#399

backend/app/models/post.rb

@@ -1,4 +1,5 @@
 class Post < ApplicationRecord
+  require 'date'
   require 'mini_magick'
   require 'stringio'
 
@@ -237,15 +238,43 @@ class Post < ApplicationRecord
     value = raw_value.to_s.strip
     return nil if value.blank?
 
-    if value.match?(/\A\d{4}-\d{2}-\d{2}T\d{2}:\d{2}\z/)
-      return Time.zone.local(value[0, 4].to_i,
-                             value[5, 2].to_i,
-                             value[8, 2].to_i,
-                             value[11, 2].to_i,
-                             value[14, 2].to_i)
+    if (match = value.match(/\A(\d{4})-(\d{2})-(\d{2})T(\d{2}):(\d{2})\z/))
+      year = match[1].to_i
+      month = match[2].to_i
+      day = match[3].to_i
+      hour = match[4].to_i
+      minute = match[5].to_i
+      return nil unless valid_original_created_components?(year, month, day, hour, minute, 0)
+
+      return Time.zone.local(year, month, day, hour, minute)
     end
 
-    Time.iso8601(value).in_time_zone
+    match =
+        value.match(
+            /\A(\d{4})-(\d{2})-(\d{2})T(\d{2}):(\d{2})/ \
+            '(?::(\d{2})(?:\.(\d+))?)?' \
+            '(Z|[+-]\d{2}:?\d{2})\z/')
+    return nil if match.nil?
+
+    year = match[1].to_i
+    month = match[2].to_i
+    day = match[3].to_i
+    hour = match[4].to_i
+    minute = match[5].to_i
+    second = match[6]&.to_i || 0
+    fraction = match[7]
+    offset = match[8]
+    return nil unless valid_original_created_components?(year, month, day, hour, minute, second)
+    return nil unless valid_original_created_offset?(offset)
+
+    Time.new(
+        year,
+        month,
+        day,
+        hour,
+        minute,
+        second + Rational(parse_original_created_nanoseconds(fraction), 1_000_000_000),
+        normalise_original_created_offset(offset)).in_time_zone
   rescue ArgumentError, TypeError
     nil
   end
@@ -254,6 +283,38 @@ class Post < ApplicationRecord
     value.sec.zero? && value.nsec.zero?
   end
 
+  def valid_original_created_components? year, month, day, hour, minute, second
+    return false unless Date.valid_date?(year, month, day)
+    return false unless hour.between?(0, 23)
+    return false unless minute.between?(0, 59)
+    return false unless second.between?(0, 59)
+
+    true
+  end
+
+  def valid_original_created_offset? value
+    match = value.match(/\A([+-])(\d{2}):?(\d{2})\z/)
+    return true if value == 'Z'
+    return false if match.nil?
+
+    hours = match[2].to_i
+    minutes = match[3].to_i
+    hours.between?(0, 23) && minutes.between?(0, 59)
+  end
+
+  def parse_original_created_nanoseconds value
+    return 0 if value.blank?
+
+    digits = value[0, 9].ljust(9, '0')
+    Integer(digits, 10)
+  end
+
+  def normalise_original_created_offset value
+    return '+00:00' if value == 'Z'
+
+    value.match?(/\A[+-]\d{2}:\d{2}\z/) ? value : "#{ value[0, 3] }:#{ value[3, 2] }"
+  end
+
   def skip_original_created_validation?
     return false if new_record?
     return false if will_save_change_to_original_created_from?