#!/usr/bin/env ruby

# This groups emails into senders and then calculates some basic stats for the
# times of those emails - the earliest, latest and average
#
# Note that there is some oddity relating to my specific needs around timezone
# handling - this is in the code below the comment starting "Normalise"

# These two are for debugging
#require 'awesome_print'
#require 'byebug'
require 'net/imap'
require 'progressbar'
require 'active_support/all'
require 'yaml'
require 'yaml/store'

begin
  # Make sure we have everything we need to connect
  fail IOError unless File.exist?('settings.yml')
  settings = YAML.load_file('settings.yml')
  password = ENV['ES_PASSWORD']
  fail ArgumentError unless password
  fail NameError unless settings['server'] && settings['email']

  # Connect and login to the server
  imap = Net::IMAP.new(settings['server'], 993, true)
  imap.login(settings['email'], password)
  imap.select('INBOX.Prices')

  # Get all mail in the folder
  mail_ids = imap.search(['ALL'])

  puts "Found #{mail_ids.count} emails. Fetching mail headers..."

  # Create a new progressbar
  bar = ProgressBar.new 'progress', mail_ids.count

  time_regex = /\d{2}:\d{2}:\d{2}\s([+-]\d{4}|UTC)/

  # Fetch mail details
  stats = imap.fetch(mail_ids, 'ENVELOPE').map do |mail|
    bar.inc

    sender = mail.attr['ENVELOPE'].sender.first
    time = Time.parse(mail.attr.first.second.date.match(time_regex).to_s).utc

    # Normalise the days for my use case
    time += 1.day if time.hour < 6 && time.day == Date.current.day ||
                     time.day == Date.yesterday.day

    ["#{sender.mailbox}@#{sender.host}", time.to_i]
  end

  # Calculate the stats for the emails
  stats = stats.group_by { |sender, _| sender }
  parsed_stats = Hash[stats.map do |group, details|
    times = details.map(&:last).sort
    [group, {
      earliest: Time.at(times.first),
      latest: Time.at(times.last),
      average: Time.at(times.sum.to_f / times.count)
    }]
  end]

  # Output results
  bar.finish
  puts ''

  parsed_stats.map do |address, numbers|
    puts address
    puts '-----------------------------'
    puts numbers[:earliest].strftime('%H:%M')
    puts numbers[:latest].strftime('%H:%M')
    puts numbers[:average].strftime('%H:%M')
    puts ''
  end
rescue IOError
  # The setting file doesn't exist, so create it
  store = YAML::Store.new('settings.yml')
  store.transaction do
    store['server'] = nil
    store['email'] = nil
  end
  puts 'Created configuration file - please update it and try again.'
rescue ArgumentError
  # Probably no password supplied
  puts 'Password not supplied - please supply a value in the ES_PASSWORD ' \
       'environment variable'
rescue NameError
  # Probably invalid settings
  puts 'Settings are invalid. Please check the settings file for server and ' \
       'email options'
end