gistfile1.rb

class DateTime
  def to_db
    strftime("%Y-%m-%d")
  end
end

class Generator

  class << self

    attr_accessor :attributes, :number, :function_name, :children, :id

    def set_number(n)
      @number = n
    end

    def set_function_name(name)
      @function_name = name
    end

    def attribute(name, type, &block)
      @attributes ||= {}
      @attributes[name] = { type: type, block: block }
    end

    def set_children(&block)
      @children = block
    end

    def inc_id
      @id ||= 0
      @id += 1
    end

  end

  def initialize(attrs = {})
    @attrs = attrs
  end

  def output
    "\n" + generate + children
  end

  def generate
    out = []
    @children_res = ""

    @result = {}

    self.class.number.times do
      a = {}
      id = self.class.inc_id

      self.class.attributes.each do |name, values|
        a[name] = escape(values[:block].call(@attrs.merge(:parent_id => self.class.id)), values[:type])
      end

      @children_res << self.class.children.call(@attrs.merge(:parent_id => self.class.id)) if self.class.children

      out << a

      @result[id] = a
    end

    format(out) + "\n"
  end

  def data
    @result
  end

  def children
    @children_res
  end

  def escape(value, type)

    if value.nil?
      return 'null'
    else
      case type
        when :null
          %{NULL}
        when :string
          if value == 'NULL'
            %{NULL}
          else
            %{'#{value.gsub("'", "")}'}
          end
        when :integer
          value.to_s
        when :daterange
          # '[2014-02-01, 2014-10-01)'
          %{'[#{value.first.to_db}, #{value.last.to_db})'}
        when :datetime
          %{date '#{value.to_db}'}
      end
    end

  end

  def format(array)
    array.map do |attributes|
      "select #{self.class.function_name}(#{attributes.values.join(', ')});"
    end.join("\n")
  end

end