Merge pull request #55 from azuyalabs/easter_days

Fallback Calculation easter_days (when calendar extension is not loaded)
azuyalabs · Feb 6, 2017 · ee930a1 · ee930a1
2 parents c58dbbe + 6d8cc15
commit ee930a1
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Showing 14 changed files with 153 additions and 28 deletions.
diff --git a/src/Yasumi/Provider/ChristianHolidays.php b/src/Yasumi/Provider/ChristianHolidays.php
@@ -564,9 +564,17 @@ public function reformationDay($year, $timezone, $locale, $type = Holiday::TYPE_
      * Easter is a festival and holiday celebrating the resurrection of Jesus Christ from the dead. Easter is celebrated
      * on a date based on a certain number of days after March 21st.
      *
-     * This function uses the standard PHP 'easter_days'.
+     * This function uses the standard PHP 'easter_days' function if the calendar extension is enabled. In case the
+     * calendar function is not enabled, a fallback calculation has been implemented that is based on the same
+     * 'easter_days' c function.
      *
-     * @see easter_days
+     * Note: In calendrical calculations, frequently operations called integer division are used.
+     *
+     * @see  easter_days
+     *
+     * @link https://github.com/php/php-src/blob/c8aa6f3a9a3d2c114d0c5e0c9fdd0a465dbb54a5/ext/calendar/easter.c
+     * @link http://www.gmarts.org/index.php?go=415#EasterMallen
+     * @link http://www.tondering.dk/claus/cal/easter.php
      *
      * @param int    $year     the year for which Easter needs to be calculated
      * @param string $timezone the timezone in which Easter is celebrated
@@ -575,8 +583,55 @@ public function reformationDay($year, $timezone, $locale, $type = Holiday::TYPE_
      */
     protected function calculateEaster($year, $timezone)
     {
+        if (extension_loaded('calendar')) {
+            $easter_days = \easter_days($year);
+        } else {
+            $golden = (int)(($year % 19) + 1); // The Golden Number
+
+            // The Julian calendar applies to the original method from 326AD. The Gregorian calendar was first
+            // introduced in October 1582 in Italy. Easter algorithms using the Gregorian calendar apply to years
+            // 1583 AD to 4099 (A day adjustment is required in or shortly after 4100 AD).
+            // After 1752, most western churches have adopted the current algorithm.
+            if ($year <= 1752) {
+                $dom = ($year + (int)($year / 4) + 5) % 7; // The 'Dominical number' - finding a Sunday
+                if ($dom < 0) {
+                    $dom += 7;
+                }
+
+                $pfm = (3 - (11 * $golden) - 7) % 30; // Uncorrected date of the Paschal full moon
+                if ($pfm < 0) {
+                    $pfm += 30;
+                }
+            } else {
+                $dom = ($year + (int)($year / 4) - (int)($year / 100) + (int)($year / 400)) % 7; // The 'Dominical number' - finding a Sunday
+                if ($dom < 0) {
+                    $dom += 7;
+                }
+
+                $solar = (int)(($year - 1600) / 100) - (int)(($year - 1600) / 400); // The solar correction
+                $lunar = (int)(((int)(($year - 1400) / 100) * 8) / 25); // The lunar correction
+
+                $pfm = (3 - (11 * $golden) + $solar - $lunar) % 30; // Uncorrected date of the Paschal full moon
+                if ($pfm < 0) {
+                    $pfm += 30;
+                }
+            }
+
+            // Corrected date of the Paschal full moon, - days after 21st March
+            if (($pfm == 29) || ($pfm == 28 && $golden > 11)) {
+                --$pfm;
+            }
+
+            $tmp = (4 - $pfm - $dom) % 7;
+            if ($tmp < 0) {
+                $tmp += 7;
+            }
+
+            $easter_days = (int)($pfm + $tmp + 1); // Easter as the number of days after 21st March
+        }
+
         $easter = new DateTime("$year-3-21", new DateTimeZone($timezone));
-        $easter->add(new DateInterval('P' . \easter_days($year) . 'D'));
+        $easter->add(new DateInterval('P' . $easter_days . 'D'));
 
