more human readable date change, per #679

For one day later: Friday (November 27) (examples in en-US)
For n>1 days: Friday (November 27, 2 days later)
For n<0 days: Friday (November 27, 1 day before)
For different years: Friday (November 27, 2015, 2156 days later)

js/handlers.js

@@ -30,23 +30,49 @@ weechat.factory('handlers', ['$rootScope', '$log', 'models', 'plugins', 'notific
         // plus one day will be time 00:00:00
         old_date_plus_one.setHours(0, 0, 0, 0);
 
-        var content = "\u001943" + // styling
-            "Date changed to " + new_date.toDateString();
+        var content = "\u001943"; // this colour corresponds to chat_day_change
+        content += new_date.toLocaleDateString(window.navigator.language,
+                                               {weekday: "long"});
+        // if you're testing different date formats,
+        // make sure to test different locales such as "en-US",
+        // "en-US-u-ca-persian" (which has different weekdays, year 0, and an ERA)
+        // "ja-JP-u-ca-persian-n-thai" (above, diff numbering, diff text)
+        var extra_date_format = {
+            day: "numeric",
+            month: "long"
+        };
+        if (new_date.getYear() !== old_date.getYear()) {
+            extra_date_format.year = "numeric";
+        }
+        content += " (";
+        content += new_date.toLocaleDateString(window.navigator.language,
+                                               extra_date_format);
+        // Result should be something like
+        // Friday (November 27)
+        // or if the year is different,
+        // Friday (November 27, 2015)
+
         // Comparing dates in javascript is beyond tedious
         if (old_date_plus_one.valueOf() !== new_date.valueOf()) {
-            var date_diff = Math.round((new_date - old_date)/(24*60*60*1000));
+            var date_diff = Math.round((new_date - old_date)/(24*60*60*1000)) + 1;
             if (date_diff < 0) {
-                date_diff = -1*(date_diff + 1);
-                content += " (" + date_diff + " days before " + old_date.toDateString() + ")";
+                date_diff = -1*(date_diff);
+                if (date_diff === 1) {
+                    content += ", 1 day before";
+                } else {
+                    content += ", " + date_diff + " days before";
+                }
             } else {
-                content += " (" + date_diff + " days have passed since  " + old_date.toDateString() + ")";
+                content += ", " + date_diff + " days later";
             }
+            // Result: Friday (November 27, 5 days later)
         }
+        content += ")";
 
         var line = {
             buffer: buffer,
             date: new_date,
-            prefix: '\u001943\u2500\u2500',
+            prefix: '\u001943\u2500',
             tags_array: [],
             displayed: true,
             highlight: 0,