require 'log'
require 'forwardable'
module MediaShelf
  module Shovel
    #This class represents a "workflow" for a file contained in an ingest file being
    #processed by Shovel
    #See +Shovel+ for more information and an example
    class Flow
      extend Forwardable
      def_delegators Log.instance, :d, :e, :w, :i
      attr_reader :reaction_map, :exception_map


      def initialize #:nodoc:
        @reaction_map={:stable=>[], :added=>[], :removed=>[], :modified=>[]}
        @exception_map = {}
      end
      #add a process to the flow, to be executed by the Shovel when the
      #supplied event occurrs.
      #
      #event:: the event type, one of :stable, :added, :removed or :modified
      #block:: your process. the process will be passed hte file extracted \
      #from your archive (most likely).       
      #
      #This method (and on_exception) returns self, so calls 
      #to add_reaction can be chained.
      def add_reaction(event, &block)
        @reaction_map[event] <<  block
        return self
      end
      #add a process to the flow, to be executed by the Shovel when the
      #supplied Exception occurrs.
      #klazz:: a class which might be raised at some point in the ingest process
      #block:: what you want to do about it. The block is passed the file,  \
      #and the exception instance.
      #
      #This method (and add_reaction) returns self, so calls 
      #to add_reaction can be chained.
      def on_exception(klazz, &block)
        @exception_map[klazz.name.to_sym]=block
        return self
      end

      #The exception handler.  It will try to find processes mapped to
      #the given exception, and invoke on them. If it can't find a handler
      #it just logs the exception and bails.
      def handle_exception(f,x)
        if @exception_map[x.class.name.to_sym]
          p = @exception_map[x.class.name.to_sym]
          p.call(f, x)
        else
          log_exception(f,x)
        end
      end

      def log_exception(f,x)#:nodoc:
        e("Error : #{f} #{x.message}. Stack trace follows:")
        e(x.backtrace.join("\n"))
      end
    end
  end
end