payment_service.rb

class PaymentService
  VALID_CURRENCIES = Money::Currency.table.keys.map(&:upcase)
  DEFAULT_CURRENCY = :EUR
  APP_FEE          = ->(amount) { amount * 15 / 100}

  def initialize(user)
    @user       = user
    @app_id     = ENV['STRIPE_APP_ID']
    @app_secret = ENV['STRIPE_KEY']
    @client     = OAuth2::Client.new(@app_id, @app_secret, site: 'https://connect.stripe.com')
  end

  def exchange_token(auth_code)
    begin
      resp     = @client.auth_code.get_token(auth_code, params: { scope: 'read_write'})
      token    = resp.params['stripe_publishable_key']
      customer = create_customer(@app_secret)
      @user.profile.payment_info.update(stripe: { token: token, customer_id: customer.id })
    rescue OAuth2::Error => e
      Bugsnag.notify(e)
      Rails.logger.error e.message
      false
    end
  end

  def charge_customer(customer, amount)
    check_stripe_connect!(@user, customer)

    charger_token = access_token_for(@user)
    chargee_customer_id = customer_id_for(customer)
    token = Stripe::Token.create({ customer: chargee_customer_id }, charger_token)

    Stripe::Charge.create(
      amount: amount,
      currency: user_currency,
      card: token['id'],
      description: payment_description(customer)
      #application_fee: APP_FEE[amount] # TODO: re-enable after response from Stripe
    )
  end

  private
  def create_customer(token)
    Stripe::Customer.create(
      { email: @user.email, description: @user.full_name },
      token
    )
  end

  def check_stripe_connect!(*users)
    raise StripeNotConnectedError unless users.all?(&:stripe_connected?)
  end

  def customer_id_for(user)
    stripe_info_for(user)['customer_id']
  end

  def access_token_for(user)
    stripe_info_for(user)['token']
  end

  def stripe_info_for(user)
    user.profile.payment_info.stripe
  end

  def self.find_customer(user)
    Stripe::Customer.retrieve(customer_id_for(user))
  end

  def payment_description(customer)
    "Payment to #{@user.full_name} (#{@user.username})"
  end

  def user_currency
    currency = @user.profile.payment_info.default_currency || DEFAULT_CURRENCY
    currency.to_s.downcase
  end
end