         return $easter;
     }

diff --git a/tests/Australia/EasterMondayTest.php b/tests/Australia/EasterMondayTest.php
@@ -53,8 +53,8 @@ public function HolidayDataProvider()
 
         for ($y = 0; $y < 50; $y++) {
             $year = $this->generateRandomYear();
-            $date = new DateTime("$year-3-21", new DateTimeZone($this->timezone));
-            $date->add(new DateInterval('P' . (easter_days($year) + 1) . 'D'));
+            $date = $this->calculateEaster($year, $this->timezone);
+            $date->add(new DateInterval('P1D'));
 
             $data[] = [$year, $date->format('Y-m-d')];
         }

diff --git a/tests/Australia/GoodFridayTest.php b/tests/Australia/GoodFridayTest.php
@@ -53,8 +53,7 @@ public function HolidayDataProvider()
 
         for ($y = 0; $y < 50; $y++) {
             $year = $this->generateRandomYear();
-            $date = new DateTime("$year-3-21", new DateTimeZone($this->timezone));
-            $date->add(new DateInterval('P' . easter_days($year) . 'D'));
+            $date = $this->calculateEaster($year, $this->timezone);
             $date->sub(new DateInterval('P2D'));
             $data[] = [$year, $date->format('Y-m-d')];
         }

diff --git a/tests/Ireland/EasterMondayTest.php b/tests/Ireland/EasterMondayTest.php
@@ -53,8 +53,8 @@ public function HolidayDataProvider()
 
         for ($y = 0; $y < self::TEST_ITERATIONS; $y++) {
             $year = $this->generateRandomYear();
-            $date = new DateTime("$year-3-21", new DateTimeZone(self::TIMEZONE));
-            $date->add(new DateInterval('P' . (easter_days($year) + 1) . 'D'));
+            $date = $this->calculateEaster($year, self::TIMEZONE);
+            $date->add(new DateInterval('P1D'));
 
             $data[] = [$year, $date->format('Y-m-d')];
         }

diff --git a/tests/Ireland/EasterTest.php b/tests/Ireland/EasterTest.php
@@ -12,7 +12,6 @@
 
 namespace Yasumi\tests\Ireland;
 
-use DateInterval;
 use DateTime;
 use DateTimeZone;
 use Yasumi\Holiday;
@@ -53,8 +52,7 @@ public function HolidayDataProvider()
 
         for ($y = 0; $y < self::TEST_ITERATIONS; $y++) {
             $year = $this->generateRandomYear();
-            $date = new DateTime("$year-3-21", new DateTimeZone(self::TIMEZONE));
-            $date->add(new DateInterval('P' . easter_days($year) . 'D'));
+            $date = $this->calculateEaster($year, self::TIMEZONE);
 
             $data[] = [$year, $date->format('Y-m-d')];
         }

diff --git a/tests/Ireland/GoodFridayTest.php b/tests/Ireland/GoodFridayTest.php
@@ -53,8 +53,7 @@ public function HolidayDataProvider()
 
         for ($y = 0; $y < self::TEST_ITERATIONS; $y++) {
             $year = $this->generateRandomYear();
-            $date = new DateTime("$year-3-21", new DateTimeZone(self::TIMEZONE));
-            $date->add(new DateInterval('P' . easter_days($year) . 'D'));
+            $date = $this->calculateEaster($year, self::TIMEZONE);
             $date->sub(new DateInterval('P2D'));
             $data[] = [$year, $date->format('Y-m-d')];
         }

diff --git a/tests/Ireland/PentecostTest.php b/tests/Ireland/PentecostTest.php
@@ -54,8 +54,7 @@ public function HolidayDataProvider()
         //for ($y = 0; $y < self::TEST_ITERATIONS; $y++) {
         for ($y = 0; $y < 2; $y++) {
             $year = $this->generateRandomYear();
-            $date = new DateTime("$year-3-21", new DateTimeZone(self::TIMEZONE));
-            $date->add(new DateInterval('P' . \easter_days($year) . 'D'));
+            $date = $this->calculateEaster($year, self::TIMEZONE);
             $date->add(new DateInterval('P49D'));
             $data[] = [$year, $date->format('Y-m-d')];
         }

