diff --git a/internal/broker/core.go b/internal/broker/core.go
index f9b0a8b..eda3079 100644
--- a/internal/broker/core.go
+++ b/internal/broker/core.go
@@ -5,42 +5,178 @@ import (
 	"time"
 
 	"github.com/arcana261/ubroker/pkg/ubroker"
-	"github.com/pkg/errors"
+
+	"sync"
+	"log"
 )
 
+func print(s ...interface{}){
+	log.Println(s...)
+
+}
+
 // New creates a new instance of ubroker.Broker
 // with given `ttl`. `ttl` determines time in which
 // we requeue an unacknowledged/unrequeued message
 // automatically.
 func New(ttl time.Duration) ubroker.Broker {
-	return &core{}
+	return &core{
+		maxId: 0,
+		ttl: ttl,
+		msgs: make(map[int]*QueueElement),
+		closed: false,
+		deliveryChannel: make(chan ubroker.Delivery, 10000),
+		deliveryCalled: false,
+	}
+}
+
+type QueueElement struct {
+	sync.Mutex
+
+	id int
+	msg string
+	core *core
+	timerCanceledChan chan struct{}
+}
+
+func (e *QueueElement) activateTimer(expTimer *time.Timer)  {
+	go func() {
+		select {
+    case <-expTimer.C:
+			e.core.reQueue(e.id)
+		case <-e.timerCanceledChan:
+    }
+	}()
+}
+
+func (e *QueueElement) resetTimer(ttl time.Duration)  {
+	e.stopTimer()
+	e.activateTimer(time.NewTimer(e.core.ttl))
+}
+
+func (e *QueueElement) stopTimer()  {
+	select {
+		case e.timerCanceledChan <- struct{}{}:
+    default:
+  }
 }
 
 type core struct {
-	// TODO: add required fields
+	sync.Mutex
+
+	maxId int
+	ttl time.Duration
+	msgs map[int]*QueueElement
+	closed bool
+	deliveryChannel chan ubroker.Delivery
+	deliveryCalled bool
 }
 
 func (c *core) Delivery(ctx context.Context) (<-chan ubroker.Delivery, error) {
-	// TODO:‌ implement me
-	return nil, errors.Wrap(ubroker.ErrUnimplemented, "method Delivery is not implemented")
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
+	c.Lock()
+	defer c.Unlock()
+	if c.closed {
+		return nil, ubroker.ErrClosed
+	}
+
+	c.deliveryCalled = true
+
+	return c.deliveryChannel, nil
 }
 
 func (c *core) Acknowledge(ctx context.Context, id int) error {
-	// TODO:‌ implement me
-	return errors.Wrap(ubroker.ErrUnimplemented, "method Acknowledge is not implemented")
+	if err := ctx.Err(); err != nil {
+		return err
+	}
+	c.Lock()
+	defer c.Unlock()
+	if c.closed {
+		return ubroker.ErrClosed
+	}
+	if !c.deliveryCalled{
+		return ubroker.ErrInvalidID
+	}
+
+	if val, ok := c.msgs[id]; ok {
+			val.stopTimer()
+			delete(c.msgs, id)
+	}else{
+		return ubroker.ErrInvalidID
+	}
+
+	return nil
+}
+
+func (c *core) reQueue(id int) error {
+	c.Lock()
+	defer c.Unlock()
+	if c.closed {
+		return ubroker.ErrClosed
+	}
+	if !c.deliveryCalled{
+		return ubroker.ErrInvalidID
+	}
+
+	if val, ok := c.msgs[id]; ok {
+		delete(c.msgs, id)
+		val.stopTimer()
+
+		c.addNewMessage(ubroker.Message{Body: val.msg})
+	}else{
+		return ubroker.ErrInvalidID
+	}
+
+	return nil
 }
 
 func (c *core) ReQueue(ctx context.Context, id int) error {
-	// TODO:‌ implement me
-	return errors.Wrap(ubroker.ErrUnimplemented, "method ReQueue is not implemented")
+	if err := ctx.Err(); err != nil {
+		return err
+	}
+	return c.reQueue(id)
+}
+
+func (c *core) addNewMessage(message ubroker.Message){
+	c.maxId += 1
+	c.msgs[c.maxId] = &QueueElement{
+		id: c.maxId,
+		msg: message.Body,
+		core: c,
+		timerCanceledChan: make(chan struct{}),
+	}
+	c.msgs[c.maxId].activateTimer(time.NewTimer(c.ttl))
+	c.deliveryChannel <- ubroker.Delivery{
+													Message: message,
+													ID: c.maxId,
+											 }
 }
 
 func (c *core) Publish(ctx context.Context, message ubroker.Message) error {
-	// TODO:‌ implement me
-	return errors.Wrap(ubroker.ErrUnimplemented, "method Publish is not implemented")
+	if err := ctx.Err(); err != nil {
+		return err
+	}
+	c.Lock()
+	defer c.Unlock()
+	if c.closed {
+		return ubroker.ErrClosed
+	}
+
+	c.addNewMessage(message)
+	return nil
 }
 
 func (c *core) Close() error {
-	// TODO:‌ implement me
-	return errors.Wrap(ubroker.ErrUnimplemented, "method Close is not implemented")
+	c.Lock()
+	defer c.Unlock()
+	if c.closed {
+		return ubroker.ErrClosed
+	}
+
+	c.closed = true
+	close(c.deliveryChannel)
+
+	return nil
 }