require 'rubygems'
require 'tzinfo'

module Barometer
  #
  # A simple Zone class
  # 
  # Used for building and converting timezone aware date and times
  # Really, these are just wrappers for TZInfo conversions plus
  # some extras.
  #
  class Data::Zone
    
    @@zone_codes_file = File.expand_path(
      File.join(File.dirname(__FILE__), '..', 'translations', 'zone_codes.yml'))
    @@zone_codes = nil

    attr_accessor :zone_full, :zone_code, :zone_offset, :tz
    
    def initialize(zone)
      if Data::Zone.is_zone_full?(zone)
        @zone_full = zone
        @tz = TZInfo::Timezone.get(zone)
      elsif Data::Zone.is_zone_offset?(zone)
        @zone_offset = zone
      elsif Data::Zone.is_zone_code?(zone)
        @zone_code = zone
      else
        raise(ArgumentError, "invalid time zone")
      end
    end
    
    def current
      @zone_full || @zone_offset || @zone_code
    end
    
    # what is the Timezone Short Code for the current timezone
    def code
      return @zone_code if @zone_code
      return nil unless @tz
      @tz.period_for_utc(Time.now.utc).zone_identifier.to_s
    end
    
    def full
      @zone_full || nil
    end
    
    def offset
      if @zone_offset
        @zone_offset.to_f * 60 * 60
      elsif @zone_code
        Data::Zone.zone_to_offset(@zone_code)
      elsif @zone_full
      end
    end
    
    # is the current timezone in daylights savings mode?
    def dst?
      return nil unless @tz
      @tz.period_for_utc(Time.now.utc).dst?
    end
    
    # return Time.now.utc for the set timezone
    def now(convert=false)
      if @zone_full
        now = @tz.utc_to_local(Time.now.utc)
      elsif @zone_offset || @zone_code
        now = Time.now.utc + self.offset
      end
      convert ? Data::LocalTime.parse(now) : now
    end
    
    # return Date.today for the set timezone
    def today
      now = self.now
      Date.new(now.year, now.month, now.day)
    end
    
    def local_to_utc(local_time)
      if @zone_full
        @tz.local_to_utc(local_time)
      elsif @zone_offset || @zone_code
        local_time -= self.offset
        Time.utc(local_time.year,local_time.month,local_time.day,
          local_time.hour,local_time.min,local_time.sec)
      end
    end
    
    def utc_to_local(utc_time)
      if @zone_full
        @tz.utc_to_local(utc_time)
      elsif @zone_offset || @zone_code
        utc_time + self.offset
      end
    end
    
    #
    # Class Methods
    #
    
    def self.is_zone_code?(zone)
      return false unless (zone && zone.is_a?(String))
      _load_zone_codes unless @@zone_codes
      Time.zone_offset(zone) || (@@zone_codes && @@zone_codes.has_key?(zone))
    end
    
    def self.is_zone_full?(zone)
      return false unless (zone && zone.is_a?(String))
      zone.match(/[A-Za-z]+\/[A-Za-z]+/) ? true : false
    end
    
    def self.is_zone_offset?(zone)
      return false unless (zone && (zone.is_a?(Fixnum) || zone.is_a?(Float)))
      zone.to_f.abs <= 14
    end

    #
    # Known conflicts
    # IRT (ireland and india)
    # CST (central standard time, china standard time)
    #
    def self.zone_to_offset(timezone)
      offset = 0
      seconds_in_hour = 60*60
      # try to use Time
      unless offset = Time.zone_offset(timezone)
        # that would have been too easy, do it manually
        # http://www.timeanddate.com/library/abbreviations/timezones/
        # http://www.worldtimezone.com/wtz-names/timezonenames.html
        offset = (@@zone_codes[timezone.to_s.upcase] || 0) * seconds_in_hour
      end
      offset
    end
    
    def self._load_zone_codes
      $:.unshift(File.dirname(__FILE__))
      @@zone_codes ||= YAML.load_file(@@zone_codes_file)
    end
    
  end
end