require 'get_set_method'

class Invoice
  module Currency
    class Symbols
      @@map = {}
      def self.map
        @@map
      end
    end
    
    class Convertor
      @@records = {}

      def self.records
        @@records
      end
      
      def self.add(c1, c2, ratio)
        @@records["#{c1}:#{c2}"] = ratio
        @@records["#{c2}:#{c1}"] = 1/ratio.to_f
      end
  
      def self.get(c1, c2)
        raise 'Finding identity!' if c1 == c2
        @@records["#{c1}:#{c2}"]
      end
      
      def initialize(amount)
        @amount = amount
      end
  
      def method_missing(sym, *args)
        # Workaround for rspec
        return super(sym, *args) if sym.to_s.match(/^should/)
        Amount.new(sym.to_s, @@records["#{@amount.name}:#{sym.to_s}"] * @amount.amount)
      end
    end
  
    class Amount < Numeric
      attr_reader :name, :amount

      def initialize(name, amt)
        @name = name
        @name += 's' if @name[-1..-1] != 's' 
        @amount = amt.to_f
      end

      include GetSetMethod
      
      # A bit of a hack. We need this operation value so that we know in the container what sum was performed,
      # so we can calibrate the output.
      get_set_method :last_operation_value

      ['+','-'].each do |op|
        class_eval("def #{op}(rhs); ret = Amount.new(name, @amount #{op} find_amount(rhs)); ret.last_operation_value(rhs.to_f); ret; end")
      end

      ['*','/'].each do |op|
        class_eval("def #{op}(rhs); ret = Amount.new(name, @amount #{op} rhs.to_f); ret.last_operation_value(rhs.to_f); ret; end")
      end
      
      def coerce(numeric)
        return [Amount.new(name, numeric), self]
      end

      def to_s
        "%.2f" % @amount.to_s
      end
    
      def to_f
        @amount
      end
      
      def currency_symbol
        Symbols.map[@name]
      end
    
      def in
        return Convertor.new(self)
      end
      
      def ==(other)
        return false if other.class != Amount
        if @name == other.name
          return @amount == other.amount
        else
          return other.amount == Convertor.get(name, other.name) * @amount rescue false
        end
      end
    
      def |(other)
        Convertor.add(name, other.name, other.amount.to_f/amount.to_f)
      end
      alias :are_worth :|
      alias :is_worth :|
      
      def find_amount(rhs)
        return rhs if rhs.class != Amount
        return rhs.amount if rhs.name == name
        Convertor.get(rhs.name, name) * rhs.amount
      end
    end
  end
end

class Numeric
  def method_missing(sym, *args)
    # Workaround for rspec
    return super(sym, *args) if sym.to_s.match(/^should/)
    amt = Invoice::Currency::Amount.new(sym.to_s, self)
    # Add the 'symbol' if it exists
    Invoice::Currency::Symbols.map[amt.name] = args[0] if args.length > 0 
    amt   
  end
end