require 'net/sftp'

module Dreamback
  class Backup
    BACKUP_FOLDER = "./dreamback"

    # Manage the backup process
    def self.start
      # rotate the backup folders
      backup_to_link = rotate_backups
      # rsync backup of dreamhost user accounts
      rsync_backup(backup_to_link)
      # mysql backup
      # TODO: Add mysql backups
    end

    # Rotate out the backups that are past our limit
    # @returns [String] name of the most recent folder to link against
    def self.rotate_backups
      backup_to_link = nil
      Net::SFTP.start(Dreamback.settings[:backup_server], Dreamback.settings[:backup_server_user]) do |sftp|
        # Create the backup folder if it doesn't exist
        backup_folder_exists = false
        begin
          sftp.stat!(BACKUP_FOLDER) do |response|
            backup_folder_exists = response.ok?
          end
        rescue Net::SFTP::StatusException => e
          backup_folder_exists = false if e.code == 2
        end

        # Get a list of all backup directories
        backup_folders = []
        if backup_folder_exists
          sftp.dir.foreach(BACKUP_FOLDER) do |entry|
            # Names should be like "dreamback.20120520", so we can sort on the folder name
            backup_folders << [ entry.name, entry.name.split(".")[1].to_i ] if entry.name.include?("dreamback")
            backup_folders.sort! {|a,b| b <=> a}
          end
        end

        # Don't rotate if there aren't any previous folders
        unless backup_folders.empty?
          # Get yesterday's folder to link against
          backup_to_link = backup_folders.first[0]
          # If this would link us to the same folder, don't do that. Try yesterday's instead.
          if backup_to_link.eql? "dreamback." + Date.today.strftime("%Y%m%d")
            backup_to_link = "dreamback." + (Date.today - 1).strftime("%Y%m%d")
          end

          # Delete any folders older than our limit
          if Dreamback.settings[:days_to_keep]
            folders_to_delete = rotate_daily(backup_folders)
          elsif Dreamback.settings[:keep_time_machine]
            folders_to_delete = rotate_time_machine(backup_folders)[:delete]
          else
            folders_to_delete = nil
          end
          rsync_delete(folders_to_delete)
        end
      end

      backup_to_link
    end

    # This uses a hack where we sync an empty directory to remove files
    # We do this because sftp has no recursive delete method
    # @params [Array[String]] list of backup directories
    def self.rsync_delete(directories)
      return if directories.nil? || directories.empty?
      empty_dir_path = File.expand_path("../.dreamback_empty_dir", __FILE__)
      empty_dir = Dir.mkdir(empty_dir_path) unless File.exists?(empty_dir_path)
      begin
        directories.each do |dir|
          `rsync --delete -a #{empty_dir_path}/ #{Dreamback.settings[:backup_server_user]}@#{Dreamback.settings[:backup_server]}:#{BACKUP_FOLDER}/#{dir}`
          Net::SFTP.start(Dreamback.settings[:backup_server], Dreamback.settings[:backup_server_user]) do |sftp|
            sftp.rmdir!("#{BACKUP_FOLDER}/#{dir}")
          end
        end
      ensure
        Dir.delete(empty_dir_path)
      end
    end

