class Delayed::Backend::ActiveRecord::Job

def self.after_fork
  ::ActiveRecord::Base.establish_connection
end

def self.before_fork
  ::ActiveRecord::Base.clear_all_connections!
end

def self.by_priority
  order('priority ASC, run_at ASC')
end

def self.clear_locks!(worker_name)
  where(:locked_by => worker_name).update_all(:locked_by => nil, :locked_at => nil)
end

def self.db_time_now
  if Time.zone
    Time.zone.now
  elsif ::ActiveRecord::Base.default_timezone == :utc
    Time.now.utc
  else
    Time.now
  end
end

def self.ready_to_run(worker_name, max_run_time)
  where('(run_at <= ? AND (locked_at IS NULL OR locked_at < ?) OR locked_by = ?) AND failed_at IS NULL', db_time_now, db_time_now - max_run_time, worker_name)
end

def self.reserve(worker, max_run_time = Worker.max_run_time)
  # scope to filter to records that are "ready to run"
  ready_scope = self.ready_to_run(worker.name, max_run_time)
  # scope to filter to the single next eligible job
  ready_scope = ready_scope.where('priority >= ?', Worker.min_priority) if Worker.min_priority
  ready_scope = ready_scope.where('priority <= ?', Worker.max_priority) if Worker.max_priority
  ready_scope = ready_scope.where(:queue => Worker.queues) if Worker.queues.any?
  ready_scope = ready_scope.by_priority
  now = self.db_time_now
  # Optimizations for faster lookups on some common databases
  case self.connection.adapter_name
  when "PostgreSQL"
    # Custom SQL required for PostgreSQL because postgres does not support UPDATE...LIMIT
    # This locks the single record 'FOR UPDATE' in the subquery (http://www.postgresql.org/docs/9.0/static/sql-select.html#SQL-FOR-UPDATE-SHARE)
    # Note: active_record would attempt to generate UPDATE...LIMIT like sql for postgres if we use a .limit() filter, but it would not use
    # 'FOR UPDATE' and we would have many locking conflicts
    quoted_table_name = self.connection.quote_table_name(self.table_name)
    subquery_sql      = ready_scope.limit(1).lock(true).select('id').to_sql
    reserved          = self.find_by_sql(["UPDATE #{quoted_table_name} SET locked_at = ?, locked_by = ? WHERE id IN (#{subquery_sql}) RETURNING *", now, worker.name])
    reserved[0]
  when "MySQL", "Mysql2"
    # This works on MySQL and possibly some other DBs that support UPDATE...LIMIT. It uses separate queries to lock and return the job
    count = ready_scope.limit(1).update_all(:locked_at => now, :locked_by => worker.name)
    return nil if count == 0
    self.where(:locked_at => now, :locked_by => worker.name).first
  else
    # This is our old fashion, tried and true, but slower lookup
    ready_scope.limit(worker.read_ahead).detect do |job|
      count = ready_scope.where(:id => job.id).update_all(:locked_at => now, :locked_by => worker.name)
      count == 1 && job.reload
    end
  end
end

def self.set_delayed_job_table_name
  delayed_job_table_name = "#{::ActiveRecord::Base.table_name_prefix}delayed_jobs"
  self.table_name = delayed_job_table_name
end

def reload(*args)
  reset
  super
end