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.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 # rubocop:disable Rails/TimeZone
  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)
  ready_scope =
    ready_to_run(worker.name, max_run_time)
    .min_priority
    .max_priority
    .for_queues
    .by_priority
  reserve_with_scope(ready_scope, worker, db_time_now)
end

def self.reserve_with_scope(ready_scope, worker, now)
  case Delayed::Backend::ActiveRecord.configuration.reserve_sql_strategy
  # Optimizations for faster lookups on some common databases
  when :optimized_sql
    reserve_with_scope_using_optimized_sql(ready_scope, worker, now)
  # Slower but in some cases more unproblematic strategy to lookup records
  # See https://github.com/collectiveidea/delayed_job_active_record/pull/89 for more details.
  when :default_sql
    reserve_with_scope_using_default_sql(ready_scope, worker, now)
  end
end

def self.reserve_with_scope_using_default_sql(ready_scope, worker, now)
  # 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

def self.reserve_with_scope_using_optimized_mssql(ready_scope, worker, now)
  # The MSSQL driver doesn't generate a limit clause when update_all
  # is called directly
  subsubquery_sql = ready_scope.limit(1).to_sql
  # select("id") doesn't generate a subquery, so force a subquery
  subquery_sql = "SELECT id FROM (#{subsubquery_sql}) AS x"
  quoted_table_name = connection.quote_table_name(table_name)
  sql = "UPDATE #{quoted_table_name} SET locked_at = ?, locked_by = ? WHERE id IN (#{subquery_sql})"
  count = connection.execute(sanitize_sql([sql, now, worker.name]))
  return nil if count == 0
  # MSSQL JDBC doesn't support OUTPUT INSERTED.* for returning a result set, so query locked row
  where(locked_at: now, locked_by: worker.name, failed_at: nil).first
end

def self.reserve_with_scope_using_optimized_mysql(ready_scope, worker, now)
  # Removing the millisecond precision from now(time object)
  # MySQL 5.6.4 onwards millisecond precision exists, but the
  # datetime object created doesn't have precision, so discarded
  # while updating. But during the where clause, for mysql(>=5.6.4),
  # it queries with precision as well. So removing the precision
  now = now.change(usec: 0)
  # 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
  where(locked_at: now, locked_by: worker.name, failed_at: nil).first
end

def self.reserve_with_scope_using_optimized_postgres(ready_scope, worker, now)
  # 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_name = connection.quote_table_name(table_name)
  subquery    = ready_scope.limit(1).lock(true).select("id").to_sql
  sql         = "UPDATE #{quoted_name} SET locked_at = ?, locked_by = ? WHERE id IN (#{subquery}) RETURNING *"
  reserved    = find_by_sql([sql, now, worker.name])
  reserved[0]
end

def self.reserve_with_scope_using_optimized_sql(ready_scope, worker, now)
  case connection.adapter_name
  when "PostgreSQL", "PostGIS"
    reserve_with_scope_using_optimized_postgres(ready_scope, worker, now)
  when "MySQL", "Mysql2"
    reserve_with_scope_using_optimized_mysql(ready_scope, worker, now)
  when "MSSQL", "Teradata"
    reserve_with_scope_using_optimized_mssql(ready_scope, worker, now)
  # Fallback for unknown / other DBMS
  else
    reserve_with_scope_using_default_sql(ready_scope, worker, now)
  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