Calculate distance using PostGIS ST_Distance with LAG

app/models/concerns/distanceable.rb

@@ -11,6 +11,66 @@ module Distanceable
     yd: 0.9144 # to meters
   }.freeze
 
+  module ClassMethods
+    def total_distance(points = nil, unit = :km)
+      # Handle method being called directly on relation vs with array
+      if points.nil?
+        calculate_distance_for_relation(unit)
+      else
+        calculate_distance_for_array(points, unit)
+      end
+    end
+
+    private
+
+    def calculate_distance_for_relation(unit)
+      unless DISTANCE_UNITS.key?(unit.to_sym)
+        raise ArgumentError, "Invalid unit. Supported units are: #{DISTANCE_UNITS.keys.join(', ')}"
+      end
+
+      distance_in_meters = connection.select_value(<<-SQL.squish)
+        WITH points_with_previous AS (
+          SELECT
+            lonlat,
+            LAG(lonlat) OVER (ORDER BY timestamp) as prev_lonlat
+          FROM (#{to_sql}) AS points
+        )
+        SELECT COALESCE(
+          SUM(
+            ST_Distance(
+              lonlat::geography,
+              prev_lonlat::geography
+            )
+          ),
+          0
+        )
+        FROM points_with_previous
+        WHERE prev_lonlat IS NOT NULL
+      SQL
+
+      distance_in_meters.to_f / DISTANCE_UNITS[unit.to_sym]
+    end
+
+    def calculate_distance_for_array(points, unit = :km)
+      unless DISTANCE_UNITS.key?(unit.to_sym)
+        raise ArgumentError, "Invalid unit. Supported units are: #{DISTANCE_UNITS.keys.join(', ')}"
+      end
+
+      return 0 if points.length < 2
+
+      total_meters = points.each_cons(2).sum do |point1, point2|
+        connection.select_value(<<-SQL.squish)
+          SELECT ST_Distance(
+            ST_GeomFromEWKT('#{point1.lonlat}')::geography,
+            ST_GeomFromEWKT('#{point2.lonlat}')::geography
+          )
+        SQL
+      end
+
+      total_meters.to_f / DISTANCE_UNITS[unit.to_sym]
+    end
+  end
+
   def distance_to(other_point, unit = :km)
     unless DISTANCE_UNITS.key?(unit.to_sym)
       raise ArgumentError, "Invalid unit. Supported units are: #{DISTANCE_UNITS.keys.join(', ')}"

app/models/stat.rb

@@ -37,7 +37,7 @@ class Stat < ApplicationRecord
   def calculate_daily_distances(monthly_points)
     timespan.to_a.map.with_index(1) do |day, index|
       daily_points = filter_points_for_day(monthly_points, day)
-      distance = calculate_distance(daily_points)
+      distance = Point.total_distance(daily_points, DISTANCE_UNIT)
       [index, distance.round(2)]
     end
   end
@@ -48,10 +48,4 @@ class Stat < ApplicationRecord
 
     points.select { |p| p.timestamp.between?(beginning_of_day, end_of_day) }
   end
-
-  def calculate_distance(points)
-    points.each_cons(2).sum do |point1, point2|
-      DistanceCalculator.new(point1, point2).call
-    end
-  end
 end

app/models/trip.rb

@@ -14,7 +14,6 @@ class Trip < ApplicationRecord
     calculate_distance
   end
 
-
   def points
     user.tracked_points.where(timestamp: started_at.to_i..ended_at.to_i).order(:timestamp)
   end
@@ -52,13 +51,8 @@ class Trip < ApplicationRecord
     self.path = trip_path
   end
 
-
   def calculate_distance
-    distance = 0
-
-    points.each_cons(2) do |point1, point2|
-      distance += DistanceCalculator.new(point1, point2).call
-    end
+    distance = Point.total_distance(points, DISTANCE_UNIT)
 
     self.distance = distance.round
   end

app/services/distance_calculator.rb

@@ -1,18 +0,0 @@
-# frozen_string_literal: true
-
-class DistanceCalculator
-  def initialize(point1, point2)
-    @point1 = point1
-    @point2 = point2
-  end
-
-  def call
-    Geocoder::Calculations.distance_between(
-      point1.to_coordinates, point2.to_coordinates, units: ::DISTANCE_UNIT
-    )
-  end
-
-  private
-
-  attr_reader :point1, :point2
-end

app/services/stats/calculate_month.rb

@@ -46,7 +46,7 @@ class Stats::CalculateMonth
               .tracked_points
               .without_raw_data
               .where(timestamp: start_timestamp..end_timestamp)
-              .select(:latitude, :longitude, :timestamp, :city, :country)
+              .select(:lonlat, :timestamp, :city, :country)
               .order(timestamp: :asc)
   end
 

spec/services/stats/calculate_month_spec.rb

@@ -53,7 +53,7 @@ RSpec.describe Stats::CalculateMonth do
         it 'calculates distance' do
           calculate_stats
 
-          expect(user.stats.last.distance).to eq(338)
+          expect(user.stats.last.distance).to eq(339)
         end
 
         context 'when there is an error' do
@@ -81,7 +81,7 @@ RSpec.describe Stats::CalculateMonth do
         it 'calculates distance' do
           calculate_stats
 
-          expect(user.stats.last.distance).to eq(210)
+          expect(user.stats.last.distance).to eq(211)
         end
 
         context 'when there is an error' do