diff --git a/tests/Ireland/pentecostMondayTest.php b/tests/Ireland/pentecostMondayTest.php
@@ -58,8 +58,7 @@ public function HolidayDataProvider()
 
         for ($y = 0; $y < self::TEST_ITERATIONS; $y++) {
             $year = $this->generateRandomYear(1000, self::ABOLISHMENT_YEAR);
-            $date = new DateTime("$year-3-21", new DateTimeZone(self::TIMEZONE));
-            $date->add(new DateInterval('P' . \easter_days($year) . 'D'));
+            $date = $this->calculateEaster($year, self::TIMEZONE);
             $date->add(new DateInterval('P50D'));
             $data[] = [$year, $date->format('Y-m-d')];
         }

diff --git a/tests/NewZealand/EasterMondayTest.php b/tests/NewZealand/EasterMondayTest.php
@@ -53,8 +53,8 @@ public function HolidayDataProvider()
 
         for ($y = 0; $y < 50; $y++) {
             $year = $this->generateRandomYear();
-            $date = new DateTime("$year-3-21", new DateTimeZone(self::TIMEZONE));
-            $date->add(new DateInterval('P' . (easter_days($year) + 1) . 'D'));
+            $date = $this->calculateEaster($year, self::TIMEZONE);
+            $date->add(new DateInterval('P1D'));
 
             $data[] = [$year, $date->format('Y-m-d')];
         }

diff --git a/tests/NewZealand/GoodFridayTest.php b/tests/NewZealand/GoodFridayTest.php
@@ -53,8 +53,7 @@ public function HolidayDataProvider()
 
         for ($y = 0; $y < 50; $y++) {
             $year = $this->generateRandomYear();
-            $date = new DateTime("$year-3-21", new DateTimeZone(self::TIMEZONE));
-            $date->add(new DateInterval('P' . easter_days($year) . 'D'));
+            $date = $this->calculateEaster($year, self::TIMEZONE);
             $date->sub(new DateInterval('P2D'));
             $data[] = [$year, $date->format('Y-m-d')];
         }

diff --git a/tests/SouthAfrica/FamilyDayTest.php b/tests/SouthAfrica/FamilyDayTest.php
@@ -62,8 +62,7 @@ public function HolidayDataProvider()
 
         for ($y = 0; $y < 50; $y++) {
             $year = $this->generateRandomYear(self::ESTABLISHMENT_YEAR);
-            $date = new DateTime("$year-3-21", new DateTimeZone(self::TIMEZONE));
-            $date->add(new DateInterval('P' . easter_days($year) . 'D'));
+            $date = $this->calculateEaster($year, self::TIMEZONE);
             $date->add(new DateInterval('P1D'));
             $data[] = [$year, $date->format('Y-m-d')];
         }

diff --git a/tests/SouthAfrica/GoodFridayTest.php b/tests/SouthAfrica/GoodFridayTest.php
@@ -62,8 +62,7 @@ public function HolidayDataProvider()
 
         for ($y = 0; $y < 50; $y++) {
             $year = $this->generateRandomYear(self::ESTABLISHMENT_YEAR);
-            $date = new DateTime("$year-3-21", new DateTimeZone(self::TIMEZONE));
-            $date->add(new DateInterval('P' . easter_days($year) . 'D'));
+            $date = $this->calculateEaster($year, self::TIMEZONE);
             $date->sub(new DateInterval('P2D'));
             $data[] = [$year, $date->format('Y-m-d')];
         }

diff --git a/tests/UnitedKingdom/EasterMondayTest.php b/tests/UnitedKingdom/EasterMondayTest.php
@@ -53,8 +53,8 @@ public function HolidayDataProvider()
 
         for ($y = 0; $y < 50; $y++) {
             $year = $this->generateRandomYear();
-            $date = new DateTime("$year-3-21", new DateTimeZone(self::TIMEZONE));
-            $date->add(new DateInterval('P' . (easter_days($year) + 1) . 'D'));
+            $date = $this->calculateEaster($year, self::TIMEZONE);
+            $date->add(new DateInterval('P1D'));
 
