Hide duplicate timestamps on item trades page

Just a small visual cleanup because I happened to click on item trades
today! We don't need to repeat "This Week" a million times. Just output
it for the first row, then hide it for the following. (We still include
it in screen reader output for semantic clarity; this is just a visual
cleanup.)

app/assets/stylesheets/item_trades/index.sass

@@ -18,6 +18,16 @@
 			overflow: hidden
 			text-overflow: ellipsis
 
+	td[data-is-same-as-prev]
+		// Visually hidden
+		clip: rect(0 0 0 0)
+		clip-path: inset(50%)
+		height: 1px
+		overflow: hidden
+		position: absolute
+		white-space: nowrap
+		width: 1px
+
 	.trade-list-names
 		list-style: none
 

app/helpers/item_trades_helper.rb

@@ -1,22 +1,28 @@
 module ItemTradesHelper
-	def vague_trade_timestamp(last_trade_activity_at)
+	def vague_trade_timestamp(trade)
-		if last_trade_activity_at >= 1.week.ago
+		return nil if trade.nil?
+
+		if trade.last_activity_at >= 1.week.ago
 			translate "item_trades.index.table.last_active.this_week"
 		else
-			last_trade_activity_at.strftime("%b %Y")
+			trade.last_activity_at.to_date.to_fs(:month_and_year)
 		end
 	end
 
+	def same_vague_trade_timestamp?(trade1, trade2)
+		vague_trade_timestamp(trade1) == vague_trade_timestamp(trade2)
+	end
+
 	def sorted_vaguely_by_trade_activity(trades)
 		# First, sort the list in ascending order.
 		trades_ascending = trades.sort_by do |trade|
-			if trade.user.last_trade_activity_at >= 1.week.ago
+			if trade.last_activity_at >= 1.week.ago
 				# Sort recent trades in a random order, but still collectively as the
 				# most recent. (This discourages spamming updates to game the system!)
 				[1, rand]
 			else
 				# Sort older trades by last trade activity.
-				[0, trade.user.last_trade_activity_at]
+				[0, trade.last_activity_at]
 			end
 		end
 

app/models/closet_hanger.rb

@@ -183,6 +183,10 @@ class ClosetHanger < ApplicationRecord
     def lists
       hangers.map(&:list).filter(&:present?)
     end
+
+    def last_activity_at
+      user.last_trade_activity_at
+    end
   end
 
   protected

app/views/item_trades/index.html.haml

@@ -17,10 +17,13 @@
 				%th= t(".table.headings.user.#{@type}")
 				%th= t(".table.headings.lists")
 		%tbody
+			- prev_trade = nil
 			- sorted_vaguely_by_trade_activity(@trades).each do |trade|
 				%tr
-					%td
+					%td{
-						= vague_trade_timestamp trade.user.last_trade_activity_at
+						'data-is-same-as-prev': same_vague_trade_timestamp?(trade, prev_trade)
+					}
+						= vague_trade_timestamp trade
 					%td= trade.user.name
 					%td
 						- if trade.lists.present?
@@ -32,6 +35,7 @@
 							= link_to t(".table.not_in_a_list.#{@type}"), user_closet_hangers_path(trade.user,
 								anchor: "closet-hangers-group-#{@type == :offering}"),
 								class: "not-in-a-list"
+				- prev_trade = trade
 - else
 	%p= t(".no_trades_yet")
 

config/initializers/date_formats.rb

@@ -1,4 +1,5 @@
 Date::DATE_FORMATS[:month_and_day] = "%B %e"
+Date::DATE_FORMATS[:month_and_year] = "%b %Y"
 Time::DATE_FORMATS[:long_nst] = lambda { |time|
 	time.in_time_zone("Pacific Time (US & Canada)").
 		to_formatted_s(:long) + " NST"