Add Australian Holidays

These are the national holidays (for the majority of states)

src/Countries/Australia.php

@@ -0,0 +1,39 @@
+<?php
+
+namespace Spatie\Holidays\Countries;
+
+use Carbon\CarbonImmutable;
+
+class Australia extends Country
+{
+    public function countryCode(): string
+    {
+        return 'au';
+    }
+
+    /** @return array<string, CarbonImmutable> */
+    protected function allHolidays(int $year): array
+    {
+        return array_merge([
+            'New Year\'s Day' => '01-01',
+            'Australia Day' => '01-26',
+            'Anzac Day' => '04-25',
+            'Christmas Day' => '12-25',
+            'Boxing Day' => '12-26',
+        ], $this->variableHolidays($year));
+    }
+
+    /** @return array<string, CarbonImmutable> */
+    protected function variableHolidays(int $year): array
+    {
+        $easter = CarbonImmutable::createFromTimestamp(easter_date($year))->setTimezone('Australia/Sydney');
+
+        return [
+            'Queen\'s Birthday' => CarbonImmutable::parse('second monday of june'),
+            'Good Friday' => $easter->subDays(2),
+            'Easter Saturday' => $easter->subDay(),
+            'Easter Sunday' => $easter,
+            'Easter Monday' => $easter->addDay(),
+        ];
+    }
+}

tests/.pest/snapshots/Countries/AustraliaTest/it_can_calculate_australian_holidays.snap

@@ -0,0 +1,42 @@
+[
+    {
+        "name": "New Year's Day",
+        "date": "2024-01-01"
+    },
+    {
+        "name": "Australia Day",
+        "date": "2024-01-26"
+    },
+    {
+        "name": "Good Friday",
+        "date": "2024-03-29"
+    },
+    {
+        "name": "Easter Saturday",
+        "date": "2024-03-30"
+    },
+    {
+        "name": "Easter Sunday",
+        "date": "2024-03-31"
+    },
+    {
+        "name": "Easter Monday",
+        "date": "2024-04-01"
+    },
+    {
+        "name": "Anzac Day",
+        "date": "2024-04-25"
+    },
+    {
+        "name": "Queen's Birthday",
+        "date": "2024-06-10"
+    },
+    {
+        "name": "Christmas Day",
+        "date": "2024-12-25"
+    },
+    {
+        "name": "Boxing Day",
+        "date": "2024-12-26"
+    }
+]

tests/Countries/AustraliaTest.php

@@ -0,0 +1,18 @@
+<?php
+
+namespace Spatie\Holidays\Tests\Countries;
+
+use Carbon\CarbonImmutable;
+use Spatie\Holidays\Holidays;
+
+it('can calculate australian holidays', function () {
+    CarbonImmutable::setTestNowAndTimezone('2024-01-01', 'Australia/Melbourne');
+
+    $holidays = Holidays::for(country: 'au')->get();
+
+    expect($holidays)
+        ->toBeArray()
+        ->not()->toBeEmpty();
+
+    expect(formatDates($holidays))->toMatchSnapshot();
+});