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# frozen_string_literal: true
class CohortsService
MONTHS_INCLUDED = 12
def execute
{
months_included: MONTHS_INCLUDED,
cohorts: cohorts
}
end
# Get an array of hashes that looks like:
#
# [
# {
# registration_month: Date.new(2017, 3),
# activity_months: [3, 2, 1],
# total: 3
# inactive: 0
# },
# etc.
#
# The `months` array is always from oldest to newest, so it's always
# non-strictly decreasing from left to right.
def cohorts
months = Array.new(MONTHS_INCLUDED) { |i| i.months.ago.beginning_of_month.to_date }
Array.new(MONTHS_INCLUDED) do
registration_month = months.last
activity_months = running_totals(months, registration_month)
# Even if no users registered in this month, we always want to have a
# value to fill in the table.
inactive = counts_by_month[[registration_month, nil]].to_i
months.pop
{
registration_month: registration_month,
activity_months: activity_months[1..],
total: activity_months.first[:total],
inactive: inactive
}
end
end
private
# Calculate a running sum of active users, so users active in later months
# count as active in this month, too. Start with the most recent month first,
# for calculating the running totals, and then reverse for displaying in the
# table.
#
# Each month has a total, and a percentage of the overall total, as keys.
def running_totals(all_months, registration_month)
month_totals =
all_months
.map { |activity_month| counts_by_month[[registration_month, activity_month]] }
.reduce([]) { |result, total| result << result.last.to_i + total.to_i }
.reverse
overall_total = month_totals.first
month_totals.map do |total|
{ total: total, percentage: total == 0 ? 0 : 100 * total / overall_total }
end
end
# Get a hash that looks like:
#
# {
# [created_at_month, last_activity_on_month] => count,
# [created_at_month, last_activity_on_month_2] => count_2,
# # etc.
# }
#
# created_at_month can never be nil, but last_activity_on_month can (when a
# user has never logged in, just been created). This covers the last
# MONTHS_INCLUDED months.
# rubocop: disable CodeReuse/ActiveRecord
def counts_by_month
@counts_by_month ||=
begin
created_at_month = column_to_date('created_at')
last_activity_on_month = column_to_date('last_activity_on')
User
.where('created_at > ?', MONTHS_INCLUDED.months.ago.end_of_month)
.group(created_at_month, last_activity_on_month)
.reorder(Arel.sql("#{created_at_month} ASC, #{last_activity_on_month} ASC"))
.count
end
end
# rubocop: enable CodeReuse/ActiveRecord
def column_to_date(column)
"CAST(DATE_TRUNC('month', #{column}) AS date)"
end
end
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