How to send email to user after payment is done with paypal - ruby-on-rails

Question

I want to sent email to user after transcation done. now paypal is working fine for me, but user is not getting mail notification after transcation done? how to get email notification for user .
Here is my code
This is my controller code
This is my paypal function
def pay
if #order.update order_params
#order.update_attributes(:invoice_id => rand.to_s[2..11])
if current_user.billing_address.blank?
current_user.create_billing_address(#order.billing_address.dup.attributes)
end
if current_user.shipping_address.blank?
current_user.create_shipping_address(#order.shipping_address.dup.attributes)
end
# #cart.calculate_shipping
if #order.total == 0
return redirect_to checkout_thank_you_path
end
# if !params['payment'].present?
# return redirect_to :back, notice: 'Select Payment Gateway!'
# end
# if params['payment']=='paypal'
#order.order_statuses.create(status_type: 1)
item_details=[]
#order.line_items.each do |item|
item_details << {:name => item.title, :quantity => item.quantity, :amount => item.amount.fractional}
end
logger.info item_details.inspect
response = EXPRESS_GATEWAY.setup_purchase(#cart.total.fractional,
:ip => request.remote_ip,
:currency =>"USD",
:items => item_details,
:order_id => #order.invoice_id,
:return_url => checkout_thank_you_url,
:cancel_return_url => cart_url
)
return redirect_to EXPRESS_GATEWAY.redirect_url_for(response.token)
# else
# return redirect_to 'https://www.payumoney.com/'
# end
else
flash[:alert] = 'Billing and shipping address fields are required!'
render :addresses
end
end
This is my thank function for paypal
def thank_you
#order = Order.find(session[:order_id])
details = EXPRESS_GATEWAY.details_for(params[:token])
response = EXPRESS_GATEWAY.purchase(#cart.total.fractional, {
ip: request.remote_ip,
token: params[:token],
payer_id: details.payer_id,
items: #order.line_items.map{|l| {name: l.title, quantity: l.quantity, amount: l.amount.fractional}}
})
if response.success?
# logger.info payment_params.inspect
payment_params = {gateway: 'PayPal Express Checkout', transaction_id: response.params['token'], ip: request.remote_ip, amount: response.params['gross_amount']}
#cart.order.created_at = DateTime.now
#cart.order.status = 'Paid'
#cart.order.save
session.delete :order_id
# OrderMailer.order_confirmation(#order).deliver
# OrderMailer.admin_receipt(#order).deliver
else
redirect_to :cart_checkout, alert: 'Something went wrong. Please try again. If the problem persists, please contact us.'
end
#cart = Cart.new current_or_null_user.id, session[:order_id], session[:currency] # Start a new cart
end
Any help is appreciatable