require 'yaml'

require 'facet/kernel/constant'
require 'facet/synchash'
require 'facet/dictionary'
require 'facet/string/capitalized'

module Glue

# A Configuration holds a group of Settings organized by
# Owners. An owner is a class that represents the system to be
# configured. An alias for this class is Settings.
#
# You can pass strings, constants or symbols as keys for the
# classes to be configured. Passing symbols you can configure
# classes even before they are defined.
#--
# 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.
  # 
  # Please note the difference between :default and :value,
  # :default does NOT override :value.
    
  class Setting
    attr_accessor :owner, :name, :type, :value, :options
    
    def initialize(owner, name, options)
      if options.key? :value
        @value = options[:value]
      elsif options.key? :default 
        @value = options[:default]
      else
        raise ArgumentError.new('A value is required')
      end
      
      @owner, @name = owner, name
      @options = options      
      @type = options[:type] = options[:type] || @value.class
    end

    # Update the setting from an options hash. The update does
    # NOT take default values into account!
    
    def update(hash)
      if hash.key? :value
        @value = hash[:value]
        @type = @value.class
      end
      
      if hash.key? :type
        @type = hash[:type]
      end

      @options.update(hash)
    end
    
    # Text representation of this setting.
    
    def to_s
      @value.to_s
    end

  end

  # A collection of Settings. This helper enables intuitive
  # settings initialization like this:
  #
  # Configuration.Compiler.template_root = 'public'
  # instead of
  # Configuration.setting :compiler, :template_root, :value => 'public'
  
  class SettingCollection < Hash
    attr_accessor :owner
    
    # Handles setting readers and writers.
    
    def method_missing(sym, *args)
      if sym.to_s =~ /=$/
        # Remove trailing 
        sym = sym.to_s.gsub(/=/, '').to_sym
        Configuration.setting @owner, sym, :value => args.first
      else
        self[sym]
      end
    end
  end
    
  class << self
  
    # Inject the configuration parameters provided as a hash
    # (dictionary, ordered) to classes to be configured.
    # 
    # === Warning: Pass an ordered hash (dictionary)
    
    def setup(options)
      options.each do |owner, ss|
        next unless ss
        ss.each do |name, s|
          add_setting(owner, name.to_sym, :value => s)
        end 
      end
    end

    # Parse configuration parameters in yaml format.
    
    def parse(options)
      temp = YAML::load(options)
      options = Dictionary.new
      temp.each do |k, v| 
        begin
          options[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

    # Manually add a configuration setting. The class key can
    # be the actual class name constant or a symbol. If the
    # setting is already defined it updates it. 
    # 
    # === Examples
    #
    # Configuration.add_setting Compiler, :verification, :value => 12, :doc => '...'
    # Configuration.setting :IdPart, :verify_registration_email, :value => false
    # s = Configuration.Compiler.verification.value 
        
    def add_setting(owner, name, options)
      owner = owner.to_s.to_sym 
      @@owners[owner] ||= {}
      if s = @@owners[owner][name]
        # The setting already exists, update it.
        s.update(options)
      else
        # The setting does not exist, create it.
        @@owners[owner][name] = Setting.new(owner, name, options)
      end
    end
    alias_method :setting, :add_setting

    # Return the settings for the given owner. The owner is 
    # typically the Class that represents the system to be 
    # configured. If no class is provided, it returns all the
    # registered settings.
        
    def settings(owner = nil)
      if owner
        owner = owner.to_s.to_sym 
        @@owners[owner]
      else
        @@owners.values.inject([]) { |memo, obj| memo.concat(obj.values) }
      end
    end
    alias_method :all, :settings
    alias_method :[], :settings


    #--
    # FIXME: this does not work as expected.
    #++
    
    def method_missing(sym)
      if sym.to_s.capitalized?
         bdl = SettingCollection.new
         bdl.owner = sym
         if hash = self[sym]
           bdl.update(hash)
         end
         return bdl
      end
    end
  end
  
end

# Alias for the Configuration class (shorter).

Settings = Configuration

end

class Module

  # Defines a configuration setting for the enclosing class.
  #
  # === Example
  #
  # class Compiler
  #   setting :template_root, :default => 'src/template', :doc => 'The template root dir'
  # end
  
  def setting(sym, options = {})
    Glue::Configuration.add_setting(self, sym, options)
    
    module_eval %{
      def self.#{sym}
        Glue::Configuration[#{self}][:#{sym}].value
      end
      
      def self.#{sym}=(obj)
        Glue::Configuration.setting #{self}, :#{sym}, :value => obj
      end
    }
  end
  
end

# * George Moschovitis <gm@navel.gr>