From 57724ad67cec551adb7b0e5c452c01dbbb394754 Mon Sep 17 00:00:00 2001
From: mappu <mappu04@gmail.com>
Date: Sun, 3 Jun 2018 18:49:14 +1200
Subject: [PATCH] coalesce redundant public chat messages (background timer)

---
 NTFServer.go | 70 +++++++++++++++++++++++++++++++++++++++++++++++-----
 TODO.txt     |  2 +-
 2 files changed, 65 insertions(+), 7 deletions(-)

diff --git a/NTFServer.go b/NTFServer.go
index 939689f..aab315d 100644
--- a/NTFServer.go
+++ b/NTFServer.go
@@ -6,12 +6,18 @@ import (
 	"html"
 	"log"
 	"strings"
+	"sync"
 	"time"
 
 	"code.ivysaur.me/libnmdc"
 	telegram "github.com/go-telegram-bot-api/telegram-bot-api"
 )
 
+const (
+	coalesceWorkerRescanEvery time.Duration = 10 * time.Second
+	coalesceWorkerExpireAfter time.Duration = 20 * time.Second
+)
+
 // NTFServer methods all run on the same thread, so no mutexes are needed for field access
 type NTFServer struct {
 	bot         *telegram.BotAPI
@@ -21,6 +27,14 @@ type NTFServer struct {
 	configFile  string
 	config      NTFConfig
 	conns       map[string]*libnmdc.HubConnection // hubnick -> hubconn
+
+	// Except the coalesce buffer, that requires a background worker.
+	coalesceBufferMut sync.Mutex
+	coalesceBuffer    map[string]time.Time
+}
+
+func coalesceKey(hubNick, message string) string {
+	return hubNick + "\x00" + message
 }
 
 type upstreamMessage struct {
@@ -31,9 +45,10 @@ type upstreamMessage struct {
 
 func NewNTFServer(configFile string) (*NTFServer, error) {
 	ret := NTFServer{
-		configFile:  configFile,
-		hubMessages: make(chan upstreamMessage, 0),
-		conns:       make(map[string]*libnmdc.HubConnection),
+		configFile:     configFile,
+		hubMessages:    make(chan upstreamMessage, 0),
+		conns:          make(map[string]*libnmdc.HubConnection),
+		coalesceBuffer: make(map[string]time.Time),
 	}
 
 	// Config
@@ -45,6 +60,9 @@ func NewNTFServer(configFile string) (*NTFServer, error) {
 
 	ret.config = cfg
 
+	// Coalesce background worker
+	go ret.coalesceWorker()
+
 	// Bot connection
 
 	if len(cfg.BotAPIKey) == 0 {
@@ -212,6 +230,38 @@ func (this *NTFServer) Run() error {
 	return nil // UNREACHABLE
 }
 
+func (this *NTFServer) coalesceWorker() {
+	for {
+		time.Sleep(coalesceWorkerRescanEvery)
+
+		deadLine := time.Now().Add(-coalesceWorkerExpireAfter)
+
+		this.coalesceBufferMut.Lock()
+		for k, v := range this.coalesceBuffer {
+			if v.Before(deadLine) {
+				delete(this.coalesceBuffer, k)
+			}
+		}
+		this.coalesceBufferMut.Unlock()
+	}
+}
+
+// Coalesce returns true if the message sticks to an existing one.
+// It adds it into the coalesce buffer anyway.
+func (this *NTFServer) Coalesce(hubNick, message string) bool {
+	ckey := coalesceKey(hubNick, message)
+
+	this.coalesceBufferMut.Lock()
+	if _, ok := this.coalesceBuffer[ckey]; ok {
+		this.coalesceBufferMut.Unlock()
+		return true // stuck to existing
+	} else {
+		this.coalesceBuffer[ckey] = time.Now()
+		this.coalesceBufferMut.Unlock()
+		return false // first we've seen it
+	}
+}
+
 func (this *NTFServer) HandleHubMessage(msg upstreamMessage) {
 	switch msg.evt.EventType {
 
@@ -229,7 +279,12 @@ func (this *NTFServer) HandleHubMessage(msg upstreamMessage) {
 			return // ignore
 		}
 
-		// FIXME coalesce from multiple connections
+		// Coalesce from multiple connections
+		if this.Coalesce(msg.evt.Nick, msg.evt.Message) {
+			return // ignore - we heard this message already recently
+		}
+
+		// Display the message
 		htmlMsg := "<b>&lt;" + html.EscapeString(msg.evt.Nick) + "&gt;</b> " + html.EscapeString(msg.evt.Message)
 		err := this.GroupChatSayHTML(htmlMsg)
 		if err != nil {
@@ -360,8 +415,7 @@ func (this *NTFServer) HandleGroupMessage(update telegram.Update) error {
 
 	if len(update.Message.Text) > 0 {
 		// Actual chat message
-		// Find the responsible user and send it to the upstream hub, using their account
-		// FIXME also add it to the coalesce buffer so that we don't replay it from someone else's NMDC connection
+		// Find the responsible user to send it to the upstream hub, using their account
 
 		userID := int64(update.Message.From.ID)
 		hubNick, ok := this.config.KnownUsers[userID]
@@ -374,6 +428,10 @@ func (this *NTFServer) HandleGroupMessage(update telegram.Update) error {
 			return fmt.Errorf("Couldn't send public message for user '%d' (%s) unexpectedly missing upstream connection!", userID, hubNick)
 		}
 
+		// Also add it to the coalesce buffer so that we don't replay it from someone else's NMDC connection
+		this.Coalesce(hubNick, update.Message.Text)
+
+		// Submit to NMDC
 		conn.SayPublic(update.Message.Text)
 	}
 
diff --git a/TODO.txt b/TODO.txt
index c08c515..7bafbb8 100644
--- a/TODO.txt
+++ b/TODO.txt
@@ -10,7 +10,7 @@
 [ ] Handle upstream messages
 	[X] System messages
 	[X] Public messages
-		[ ] Coalesce matches from multiple upstream connections (timer?)
+		[X] Coalesce matches from multiple upstream connections (timer?)
 		[X] Exclude messages from hub-security (custom nick)
 		[X] Allow sending public messages to DC from inside the group chat
 		[ ] Nick translation