require 'facet/string/plural'
require 'facet/string/singular'
require 'facet/string/demodulize'
require 'facet/string/underscore'
require 'facet/macro'

module Og

# Implements the Nested Sets pattern for hierarchical 
# SQL queries.
#--
# TODO: use active collections.
#++

module NestedSets

	def self.append_dynamic_features(base, options)
		c = { 
			:left => 'lft', 
			:right => 'rgt', 
			:type => Fixnum, 
			:parent => base.to_s.demodulize.underscore.downcase,
			:children => base.to_s.demodulize.underscore.downcase.plural  
		}
		c.update(options) if options

		parent = "#{c[:parent]}_oid"
		left = c[:left]
		right = c[:right]
		children = c[:children]
		child = children.singular

	 	if c[:scope].is_a?(Symbol) && c[:scope].to_s !~ /_oid$/
			c[:scope] = "#{c[:scope]}_oid".intern
		end

		scope = c[:scope]
		
		if scope
			if scope.is_a?(Symbol)
				scope = %{(#{scope} ? "#{scope} = \#{@#{scope}}" : "#{scope} IS NULL")}
			end
		
			cond = 'condition => ' + scope
			cond_and = ':condition => ' + scope + ' + " AND " +'
		else
			cond = ':condition => nil'
			cond_and = ':condition => '
		end		

		base.module_eval <<-EOE, __FILE__, __LINE__		
			property :#{parent}, Fixnum, :sql_index => true
			property :#{left}, :#{right}, #{c[:type]}

			def root?
				(@#{parent}.nil? || @#{parent} == 0) && (@#{left} == 1) && (@#{right} > @#{left})			
			end
		
			def child?
				(@#{parent} &&  @#{parent} != 0) && (@#{left} > 1) && (@#{right} > @#{left})			
			end

			def parent
				if root?
					nil
				else
					#{base}[@#{parent}]
				end
			end
                                   
			def #{children}_count
				return (@#{right} - @#{left} - 1)/2
			end

			def full_#{children}(options = {})
				options.update(#{cond_and}"(#{left} BETWEEN \#\{@#{left}\} AND \#{@#{right}})")
				#{base}.all(options)
			end

			def #{children}(options = {})
				options.update(#{cond_and}"(#{left} > \#\{@#{left}\}) AND (#{right} < \#{@#{right}})")
				#{base}.all(options)
			end
														
			def direct_#{children}(options = {})
				options.update(#{cond_and}"#{parent} = \#{pk}")
				#{base}.all(options)
			end

			def add_#{child}(child)
				self.reload if pk
				child.reload if child.pk
				
				if @#{left}.nil? || @#{left} == 0 || @#{right}.nil? || @#{right} == 0
					@#{left} = 1
					@#{right} = 2 
				end
			
				child.#{parent} = pk
				child.#{left} = pivot = @#{right}
				child.#{right} = pivot + 1
				@#{right} = pivot + 2

				#{base}.transaction do
					#{base}.update_property("#{left} = (#{left} + 2)",  #{cond_and}"#{left} >= \#{pivot}")
					#{base}.update_property("#{right} = (#{right} + 2)", #{cond_and}"#{right} >= \#{pivot}")
				end
			
				self.save
				child.save
			end
		EOE
	end

end

# Transform the base class to a hierarchical node.
# A selection of different implementation strategies
# are provided.
#
# === Example
#
# class Comment
#		include Hierarchical, :method => :nested_sets
# end
#
# [+:method+]
# 	:simple
# 	:nested_sets
# 	:nested_intervals

module Hierarchical

	def self.append_dynamic_features(base, options)
		o = { 
			:method => :nested_sets, 
		}
		o.update(options) if options

		base.include(NestedSets, o)
	end

end

end 

# * George Moschovitis <gm@navel.gr>
# * Aleksi Niemela <Aleksi.Niemela@cs.helsinki.fi>