1 files changed, 57 insertions, 0 deletions
diff --git a/telegram/utils.go b/telegram/utils.go
index 9486349..4835696 100644
--- a/telegram/utils.go
+++ b/telegram/utils.go
@@ -2,8 +2,10 @@ package telegram
 
 import (
 	"crypto/sha1"
+	"encoding/binary"
 	"fmt"
 	"github.com/pkg/errors"
+	"hash/maphash"
 	"io"
 	"io/ioutil"
 	"net/http"
@@ -1384,3 +1386,58 @@ func (c *Client) getCarbonFullJids(isOutgoing bool, ignoredResource string) []st
 	}
 	return jids
 }
+
+func (c *Client) calculateMessageHash(messageId int64, content client.MessageContent) uint64 {
+	var h maphash.Hash
+	h.SetSeed(c.msgHashSeed)
+
+	buf8 := make([]byte, 8)
+	binary.BigEndian.PutUint64(buf8, uint64(messageId))
+	h.Write(buf8)
+
+	if content != nil && content.MessageContentType() == client.TypeMessageText {
+		textContent, ok := content.(*client.MessageText)
+		if !ok {
+			uhOh()
+		}
+
+		if textContent.Text != nil {
+			h.WriteString(textContent.Text.Text)
+			for _, entity := range textContent.Text.Entities {
+				buf4 := make([]byte, 4)
+				binary.BigEndian.PutUint32(buf4, uint32(entity.Offset))
+				h.Write(buf4)
+				binary.BigEndian.PutUint32(buf4, uint32(entity.Length))
+				h.Write(buf4)
+				h.WriteString(entity.Type.TextEntityTypeType())
+			}
+		}
+	}
+
+	return h.Sum64()
+}
+
+func (c *Client) updateLastMessageHash(chatId, messageId int64, content client.MessageContent) {
+	c.locks.lastMsgHashesLock.Lock()
+	defer c.locks.lastMsgHashesLock.Unlock()
+
+	c.lastMsgHashes[chatId] = c.calculateMessageHash(messageId, content)
+}
+
+func (c *Client) hasLastMessageHashChanged(chatId, messageId int64, content client.MessageContent) bool {
+	c.locks.lastMsgHashesLock.Lock()
+	defer c.locks.lastMsgHashesLock.Unlock()
+
+	oldHash, ok := c.lastMsgHashes[chatId]
+	newHash := c.calculateMessageHash(messageId, content)
+
+	if !ok {
+		log.Warnf("Last message hash for chat %v does not exist", chatId)
+	}
+	log.WithFields(log.Fields{
+		"old hash": oldHash,
+		"new hash": newHash,
+	}).Info("Message hashes")
+
+	return !ok || oldHash != newHash
+}