require 'yaml'

require 'nano/kernel/constant'
require 'mega/synchash'

require 'glue/attribute'
require 'glue/flexob'

# A Configuration holds a group of Settings organized by
# Owners.
#--
# TODO: implement with annotations.
#++

class Configuration

  # A hash of setting owners. Use double @'s to allow for
  # the Settings alias.
  #--
  # TODO: find a better name.
  #++
    
  @@owners = SyncHash.new  

  # A datastructure to store Settings metadata.
  
  class Setting
    attr_accessor :owner, :name, :type, :value, :options
    
    def initialize(owner, name, options)
      raise ArgumentError.new('A default value is required') unless options.key?(:default)
      @owner, @name = owner, name
      @options = options
      @value = options[:default]
      @type = options[:type] = options[:type] || @value.class
    end

    def value=(value)
      @value = value
      constant(@owner).module_eval %{
        @@#{@name} = #{value.inspect}
      }
    end

    def to_s
      @value.to_s
    end
  end
  
  class << self
  
    # Inject the configuration parameters to configuration
    # classes.
    
    def setup(options)
      options.each do |owner, ss|
        next unless ss
        begin
          owner = constant(owner)
        rescue NameError
          next
        end
        ss.each do |name, s|
          @@owners[owner][name.to_sym].value = s
          owner.module_eval %{
            @@#{name} = #{s.inspect}
          }
        end 
      end
    end

    # Parse configuration parameters in yaml format.
    
    def parse(options)
      temp = YAML::load(options)
      options = {}
      temp.each do |k, v| 
        begin
          options[constant(k.gsub(/\./, '::').to_sym)] = v 
        rescue Object
          options[k] = v 
        end
      end
      setup(options)
    end
    
    # Load and parse an external yaml configuration file.
    
    def load(filename)
      parse(File.read(filename))
    end
    
    def add_setting(owner, name, options)
      s = @@owners[owner] || {}
      s[name] = Setting.new(owner, name, options)
      @@owners[owner] = s
    end
    
    def settings(owner = nil)
      if owner
        @@owners[owner]
      else
        @@owners.values.inject([]) { |memo, obj| memo.concat(obj.values) }
      end
    end
    alias_method :all, :settings
    alias_method :[], :settings

    def method_missing(sym)
      if sym.to_s =~ /[A-Z]/ # nano's capitalized? is buggy at the moment.
        Flexob.new(self[constant(sym)])
      end
    end
  end
  
end

# Alias for the Configuration class (shorter).

class Settings < Configuration
end

class Module

  # Defines a configuration setting.
  #--
  # TODO: implement with annotations.
  #++
  
  def setting(sym, options = {})
    Configuration.add_setting(self, sym, options)
    module_eval %{
      mattr_accessor sym, options[:default]
      
      def self.#{sym.id2name}=(obj)
        @@#{sym.id2name} = obj
        Configuration[#{self}][:#{sym}].value = obj
      end
    }
  end
  
end

# * George Moschovitis <gm@navel.gr>