             $data[] = [$year, $date->format('Y-m-d')];
         }

diff --git a/tests/YasumiBase.php b/tests/YasumiBase.php
@@ -12,6 +12,7 @@
 
 namespace Yasumi\tests;
 
+use DateInterval;
 use DateTime;
 use DateTimeZone;
 use Faker\Factory as Faker;
@@ -219,4 +220,82 @@ public function generateRandomYear($lowerLimit = 1000, $upperLimit = 9999)
     {
         return (int)Faker::create()->numberBetween($lowerLimit, $upperLimit);
     }
+
+    /**
+     * Calculates the date for Easter.
+     *
+     * Easter is a festival and holiday celebrating the resurrection of Jesus Christ from the dead. Easter is celebrated
+     * on a date based on a certain number of days after March 21st.
+     *
+     * This function uses the standard PHP 'easter_days' function if the calendar extension is enabled. In case the
+     * calendar function is not enabled, a fallback calculation has been implemented that is based on the same
+     * 'easter_days' c function.
+     *
+     * Note: In calendrical calculations, frequently operations called integer division are used.
+     *
+     * @see  easter_days
+     *
+     * @link https://github.com/php/php-src/blob/c8aa6f3a9a3d2c114d0c5e0c9fdd0a465dbb54a5/ext/calendar/easter.c
+     * @link http://www.gmarts.org/index.php?go=415#EasterMallen
+     * @link http://www.tondering.dk/claus/cal/easter.php
+     *
+     * @param int    $year     the year for which Easter needs to be calculated
+     * @param string $timezone the timezone in which Easter is celebrated
+     *
+     * @return \DateTime date of Easter
+     */
+    protected function calculateEaster($year, $timezone)
+    {
+        if (extension_loaded('calendar')) {
+            $easter_days = \easter_days($year);
+        } else {
+            $golden = (int)(($year % 19) + 1); // The Golden Number
+
+            // The Julian calendar applies to the original method from 326AD. The Gregorian calendar was first
+            // introduced in October 1582 in Italy. Easter algorithms using the Gregorian calendar apply to years
+            // 1583 AD to 4099 (A day adjustment is required in or shortly after 4100 AD).
+            // After 1752, most western churches have adopted the current algorithm.
+            if ($year <= 1752) {
+                $dom = ($year + (int)($year / 4) + 5) % 7; // The 'Dominical number' - finding a Sunday
+                if ($dom < 0) {
+                    $dom += 7;
+                }
+
+                $pfm = (3 - (11 * $golden) - 7) % 30; // Uncorrected date of the Paschal full moon
+                if ($pfm < 0) {
+                    $pfm += 30;
+                }
+            } else {
+                $dom = ($year + (int)($year / 4) - (int)($year / 100) + (int)($year / 400)) % 7; // The 'Dominical number' - finding a Sunday
+                if ($dom < 0) {
+                    $dom += 7;
+                }
+
+                $solar = (int)(($year - 1600) / 100) - (int)(($year - 1600) / 400); // The solar correction
+                $lunar = (int)(((int)(($year - 1400) / 100) * 8) / 25); // The lunar correction
+
+                $pfm = (3 - (11 * $golden) + $solar - $lunar) % 30; // Uncorrected date of the Paschal full moon
+                if ($pfm < 0) {
+                    $pfm += 30;
+                }
+            }
+
+            // Corrected date of the Paschal full moon, - days after 21st March
+            if (($pfm == 29) || ($pfm == 28 && $golden > 11)) {
+                --$pfm;
+            }
+
+            $tmp = (4 - $pfm - $dom) % 7;
+            if ($tmp < 0) {
+                $tmp += 7;
+            }
+
+            $easter_days = (int)($pfm + $tmp + 1); // Easter as the number of days after 21st March
+        }
+
+        $easter = new DateTime("$year-3-21", new DateTimeZone($timezone));
+        $easter->add(new DateInterval('P' . $easter_days . 'D'));
+
+        return $easter;
+    }
 }