require 'units/units_unit'
require 'methodic_hash'

# A UnitsSystem groups units that measure the same quality and are
# conceptually organized together within a UnitsMeasure. Its a MethodicHash
# of unit names to UnitsUnit instances.
class UnitsSystem < MethodicHash
  
  # The UnitsMeasure to which this instance is associated.
  attr_reader :units_measure
  # The name of this UnitsSystem
  attr_reader :name

  def initialize(units_measure,name) # :nodoc:
    @units_measure = units_measure
    @name = name
  end
  
  # Defines a new UnitsUnit. If ten-based or two-based greeking is defined,
  # it is applied.
  def unit(attributes)
    unit = nil
    if !Units.holding_forward_reference?
      unit = UnitsUnit.new self, attributes
      self[unit.name] = unit
      Units.add_unit unit
      case unit.greek
        when :ten then greek_ten unit
        when :two then greek_two unit
      end
    else
      Units.hold_forward_reference nil
    end
    Units.continue_forward_reference_resolution
    unit
  end

  # Associates the name of a format with an output formatter in the instance's
  # UnitsMeasure.
  def format(options)
    @units_measure.format(options)
  end
  
  def greek_ten(base) # :nodoc:
    greek_unit base, "yocto", "y",  0.000000000000000000000001
    greek_unit base, "zepto", "z",  0.000000000000000000001
    greek_unit base, "atto",  "a",  0.000000000000000001
    greek_unit base, "femto", "f",  0.000000000000001
    greek_unit base, "pico",  "p",  0.000000000001
    greek_unit base, "nano",  "n",  0.000000001
    greek_unit base, "micro", "u",  0.000001
    greek_unit base, "milli", "m",  0.001
    greek_unit base, "centi", "c",  0.01
    greek_unit base, "deci",  "d",  0.1
    greek_unit base, "deca",  "da", 10.0
    greek_unit base, "hecto", "h",  100.0
    greek_unit base, "kilo",  "k",  1000.0
    greek_unit base, "mega",  "M",  1000000.0
    greek_unit base, "giga",  "G",  1000000000.0
    greek_unit base, "tera",  "T",  1000000000000.0
    greek_unit base, "peta",  "P",  1000000000000000.0
    greek_unit base, "exa",   "E",  1000000000000000000.0
    greek_unit base, "zetta", "Z",  1000000000000000000000.0
    greek_unit base, "yotta", "Y",  1000000000000000000000000.0
  end
  
  def greek_two(base) # :nodoc:
    greek_unit base, "kilo",  "k", 2**10
    greek_unit base, "mega",  "m", 2**20
    greek_unit base, "giga",  "g", 2**30
    greek_unit base, "tera",  "t", 2**40
    greek_unit base, "peta",  "p", 2**50
    greek_unit base, "exa",   "e", 2**60
    greek_unit base, "zetta", "z", 2**70
    greek_unit base, "yotta", "y", 2**80
  end
  
  def greek_unit(base,prefix,abbrev_prefix,scalar) # :nodoc:
    unit :name => prefix+base.name,
         :plural => prefix+base.plural,
         :abbrevs => base.abbrevs.collect { |abbrev| abbrev_prefix+abbrev },
         :equals => base.equals * scalar
  end
  
end