fix(reports): correct date calculation in AccountReport

fyo.getValue(*, 'fiscalYear{Start,End}') returns a javascript Date object
that encodes the filcal year as local time (01-01 and 12-31 at midnight).
This date must not be converted to UTC else east timezones will return
the day before (12-31 and 12-30). Use locale time values instead.

When computing the monthly/quaterly/half yearly time periods, correct the
dates in the particular case where the last day of the month is selected
as reference date (yields series 12-31 11-30 10-31 09-30 ...) instead of
(12-31 11-30 10-30 09-30 ...).

reports/AccountReport.ts

@@ -236,6 +236,17 @@ export abstract class AccountReport extends LedgerReport {
     return null;
   }
 
+  // Fix arythmetic on dates when adding or substracting months. If the
+  // reference date was the last day in month, ensure that the resulting date is
+  // also the last day.
+  _fixMonthsJump(refDate: DateTime, date: DateTime): DateTime {
+    if (refDate.day == refDate.daysInMonth && date.day != date.daysInMonth) {
+      return date.set({day: date.daysInMonth})
+    } else {
+      return date
+    }
+  }
+
   async _getDateRanges(): Promise<DateRange[]> {
     const endpoints = await this._getFromAndToDates();
     const fromDate = DateTime.fromISO(endpoints.fromDate);
@@ -252,7 +263,7 @@ export abstract class AccountReport extends LedgerReport {
 
     const months: number = monthsMap[this.periodicity];
     const dateRanges: DateRange[] = [
-      { toDate, fromDate: toDate.minus({ months }) },
+      { toDate, fromDate: this._fixMonthsJump(toDate, toDate.minus({ months })) },
     ];
 
     let count = this.count ?? 1;
@@ -264,7 +275,7 @@ export abstract class AccountReport extends LedgerReport {
       const lastRange = dateRanges.at(-1)!;
       dateRanges.push({
         toDate: lastRange.fromDate,
-        fromDate: lastRange.fromDate.minus({ months }),
+        fromDate: this._fixMonthsJump(toDate, lastRange.fromDate.minus({ months })),
       });
     }
 
@@ -445,14 +456,15 @@ export async function getFiscalEndpoints(
 
   const fromDate = [
     fromYear,
-    fys.toISOString().split('T')[0].split('-').slice(1),
-  ]
-    .flat()
-    .join('-');
-
-  const toDate = [toYear, fye.toISOString().split('T')[0].split('-').slice(1)]
-    .flat()
-    .join('-');
+    (fys.getMonth() + 1).toString().padStart(2, '0'),
+    fys.getDate().toString().padStart(2, '0')
+  ].join('-');
+
+  const toDate = [
+    toYear,
+    (fye.getMonth() + 1).toString().padStart(2, '0'),
+    fye.getDate().toString().padStart(2, '0')
+  ].join('-');
 
   return { fromDate, toDate };
 }