require 'slack-ruby-client'

TOKEN = 'AUTH TOKEN'.freeze
CHANNEL = 'CHANNEL ID'.freeze
MESSAGES_PER_REQUEST = 1_000 # 1000 is the limit per request

# :nodoc:
class LogChannelHistory
  def initialize
    Slack.configure { |config| config.token = TOKEN }
    @client = Slack::Web::Client.new
  end

  def process_log
    request_params = { channel: CHANNEL, count: MESSAGES_PER_REQUEST }

    first_batch = get_batch(request_params)
    save_to_file(first_batch)

    request_count = 1

    while first_batch.has_more?
      request_params[:latest] = first_batch.messages.last['ts']
      first_batch = get_batch(request_params)
      save_to_file(first_batch)
      request_count += 1

      sleep 5 if request_count % 5 == 0
    end
  end

  private

  def users
    @users ||=
      Hash[@client.users_list['members'].map { |m| [m['id'], m['name']] }]
  end

  def list_channels
    @client.channels_list.channels.each { |ch| "#{ch.name} | #{ch.id}" }
  end

  def get_batch(request_params)
    @client.channels_history(request_params)
  end

  def save_to_file(batch)
    File.open('log.txt', 'a+') do |file|
      batch.messages.each do |message|
        username = users[message['user']]
        text = message['text'].inspect
        time = Time.at message['ts'].to_f
        file << "#{time} - #{username}: #{text} \n"
      end
    end
  end
end

# client.channels_list.channels.each { |ch| puts "#{ch.name} | #{ch.id}" }
if __FILE__ == $0
  LogChannelHistory.new.process_log
  puts "Logged channel history"
end