Refactor H3 hexagon calculation logic to improve clarity and maintainability

app/services/stats/calculate_month.rb

@@ -1,8 +1,6 @@
 # frozen_string_literal: true
 
 class Stats::CalculateMonth
-  include ActiveModel::Validations
-
   def initialize(user_id, year, month)
     @user = User.find(user_id)
     @year = year.to_i
@@ -87,6 +85,6 @@ class Stats::CalculateMonth
   end
 
   def calculate_h3_hex_ids
-    Stats::HexagonCalculator.new(user.id, year, month).calculate_h3_hex_ids
+    Stats::HexagonCalculator.new(user.id, year, month).call
   end
 end

app/services/stats/hexagon_calculator.rb

@@ -14,70 +14,63 @@ class Stats::HexagonCalculator
   end
 
   def call(h3_resolution: DEFAULT_H3_RESOLUTION)
-    calculate_h3_hexagon_centers_with_resolution(h3_resolution)
+    calculate_h3_hexagon_centers(h3_resolution)
   end
 
   def calculate_h3_hex_ids
-    return {} if points.empty?
+    result = calculate_hexagons(DEFAULT_H3_RESOLUTION)
+    return {} if result.nil?
 
-    begin
-      result = call
-
-      if result.empty?
-        Rails.logger.info "No H3 hex IDs calculated for user #{user.id}, #{year}-#{month} (no data)"
-        return {}
-      end
-
-      # Convert array format to hash format: { h3_index => [count, earliest, latest] }
-      hex_hash = result.each_with_object({}) do |hex_data, hash|
-        h3_index, count, earliest, latest = hex_data
-        hash[h3_index] = [count, earliest, latest]
-      end
-
-      Rails.logger.info "Pre-calculated #{hex_hash.size} H3 hex IDs for user #{user.id}, #{year}-#{month}"
-      hex_hash
-    rescue PostGISError => e
-      Rails.logger.warn "H3 hex IDs calculation failed for user #{user.id}, #{year}-#{month}: #{e.message}"
-      {}
-    end
+    result
   end
 
   private
 
   attr_reader :user, :year, :month
 
-  def calculate_h3_hexagon_centers_with_resolution(h3_resolution)
-    points = fetch_user_points_for_period
+  def calculate_h3_hexagon_centers(h3_resolution)
+    result = calculate_hexagons(h3_resolution)
+    return [] if result.nil?
 
-    return [] if points.empty?
-
-    h3_indexes_with_counts = calculate_h3_indexes(points, h3_resolution)
-
-    if h3_indexes_with_counts.size > MAX_HEXAGONS
-      Rails.logger.warn "Too many hexagons (#{h3_indexes_with_counts.size}), using lower resolution"
-      # Try with lower resolution (larger hexagons)
-      lower_resolution = [h3_resolution - 2, 0].max
-      Rails.logger.info "Recalculating with lower H3 resolution: #{lower_resolution}"
-      # Create a new instance with lower resolution for recursion
-      return self.class.new(user.id, year, month)
-                        .calculate_h3_hexagon_centers_with_resolution(lower_resolution)
-    end
-
-    Rails.logger.info "Generated #{h3_indexes_with_counts.size} H3 hexagons at resolution #{h3_resolution} for user #{user.id}"
-
-    # Convert to format: [h3_index_string, point_count, earliest_timestamp, latest_timestamp]
-    h3_indexes_with_counts.map do |h3_index, data|
+    # Convert to array format: [h3_index_string, point_count, earliest_timestamp, latest_timestamp]
+    result.map do |h3_index_string, data|
       [
-        h3_index.to_s(16), # Store as hex string
-        data[:count],
-        data[:earliest],
-        data[:latest]
+        h3_index_string,
+        data[0], # count
+        data[1], # earliest
+        data[2]  # latest
       ]
     end
-  rescue StandardError => e
-    message = "Failed to calculate H3 hexagon centers: #{e.message}"
-    ExceptionReporter.call(e, message) if defined?(ExceptionReporter)
-    raise PostGISError, message
+  end
+
+  # Unified hexagon calculation method
+  def calculate_hexagons(h3_resolution)
+    return nil if points.empty?
+
+    begin
+      h3_hash = calculate_h3_indexes(points, h3_resolution)
+
+      if h3_hash.empty?
+        Rails.logger.info "No H3 hex IDs calculated for user #{user.id}, #{year}-#{month} (no data)"
+        return nil
+      end
+
+      if h3_hash.size > MAX_HEXAGONS
+        Rails.logger.warn "Too many hexagons (#{h3_hash.size}), using lower resolution"
+        # Try with lower resolution (larger hexagons)
+        lower_resolution = [h3_resolution - 2, 0].max
+        Rails.logger.info "Recalculating with lower H3 resolution: #{lower_resolution}"
+        # Create a new instance with lower resolution for recursion
+        return self.class.new(user.id, year, month).calculate_hexagons(lower_resolution)
+      end
+
+      Rails.logger.info "Generated #{h3_hash.size} H3 hexagons at resolution #{h3_resolution} for user #{user.id}"
+      h3_hash
+    rescue StandardError => e
+      message = "Failed to calculate H3 hexagon centers: #{e.message}"
+      ExceptionReporter.call(e, message) if defined?(ExceptionReporter)
+      raise PostGISError, message
+    end
   end
 
   def start_timestamp
@@ -95,30 +88,13 @@ class Stats::HexagonCalculator
               .points
               .without_raw_data
               .where(timestamp: start_timestamp..end_timestamp)
+              .where.not(lonlat: nil)
               .select(:lonlat, :timestamp)
               .order(timestamp: :asc)
   end
 
-  def start_date_iso8601
-    @start_date_iso8601 ||= DateTime.new(year, month, 1).beginning_of_day.iso8601
-  end
-
-  def end_date_iso8601
-    @end_date_iso8601 ||= DateTime.new(year, month, -1).end_of_day.iso8601
-  end
-
-  def fetch_user_points_for_period
-    start_timestamp = DateTime.parse(start_date_iso8601).to_i
-    end_timestamp = DateTime.parse(end_date_iso8601).to_i
-
-    Point.where(user_id: user.id)
-         .where(timestamp: start_timestamp..end_timestamp)
-         .where.not(lonlat: nil)
-         .select(:id, :lonlat, :timestamp)
-  end
-
   def calculate_h3_indexes(points, h3_resolution)
-    h3_data = Hash.new { |h, k| h[k] = { count: 0, earliest: nil, latest: nil } }
+    h3_data = {}
 
     points.find_each do |point|
       # Extract lat/lng from PostGIS point
@@ -126,14 +102,19 @@ class Stats::HexagonCalculator
 
       # Get H3 index for this point
       h3_index = H3.from_geo_coordinates(coordinates, h3_resolution.clamp(0, 15))
+      h3_index_string = h3_index.to_s(16) # Convert to hex string immediately
 
-      # Aggregate data for this hexagon
-      data = h3_data[h3_index]
-      data[:count] += 1
-      data[:earliest] = [data[:earliest], point.timestamp].compact.min
-      data[:latest] = [data[:latest], point.timestamp].compact.max
+      # Initialize or update data for this hexagon
+      if h3_data[h3_index_string]
+        data = h3_data[h3_index_string]
+        data[0] += 1 # increment count
+        data[1] = [data[1], point.timestamp].min # update earliest
+        data[2] = [data[2], point.timestamp].max # update latest
+      else
+        h3_data[h3_index_string] = [1, point.timestamp, point.timestamp] # [count, earliest, latest]
+      end
     end
 
     h3_data
   end
-end
+end