ActionMailer message delivery content

I have the ability to send email to a user if a certain user has
requested interest in their product. In my email I want to include
certain information that is pulled from users but at the moment I am
getting errors because it states that they are undefined despite these
lines being used elsewhere in my application. I shall copy the email
below and anything between the <% %> is what I wish to include and was
wondering if anyone could point me in the right direction and tell me
which are those that are correct and are not. Any help would be
wonderful. The message I want to send is as followed:

Hello <%@user.username%>

The user <% current_user.username %> has registered an interest in the
following product of yours:

<% @book.book_name %>

The user <% current_user.usernames %> has the following games for offer:

<% current_user.book.book_name %>

To view <% current_user.username %> profile click <% link_to "here",
current_user.show %>
If you wish to contact the user by email then contact the following
email <% current_user.email %>.

Below is my mailer class. I believe this is why it does not recognize
the game command but I tried putting a similar line in as I had with
user and it did not work. Any idess? My @user.username in the email
works fine.

  class GameTrade < ActionMailer::Base
    default :from => "Roger@gmail.com"

    def book_interest(user)
      @user = user
      mail :to => user.email, :subject => "book Interest"
    end
  end

My final problem is that I have been lead to believe that current_user
does not work in the email delivery, how would I go about adding such
feature or is it not possible?