# frozen_string_literal: true

class Stats::DailyDistanceQuery
  def initialize(monthly_points, timespan)
    @monthly_points = monthly_points
    @timespan = timespan
  end

  def call
    daily_distances = daily_distances(monthly_points)
    distance_by_day_map = distance_by_day_map(daily_distances)

    convert_to_daily_distances(distance_by_day_map)
  end

  private

  attr_reader :monthly_points, :timespan

  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,
          CASE
            WHEN LAG(lonlat) OVER (
              PARTITION BY EXTRACT(day FROM to_timestamp(timestamp))
              ORDER BY timestamp
            ) IS NOT NULL THEN
              ST_Distance(
                lonlat::geography,
                LAG(lonlat) OVER (
                  PARTITION BY EXTRACT(day FROM to_timestamp(timestamp))
                  ORDER BY timestamp
                )::geography
              )
            ELSE 0
          END as segment_distance
        FROM (#{monthly_points.to_sql}) as points
      )
      SELECT
        day_of_month,
        ROUND(COALESCE(SUM(segment_distance), 0)) as distance_meters
      FROM points_with_distances
      GROUP BY day_of_month
      ORDER BY day_of_month
    SQL
  end

  def distance_by_day_map(daily_distances)
    daily_distances.index_by do |row|
      row['day_of_month'].to_i
    end
  end

  def convert_to_daily_distances(distance_by_day_map)
    timespan.to_a.map.with_index(1) do |day, index|
      distance_meters =
        distance_by_day_map[day.day]&.fetch('distance_meters', 0) || 0

      [index, distance_meters.to_i]
    end
  end
end