#!/usr/bin/env ruby

# Synchronizes ZFS filesystems.
#
# Takes three args: source pool, destination pool, and filesystem name.
#
# Syncs most recent snapshot of filesystem from source to destination pool,
# using incremental transfer if possible.

# Take a snapshot line from zfs list -t snapshot and emit a struct
class Snapshot
  attr_reader :pool
  attr_reader :fs
  attr_reader :snap

  def initialize(str)
    str =~ /\A(.+?)\/(.+?)@(.+?)\s+/
    @pool, @fs, @snap = $1, $2, $3
  end

  # Map back into the same representation ZFS tools use
  def to_s
    "#{pool}/#{fs}@#{snap}"
  end
end

# Parse args
src_pool, dest_pool, fs = ARGV
unless src_pool
  puts "No source pool given."
  exit 1
end

unless dest_pool
  puts "No destination pool given."
  exit 1
end

unless fs
  puts "No filesystem given."
  exit 1
end

# All snapshots for the given filesystem
snapshots = `zfs list -t snapshot`.lines.map do |l|
  Snapshot.new l
end.select do |s|
  s.fs == fs
end

# Find most recent snapshots from both pools
last_src  = snapshots.select { |s| s.pool == src_pool }.last
last_dest = snapshots.select { |s| s.pool == dest_pool }.last

unless last_src
  puts "No snapshots for filesystem #{fs} on source pool #{src_pool}"
  exit 2
end

unless last_dest
  puts "No snapshots for filesystem #{fs} on dest pool #{dest_pool}"
  exit 2
end

if last_src.snap == last_dest.snap
  puts "Up to date! :D"
  exit 0
end

# Find corresponding snapshot in source pool
prev_src = snapshots.find do |s|
  s.pool == src_pool and s.snap == last_dest.snap
end

if prev_src
  # Incremental
  puts "Incremental sync"
  cmd = "zfs send -i '#{prev_src}' '#{last_src}' | zfs recv '#{dest_pool}/#{fs}'"
else
  # Full
  puts "Full sync"
  cmd = "zfs send '#{last_src}' | zfs recv '#{dest_pool}/#{fs}'"
end

puts cmd
exec cmd