    # Sync to the backup server using link-dest to save space
    # @param [String] name of the most recent backup folder prior to starting this run to link against
    def self.rsync_backup(link_dir)
      tmp_dir_path = "~/.dreamback_tmp"
      tmp_dir = File.expand_path(tmp_dir_path)
      Dir.mkdir(tmp_dir) unless File.exists?(tmp_dir)
      user_exclusions_path = File.expand_path("~/.dreamback_exclusions")
      default_exclusions_path = File.expand_path("../exclusions.txt", __FILE__)
      exclusions_path = File.exists?(user_exclusions_path) ? user_exclusions_path : default_exclusions_path
      begin
        backup_server_user = Dreamback.settings[:backup_server_user]
        backup_server = Dreamback.settings[:backup_server]
        today = Time.now.strftime("%Y%m%d")
        Dreamback.settings[:dreamhost_users].each do |dreamhost|
          # User that we're going to back up
          user = dreamhost[:user]
          server = dreamhost[:server]
          # rsync won't do remote<->remote syncing, so we stage everything here first
          `rsync -e ssh -av --keep-dirlinks --exclude-from #{exclusions_path} --copy-links #{user}@#{server}:~/ #{tmp_dir}/#{user}@#{server}`
        end
        # Now we can sync local to remote. Only use link-dest if a previous folder to link to exists.
        link_dest = link_dir.nil? ? "" : "--link-dest=~#{BACKUP_FOLDER.gsub(".", "")}/#{link_dir}"
        `rsync -e ssh -av --delete --copy-links --keep-dirlinks #{link_dest} #{tmp_dir}/ #{backup_server_user}@#{backup_server}:#{BACKUP_FOLDER}/dreamback.#{today}`
      ensure
        # Remove the staging directory
        `rm -rf #{File.expand_path(tmp_dir_path)}`
      end
    end

    # Rotate folders based on the number of days to keep
    # @param [Array] folders to rotate in Dreamback format (dreamback.20120521)
    # @return [Array] list of folders to delete
    def self.rotate_daily(backup_folders)
      # Subtract one to account for the folder we're about to create
      # Normally we remove a folder so that our count is one less than the "days to keep"
      # However, if today's folder already exists then there's no need
      offset = backup_folders.include?("dreamback.#{Time.now.strftime("%Y%m%d")}") ? 0 : 1
      if backup_folders.length >= Dreamback.settings[:days_to_keep] - offset
        folders_to_delete = backup_folders.slice(Dreamback.settings[:days_to_keep] - offset, backup_folders.length)
        folders_to_delete.map! {|f| f[0]}
      end
      folders_to_delete ||= nil
    end

    # Use a time machine-like algorithm to rotate backups. This will keep daily backups for seven days, weeklies for three months, and monthlies forever
    # @param [Date] the day to count as "today", where the rotation will start
    # @param [Array] folders to rotate in Dreamback format (dreamback.20120521)
    # @return [Hash] :keep => list of folders to retain, :delete => folders marked for deletion
    def self.rotate_time_machine(folders, today = nil)
      today ||= Date.today
      ymd = "%Y%m%d"

      folder_data = {}
      folders.each do |f|
        folder_data[f] = {
          :date => Date.strptime(f[1].to_s, ymd)
        }
      end

      keep = []
      one_week_ago = today - 7
      three_months_ago = today << 3

      week_hash = {}
      month_hash = {}
      folder_data.each do |k, v|
        if v[:date] >= one_week_ago
          keep << k
        elsif v[:date] >= three_months_ago
          week_hash[v[:date].cweek] = [] if week_hash[v[:date].cweek].nil?
          week_hash[v[:date].cweek] << [k, v]
        else
          ym = v[:date].strftime("%Y%m").to_i
          month_hash[ym] = [] if month_hash[ym].nil?
          month_hash[ym] << [k, v]
        end
      end

      week_hash.each do |week, dates|
        dates.sort! {|a, b| a[1][:date] <=> b[1][:date]}
      end

      week_hash.each do |week, dates|
        keep << dates.shift[0] unless dates.empty?
      end

      month_hash.each do |month, dates|
        dates.sort! {|a, b| a[1][:date] <=> b[1][:date]}
      end

      month_hash.each do |month, dates|
        keep << dates.shift[0] unless dates.empty?
      end

      keep.sort!.compact!

      # Convert elements from ["dreamback.20120701", "20120701"] to "dreamback.20120701"
      keep_clean = keep.map {|folder| folder.shift}
      delete = (folders - keep).map {|folder| folder.shift}

      { :keep => keep_clean, :delete => delete}
    end
  end
end