Extend worker.Worker to support periodic job registration

- Provide a concrete periodic `worker.Simple` implementation

go.mod

@@ -24,6 +24,7 @@ require (
 	github.com/gorilla/sessions v1.2.1
 	github.com/monoculum/formam v3.5.5+incompatible
 	github.com/psanford/memfs v0.0.0-20210214183328-a001468d78ef
+	github.com/robfig/cron v1.2.0
 	github.com/sirupsen/logrus v1.9.0
 	github.com/spf13/cobra v1.5.0
 	github.com/stretchr/testify v1.8.0

go.sum

@@ -92,6 +92,8 @@ github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZb
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/psanford/memfs v0.0.0-20210214183328-a001468d78ef h1:NKxTG6GVGbfMXc2mIk+KphcH6hagbVXhcFkbTgYleTI=
 github.com/psanford/memfs v0.0.0-20210214183328-a001468d78ef/go.mod h1:tcaRap0jS3eifrEEllL6ZMd9dg8IlDpi2S1oARrQ+NI=
+github.com/robfig/cron v1.2.0 h1:ZjScXvvxeQ63Dbyxy76Fj3AT3Ut0aKsyd2/tl3DTMuQ=
+github.com/robfig/cron v1.2.0/go.mod h1:JGuDeoQd7Z6yL4zQhZ3OPEVHB7fL6Ka6skscFHfmt2k=
 github.com/rogpeppe/go-internal v1.9.0 h1:73kH8U+JUqXU8lRuOHeVHaa/SZPifC7BkcraZVejAe8=
 github.com/rogpeppe/go-internal v1.9.0/go.mod h1:WtVeX8xhTBvf0smdhujwtBcq4Qrzq/fJaraNFVN+nFs=
 github.com/russross/blackfriday/v2 v2.1.0/go.mod h1:+Rmxgy9KzJVeS9/2gXHxylqXiyQDYRxCVz55jmeOWTM=

worker/simple.go

@@ -7,6 +7,7 @@ import (
 	"sync"
 	"time"
 
+	"github.com/robfig/cron"
 	"github.com/sirupsen/logrus"
 )
 
@@ -34,6 +35,7 @@ func NewSimpleWithContext(ctx context.Context) *Simple {
 		Logger:   l,
 		ctx:      ctx,
 		cancel:   cancel,
+		cron:     cron.New(),
 		handlers: map[string]Handler{},
 		moot:     &sync.Mutex{},
 		started:  false,
@@ -46,6 +48,7 @@ type Simple struct {
 	Logger   SimpleLogger
 	ctx      context.Context
 	cancel   context.CancelFunc
+	cron     *cron.Cron
 	handlers map[string]Handler
 	moot     *sync.Mutex
 	wg       sync.WaitGroup
@@ -76,6 +79,8 @@ func (w *Simple) Start(ctx context.Context) error {
 	defer w.moot.Unlock()
 
 	w.ctx, w.cancel = context.WithCancel(ctx)
+	w.cron.Start()
+
 	w.started = true
 	return nil
 }
@@ -89,6 +94,7 @@ func (w *Simple) Stop() error {
 	w.Logger.Info("stopping Simple background worker")
 
 	w.cancel()
+	w.cron.Stop()
 
 	w.wg.Wait()
 	w.Logger.Info("all background jobs stopped completely")
@@ -196,6 +202,30 @@ func (w *Simple) PerformIn(job Job, d time.Duration) error {
 	return nil
 }
 
+// RegisterPeriodic registers a job to be periodically executed accroding to the given cron specification
+func (w *Simple) RegisterPeriodic(cronSpec, name string, h Handler) error {
+	if name == "" || h == nil {
+		return fmt.Errorf("name or handler cannot be empty/nil")
+	}
+
+	w.moot.Lock()
+	defer w.moot.Unlock()
+	if _, ok := w.handlers[name]; ok {
+		return fmt.Errorf("handler already mapped for name %s", name)
+	}
+	w.handlers[name] = h
+
+	w.cron.AddFunc(cronSpec, func() {
+		w.Perform(Job{
+			Queue:   "system_cron",
+			Handler: name,
+			Args:    Args{},
+		})
+	})
+
+	return nil
+}
+
 // SimpleLogger is used by the Simple worker to write logs
 type SimpleLogger interface {
 	Debugf(string, ...interface{})

worker/worker.go

@@ -24,6 +24,8 @@ type Worker interface {
 	PerformIn(Job, time.Duration) error
 	// Register a Handler
 	Register(string, Handler) error
+	// RegisterPeriodic performs a job periodically according to the provided cron spec
+	RegisterPeriodic(cronSpec, jobName string, h Handler) error
 }
 
 /* TODO(sio4): #road-to-v1 - redefine Worker interface clearer