Stats calculation is now timezone-aware.

app/models/stat.rb

@@ -37,6 +37,16 @@ class Stat < ApplicationRecord
   end
 
   def calculate_daily_distances(monthly_points)
-    Stats::DailyDistanceQuery.new(monthly_points, timespan).call
+    Stats::DailyDistanceQuery.new(monthly_points, timespan, user_timezone).call
+  end
+
+  private
+
+  def user_timezone
+    # Future: Once user.timezone column exists, uncomment the line below
+    # user.timezone.presence || Time.zone.name
+
+    # For now, use application timezone
+    Time.zone.name
   end
 end

app/queries/stats/daily_distance_query.rb

@@ -1,9 +1,10 @@
 # frozen_string_literal: true
 
 class Stats::DailyDistanceQuery
-  def initialize(monthly_points, timespan)
+  def initialize(monthly_points, timespan, user_timezone = nil)
     @monthly_points = monthly_points
     @timespan = timespan
+    @user_timezone = user_timezone || 'UTC'
   end
 
   def call
@@ -15,22 +16,22 @@ class Stats::DailyDistanceQuery
 
   private
 
-  attr_reader :monthly_points, :timespan
+  attr_reader :monthly_points, :timespan, :user_timezone
 
   def daily_distances(monthly_points)
     Stat.connection.select_all(<<-SQL.squish)
       WITH points_with_distances AS (
         SELECT
-          EXTRACT(day FROM to_timestamp(timestamp)) as day_of_month,
+          EXTRACT(day FROM (to_timestamp(timestamp) AT TIME ZONE 'UTC' AT TIME ZONE '#{user_timezone}')) as day_of_month,
           CASE
             WHEN LAG(lonlat) OVER (
-              PARTITION BY EXTRACT(day FROM to_timestamp(timestamp))
+              PARTITION BY EXTRACT(day FROM (to_timestamp(timestamp) AT TIME ZONE 'UTC' AT TIME ZONE '#{user_timezone}'))
               ORDER BY timestamp
             ) IS NOT NULL THEN
               ST_Distance(
                 lonlat::geography,
                 LAG(lonlat) OVER (
-                  PARTITION BY EXTRACT(day FROM to_timestamp(timestamp))
+                  PARTITION BY EXTRACT(day FROM (to_timestamp(timestamp) AT TIME ZONE 'UTC' AT TIME ZONE '#{user_timezone}'))
                   ORDER BY timestamp
                 )::geography
               )

benchmark_stats.rb

@@ -0,0 +1,30 @@
+require 'benchmark'
+
+# Test the optimized stats calculation
+data = Benchmark.measure do
+  user_id = 7
+
+  last_calculated_at = DateTime.new(1970, 1, 1)
+
+  time_diff = last_calculated_at.to_i..Time.current.to_i
+  timestamps = Point.where(user_id:, timestamp: time_diff).pluck(:timestamp).uniq
+
+  months = timestamps.group_by do |timestamp|
+    time = Time.zone.at(timestamp)
+    [time.year, time.month]
+  end.keys
+
+  months.each do |year, month|
+    Stats::CalculateMonth.new(user_id, year, month).call
+  end
+end
+
+puts "Stats calculation benchmark:"
+puts "User Time: #{data.utime}s"
+puts "System Time: #{data.stime}s"
+puts "Total Time: #{data.real}s"
+
+# @real=28.869485000148416,
+# @stime=2.4980050000000027,
+# @total=20.303141999999976,
+# @utime=17.805136999999974>

db/migrate/future_add_timezone_to_users.rb.example

@@ -0,0 +1,16 @@
+# Example migration for adding per-user timezone support
+# To use: rename this file to remove .example and run rails db:migrate
+
+class AddTimezoneToUsers < ActiveRecord::Migration[7.1]
+  def change
+    add_column :users, :timezone, :string, default: 'UTC'
+    add_index :users, :timezone
+    
+    # Populate existing users with application timezone
+    reversible do |dir|
+      dir.up do
+        User.update_all(timezone: Time.zone.name)
+      end
+    end
+  end
+end