fix: double months on web + wrong layout when range was last day or first day

Author: RichardLindhout

src/Date/Calendar.tsx

@@ -117,26 +117,24 @@ function Calendar(props: CalendarSingleProps | CalendarRangeProps) {
       <Swiper
         selectedYear={selectedYear}
         scrollMode={scrollMode}
-        renderItem={({ index }) => {
-          return (
-            <Month
-              mode={mode}
-              key={index}
-              index={index}
-              startDate={startDate}
-              endDate={endDate}
-              date={date}
-              onPressYear={onPressYear}
-              selectedYear={selectedYear}
-              selectingYear={selectingYear}
-              onPressDate={onPressDate}
-              scrollMode={scrollMode}
-              primaryColor={theme.colors.primary}
-              selectColor={selectColor}
-              roundness={theme.roundness}
-            />
-          )
-        }}
+        renderItem={({ index }) => (
+          <Month
+            mode={mode}
+            key={index}
+            index={index}
+            startDate={startDate}
+            endDate={endDate}
+            date={date}
+            onPressYear={onPressYear}
+            selectedYear={selectedYear}
+            selectingYear={selectingYear}
+            onPressDate={onPressDate}
+            scrollMode={scrollMode}
+            primaryColor={theme.colors.primary}
+            selectColor={selectColor}
+            roundness={theme.roundness}
+          />
+        )}
         renderHeader={({ onPrev, onNext }) => (
           <CalendarHeader
             onPrev={onPrev}

src/Date/Month.tsx

@@ -143,8 +143,9 @@ function Month({
                 })
               : false
 
-          let leftCrop: boolean = selectedStartDay || dayOfMonth === 1
-          let rightCrop: boolean = selectedEndDay || dayOfMonth === daysInMonth
+          let leftCrop: boolean = selectedStartDay || dayOfMonth === 0
+          let rightCrop: boolean =
+            selectedEndDay || dayOfMonth - 1 === daysInMonth
 
           if (dayIndex === 0 && !selectedStartDay) {
             leftCrop = false

src/Date/dateUtils.tsx

@@ -3,8 +3,18 @@ export function dateToUnix(d: Date): number {
 }
 
 export function addMonths(date: Date, count: number) {
-  const dt = new Date(date.getFullYear(), date.getMonth(), 0)
-  return new Date(dt.setMonth(dt.getMonth() + count))
+  let n = date.getDate()
+  let n2 = new Date(date.getTime())
+  n2.setDate(1)
+  n2.setMonth(n2.getMonth() + count)
+  n2.setDate(
+    Math.min(
+      n,
+      getDaysInMonth({ year: n2.getFullYear(), month: n2.getMonth() })
+    )
+  )
+
+  return n2
 }
 
 // https://stackoverflow.com/a/1185068/2508481