# Copyright (c) 2006, Chris Parsons (chris@edendevelopment.co.uk)
# All rights reserved.
# 
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions are met:
# 
# * Redistributions of source code must retain the above copyright notice,
#   this list of conditions and the following disclaimer.
# * Redistributions in binary form must reproduce the above copyright notice,
#   this list of conditions and the following disclaimer in the documentation
#   and/or other materials provided with the distribution.
# * Neither the name of Chris Parsons nor the names of its contributors may be
#   used to endorse or promote products derived from this software without
#   specific prior written permission.
# 
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
# ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
# LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
# CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
# SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
# INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
# CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
# ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
# POSSIBILITY OF SUCH DAMAGE.

require 'time'
require 'currency'
require 'get_set_method'

def new_invoice(&block)
  inv = Invoice.new
  inv.instance_eval &block
  Invoice.invoices << inv
  inv
end


class Invoice
  module TimeMethods
    # Time functions
    def second; 1; end; alias :seconds :second
    def minute; second * 60; end; alias :minutes :minute
    def hour; minute * 60; end; alias :hours :hour
    def day; hour * 8; end; alias :days :day
    def week; day * 5; end; alias :weeks :week
    def month; week * 4; end; alias :months :month
  end
  module WhatMethods
    def on(what)
      { :count => self, :what => what }
    end
    alias :to :on
    alias :for :on
    alias :of :on
  end
  
  module Currency
    class Amount
      include WhatMethods
    end
  end
  
  include TimeMethods
  include GetSetMethod
  
  MILEAGE_RATE = 0.40 # Current UK IR mileage rate

  attr_reader :items, :expenses

  def initialize
    @expenses ||= []
    @items ||= []
    @vat = 17.5
    @date = Time.now
    @default_time_interval = seconds
  end

  def self.invoices(newinv = nil)
    @@invoices ||= []
    @@invoices << newinv unless newinv.nil?
    @@invoices
  end

  get_set_method :code, :address, :vat, :currency
  

  def expense(hash)
    @expenses << Invoice::Expense.new(hash)
  end

  def date(dt = nil)
    if dt.nil?
      return @date
    else
      @date = dt.class == Time ? dt : Time.parse(dt)
    end
  end

  def work_at(amt, &block)
    ig = Invoice::ItemGroup.new
    ig.rate = amt

    # Discern the rate from a currency amount's operation value
    if amt.class == Invoice::Currency::Amount && !amt.last_operation_value.nil?
      ig.default_time_interval = amt.last_operation_value
    else
      ig.default_time_interval = 1
    end

    ig.instance_eval &block
    @items.push *(ig.expand)
  end
  alias :mileage_at :work_at
  
  def add(hash)
    @items << Item.new(hash[:rate], hash[:count], hash[:what], hash[:date])
  end
  
  def total
    t = total_items
    @expenses.map { |e| t += e.amount }
    t
  end
    
  def total_items
    t = 0
    @items.map { |i| t += i.total }
    to_currency(t)
  end 

  def to_currency(amt)
    currency ? eval("amt.in.#{currency}") : amt
  end

  def total_vat
    total_items * @vat/100
  end
  
  class Item
    attr_reader :rate, :count, :what, :date, :default_time_interval

    def initialize(rate, count, what, date = nil, default_time_interval = 1)
      @rate = rate
      @count = count
      @what = what
      @date = date
      @default_time_interval = default_time_interval
    end

    def rate
      @rate * @default_time_interval
    end
    
    def count
      @count / @default_time_interval
    end
    
    def total
      @rate * @count
    end
  end
  
  class Expense
    attr_reader :amount, :what
    
    def initialize(hash)
      @amount = hash[:count]
      @what = hash[:what]
    end
  end
    
  class ItemGroup
    attr_accessor :rate, :default_time_interval
    
    def spent(hash)
      @items ||= []
      @items << hash
    end
    def drove(hash)
      hash[:what] = "Mileage: #{hash[:what]}"
      spent(hash)
    end
    def expand
      @items.collect { |i| Invoice::Item.new(@rate, i[:count], i[:what], i[:date], @default_time_interval) }
    end
  end
end

class Numeric
  include Invoice::WhatMethods
  include Invoice::TimeMethods
  # Redefining the 'second' value adjusts all 
  # the other methods to return the correct value also
  def second; self; end
end

class Hash
  def on(datetext)
    self[:date] = Time.parse(datetext)
    self
  end
  
  def costing(rate)
    self[:rate] = rate.class == String ? rate.to_f : rate
    self
  end
end