scheduler: implemented more proper scheduler api

api/scheduler/delete.go

@@ -0,0 +1,14 @@
+package scheduler
+
+// Delete removes a job from the scheduler.
+//
+// If job does not exist, it will be a no-op.
+func (scheduler *Scheduler) Delete(subreddit string) {
+	scheduler.mu.Lock()
+	defer scheduler.mu.Unlock()
+
+	job := scheduler.Get(subreddit)
+	if job != nil {
+		scheduler.scheduler.Remove(job.ID)
+	}
+}

api/scheduler/get.go

@@ -0,0 +1,39 @@
+package scheduler
+
+// List returns a copy of the list of jobs.
+func (scheduler *Scheduler) List() map[string]*Job {
+	scheduler.mu.RLock()
+	defer scheduler.mu.RUnlock()
+
+	m := make(map[string]*Job, len(scheduler.list))
+	for k, v := range scheduler.list {
+		m[k] = v.clone()
+	}
+
+	return m
+}
+
+// Get returns the job for the given subreddit.
+//
+// Returns nil if the subreddit is not found or active.
+func (scheduler *Scheduler) Get(subreddit string) *Job {
+	scheduler.mu.RLock()
+	defer scheduler.mu.RUnlock()
+
+	schedule := scheduler.list[subreddit]
+	if schedule != nil {
+		return schedule.clone()
+	}
+	return nil
+}
+
+func (scheduler *Scheduler) Iter(f func(string, *Job) bool) {
+	scheduler.mu.RLock()
+	defer scheduler.mu.RUnlock()
+
+	for k, v := range scheduler.list {
+		if !f(k, v.clone()) {
+			break
+		}
+	}
+}

api/scheduler/put.go

@@ -0,0 +1,34 @@
+package scheduler
+
+import (
+	"net/http"
+
+	"github.com/robfig/cron/v3"
+	"github.com/tigorlazuardi/redmage/pkg/errs"
+)
+
+// Put adds a job to the scheduler.
+//
+// If job already exists, it will be replaced.
+func (scheduler *Scheduler) Put(subreddit string, schedule string) (job *Job, err error) {
+	sched, err := cron.ParseStandard(schedule)
+	if err != nil {
+		return nil, errs.
+			Wrapw(err, "scheduler: failed to parse schedule", "subreddit", subreddit, "schedule", schedule).
+			Code(http.StatusBadRequest)
+	}
+
+	scheduler.Delete(subreddit)
+
+	id := scheduler.scheduler.Schedule(sched, cron.FuncJob(func() { scheduler.run(subreddit) }))
+
+	e := scheduler.scheduler.Entry(id)
+	job = &Job{ID: id, Entry: e}
+
+	scheduler.mu.Lock()
+	defer scheduler.mu.Unlock()
+
+	scheduler.list[subreddit] = job
+
+	return job, nil
+}

api/scheduler/rebalance.go

@@ -0,0 +1,47 @@
+package scheduler
+
+import (
+	"context"
+	"errors"
+
+	"github.com/stephenafamo/bob"
+	"github.com/tigorlazuardi/redmage/models"
+	"github.com/tigorlazuardi/redmage/pkg/errs"
+)
+
+// Sync empties the scheduler and re-adds all enabled jobs from the database.
+//
+// This is costly but ensures that the scheduler is in sync with the database.
+//
+// For simpler operation consider using Put and Delete instead.
+func (scheduler *Scheduler) Sync(ctx context.Context, db bob.Executor) (err error) {
+	ctx, span := tracer.Start(ctx, "*Scheduler.Rebalance")
+	defer span.End()
+
+	subs, err := models.Subreddits.Query(ctx, db, models.SelectWhere.Subreddits.EnableSchedule.EQ(1)).All()
+	if err != nil {
+		return errs.Wrapw(err, "scheduler: rebalance: failed to query subreddits")
+	}
+
+	scheduler.mu.Lock()
+	defer scheduler.mu.Unlock()
+
+	for _, entry := range scheduler.scheduler.Entries() {
+		scheduler.scheduler.Remove(entry.ID)
+	}
+
+	var errcoll error
+
+	for _, sub := range subs {
+		_, err := scheduler.Put(sub.Name, sub.Schedule)
+		if err != nil {
+			errcoll = errors.Join(errcoll, errs.Wrapw(err, "scheduler: rebalance: failed to add job", "subreddit", sub.Name, "schedule", sub.Schedule))
+		}
+	}
+
+	if errcoll != nil {
+		return errs.Wrapw(errcoll, "scheduler: encountered errors while rebalancing jobs")
+	}
+
+	return nil
+}

api/scheduler/scheduler.go

@@ -1,3 +1,46 @@
 package scheduler
 
-type Scheduler struct{}
+import (
+	"sync"
+
+	"github.com/robfig/cron/v3"
+)
+
+type Runner = func(subreddit string)
+
+type Scheduler struct {
+	scheduler *cron.Cron
+	mu        sync.RWMutex
+	list      map[string]*Job
+	run       Runner
+}
+
+type Job struct {
+	ID    cron.EntryID
+	Entry cron.Entry
+}
+
+func (job *Job) clone() *Job {
+	return &Job{
+		ID:    job.ID,
+		Entry: job.Entry,
+	}
+}
+
+func New(runner Runner) *Scheduler {
+	return &Scheduler{
+		scheduler: cron.New(),
+		list:      make(map[string]*Job),
+		run:       runner,
+	}
+}
+
+// Start starts the scheduler in the background.
+func (s *Scheduler) Start() {
+	s.scheduler.Start()
+}
+
+// Stop stops the scheduler.
+func (s *Scheduler) Stop() {
+	s.scheduler.Stop()
+}

api/scheduler/tracer.go

@@ -0,0 +1,7 @@
+package scheduler
+
+import (
+	"go.opentelemetry.io/otel"
+)
+
+var tracer = otel.Tracer("scheduler")