function ad2bs(adDate) { // AD to BS conversion constants const BS_START_YEAR = 2000; const BS_START_MONTH = 9; const BS_START_DAY = 17; const AD_START_YEAR = 1943; const AD_START_MONTH = 4; const AD_START_DAY = 14; const TOTAL_BS_MONTHS = 12; const TOTAL_AD_MONTHS = 12; const DAYS_IN_MONTH = [32, 32, 31, 32, 31, 31, 32, 32, 31, 30, 31, 30, 31]; const MONTH_NAMES = [ 'Baishakh', 'Jestha', 'Ashadh', 'Shrawan', 'Bhadra', 'Ashwin', 'Kartik', 'Mangsir', 'Poush', 'Magh', 'Falgun', 'Chaitra' ]; // Calculate the number of days between the AD start date and the input AD date const adDateObj = new Date(adDate); const adYear = adDateObj.getFullYear(); const adMonth = adDateObj.getMonth() + 1; const adDay = adDateObj.getDate(); const totalDaysInAD = Math.floor((adYear - AD_START_YEAR) * 365.25) + Math.floor((adMonth - AD_START_MONTH) * 30.44) + (adDay - AD_START_DAY); // Calculate the number of days between the BS start date and the input AD date const totalDaysInBS = totalDaysInAD + Math.floor((BS_START_YEAR - adYear) * 365.25) + Math.floor((BS_START_MONTH - adMonth) * 30.44) + (BS_START_DAY - adDay); // Calculate the BS year, month, and day from the total number of days let bsYear = BS_START_YEAR; let bsMonth = BS_START_MONTH; let bsDay = BS_START_DAY; let remainingDays = totalDaysInBS; while (remainingDays !== 0) { // Calculate the number of days in the current BS month const daysInMonth = DAYS_IN_MONTH[bsMonth - 1]; // If the remaining days are less than the number of days in the current month, // we have found the BS year, month, and day corresponding to the input AD date if (remainingDays < daysInMonth) { bsDay += remainingDays; break; } // Otherwise, subtract the number of days in the current month from the remaining days, // and move on to the next BS month remainingDays -= daysInMonth; bsMonth++; // If we have reached the end of the current BS year, move on to the next BS year if (bsMonth > TOTAL_BS_MONTHS) { bsYear++; bsMonth = 1; } } // Return the BS date as a string in the format "YYYY-MM-DD" const bsDateStr = `${bsYear}-${bsMonth.toString().padStart(2, '0')}-${bsDay.toString().padStart(2, '0')}`; return bsDateStr; }

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