defmodule CoinbasePro do
  @moduledoc """
  General API
  """

  defp api_path do
    Application.get_env(:coinbase_pro, :api_path, "localhost:8080")
  end

  defp http_client do
    CoinbasePro.Http.Poison
  end

  @doc """
  https://docs.pro.coinbase.com/?ruby#get-products
  """
  def products do
    (api_path() <> "/products")
    |> http_client().get()
  end

  @doc """
  https://docs.pro.coinbase.com/?ruby#get-24hr-stats
  """
  def get_24h_stats(product) do
    (api_path() <> "/products/" <> product <> "/stats")
    |> http_client().get()
  end

  @doc """
  https://docs.pro.coinbase.com/?ruby#list-accounts
  """
  def accounts do
    path = "/accounts"

    headers =
      signature_headers(
        %{
          api_key: Application.get_env(:coinbase_pro, :api_key),
          api_passphrase: Application.get_env(:coinbase_pro, :api_passphrase),
          secret_key: Application.get_env(:coinbase_pro, :secret_key)
        },
        %{path: path, body: "", timestamp: System.system_time(:second), method: "GET"}
      )

    (api_path() <> path)
    |> http_client().get(headers)
  end

  @doc """
  https://docs.pro.coinbase.com/?ruby#place-a-new-order
  """
  def buy_btc_on(%{eur: eur_amount}) do
    path = "/orders"

    body =
      %{
        type: "market",
        side: "buy",
        product_id: "BTC-EUR",
        funds: eur_amount
      }
      |> Jason.encode!()

    headers =
      signature_headers(
        %{
          api_key: Application.get_env(:coinbase_pro, :api_key),
          api_passphrase: Application.get_env(:coinbase_pro, :api_passphrase),
          secret_key: Application.get_env(:coinbase_pro, :secret_key)
        },
        %{
          path: path,
          body: body,
          timestamp: System.system_time(:second),
          method: "POST"
        }
      )

    (api_path() <> path)
    |> http_client().post(body, headers)
  end

  # see https://docs.pro.coinbase.com/?python#signing-a-message
  def signature_headers(
        %{api_key: api_key, api_passphrase: api_passphrase, secret_key: secret_key},
        %{
          path: path,
          body: body,
          timestamp: timestamp,
          method: method
        }
      ) do
    method = String.upcase(method)
    data = "#{timestamp}#{method}#{path}" <> body

    hmac_key = :base64.decode(secret_key)
    sign = :crypto.hmac(:sha256, hmac_key, data) |> :base64.encode()

    [
      {"CB-ACCESS-KEY", api_key},
      {"CB-ACCESS-SIGN", "#{sign}"},
      {"CB-ACCESS-TIMESTAMP", timestamp},
      {"CB-ACCESS-PASSPHRASE", api_passphrase},
      {"Content-Type", "application/json"}
    ]
  end
end