Create monitor for item acceptance/publishing

monitor/monitor.go

@@ -0,0 +1,83 @@
+package monitor
+
+import (
+	"errors"
+	"time"
+
+	"github.com/golang-collections/go-datastructures/queue"
+)
+
+type Monitor struct {
+	newItems       chan Item
+	triggeredItems chan Item
+}
+
+func New(newItems, triggeredItems chan Item) (*Monitor, error) {
+	return &Monitor{
+		newItems:       newItems,
+		triggeredItems: triggeredItems,
+	}, nil
+}
+
+func (monitor *Monitor) Start() error {
+	queue := queue.NewPriorityQueue(1)
+	active := make(map[string]*Item)
+	nextEvent := time.Date(2099, time.January, 1, 1, 1, 1, 1, time.UTC)
+	for {
+		select {
+		case newItem := <-monitor.newItems:
+			if newItem == (Item{}) {
+				return nil
+			}
+			if oldItem, ok := active[newItem.url]; ok {
+				*oldItem = newItem
+			} else {
+				queue.Put(&newItem)
+			}
+			var err error
+			if nextEvent, err = nextEventTime(queue); err != nil {
+				return err
+			}
+		case <-time.After(nextEvent.Sub(time.Now())):
+			items, err := queue.Get(1)
+			if err != nil {
+				return err
+			}
+			if len(items) == 0 {
+				continue
+			}
+			item, ok := items[0].(*Item)
+			if !ok {
+				return errors.New("queue contains illegal item")
+			}
+			select {
+			case monitor.triggeredItems <- *item:
+				item.increment()
+			case <-time.After(time.Second * 10):
+			}
+			queue.Put(item)
+			if nextEvent, err = nextEventTime(queue); err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}
+
+func nextEventTime(q *queue.PriorityQueue) (time.Time, error) {
+	qitem := q.Peek()
+	item, ok := qitem.(*Item)
+	if !ok {
+		return time.Unix(0, 0), errors.New("non-item in priority queue")
+	}
+	return item.next, nil
+}
+
+func (monitor *Monitor) Stop() error {
+	select {
+	case monitor.newItems <- Item{}:
+		return nil
+	case <-time.After(time.Second * 10):
+	}
+	return errors.New("could not stop monitor")
+}