#!/usr/bin/ruby
#
# Program to free up space on the backup-storage volume, by removing
# backups (whether by age, or importance).
#

$LOAD_PATH.unshift('/usr/lib/byteback')

require 'trollop'
require 'byteback'
require 'sys/filesystem'
include Byteback
include Byteback::Log
include Byteback::Util

opts = Trollop.options do
  banner "Prune old backup directories to ensure there's enough space"

  opt :minpercent, 'Start prune when disk has less than this %age free',
      :type => :integer,
      :default => 5

  opt :maxpercent, 'Stop prune when disk has more than this %age free',
      :type => :integer,
      :default => 10

  opt :list, 'List backups in pruning order, no other action'

  opt :prune, 'Prune the next backup if necessary'

  opt :prune_force, 'Prune the next backup regardless'

  opt :order, "Order backups by 'age' or 'importance'",
      :type => :string,
      :default => 'importance'

  opt :verbose, 'Show debugging messages'
end

@order = opts[:order]
@verbose = opts[:verbose]
@do_list = opts[:list]
@do_prune = opts[:prune]
@do_prune_force = opts[:prune_force]
@minpercent = opts[:minpercent]
@maxpercent = opts[:maxpercent]

@do_prune = true if @do_prune_force

fatal('Must specify one of --prune or --list') unless
  (@do_prune || @do_list) &&
  !(@do_prune && @do_list)

fatal("Must specify --order as 'age' or 'importance'") unless
  @order == 'age' || @order == 'importance'

if BackupDirectory.all.empty?
  fatal('No backup directories found, need to run byteback-snapshot')
end

lock_out_other_processes('byteback-prune')

@df_history = DiskFreeHistory.new(ENV['HOME'])
begin
  @df_history.new_reading!
rescue Errno::ENOSPC
  if @do_list
    warn("Couldn't write disk history file due to lack of space, ignoring")
  else
    warn("Couldn't write disk history file due to lack of space, going to --prune-force")
    @do_prune = @do_prune_force = true
  end
rescue => anything_else
  error("Couldn't record disk history of #{@df_history.mountpoint} in #{@df_history.history_file}, installation problem?")
  raise
end

gradient_30m = @df_history.gradient(1800)

# Check whether we should still be pruning
#
@free = @df_history.list.last.percent_free
PRUNING_FLAG = "#{ENV['HOME']}/.byteback.pruning"

if @do_prune_force
  info('Forcing prune')
elsif @free <= @minpercent && !File.exist?(PRUNING_FLAG)
  info("Starting prune #{@free}% -> #{@maxpercent} free")
  File.write(PRUNING_FLAG, '')
elsif @free >= @maxpercent && File.exist?(PRUNING_FLAG)
  info("Stopping prune, reached #{@free}% free")
  File.unlink(PRUNING_FLAG)
elsif File.exist?(PRUNING_FLAG)
  info("Continuing prune #{@free}% -> #{@maxpercent}, gradient = #{gradient_30m}")
end

debug("Disc free #{@free}%, 30m gradient = #{gradient_30m}")

def snapshots_in_order
  list = BackupDirectory.all_snapshots
  if @order == 'importance'
    Snapshot.sort_by_importance(list)
  elsif @order == 'age'
    list.sort.reverse
  else
    fail ArgumentError.new("Unknown snapshot sort method #{method}")
  end
end

snapshots = snapshots_in_order

if @do_list
  print "Backups by #{@order}:\n"
  snapshots.each_with_index do |snapshot, index|
    print "#{sprintf('% 3d', index)}: #{snapshot.path}\n"
  end
end

# Don't do anything if we've not got two hours of readings
#
unless @do_prune_force
  if @df_history.list.last.time - @df_history.list.first.time < 1800
    warn('Not enough disc space history to make a decision')
    exit 0
  end
end

exit 0 unless
  (@do_prune && File.exist?(PRUNING_FLAG)) ||
  @do_prune_force

exit 0 unless @do_prune_force || gradient_30m == 0

if snapshots.empty?
  error('No snapshots to delete, is there enough disc space?')
  exit 1
end

info("Deleting #{snapshots.last.path}")
log_system("/sbin/btrfs subvolume delete #{snapshots.last.path}")