Added julian timestamp utility methods

TODO.taskpaper

@@ -43,6 +43,71 @@ Other:
         - scrape @done(2009-02-23 23:13:51)
         - publish @done(2009-02-23 23:13:52)
 
+
+
+Tables:
+    Dates: 
+        - key 'date/#{jd}'
+        - type 'Date'
+        - jd #{jd}
+        - ord "yyyy-ddd"
+        - iso "yyyy-mm-dd"
+
+    Tweets:
+        - key = 'tweet/#{status_id}' where id is item minux xml
+        - type 'Tweet'
+        - status_id
+        - author (username)
+        - text ( full text )
+        - url
+        - destinationurl
+        - source
+        - at
+        - author_snapshot ( 'author/#{username}/#{jd}' )
+        - post_date    ( julan day of at )
+        - post_at      ( julian time of at )
+        - split_at     ( julian time )
+        - scrape_at    ( julian time )
+        - store_at     ( julian time )
+        - publish_at   ( julian time )
+        - tags (csv)
+        - mentions (csv)
+        - urls (csv)
+
+    Authors:
+        - id = 'author/#{username}'
+        - type 'Author'
+        - username 
+        - name
+        - location
+        - website
+        - bio
+        - picture_url
+        - follower_count
+        - following_count
+        - update_count
+        - first_snap_date( julian day)
+        - snap_date      ( julian day )
+        - snap_at        ( julian time )
+
+    AuthorSnapshots:
+        - id = 'author/#{username}/snapshot/#{jd}
+        - type 'AuthorSnapshot'
+        - snap_date (  jd )
+        - snap_at ( julian time )
+        - everything else from Authors
+
+    Follows:
+        - id = 'author/#{username}/follows/#{username}'
+        - 
+        - type 'Follow'
+        - first_snap_date
+        - last_snap_date
+        - is_current
+
+
+
+
 Gnip v2.1
     - switch to that notification stream
     - start publishing

lib/snipe/julian.rb

@@ -0,0 +1,84 @@
+#
+# Julian Time helpers
+#
+# 
+# The date conversions are currently easily enough done with the standard ruby
+# libraries.  Snipe uses Modified Julian Day for day values and fractional day 
+# in the sense of Julian Day
+#
+require 'date'
+module Snipe
+  module Julian
+    module Date
+      module ClassMethods
+        # convert a modified julian day to a civil day
+        def mjd_to_civil( mjd )
+          jd = ::Date.mjd_to_jd( mjd )
+          d = ::Date.jd_to_civil( jd )
+        end
+      end
+      ::Date.extend( ClassMethods )
+    end
+
+    module Time
+
+      SECONDS_PER_DAY = 86400
+
+      module ClassMethods
+
+        # convert from a modified julian day to a Time
+        def from_mjd( mjd )
+          d = ::Date.mjd_to_civl( mjd )
+          ::Time.gm( d.year, d.month, d.day )
+        end
+
+        # convert from a modified julian day stamp to a Time
+        def from_mjd_stamp( mjd_stamp )
+          mjd, fraction = mjd_stamp.split(".")
+          d = ::Date.new( *::Date.mjd_to_civil( mjd.to_i ) )
+
+          fraction      = Float( "0.#{fraction}")
+          amt = (SECONDS_PER_DAY * fraction).round
+
+          ss  = amt % 60
+          amt = (amt - ss) / 60
+          mm  = amt % 60
+          hh  = (amt - mm) / 60
+
+          ::Time.gm( d.year, d.month, d.day, hh, mm, ss )
+        end
+      end
+      ::Time.extend( ClassMethods )
+
+      module InstanceMethods
+        def seconds_of_day
+          ((hour * 3600) + (min * 60) + (sec) + (usec/1_000_000)).to_f
+        end
+
+        def to_date
+          Date.new( year, month, day )
+        end
+
+        # calculate the modified julian day fraction
+        def mjd_fraction
+          seconds_of_day / SECONDS_PER_DAY
+        end
+
+        # the iteger portion of a modified julian day
+        def mjd
+          to_date.mjd
+        end
+
+        # generate a #####.##### stringn that is the modified julian day plus
+        # the fractional portion of the day.
+        def mjd_stamp
+        "%0.5f" % (mjd + mjd_fraction)
+        end
+      end
+    end
+  end
+end
+
+class Time
+  include Snipe::Julian::Time::InstanceMethods
+end

spec/julian_spec.rb

@@ -0,0 +1,13 @@
+require File.expand_path( File.join( File.dirname( __FILE__ ),"spec_helper.rb"))
+require 'snipe/julian'
+
+describe Snipe::Julian do
+
+  it "can round trip a time from now to modified julan time and back" do
+    only_sec  = Time.at( Time.now.utc.to_i ).utc
+    today_mjd = only_sec.mjd_stamp
+    utc_round = Time.from_mjd_stamp( today_mjd )
+    utc_round.should == only_sec
+  end
+end
+