feat: Update Bangladesh holiday calculations

- Added new holidays to the Bangladesh holiday calculations.
- Synced holiday calculations with Hijri and Bangla calendars.
- Handles holiday calculations for Bangladesh including:
  * Islamic holidays (using Hijri calendar)
  * Hindu festivals (using lunar calendar)
  * Buddhist festivals (using lunar calendar)
  * National holidays (using Gregorian calendar)

lang/bangladesh/bn/holidays.json

@@ -1,10 +1,25 @@
 {
-    "International Mother Language Day": "Antorjatik Matribhasha Dibos",
-    "Birthday of Sheikh Mujibur Rahman": "Shekh Mujibur Rahmaner Jonmodin",
-    "Independence Day": "Swadhinota Dibos",
-    "Bengali New Year": "Bangla Noboborsho",
-    "May Day": "Antorjatik Shrom Dibos",
-    "National Mourning Day": "Jatiyo Shok Dibos",
-    "Victory Day": "Bijoy Dibos",
-    "Christmas Day": "Borodin"
-}
+    "International Mother Language Day": "শহীদ দিবস",
+    "Independence Day": "স্বাধীনতা দিবস",
+    "May Day": "মে দিবস",
+    "National Mourning Day": "জাতীয় শোক দিবস",
+    "Victory Day": "বিজয় দিবস",
+    "Christmas Day": "বড়দিন",
+    "Shab-e-Barat": "শবে বরাত",
+    "Shab-e-Qadr": "শবে কদর",
+    "Shab-e-Meraj": "শবে মেরাজ",
+    "Eid ul-Fitr": "ঈদ-উল-ফিতর",
+    "Eid ul-Fitr Eve": "ঈদ-উল-ফিতরের আগের দিন",
+    "Eid ul-Fitr Holiday": "ঈদ-উল-ফিতরের ছুটি",
+    "Eid ul-Adha": "ঈদ-উল-আযহা",
+    "Eid ul-Adha Eve": "ঈদ-উল-আযহার আগের দিন",
+    "Eid ul-Adha Holiday": "ঈদ-উল-আযহার ছুটি",
+    "Ashura": "আশুরা",
+    "Eid-e-Miladunnabi": "ঈদে মিলাদুন্নবী",
+    "Pohela Boishakh": "পহেলা বৈশাখ",
+    "Buddha Purnima": "বুদ্ধ পূর্ণিমা",
+    "Jonmashtomi": "জন্মাষ্টমী",
+    "Durga Puja": "দুর্গা পূজা",
+    "Birthday of Sheikh Mujibur Rahman": "শেখ মুজিবুর রহমানের জন্মদিন",
+    "Bengali New Year": "বাংলা নববর্ষ"
+}

