The Pigstye

# This library adds the parse_date method to the Standard Ruby Date Class.
# Its purpose is to make the entry of user friendly date formates painless
# in Rails applications.
#
# My motivation for making this was the desire for user friendly date input
# in rails applications without resorting to javascript or some kind of widget.
#
# To use: drop this file into ./lib, require it into the application 
# controller.
#
# Written by Tom Willett 
# Version 1.0
#
# with a tip of the hat to
# Stuart Rackham 
# and Datetime ToolBocks
#
# Date Formats recognized by this method:
#    YYYY-mm-dd  ISO Standard
#    mm-dd-YYYY  American
#    mm-dd      Assume current year
#    mm/dd/YYYY American standard
#    mm/dd 
#    mm.dd.yyyy  European
#    dd.mm.yyyy  
#    dd mmmmm yyyy example: 22 may 1945 or 22nd may 1945
#    dd mmmmm   example: 22 may  (current year)
#    mmmm dd yyyy  example: may 22 1945 or may 22nd 1945
#    mmmm dd, yyyy  example: may 22, 1945
#    mmmm dd     example may 22 or may 22nd
#    dd          example  4 or 4th
#    today (tod) or now   common names for days and abbreviations
#    tomorrow (tom)
#    yesterday  (yes)
#    Next Week, Last Week, Next Month, Last Month, Next Year, Last Year
#    +n[units] or -n[units]: Date from today: examples: '+22', '+22 days',
#       '+22d', '-4 weeks', '-4w', '-4week', '+6 months', '+6m', '+6month',  
#       '-2 years', '-2y'
#
class Date

  # Parse date string with one of the following formats:
  #
  # The string argument is first converted to a string with #to_s.
  # Returns nil if passed nil or an empty string.
  # Raises ArgumentError if string can't be parsed.
  #
  def self.parse_date(org_string)
    string = org_string.to_s.strip.downcase
    return nil if org_string.empty?
    today = Date.today
    if string =~ /^(\d{4})-(\d{1,2})-(\d{1,2})$/
      # YYYY-mm-dd format.  ISO Standard
      year = $1.to_i
      month = $2.to_i
      day = $3.to_i
    elsif string =~ /^(\d{1,2})-(\d{1,2})-(\d{4})$/
      # mm-dd-yyyy format
      year = $3.to_i
      month = $1.to_i
      day = $2.to_i
    elsif string =~ /^(\d{1,2})\.(\d{1,2})\.(\d{4})$/
      # mm.dd.yyyy or dd.mm.yyyy format
      year = $3.to_i
      if $1.to_i > 12
        day = $1.to_i
        month = $2.to_i
      else
        day = $2.to_i
        month = $1.to_i
      end
    elsif string =~ /^(\d{1,2})-(\d{1,2})$/
      # mm-dd format
      year = today.year.to_i
      month = $1.to_i
      day = $2.to_i
    elsif string =~ /^(\d{1,2})\/(\d{1,2})\/(\d{4})$/
      # mm/dd/yyyy format
      year = $3.to_i
      month = $1.to_i
      day = $2.to_i
    elsif string =~ /^(\d{1,2})\/(\d{1,2})$/
      # mm/dd format
      year = today.year
      month = $1.to_i
      day = $2.to_i
    elsif string =~ /^(\d{1,2})(?:st|nd|rd|th)?,? (\w+) (\d{2,4})$/
      # 'd mmmm yyyy' format
      date_array = ParseDate.parsedate("#{$1} #{$2} #{$3}", true)
      year = date_array[0].to_i
      month = date_array[1].to_i
      day = date_array[2].to_i
    elsif string =~ /^(\w+) (\d{1,2})(?:st|nd|rd|th)?,? (\d{2,4})$/
      # 'mmmm d yyyy' format
      date_array = ParseDate.parsedate("#{$2} #{$1} #{$3}", true)
      year = date_array[0].to_i
      month = date_array[1].to_i
      day = date_array[2].to_i
    elsif string =~ /^(\d{1,2})(?:st|nd|rd|th)?,? (\w+)$/
      # 'd mmmm' format
      y = today.year.to_s
      date_array = ParseDate.parsedate("#{$1} #{$2} #{y}", true)
      year = date_array[0].to_i
      month = date_array[1].to_i
      day = date_array[2].to_i
    elsif string =~ /^(\w+) (\d{1,2})(?:st|nd|rd|th)?,?$/
      # 'mmmm d' format
      y = today.year.to_s
      date_array = ParseDate.parsedate("#{$2} #{$1} #{y}", true)
      year = date_array[0].to_i
      month = date_array[1].to_i
      day = date_array[2].to_i
    elsif string =~ /^(\d{1,2})(st|nd|rd|th)?$/
      # 'd' format
      year = today.year
      month = today.month
      day = $1.to_i
    elsif string =~ /^tod[\w]+$|^now$/
      # today or now
      year = today.year
      month = today.month
      day = today.day
    elsif string =~ /^tom/
      # tomorrow
      today += 1
      year = today.year
      month = today.month
      day = today.day
    elsif string =~ /^yes/
      # yesterday
      today -= 1
      year = today.year
      month = today.month
      day = today.day
    elsif string =~ /^(next|last)\s(week|month|year)$/
      # Next Week, Last Week, Next Month, Last Month, Next Year, Last Year
      year = today.year
      month = today.month
      day = today.day
      case $2
        when 'week'
          if $1 == 'next'
            today += 7
          else
            today -= 7
          end
          year = today.year
          month = today.month
          day = today.day
        when 'month'
          month = (($1 == 'next') ? (month + 1) : (month - 1))
          if month > 12
            month = 1
            year += 1
          elsif month < 1
            month = 12
            year -= 1
          end
        when 'year'
          year = (($1 == 'next') ? (year + 1) : (year - 1))
      end
    elsif string =~ /^([+-]\d+)(?:\s*(d|days?|w|weeks?|m|months?|y|years?))?$/
      # Date intervals.
      year = today.year
      month = today.month
      day = today.day
      n = $1.to_i
      units = $2 || 'days'
      case units.first
      when 'd'
        today = today + n
        year = today.year
        month = today.month
        day = today.day
      when 'w'
        today = today + n*7
        year = today.year
        month = today.month
        day = today.day
      when 'm'
        sign = n <=> 0
        month = today.month + sign * (n.abs % 12)
        year = today.year + sign * (n.abs / 12)
        if month <1
          month += 12
          year -= 1
        elsif month > 12
          month -= 12
          year += 1
        end
      when 'y'
        year = year + n
      end
    else
      raise ArgumentError.new("\"#{org_string}\" is not recognized as a Date")
    end
    
    begin
      result = Date.new(year,month,day)
    rescue
      raise ArgumentError.new("\"#{org_string}\" is not recognized as a Date")
    end
    result
  end
end