#!/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.exists?(PRUNING_FLAG)
	info("Starting prune #{@free}% -> #{@maxpercent} free")
	File.write(PRUNING_FLAG,"")
elsif @free >= @maxpercent && File.exists?(PRUNING_FLAG)
	info("Stopping prune, reached #{@free}% free")
	File.unlink(PRUNING_FLAG)
elsif File.exists?(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
		raise 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
#
if !@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.exists?(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}")