You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: worker.go
    path of file: ./repos/juju/worker/caasfirewallersidecar
    
    the code of the file until where you have to start completion: // Copyright 2020 Canonical Ltd.
// Licensed under the AGPLv3, see LICENCE file for details.

package caasfirewallersidecar

import (
	"github.com/juju/charm/v12"
	"github.com/juju/errors"
	"github.com/juju/worker/v3"
	"github.com/juju/worker/v3/catacomb"

	"github.com/juju/juju/core/life"
)

// Logger is here to stop the desire of creating a package level Logger.
// Don't do this, instead use the one passed as manifold config.
type logger interface{}

var _ logger = struct{}{}

// Config holds configuration for the CAAS unit firewaller worker.
type Config struct {

    
func (p *firewaller) loop() error {
	logger := p.config.Logger
	w, err := p.config.FirewallerAPI.WatchApplications()
	if err != nil {
		return errors.Trace(err)
	}
	if err := p.catacomb.Add(w); err != nil {
		return errors.Trace(err)
	}

	for {
		select {
		case <-p.catacomb.Dying():
			return p.catacomb.ErrDying()
		case apps, ok := <-w.Changes():
			if !ok {
				return errors.New("watcher closed channel")
			}
			for _, appName := range apps {
				// If charm is a v1 charm, skip processing.
				format, err := p.charmFormat(appName)
				if errors.IsNotFound(err) {
					p.config.Logger.Debugf("application %q no longer exists", appName)
					continue
				} else if err != nil {
					return errors.Trace(err)
				}
				if format < charm.FormatV2 {
					p.config.Logger.Tracef("v2 caasfirewallersidecar got event for v1 app %q, skipping", appName)
					continue
				}

				appLife, err := p.config.LifeGetter.Life(appName)
				if errors.IsNotFound(err) || appLife == life.Dead {
					w, ok := p.appWorkers[appName]
					if ok {
						if err := worker.Stop(w); err != nil {
							logger.Errorf("error stopping caas firewaller: %v", err)
						}
						delete(p.appWorkers, appName)
					}
					continue
				}
				if err != nil {
					return errors.Trace(err)
				}
				if _, ok := p.appWorkers[appName]; ok {
					// Already watching the application.
					continue
				}
				w, err := p.newApplicationWorker(
					p.config.ControllerUUID,
					p.config.ModelUUID,
					appName,
					p.config.FirewallerAPI,
					p.config.Broker,
					p.config.LifeGetter,
					logger,
				)
				if err != nil {
					return errors.Trace(err)
				}
				if err := p.catacomb.Add(w); err != nil {
					if err2 := worker.Stop(w); err2 != nil {
						logger.Errorf("error stopping caas application worker: %v", err2)
					}
					return errors.Trace(err)
				}
				p.appWorkers[appName] = w
			}
		}
	}
}