[fixed] more month event layout issues

src/utils/dates.js

@@ -106,16 +106,18 @@ let dates = Object.assign(dateMath, {
     )
   },
 
-  duration(start, end, unit){
+  duration(start, end, unit, firstOfWeek){
     if (unit === 'day') unit = 'date';
-    return Math.abs(dates[unit](start) - dates[unit](end))
+    return Math.abs(dates[unit](start, undefined, firstOfWeek) - dates[unit](end, undefined, firstOfWeek))
   },
 
   diff(dateA, dateB, unit){
     if (!unit)
       return Math.abs(+dateA - +dateB)
 
-    return Math.abs((+dateA / MILLI[unit]) - (+dateB / MILLI[unit]))
+    return Math.abs(
+      (+dates.startOf(dateA, unit) / MILLI[unit]) - (+dates.startOf(dateB, unit) / MILLI[unit])
+    )
   },
 
   week(date){

src/utils/eventLevels.js

@@ -10,21 +10,21 @@ import { accessor as get } from './accessors';
 // }
 
 export function eventSegments(event, first, last, { startAccessor, endAccessor, culture }){
-  let startOfWeek = localizer.startOfWeek(culture);
-  let start = dates.duration(first, dates.max(get(event, startAccessor), first), 'weekday', startOfWeek);
+  let slots = dates.diff(first, last, 'day')
+  let start = dates.max(get(event, startAccessor), first);
+  let end = dates.min(get(event, endAccessor), dates.add(last, 1, 'day'))
 
-  let span = Math.min(dates.duration(
-      dates.max(get(event, startAccessor), first)
-    , dates.min(get(event, endAccessor), dates.add(last, 1, 'day'))
-    , 'day'), 7);
+  let span = dates.diff(start, end, 'day');
 
-  span = Math.max(span, 1);
+  span = Math.min(Math.max(span, 1), slots);
+
+  let padding = dates.diff(first, start, 'day');
 
   return {
     event,
     span,
-    left: start + 1,
-    right: Math.max(start + span, 1)
+    left: padding + 1,
+    right: Math.max(padding + span, 1)
   }
 }