feat(rtt) : add SolidarityDayResolver (Pentecost Monday via computus)

src/Service/Rtt/SolidarityDayResolver.php

@@ -0,0 +1,43 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Service\Rtt;
+
+use DateTimeImmutable;
+
+/**
+ * Résout le jour de solidarité (Lundi de Pentecôte) d'une année.
+ *
+ * Pur et déterministe : Pâques via l'algorithme de Meeus/Jones/Butcher (calendrier
+ * grégorien), sans dépendance à l'extension calendar ni au réseau. Lundi de Pentecôte
+ * = dimanche de Pâques + 50 jours.
+ */
+final class SolidarityDayResolver
+{
+    public function pentecostMonday(int $year): DateTimeImmutable
+    {
+        return $this->easterSunday($year)->modify('+50 days');
+    }
+
+    private function easterSunday(int $year): DateTimeImmutable
+    {
+        $a = $year % 19;
+        $b = intdiv($year, 100);
+        $c = $year % 100;
+        $d = intdiv($b, 4);
+        $e = $b % 4;
+        $f = intdiv($b + 8, 25);
+        $g = intdiv($b - $f + 1, 3);
+        $h = (19 * $a + $b - $d - $g + 15) % 30;
+        $i = intdiv($c, 4);
+        $k = $c % 4;
+        $l = (32 + 2 * $e + 2 * $i - $h - $k) % 7;
+        $m = intdiv($a + 11 * $h + 22 * $l, 451);
+
+        $month = intdiv($h + $l - 7 * $m + 114, 31);
+        $day   = (($h + $l - 7 * $m + 114) % 31) + 1;
+
+        return new DateTimeImmutable(sprintf('%04d-%02d-%02d', $year, $month, $day));
+    }
+}

tests/Service/Rtt/SolidarityDayResolverTest.php

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+<?php
+
+declare(strict_types=1);
+
+namespace App\Tests\Service\Rtt;
+
+use App\Service\Rtt\SolidarityDayResolver;
+use PHPUnit\Framework\Attributes\DataProvider;
+use PHPUnit\Framework\TestCase;
+
+/**
+ * @internal
+ */
+final class SolidarityDayResolverTest extends TestCase
+{
+    /**
+     * Lundi de Pentecôte = dimanche de Pâques + 50 jours.
+     * 2024 : Pâques 31/03 → 20/05 ; 2025 : Pâques 20/04 → 09/06 ; 2026 : Pâques 05/04 → 25/05.
+     */
+    #[DataProvider('pentecostCases')]
+    public function testPentecostMonday(int $year, string $expected): void
+    {
+        $resolver = new SolidarityDayResolver();
+
+        self::assertSame($expected, $resolver->pentecostMonday($year)->format('Y-m-d'));
+    }
+
+    /**
+     * @return iterable<string, array{int, string}>
+     */
+    public static function pentecostCases(): iterable
+    {
+        yield '2024' => [2024, '2024-05-20'];
+
+        yield '2025' => [2025, '2025-06-09'];
+
+        yield '2026' => [2026, '2026-05-25'];
+    }
+}