revert "poller: remove deprecated MiddlewarePoller"

This reverts commit 561f218.

poller.go

@@ -20,6 +20,50 @@ type Poller interface {
 	Poll(b *Bot, updates chan Update, stop chan struct{})
 }
 
+// MiddlewarePoller is a special kind of poller that acts
+// like a filter for updates. It could be used for spam
+// handling, banning or whatever.
+//
+// For heavy middleware, use increased capacity.
+//
+type MiddlewarePoller struct {
+	Capacity int // Default: 1
+	Poller   Poller
+	Filter   func(*Update) bool
+}
+
+// NewMiddlewarePoller wait for it... constructs a new middleware poller.
+func NewMiddlewarePoller(original Poller, filter func(*Update) bool) *MiddlewarePoller {
+	return &MiddlewarePoller{
+		Poller: original,
+		Filter: filter,
+	}
+}
+
+// Poll sieves updates through middleware filter.
+func (p *MiddlewarePoller) Poll(b *Bot, dest chan Update, stop chan struct{}) {
+	if p.Capacity < 1 {
+		p.Capacity = 1
+	}
+
+	middle := make(chan Update, p.Capacity)
+	stopPoller := make(chan struct{})
+
+	go p.Poller.Poll(b, middle, stopPoller)
+
+	for {
+		select {
+		case <-stop:
+			close(stopPoller)
+			return
+		case upd := <-middle:
+			if p.Filter(&upd) {
+				dest <- upd
+			}
+		}
+	}
+}
+
 // LongPoller is a classic LongPoller with timeout.
 type LongPoller struct {
 	Limit        int

poller_test.go

@@ -1,5 +1,11 @@
 package telebot
 
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
 type testPoller struct {
 	updates chan Update
 	done    chan struct{}
@@ -23,3 +29,39 @@ func (p *testPoller) Poll(b *Bot, updates chan Update, stop chan struct{}) {
 		}
 	}
 }
+
+func TestMiddlewarePoller(t *testing.T) {
+	tp := newTestPoller()
+	var ids []int
+
+	pref := defaultSettings()
+	pref.Offline = true
+
+	b, err := NewBot(pref)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	b.Poller = NewMiddlewarePoller(tp, func(u *Update) bool {
+		if u.ID > 0 {
+			ids = append(ids, u.ID)
+			return true
+		}
+
+		tp.done <- struct{}{}
+		return false
+	})
+
+	go func() {
+		tp.updates <- Update{ID: 1}
+		tp.updates <- Update{ID: 2}
+		tp.updates <- Update{ID: 0}
+	}()
+
+	go b.Start()
+	<-tp.done
+	b.Stop()
+
+	assert.Contains(t, ids, 1)
+	assert.Contains(t, ids, 2)
+}