module Phys

  # @visibility private
  module UnitMeasures
    def self.included(mod)
      Unit::LIST.each do |k,u|
        if /^[A-Z]\w*$/ =~ k
          const_set(k,u)
        end
      end
    end
  end

  # Defines method with unit name.
  # *Caution*: Variable names may conflict with unit names.
  # @example
  #   require 'phys/units'
  #
  #   Phys::UnitsMixin.module_eval do
  #     puts 123.4*km
  #     puts 23*mile/hr >> m/s
  #     puts h.to_si
  #     case mile/hr
  #     when m
  #       puts "length"
  #     when m/s
  #       puts "velocity"
  #     else
  #       puts "other"
  #     end
  #   end
  #
  #   extend Phys::UnitsMixin
  #
  #   1*miles/hr >> m/s    #=> Phys::Quantity[0.44704,"m/s"]
  #
  module UnitsMixin
    include UnitMeasures

    module_function

    alias method_missing_units_alias method_missing

    def method_missing(method, *args, &block)
      if unit = Unit.find_unit(method)
        raise "argument must be empty" unless args.empty?
        Quantity.new(Rational(1), method, unit)
      else
        method_missing_units_alias(method, *args, &block)
      end
    end

    def print_units(unit=nil)
      Unit::LIST.each do |k,u|
        if unit.nil? || unit===u
          len = 32 - k.size
          len = 1 if len < 1
          puts k+" "*len+"#{u.expr}"
        end
      end
      nil
    end
  end

  # ActiveSupport-like mix-in.
  # *Caution*: This kind of global change will cause unexpected problems.
  # @example
  #   require 'phys/units'
  #
  #   class Numeric
  #     include Phys::UnitsNumericMixin
  #   end
  #
  #   1.miles/hr >> m/s     #=> Phys::Quantity[0.44704,"m/s"]
  #   1.(km/s) >> miles/hr  #=> Phys::Quantity[(1/0.00044704),"miles/hr"]
  #
  module UnitsNumericMixin

    alias method_missing_units_alias method_missing

    def method_missing(method, *args, &block)
      if unit = Unit.find_unit(method)
        raise "argument must be empty" unless args.empty?
        case self
        when Integer
          Quantity.new(Rational(self), method, unit)
        when Numeric
          Quantity.new(self, method, unit)
        else
          self * Quantity.new(1, method, unit)
        end
      else
        method_missing_units_alias(method, *args, &block)
      end
    end

    def call(unit)
      self * unit
    end
  end

end