impress/app/models/fundraising/donation.rb

module Fundraising
  class Donation < ApplicationRecord
    FEATURE_COST = 500  # in cents = $5.00

    belongs_to :campaign
    belongs_to :user, optional: true
    has_many :features, class_name: 'DonationFeature'

    def to_param
      "#{id}-#{secret}"
    end

    def self.create_from_charge(campaign, user, params)
      amount = (BigDecimal.new(params[:amount]) * 100).floor

      campaign.progress += amount

      charge_params = {
        amount: amount,
        description: 'Donation (thank you!)',
        currency: 'usd'
      }

      if params[:stripe_token_type] == 'card'
        customer = Stripe::Customer.create(
          card: params[:stripe_token]
        )
        charge_params[:customer] = customer.id
      elsif params[:stripe_token_type] == 'bitcoin_receiver'
        charge_params[:card] = params[:stripe_token]
      else
        raise ArgumentError, "unexpected stripe token type #{params[:stripe_token_type]}"
      end

      charge = Stripe::Charge.create(charge_params)

      donation = campaign.donations.build
      donation.amount = amount
      donation.charge_id = charge.id
      donation.user = user
      donation.donor_name = user.try(:name)
      donation.donor_email = params[:donor_email]
      donation.secret = new_secret

      num_features = amount / FEATURE_COST
      features = []
      num_features.times do
        features << donation.features.new
      end

      Donation.transaction do
        campaign.save!
        donation.save!
        features.each(&:save!)
      end

      DonationMailer.thank_you_email(donation, donation.donor_email).deliver

      donation
    end

    def self.new_secret
      SecureRandom.urlsafe_base64 8
    end

    def self.from_param(param)
      id, secret = param.split('-', 2)
      self.where(secret: secret).find(id)
    end
  end
end