require 'rake'
require 'rake/tasklib'

module RailsConnector
  # The CacheGarbageCollectorTask allows to remove old cache files from the Rails Connector cache
  # storage path. By default, a maximum of +DEFAULT_MAX_FILE_INODES+ file inodes that were accessed
  # lately are kept in the cache directory. All other files and empty directories are removed. Log
  # output is written to the Rails environment log file.
  #
  # @example Running the garbage collector with default settings
  #
  #   bundle exec rake infopark:cache:gc
  #
  # @example Changing the maximum number of file inodes
  #
  #   bundle exec rake infopark:cache:gc MAX_FILE_INODES=5000
  class CacheGarbageCollectorTask < ::Rake::TaskLib
    DEFAULT_MAX_FILE_INODES = 100000

    attr_accessor :max_file_inodes

    def initialize
      @max_file_inodes = (ENV['MAX_FILE_INODES'] || DEFAULT_MAX_FILE_INODES).to_i

      namespace :infopark do
        namespace :cache do
          desc "Cap number of cache file inodes at #{@max_file_inodes}. Use MAX_FILE_INODES to specify the
            maximum. (default: #{DEFAULT_MAX_FILE_INODES})"
          task gc: :environment do
            run_gc
          end
        end
      end
    end

    private

    def run_gc
      announce "Cap number of cache file inodes at #{max_file_inodes} in #{cache_path}."

      directories = []
      file_inode_count = 0
      delta_disk_space = 0
      delta_count = 0

      cache_entries.each do |cache_entry|
        begin
          stat = File.stat(cache_entry)

          if stat.file?
            file_inode_count += 1
            next if file_inode_count <= max_file_inodes

            File.delete(cache_entry)

            delta_disk_space += stat.size
            delta_count += 1
          elsif stat.directory?
            directories << cache_entry
          end
        rescue Errno::ENOENT
        end
      end

      directories.sort.reverse_each do |dirname|
        begin
          Dir.rmdir(dirname)
          delta_count += 1
        rescue Errno::ENOTEMPTY, Errno::ENOENT
        end
      end

      announce "Done. Removed #{delta_count} entries. Saved at least #{delta_disk_space} Bytes."
    end

    def cache_path
      CmsCacheStorage.backend_cache.cache_path
    end

    def cache_entries
      Dir["#{cache_path}/**/*"].sort_by do |file|
        begin
          -File.atime(file).to_i
        rescue Errno::ENOENT
          # If such file or directory does not exist, sort it as if the last
          # access time is very long ago.
          0
        end
      end
    end

    def announce(message)
      message = "[#{Time.now.iso8601}] #{message}"

      Rails.logger.info(message)
    end
  end
end