module GoodJob
  module Lockable
    extend ActiveSupport::Concern

    RecordAlreadyAdvisoryLockedError = Class.new(StandardError)

    included do
      scope :joins_advisory_locks, (lambda do
        joins(<<~SQL)
          LEFT JOIN pg_locks ON pg_locks.locktype = 'advisory'
            AND pg_locks.objsubid = 1
            AND pg_locks.classid = ('x'||substr(md5(good_jobs.id::text), 1, 16))::bit(32)::int
            AND pg_locks.objid = (('x'||substr(md5(good_jobs.id::text), 1, 16))::bit(64) << 32)::bit(32)::int
        SQL
      end)

      scope :advisory_unlocked, -> { joins_advisory_locks.where(pg_locks: { locktype: nil }) }

      attr_accessor :create_with_advisory_lock

      after_create -> { advisory_lock }, if: :create_with_advisory_lock
    end

    class_methods do
      def first_advisory_locked_row(query)
        find_by_sql(<<~SQL).first
          WITH rows AS (#{query.to_sql})
          SELECT rows.*
          FROM rows
          WHERE pg_try_advisory_lock(('x'||substr(md5(id::text), 1, 16))::bit(64)::bigint)
          LIMIT 1
        SQL
      end
    end

    def advisory_lock
      self.class.connection.execute(sanitize_sql_for_conditions(["SELECT 1 as one WHERE pg_try_advisory_lock(('x'||substr(md5(?), 1, 16))::bit(64)::bigint)", id])).ntuples.positive?
    end

    def advisory_lock!
      result = advisory_lock
      result || raise(RecordAlreadyAdvisoryLockedError)
    end

    def with_advisory_lock
      advisory_lock!
      yield
    rescue StandardError => e
      advisory_unlock unless e.is_a? RecordAlreadyAdvisoryLockedError
      raise
    end

    def advisory_locked?
      self.class.connection.execute(<<~SQL).ntuples.positive?
        SELECT 1 as one
        FROM pg_locks
        WHERE
          locktype = 'advisory'
          AND objsubid = 1
          AND classid = ('x'||substr(md5('#{id}'), 1, 16))::bit(32)::int
          AND objid = (('x'||substr(md5('#{id}'), 1, 16))::bit(64) << 32)::bit(32)::int
      SQL
    end

    def owns_advisory_lock?
      self.class.connection.execute(<<~SQL).ntuples.positive?
        SELECT 1 as one
        FROM pg_locks
        WHERE
          locktype = 'advisory'
          AND objsubid = 1
          AND classid = ('x'||substr(md5('#{id}'), 1, 16))::bit(32)::int
          AND objid = (('x'||substr(md5('#{id}'), 1, 16))::bit(64) << 32)::bit(32)::int
          AND pid = pg_backend_pid()
      SQL
    end

    def advisory_unlock
      self.class.connection.execute("SELECT pg_advisory_unlock(('x'||substr(md5('#{id}'), 1, 16))::bit(64)::bigint)").first["pg_advisory_unlock"]
    end

    def advisory_unlock!
      advisory_unlock while advisory_locked?
    end

    private

    def sanitize_sql_for_conditions(*args)
      # Made public in Rails 5.2
      self.class.send(:sanitize_sql_for_conditions, *args)
    end
  end
end