src/Calendars/BangladeshiCalander.php

@@ -0,0 +1,261 @@
+<?php
+
+namespace Spatie\Holidays\Calendars;
+
+use Carbon\CarbonImmutable;
+use Carbon\CarbonPeriod;
+use Spatie\Holidays\Countries\Country;
+
+/**
+ * Handles holiday calculations for Bangladesh including:
+ * - Islamic holidays (using Hijri calendar)
+ * - Hindu festivals (using lunar calendar)
+ * - Buddhist festivals (using lunar calendar)
+ * - National holidays (using Gregorian calendar)
+ * 
+ * @mixin Country 
+ * @property string $islamicCalendarTimezone
+ */
+trait BangladeshiCalander
+{
+    use IslamicCalendar {
+        IslamicCalendar::setIslamicCalendarTimezone as private parentSetIslamicCalendarTimezone;
+    }
+
+    /*
+    |--------------------------------------------------------------------------
+    | Islamic Holiday Calculations
+    |--------------------------------------------------------------------------
+    */
+
+    /** @return array<CarbonPeriod> */
+    protected function shabEBarat(int $year): array
+    {
+        return $this->getIslamicHoliday(
+            month: self::ISLAMIC_MONTHS['SHABAN'],
+            day: '15',
+            year: $year
+        );
+    }
+
+    /** @return array<CarbonPeriod> */
+    protected function shabEQadr(int $year): array
+    {
+        return $this->getIslamicHoliday(
+            month: self::ISLAMIC_MONTHS['RAMADAN'],
+            day: '27',
+            year: $year
+        );
+    }
+
+    /** @return array<CarbonPeriod> */
+    protected function eidUlFitr(int $year): array
+    {
+        return $this->getIslamicHoliday(
+            month: self::ISLAMIC_MONTHS['SHAWWAL'],
+            day: '01',
+            year: $year,
+            daysBeforeAfter: [2, 2] // 2 days before and 2 days after
+        );
+    }
+
+    /** @return array<CarbonPeriod> */
+    protected function eidUlAdha(int $year): array
+    {
+        return $this->getIslamicHoliday(
+            month: self::ISLAMIC_MONTHS['DHU_AL_HIJJAH'],
+            day: '10',
+            year: $year,
+            daysBeforeAfter: [2, 3] // 2 days before and 3 days after
+        );
+    }
+
+    /** @return array<CarbonPeriod> */
+    protected function eideMiladunnabi(int $year): array
+    {
+        return $this->getIslamicHoliday(
+            month: self::ISLAMIC_MONTHS['RABI_AL_AWWAL'],
+            day: '12',
+            year: $year
+        );
+    }
+
+    /** @return array<CarbonPeriod> */
+    protected function ashura(int $year): array
+    {
+        return $this->getIslamicHoliday(
+            month: self::ISLAMIC_MONTHS['MUHARRAM'],
+            day: '10',
+            year: $year
+        );
+    }
+
+    /** @return array<CarbonPeriod> */
+    protected function shabEMeraj(int $year): array
+    {
+        return $this->getIslamicHoliday(
+            month: self::ISLAMIC_MONTHS['RAJAB'],
+            day: '27',
+            year: $year
+        );
+    }
+
+    /*
+    |--------------------------------------------------------------------------
+    | Bengali Calendar Holiday Calculations
+    |--------------------------------------------------------------------------
+    */
+
+    /** @return array<CarbonPeriod> */
+    protected function pohela_boishakh(int $year): array
+    {
+        // Bengali New Year is typically April 14
+        // Handles leap year adjustments
+        $date = CarbonImmutable::create($year, 4, 14);
+        if ($date->isLeapYear() && $date->month > 2) {
+            $date = $date->addDay();
+        }
+
+        return [$this->createPeriod($date->format('m-d'), $year, 1)];
+    }
+
+    /*
+    |--------------------------------------------------------------------------
+    | Hindu and Buddhist Holiday Calculations
+    |--------------------------------------------------------------------------
+    */
+
+    /** @return array<CarbonPeriod> */
+    protected function buddhaPurnima(int $year): array
+    {
+        // Calculate first full moon day of May
+        $baseDate = CarbonImmutable::create($year, 5, 1);
+        $fullMoonDate = $this->findNearestFullMoon($baseDate);
+
+        return [$this->createPeriod($fullMoonDate->format('m-d'), $year, 1)];
+    }
+
+    /** @return array<CarbonPeriod> */
+    protected function jonmashtomi(int $year): array
+    {
+        // Krishna Janmashtami falls on the eighth day of the dark fortnight
+        $baseDate = CarbonImmutable::create($year, 8, 15);
+        $ashtamiDate = $this->calculateAshtamiDate($baseDate);
+
+        return [$this->createPeriod($ashtamiDate->format('m-d'), $year, 1)];
+    }
+
+    /** @return array<CarbonPeriod> */
+    protected function durgaPuja(int $year): array
+    {
+        // Durga Puja's main days (Ashtami and Navami)
+        $baseDate = CarbonImmutable::create($year, 10, 15);
+        $ashtamiDate = $this->calculateAshtamiDate($baseDate);
+
+        return [$this->createPeriod($ashtamiDate->format('m-d'), $year, 2)];
+    }
+
+    /*
+    |--------------------------------------------------------------------------
+    | Helper Methods
+    |--------------------------------------------------------------------------
+    */
+
+    /**
+     * Helper method to calculate Islamic holiday dates
+     * 
+     * @param string $month Islamic month number
+     * @param string $day Day of the month
+     * @param int $year Gregorian year
+     * @param array<int> $daysBeforeAfter [daysBefore, daysAfter]
+     * @return array<CarbonPeriod>
+     */
+    private function getIslamicHoliday(
+        string $month,
+        string $day,
+        int $year,
+        array $daysBeforeAfter = [0, 0]
+    ): array {
+        $date = $this->islamicToGregorianDate("$month-$day", $year);
+
+        if (!empty($daysBeforeAfter)) {
+            $date = $date->subDays($daysBeforeAfter[0]);
+            $totalDays = 1 + $daysBeforeAfter[0] + $daysBeforeAfter[1];
+        } else {
+            $totalDays = 1;
+        }
+
+        return [$this->createPeriod($date->format('m-d'), $year, $totalDays)];
+    }
+
+    /**
+     * Calculate lunar phase (0 = new moon, 0.5 = full moon)
+     */
+    private function getLunarPhase(CarbonImmutable $date): float
+    {
+        $year = $date->year;
+        $month = $date->month;
+        $day = $date->day;
+
+        $c = $date->getPreciseTimestamp() / 86400;
+        $e = $c - 2451550.1;
+        $phase = $e / 29.530588853;
+
+        return $phase - floor($phase);
+    }
+
+    /**
+     * Find the nearest full moon to a given date
+     */
+    private function findNearestFullMoon(CarbonImmutable $targetDate): CarbonImmutable
+    {
+        $date = $targetDate->copy();
+        $closestDate = $date;
+        $closestDiff = 1;
+
+        // Check 15 days before and after
+        for ($i = -15; $i <= 15; $i++) {
+            $checkDate = $date->addDays($i);
+            $phase = $this->getLunarPhase($checkDate);
+            $diff = abs($phase - 0.5);
+
+            if ($diff < $closestDiff) {
+                $closestDiff = $diff;
+                $closestDate = $checkDate;
+            }
+        }
+
+        return $closestDate;
+    }
+
+    /**
+     * Calculate Ashtami (eighth day) date for Hindu festivals
+     */
+    private function calculateAshtamiDate(CarbonImmutable $baseDate): CarbonImmutable
+    {
+        $newMoon = $this->findNearestNewMoon($baseDate);
+        return $newMoon->addDays(8);
+    }
+
+    /**
+     * Find the nearest new moon to a given date
+     */
+    private function findNearestNewMoon(CarbonImmutable $date): CarbonImmutable
+    {
+        $closestDate = $date;
+        $closestDiff = 1;
+
+        for ($i = -15; $i <= 15; $i++) {
+            $checkDate = $date->addDays($i);
+            $phase = $this->getLunarPhase($checkDate);
+            $diff = min($phase, 1 - $phase);
+
+            if ($diff < $closestDiff) {
+                $closestDiff = $diff;
+                $closestDate = $checkDate;
+            }
+        }
+
+        return $closestDate;
+    }
+}