class Airbrake::Filters::GitRevisionFilter

def call(notice)
  return if notice[:context].key?(:revision)
  if @revision
    notice[:context][:revision] = @revision
    return
  end
  return unless File.exist?(@git_path)
  @revision = find_revision
  return unless @revision
  notice[:context][:revision] = @revision
end

def find_from_packed_refs(head)
  packed_refs_path = File.join(@git_path, 'packed-refs')
  return head unless File.exist?(packed_refs_path)
  File.readlines(packed_refs_path).each do |line|
    next if %w[# ^].include?(line[0])
    next unless (parts = line.split).size == 2
    return parts.first if parts.last == head
  end
  nil
end

def find_revision
  head_path = File.join(@git_path, 'HEAD')
  return unless File.exist?(head_path)
  head = File.read(head_path)
  return head unless head.start_with?(PREFIX)
  head = head.chomp[PREFIX.size..-1]
  ref_path = File.join(@git_path, head)
  return File.read(ref_path).chomp if File.exist?(ref_path)
  find_from_packed_refs(head)
end

def initialize(root_directory)
  @git_path = File.join(root_directory, '.git')
  @revision = nil
  @weight = 116
end