defmodule Mix.Tasks.Gil do
  use Mix.Task

  @shortdoc "Exchange rate check command"

  def run(args) do
    result = case currencies(args) do
      {:ok, {currency_a, currency_b}} ->
        case parse_response(get_rate(currency_a, currency_b)) do
          {:ok, rate} ->
            "#{String.upcase(currency_a)}/#{String.upcase(currency_b)}: #{rate}"
          {:error, message} ->
            message
        end
      {:error} -> "Illegal argument"
    end
    IO.puts result
  end

  def currencies(args) do
    kc = key_currency
    case args do
      [a|[b|_]] -> {:ok, {a, b}}
      [a|[a|_]] -> {:error}
      [^kc|_] -> {:error}
      [a|_] -> {:ok, {kc, a}}
      _ -> {:error}
    end
  end

  def get_rate(currency_a, currency_b) do
    url = "http://jp.investing.com/currencies/#{String.downcase(currency_a <> "-" <> currency_b)}"
    HTTPoison.start
    HTTPoison.get(url)
  end

  def parse_response(response) do
    case response do
      {:ok, %HTTPoison.Response{status_code: 200, body: body}} ->
        try do
          {:ok, rate(body)}
        rescue
          e in RuntimeError -> {:error, e.message}
        end
      {:ok, %HTTPoison.Response{status_code: 404}} ->
        {:error, "Failed to get currency rate."}
      {:error, %HTTPoison.Error{reason: reason}} ->
        {:error, "ERROR! #{reason}"}
    end
  end

  def rate(body) do
    case Floki.find(body, "#last_last") do
      {_, _, [rate|_]} -> rate
      _ -> raise "Failed to get currency rate."
    end
  end

  def key_currency do
    conf = Mix.Config.read!("config/config.exs")
    case conf[:gil][:key_currency] do
      nil -> "usd"
      key -> key
    end
  end
end