Extract enabled_tracker_ids and simplify comments

The tracker id normalization was duplicated between enabled_for? and
any_tracker_enabled?. The zone label and drift check comments are
reworded in plainer English so non-native contributors can follow the
reasoning (#20).

Author: dkastl

lib/redmine_issue_datetime.rb

@@ -16,17 +16,23 @@ def self.setup
   # optional list columns out of the column picker on an instance that has not
   # enabled the plugin anywhere.
   def self.any_tracker_enabled?
-    Array(settings['tracker_ids']).reject(&:blank?).any?
+    enabled_tracker_ids.any?
   end
 
   def self.settings
     Setting.plugin_redmine_issue_datetime
   end
 
+  # The tracker ids the plugin is enabled for. The setting is stored as an
+  # array of strings and contains a blank entry from the form's hidden field.
+  def self.enabled_tracker_ids
+    Array(settings['tracker_ids']).reject(&:blank?).map(&:to_i)
+  end
+
   def self.enabled_for?(tracker_id)
     return false if tracker_id.blank?
 
-    Array(settings['tracker_ids']).reject(&:blank?).map(&:to_i).include?(tracker_id.to_i)
+    enabled_tracker_ids.include?(tracker_id.to_i)
   end
 
   def self.time_step_minutes
@@ -46,22 +52,20 @@ def self.reference_zone
       ActiveSupport::TimeZone['UTC']
   end
 
-  # Short name of the reference zone, for labelling times in the UI.
-  #
-  # Times are stored as instants and always shown on one clock, the instance's
-  # reference zone, rather than each viewer's own. For site-based work that is
-  # the useful choice: a dispatcher and someone at the site must mean the same
-  # wall-clock time by "09:15". The label is what keeps that unambiguous.
+  # Zone labels for the UI.
   #
-  # Two labels, because the honest label depends on what is being labelled.
+  # Times are always shown on one clock, the instance's reference zone, never
+  # converted to each viewer's own zone. For work that happens at a physical
+  # place, everyone must mean the same wall-clock time by "09:15", and the
+  # visible zone label is what makes that unambiguous.
   #
-  # zone_abbreviation needs an instant and has no default: the abbreviation is
-  # daylight-saving dependent, so "now" would be wrong whenever the thing on
-  # screen is in another part of the year. Use it only where a specific time is
-  # displayed.
+  # There are two label methods because the correct label depends on context:
   #
-  # zone_name is for anywhere that covers many dates or none yet - a list header,
-  # an empty form - where no single abbreviation can be correct.
+  # - zone_abbreviation(at) is daylight-saving aware, so it requires the
+  #   instant being displayed (deliberately no default: "now" would be wrong
+  #   for a time in another part of the year). Use it next to a specific time.
+  # - zone_name is season-independent. Use it where many dates are covered,
+  #   or none yet: list headers, empty forms.
   def self.zone_abbreviation(at)
     at.in_time_zone(reference_zone).strftime('%Z')
   end

lib/redmine_issue_datetime/drift_check.rb

@@ -30,12 +30,11 @@ def initialize(zone: RedmineIssueDatetime.reference_zone)
 
     # Every disagreement, ordered by issue then field.
     #
-    # The scan is batched so a large instance never loads every row at once, and
-    # deliberately unordered: find_each batches by primary key and silently
-    # ignores an order clause (raising outright when
-    # ActiveRecord.error_on_ignored_order is set). The findings are the problems,
-    # so there are few of them, and sorting those at the end is both cheap and
-    # actually honoured.
+    # The scan is batched so a large instance never loads every row at once.
+    # It is deliberately unordered: find_each batches by primary key and
+    # silently ignores an order clause (or raises when
+    # ActiveRecord.error_on_ignored_order is set). Sorting the few findings
+    # at the end is cheap and, unlike an order clause here, actually applied.
     def findings
       results = []
       IssueDatetime.includes(:issue).find_each(batch_size: 500) do |record|