require 'mega/dynamod'
require 'glue/aspects'

module Glue

# Attach list/ordering methods to the enchanted class.

module Orderable
  include Glue::Aspects

  dynamic_feature do |opt|

    opt_position = opt[:position] || 'position'

    opt_type = opt[:type] || Fixnum

    # provide a user defined condition.
    
    opt_condition = opt[:condition]

    # provide a condition based on a key field (?)
    
    opt_scope = opt[:scope]

    # clean scope field.
    
    if opt_scope
      if opt_scope.to_s !~ /_oid$/
        opt_scope = "#{opt_scope}_oid".to_sym
      else
        opt_scope = opt_scope.to_sym
      end
    end

    define_method :orderable_position do
      opt_position
    end

    define_method :orderable_type do
      opt_type
    end

    define_method :orderable_scope do
      opt_scope
    end

    define_method :orderable_condition do
      scope = orderable_scope
      if scope
        scope_value = send(scope)
        scope = scope_value ? "#{scope} = #{scope_value}" : "#{scope} IS NULL"
      end
      return [ opt_condition, scope ].compact
    end

    # How to check if property is already defined?
    
    unless method_defined?( opt_position )
      define_method( opt_position ) do @position ; end
      define_method( "#{opt_position}=" ) do |x| @position = x ; end
      property opt_position, opt_type
    end

    # Use position for general reference.
    
    attr_accessor :position

  end #dynamic_feature

  before "add_to_bottom", :on => :og_insert
  before "decrement_position_of_lower_items", :on => :og_delete

  # Move higher.
  
  def move_higher
    if higher = higher_item
      self.class.transaction do
        higher.increment_position
        decrement_position
      end
    end
  end

  # Move lower.
  
  def move_lower
    if lower = lower_item
      self.class.transaction do
        lower.decrement_position
        increment_position
      end
    end
  end

  # Move to the top.
  
  def move_to_top
    self.class.transaction do
      increment_position_of_higher_items
      set_top_position
    end
  end

  # Move to the bottom.
  
  def move_to_bottom
    self.class.transaction do
      decrement_position_of_lower_items
      set_bottom_position
    end
  end

  # Move to a specific position.
  
  def move_to(dest_position)
    return if @position == dest_position

    pos = orderable_position
    con = orderable_condition

    self.class.transaction do
      if @position < dest_position
        adj = "#{pos} = #{pos} - 1"
        con = con + [ "#{pos} > #{@position}", "#{pos} <= #{dest_position}" ]
      else
        adj = "#{pos} = #{pos} + 1"
        con = con + [ "#{pos} < #{@position}", "#{pos} >= #{dest_position}" ]
      end
      self.class.update( adj, :condition => con.join(' AND ') )
      @position = dest_position
      update_property(:"#{pos}")
    end

    self
  end

  def add_to_top
    increment_position_of_all_items
  end

  def add_to_bottom
    @position = bottom_position + 1
  end

  def add_to
    # TODO
  end

  def higher_item
    pos = orderable_position
    con = orderable_condition + [ "#{pos} = #{@position - 1}" ]
    self.class.one( :condition => con.join(' AND ') )
  end
  alias_method :previous_item, :higher_item

  def lower_item
    pos = orderable_position
    con = orderable_condition + [ "#{pos} = #{@position + 1}" ]
    self.class.one( :condition => con.join(' AND ') )
  end
  alias_method :next_item, :lower_item

  def top_item
    # TODO
  end
  alias_method :first_item, :top_item

  def bottom_item
    pos = orderable_position
    con = orderable_condition
    con = con.empty? ? nil : con.join(' AND ')
    self.class.one(:condition => con, :order => "#{pos} DESC", :limit => 1)
  end
  alias_method :last_item, :last_item

  def top?
    @position == 1
  end
  alias_method :first?, :top?

  def bottom?
    @position == bottom_position
  end
  alias_method :last?, :bottom?

  def increment_position
    @position += 1
    update_property(:"#{orderable_position}")
  end

  def decrement_position
    @position -= 1
    update_property(:"#{orderable_position}")
  end

  def bottom_position
    item = bottom_item
    item ? item.send(orderable_position) : 0
  end

  def set_top_position
    @position = 1
    update_property(:"#{orderable_position}")
  end

  def set_bottom_position
    @position = bottom_position + 1
    update_property(:"#{orderable_position}")
  end

  def increment_position_of_higher_items
    pos = orderable_position
    con = orderable_condition + [ "#{pos} < #{@position}" ]
    self.class.update( "#{pos}=(#{pos} + 1)",  :condition => con.join(' AND ') )
  end

  def increment_position_of_all_items
    pos = orderable_position
    con = orderable_condition
    con = con.empty? ? nil : con.join(' AND ')
    self.class.update("#{pos}=(#{pos} + 1)", :condition => con )
  end

  def decrement_position_of_lower_items
    pos = orderable_position
    con = orderable_condition + [ "#{pos} > #{@position}" ]
    self.class.update( "#{pos}=(#{pos} - 1)",  :condition => con.join(' AND ') )
  end

end

end

# * George Moschovitis <gm@navel.gr>
# * Thomas Sawyer <transfire@gmail.com>