add discourse stripe service

app/services/discourse_donations/stripe.rb

@@ -0,0 +1,23 @@
+
+module DiscourseDonations
+  class Stripe
+    def initialize(secret_key, opts)
+      ::Stripe.api_key = secret_key
+      @description = opts[:description]
+      @currency = opts[:currency]
+    end
+
+    def charge(email, opts)
+      customer = ::Stripe::Customer.create(
+        email: email,
+        source: opts[:source]
+      )
+      ::Stripe::Charge.create(
+        customer: customer.id,
+        amount: opts[:amount],
+        description: @description,
+        currency: @currency
+      )
+    end
+  end
+end

spec/services/discourse_donations/stripe_spec.rb

@@ -0,0 +1,32 @@
+require 'rails_helper'
+require_relative '../../support/dd_helper'
+
+module DiscourseDonations
+  RSpec.describe DiscourseDonations::Stripe do
+    before { SiteSetting.stubs(:discourse_donations_secret_key).returns('secret-key-yo') }
+
+    let(:stripe_options) { { description: 'hi there', currency: 'AUD' } }
+    let(:email) { 'ray-zintoast@example.com' }
+    let(:customer) { stub(id: 1) }
+    let!(:subject) { described_class.new('secret-key-yo', stripe_options) }
+
+    it 'sets the api key' do
+      expect(::Stripe.api_key).to eq 'secret-key-yo'
+    end
+
+    it 'creates a customer and charges them an amount' do
+      options = { email: email, source: 'stripe-token', amount: '1234', other: 'redundant param' }
+      ::Stripe::Customer.expects(:create).with(
+        email: email,
+        source: 'stripe-token'
+      ).returns(customer)
+      ::Stripe::Charge.expects(:create).with(
+        customer: customer.id,
+        amount: options[:amount],
+        description: stripe_options[:description],
+        currency: stripe_options[:currency]
+      )
+      subject.charge(email, options)
+    end
+  end
+end