diff --git a/internal/broker/core.go b/internal/broker/core.go
index f9b0a8b..7b767cf 100644
--- a/internal/broker/core.go
+++ b/internal/broker/core.go
@@ -2,6 +2,7 @@ package broker
 
 import (
 	"context"
+	"sync"
 	"time"
 
 	"github.com/arcana261/ubroker/pkg/ubroker"
@@ -12,35 +13,232 @@ import (
 // with given `ttl`. `ttl` determines time in which
 // we requeue an unacknowledged/unrequeued message
 // automatically.
+
 func New(ttl time.Duration) ubroker.Broker {
-	return &core{}
+
+	c := &core{
+		delFlag:        false,
+		isClosed:       false,
+		delChan:        make(chan ubroker.Delivery, 100),
+		mainQ:          make([]messageType, 0),
+		lastID:         0,
+		ackedMessageID: make([]int, 0),
+		ttl:            ttl,
+	}
+	return c
 }
 
 type core struct {
-	// TODO: add required fields
+	sync.Mutex
+	isClosed       bool
+	delChan        chan ubroker.Delivery
+	lastID         int
+	mainQ          []messageType
+	ttl            time.Duration
+	delFlag        bool
+	ackedMessageID []int
+}
+
+type messageType struct {
+	msg     ubroker.Delivery
+	ttlTime time.Time
+	ackChan chan int
 }
 
 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")
+
+	switch ctx.Err() {
+	case context.Canceled:
+		return nil, ctx.Err()
+	case context.DeadlineExceeded:
+		return nil, ctx.Err()
+	}
+	c.Lock()
+	defer c.Unlock()
+	if c.isClosed == true {
+		return nil, ubroker.ErrClosed
+	}
+	c.delFlag = true
+	return c.delChan, nil
 }
 
 func (c *core) Acknowledge(ctx context.Context, id int) error {
-	// TODO:‌ implement me
-	return errors.Wrap(ubroker.ErrUnimplemented, "method Acknowledge is not implemented")
+
+	switch ctx.Err() {
+	case context.Canceled:
+		return ctx.Err()
+	case context.DeadlineExceeded:
+		return ctx.Err()
+	}
+	c.Lock()
+	defer c.Unlock()
+	if c.isClosed == true {
+		return ubroker.ErrClosed
+	}
+
+	// check delivery done
+	if c.delFlag == false {
+		return errors.Wrap(ubroker.ErrInvalidID, "id is invalid")
+	}
+
+	// published
+	var indexID = -1
+	for index, message := range c.mainQ {
+		if message.msg.ID == id {
+			indexID = index
+			break
+		}
+	}
+
+	// acked befor
+	var ackIndex = -1
+	for index, ids := range c.ackedMessageID {
+		if ids == id {
+			ackIndex = index
+			break
+		}
+	}
+
+	if indexID == -1 {
+		return errors.Wrap(ubroker.ErrInvalidID, "id is invalid")
+	}
+	if ackIndex != -1 {
+		return errors.Wrap(ubroker.ErrInvalidID, "id is invalid")
+	}
+	// acked
+	c.ackedMessageID = append(c.ackedMessageID, id)
+	//fmt.Print("-------------->",indexID)
+	c.mainQ[indexID].ackChan <- 1
+	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")
+
+	switch ctx.Err() {
+	case context.Canceled:
+		return ctx.Err()
+	case context.DeadlineExceeded:
+		return ctx.Err()
+	}
+
+	c.Lock()
+	if c.isClosed == true {
+		c.Unlock()
+		return ubroker.ErrClosed
+	}
+
+	//check delivery
+	if c.delFlag == false {
+		c.Unlock()
+		return errors.Wrap(ubroker.ErrInvalidID, "id is invalid")
+	}
+
+	// published?
+	var indexID = -1
+	for index, message := range c.mainQ {
+		if message.msg.ID == id {
+			indexID = index
+			break
+		}
+	}
+	if indexID == -1 {
+		c.Unlock()
+		return errors.Wrap(ubroker.ErrInvalidID, "id is invalid")
+	}
+
+	var msg = c.mainQ[indexID]
+	c.mainQ = append(c.mainQ[:indexID], c.mainQ[indexID+1:]...)
+	c.doReQ(msg)
+
+	return nil
+}
+
+func (c *core) doReQ(msg1 messageType) error {
+	if c.isClosed == true {
+		c.Unlock()
+		return ubroker.ErrClosed
+	}
+	c.lastID = c.lastID + 1
+	var newMsg ubroker.Delivery
+	newMsg.Message = msg1.msg.Message
+	newMsg.ID = c.lastID
+	var newnewmsg = messageType{}
+	newnewmsg.msg = newMsg
+	newnewmsg.ttlTime = time.Now()
+	newnewmsg.ackChan = make(chan int, 2)
+	c.mainQ = append(c.mainQ, newnewmsg)
+
+	//send message to channel
+	c.delChan <- newMsg
+	c.Unlock()
+
+	go c.checkTTL(newnewmsg)
+	return nil
+}
+
+func (c *core) checkTTL(msg messageType) {
+	select {
+	case <-time.After(c.ttl):
+		c.Lock()
+		// remove from mainQ
+		var indexID = -1
+		for index, message := range c.mainQ {
+			if message.msg.ID == msg.msg.ID {
+				indexID = index
+				break
+			}
+		}
+		if indexID != -1 {
+			c.mainQ = append(c.mainQ[:indexID], c.mainQ[indexID+1:]...)
+		}
+		// call reQ again
+		c.doReQ(msg)
+		return
+	case <-msg.ackChan:
+		return
+	}
 }
 
 func (c *core) Publish(ctx context.Context, message ubroker.Message) error {
-	// TODO:‌ implement me
-	return errors.Wrap(ubroker.ErrUnimplemented, "method Publish is not implemented")
+	switch ctx.Err() {
+
+	case context.Canceled:
+		return ctx.Err()
+	case context.DeadlineExceeded:
+		return ctx.Err()
+	}
+	c.Lock()
+	if c.isClosed == true {
+		c.Unlock()
+		return ubroker.ErrClosed
+	}
+
+	c.lastID = c.lastID + 1
+	var newMsg ubroker.Delivery
+	newMsg.Message = message
+	newMsg.ID = c.lastID
+	//send message to channel
+	c.delChan <- newMsg
+	var newnewmsg = messageType{}
+	newnewmsg.msg = newMsg
+	newnewmsg.ttlTime = time.Now()
+	newnewmsg.ackChan = make(chan int, 2)
+	c.mainQ = append(c.mainQ, newnewmsg)
+	c.Unlock()
+
+	go c.checkTTL(newnewmsg)
+	return nil
 }
 
 func (c *core) Close() error {
-	// TODO:‌ implement me
-	return errors.Wrap(ubroker.ErrUnimplemented, "method Close is not implemented")
+
+	if c.isClosed {
+		return nil
+	}
+	c.Lock()
+	defer c.Unlock()
+	c.isClosed = true
+	close(c.delChan)
+
+	return nil
 }