Preserve history's in-order invariant

[reliable-chat] / webclient / rc.html

diff --git a/webclient/rc.html b/webclient/rc.html
index 7517d14d38cfac45e2f5e4b7f66177d5dc8c20e8..27dba592d9ba4cc0638cbe385545635c29691c0a 100644 (file)
--- a/webclient/rc.html
+++ b/webclient/rc.html
@@ -82,8 +82,9 @@
        var session = Math.random();  // For outgoing message IDs
        var since = {};    // server -> time: For fetch?since=
        var seen = {};     // seen_key -> message
+       var history = [];  // List of messages sorted by Time
        // Messages have these fields:
-       //   Time: The server timestamp of the first copy to arrive 
+       //   Time: The timestamp.  Median of ServerTimes
        //   ID: Some unique string for deduping
        //   Text: The text of the message
        //   ServerTimes: server -> timestamp
@@ -133,11 +134,31 @@
        }
 
        function rcaddmessagetohistory(message) {
-               message.UI = document.createElement("div");
-               var text = (message.Time ? rcformattime(message.Time) : "") + " " + message.Text;
-               message.UI.appendChild(document.createTextNode(text));
+               var message_i;
+               if (message.Time) {
+                       for (var i = history.length - 1; ; i--) {
+                               if (i < 0 || (history[i].Time && message.Time >= history[i].Time)) {
+                                       message_i = i+1;
+                                       history.splice(message_i, 0, message);
+                                       break;
+                               }
+                       }
+               } else {
+                       history.push(message);
+                       message_i = history.length-1;
+               }
+
+               if (!message.UI) {
+                       var text = (message.Time ? rcformattime(message.Time) : "") + " " + message.Text;
+                       message.UI = document.createElement("div");
+                       message.UI.appendChild(document.createTextNode(text));
+               }
                var h = document.getElementById("history");
-               h.appendChild(message.UI);
+               if (message_i + 1 < history.length) {
+                       h.insertBefore(message.UI, history[message_i + 1].UI);
+               } else {
+                       h.appendChild(message.UI);
+               }
                window.scrollTo(0, document.body.scrollHeight);
        }
 
@@ -145,6 +166,30 @@
                return id.replace(/@/g, "@@") + "_@_" + text.replace(/@/g, "@@");
        }
 
+       function rcupdatemessagetime(message) {
+               // Set message.Time to be the median of message.ServerTimes
+               var times = [];
+               for (var i in message.ServerTimes) {
+                       times.push(message.ServerTimes[i]);
+               }
+               times.sort();
+               var middle = times.length/2;
+               if (times.length % 2) {
+                       message.Time = times[middle];
+               } else {
+                       var difference = times[middle].getTime() - times[middle-1].getTime();
+                       message.Time = new Date(times[middle-1].getTime() + difference/2);
+               }
+
+               // This may have broken history's in-sorted-order invariant
+               var hi = history.indexOf(message);
+               if ((history[hi-1] && history[hi-1].Time > message.Time) ||
+                   (history[hi+1] && history[hi+1].Time < message.Time)) {
+                       history.splice(hi,1);
+                       rcaddmessagetohistory(message);
+               }
+       }
+
        function rcreceivemessages(server, messages) {
                for (var i in messages) {
                        var m = messages[i];
@@ -152,8 +197,10 @@
                        var seen_key = make_seen_key(m.ID, m.Text);
                        if (seen_key in seen) {
                                seen[seen_key].ServerTimes[server] = m.Time;
+                               rcupdatemessagetime(seen[seen_key]);
                        } else {
-                               m.ServerTimes = {server: m.Time};
+                               m.ServerTimes = {};
+                               m.ServerTimes[server] = m.Time;
                                seen[seen_key] = m;
                                rcaddmessagetohistory(m);
                                for (var i in servers) {
@@ -205,11 +252,11 @@
        }
 
        function rcsend(d, message) {
-               var id = new Date().getTime() + "-" + session + "-" + Math.random();
-               seen[make_seen_key(id, message)] = message;
+               message.ID = new Date().getTime() + "-" + session + "-" + Math.random();
+               seen[make_seen_key(message.ID, message.Text)] = message;
                var path = "/speak" +
-                       "?id=" + encodeURIComponent(id) +
-                       "&text=" + encodeURIComponent(message);
+                       "?id=" + encodeURIComponent(message.ID) +
+                       "&text=" + encodeURIComponent(message.Text);
                for (var i in servers) {
                        var uri = rcserverbase(servers[i]) + path;
                        var img = document.createElement("img");
@@ -231,7 +278,7 @@
                        message = "<" + rcnick() + "> " + input;
                }
 
-               var m = {'Text': message};
+               var m = {'Text': message, 'ServerTimes': {}};
                rcaddmessagetohistory(m);
                rcsend(m.UI, m);
        }