ioquatix/periodical

# Copyright, 2012, by Samuel G. D. Williams. <http://www.codeotaku.com>
# 
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
# 
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
# 
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.

module Periodical
    Period = Struct.new(:count, :unit) do
        VALID_UNITS = [:days, :weeks, :months, :years].freeze
        
        # Plural is preferred, as in "1 or more days".
        def initialize(count = 1, unit = :days)
            super(count, unit)
        end
        
        def to_s
            if self.count != 1
                "#{self.count} #{self.unit}"
            else
                self.unit.to_s
            end
        end
        
        def advance(date, multiple = 1)
            raise TypeError unless date.is_a?(Date)
            
            self.send("advance_#{unit}", date, multiple * self.count)
        end
        
        private
        
        def advance_days(date, count)
            date + count
        end
        
        def advance_weeks(date, count)
            advance_days(date, count*7)
        end
        
        def advance_months(date, count)
            date >> count
        end
        
        def advance_years(date, count)
            advance_months(date, count*12)
        end
        
        class << self
            # Accepts strings in the format of "2 weeks" or "weeks"
            def parse(string)
                parts = string.split(/\s+/, 2)
                
                if parts.size == 1
                    count = 1
                    unit = parts[0]
                else
                    count, unit = parts
                end
                
                self.new(count.to_i, unit.to_sym)
            end
            
            def load(string)
                if string
                    string = string.strip
                    
                    parse(string) unless string.empty?
                end
            end
            
            def dump(period)
                period.to_s if period
            end
        end
    end
end