module StructPacking

  # Unpackable module provides value assign function from packed byte array.
  # 
  # A class include this module, and call struct defininesg method,
  # A instance's unpack method assign variables from packed object.
  # This module also provide read_struct_data class method
  # which construct object and assign values from packed object.
  module Unpackable
    include StructPacking::Base  
  
    private

    def self.included(base)
      base.send("include", Base)
      base.extend ClassMethods
    end
  
    # Extending methods for Unpackable class.
    #
    # Automatically extend on including StructPacking::Unpackable module.
    module ClassMethods
      
      # Construct object byte array.
      # 
      # This method is simply do object construct and values assignment.
      # If attribute defined in byte_format, 
      # but object has no attr_setter, do nothing.
      # 
      # TODO: Including class must have default constructor.
      # 
      # * _bytes_ packed structure. (see Packable.pack)
      def unpack(bytes)  
        obj = self.new
        set_values_from_byte_to_object(bytes, obj)
      end
      
      alias :from_data :unpack

      private

      def set_values_from_byte_to_object(bytes, obj)
        
        values = bytes.unpack( pack_template )

        field_names.zip(gather_array_field(values) ).each do |name,value|
          begin
            obj.instance_eval {
              send("#{name}=", value)
            }
          rescue NoMethodError
          end
        end
        obj
      end
      
      def gather_array_field(values)
        field_types.collect do |name|
          if name =~ /.*\[\w*(\d+)\w*\]\w*/
            [0..$1.to_i].to_a.collect { values.shift }
          else
            values.shift
          end
        end
      end
    end
    
    public
   
    # Set attributes from packed struct byte array.
    #
    # If attribute defined in byte_format, 
    # but object has no attr_setter, do nothing.
    def read_struct_data(bytes)
      self.class.set_values_from_byte_to_object(bytes, self)
    end

  end
end