defmodule PhoenixSessionRedis do
  @moduledoc """
  This library provide redis pool and Plug.Session.REDIS.
  Depends on eredis, poolboy and plug.

  It is assumed that application is created Phoenix Framework
  and run multi(or one) web server with one redis server for session.
  (But not limited Phoenix Framework)

  ## Examples

    config/config.exs

      config :phoenix_session_redis, :config,
        name: :redis_sessions,            # Pool name
        pool: [
          size: 2,                        # Number of worker
          max_overflow: 5,                # Max Additional worker
          name: {:local, :redis_sessions} # First is determination where the pool is run
                                          # Second is unique pool name
        ],
        redis: [                          # Worker arguments
          host: 'localhost',              # Redis host(it is char list !)
          port: 6379,                     # Redis port
        ]

    lib/endpoint.ex

      plug Plug.Session,
        store: :redis,                           # Plug.Session.REDIS module
        table: :redis_sessions,                  # Pool name
        ttl:     1 * 60 * 60                     # Redis expiration
        max_age: 1 * 60 * 60                     # Cokkie expiration
  """

  use Application

  @doc false
  def start(_type, _args) do
    import Supervisor.Spec, warn: false
    children = [
      :poolboy.child_spec(:redis_sessions, config(:pool) ++ [worker_module: :eredis], config(:redis))
    ]
    opts = [strategy: :one_for_one, name: PhoenixSessionRedis.Supervisor]
    Supervisor.start_link(children, opts)
  end

  defp config(key) do
    case Application.get_env(:phoenix_session_redis, :config)[key] do
      nil  -> raise PhoenixSessionRedis.ConfigNotFoundError
      conf -> conf
    end
  end
end