Sup's Hook System
-----------------

Sup can be easily customized via its hook system, which allows custom
user code to be injected into Sup's execution path by "hooking" the
code onto pre-defined events. When those events occur, the code is
executed.

To see which hooks are available, simply run sup -l. Each hook sits in
a file in ~/.sup/hooks/. Hooks are written in Ruby, and require no
class or method definitions, just the executable code itself.

Information passes from Sup to the hook code via Ruby variables
(actually method calls), and from the hook code back to Sup via a
return value. The values of variables persists across calls to the
same hook, but is NOT available to other hooks. To make the value of a
variable available to other hooks, use the get and set methods.  Each
hook description lists the variables and return value expected, if
any.

The following special functions are available to hooks:
* say msg
  Displays the string msg to the user at the bottom of the screen.
* log msg
  Adds the string msg to the log, which the user can access via the
  buffer list.
* ask_yes_or_no question
  Prompts the user with the string question for a yes or no
  response. Returns true if the user answered yes, false otherwise.
* get key
  Gets the cross-hook value associated with key (which is typically a
  string). If there is no value for a given key, nil is returned.
* set key value
  Sets the cross-hook value associated with key to value. key is
  typically a string, while value can be whatever type it needs to be,
  including nil.

Some example hooks:

before-poll:
  ## runs fetchmail before polling
  if (@last_fetchmail_time || Time.now) < Time.now - 60
    say "Running fetchmail..."
    system "fetchmail >& /dev/null"
    say "Done running fetchmail."
  end
  @last_fetchmail_time = Time.now


mime-decode:
  ## turn text/html attachments into plain text, unless they are part
  ## of a multipart/alternative pair
  unless sibling_types.member? "text/plain"
    case content_type
    when "text/html"
      `/usr/bin/w3m -dump -T #{content_type} '#{filename}'`
    end
  end

startup:
  ## runs a background task
  @bgtask_pid = fork
  if @bgtask_pid
    set 'bgtask_pid' @bgtask_pid
    Process.detach(@bgtask_pid) # so we don't have to wait on it when we go to kill it
  else
    exec "background-task args 2&>1 >> /tmp/logfile"
  end

after-poll:
  ## kills the background task after the first poll
  @bgtask_pid = get 'bgtask_pid'
  Process.kill("TERM", @bgtask_pid) unless @bgtask_pid == nil
  set 'bgtask_pid' nil