHERA_COMPILE_ENV") |> Mapping.env_var_to_atom()
  @compiling_for_release? @compile_env != :undefined
  @compiling_for_cloud?   Mapping.cloud?(@compile_env)

  defun compile_env()            :: t      , do: @compile_env
  defun compiling_for_release?() :: boolean, do: @compiling_for_release?
  defun compiling_for_cloud?()   :: boolean, do: @compiling_for_cloud?

  @antikythera_instance_name Application.fetch_env!(:antikythera, :antikythera_instance_name)
  defun antikythera_instance_name() :: atom, do: @antikythera_instance_name

  @gear_action_timeout_default 10_000
  @gear_action_timeout         String.to_integer(System.get_env("GEAR_ACTION_TIMEOUT") || "#{@gear_action_timeout_default}")
  @doc """
  Timeout (in milli-seconds) for gear actions.

  This can be configurable by specifying `"GEAR_ACTION_TIMEOUT"` environment variable when compiling antikythera.
  Defaults to `#{@gear_action_timeout_default}`.
  """
  defun gear_action_timeout() :: pos_integer, do: @gear_action_timeout

  @default_port             8080
  @default_port_during_test 8081

  # To see which port number to use, we have to get the current mix environment at runtime,
  # since `Mix.env()` always returns `:prod` during compilation of antikythera within a gear project.
  # However, when running with an OTP release, `Mix.env/0` is not available at runtime
  # (as `:mix` is not included in antikythera's runtime dependencies).
  # Therefore we need both compile-time- and runtime-branching.
  if @compiling_for_release? do
    defp default_port_at_runtime(), do: @default_port
  else
    defp default_port_at_runtime(), do: (if Mix.env() == :test, do: @default_port_during_test, else: @default_port)
  end

  @doc """
  TCP port to listen to for incoming web requests.

  The port can be specified by `"PORT"` runtime environment variable.
  Defaults to `#{@default_port_during_test}` during `mix test`, and `#{@default_port}` otherwise
  (thus one can run both `iex -S mix` and `mix test` at the same time).
  """
  defun port_to_listen() :: non_neg_integer do
    case System.get_env("PORT") do
      nil      -> default_port_at_runtime()
      port_str -> String.to_integer(port_str)
    end
  end

  defun default_base_url(gear_name :: v[GearName.t | GearNameStr.t], env :: v[t] \\ @compile_env) :: Url.t do
    if Mapping.cloud?(env) do
      "https://" <> Routing.default_domain(gear_name, env)
    else
      "http://" <> Routing.default_domain(gear_name, env) <> ":#{port_to_listen()}"
    end
  end
end