Add frequency iteration logic with accompanying unit tests

Implemented `getRemainingIterations` in the `Frequency` enum to calculate remaining occurrences based on specified frequencies. Added comprehensive unit tests to ensure correct behavior for daily, weekly, monthly, quarterly, yearly, and one-time frequencies.

app/Enums/Frequency.php

@@ -3,6 +3,7 @@
 namespace App\Enums;
 
 use Filament\Support\Contracts\HasLabel;
+use Illuminate\Support\Carbon;
 
 enum Frequency: string implements HasLabel
 {
@@ -17,4 +18,20 @@ public function getLabel(): ?string
     {
         return $this->name;
     }
+
+    public function getRemainingIterations(Carbon $start, Carbon $end, int $iterationsLeft): int
+    {
+        $diff = match ($this->value) {
+            self::DAILY->value => $start->diffInDays($end),
+            self::WEEKLY->value => $start->diffInWeeks($end),
+            self::MONTHLY->value => $start->diffInMonths($end, true),
+            self::QUARTERLY->value => $start->diffInQuarters($end),
+            self::YEARLY->value => $start->diffInYears($end),
+            default => 1,
+        };
+
+        $diff = floor($diff);
+
+        return min($iterationsLeft, $diff);
+    }
 }

tests/Unit/Enums/FrequencyTest.php

@@ -0,0 +1,74 @@
+<?php
+
+use App\Enums\Frequency;
+use Illuminate\Support\Carbon;
+
+it('returns correct remaining occurrences for daily frequency', function () {
+    $start = Carbon::create(2023, 1, 1);
+    $end = Carbon::create(2023, 1, 10);
+    $iterationsLeft = 5;
+
+    $remainingOccurrences = Frequency::DAILY->getRemainingIterations($start, $end, $iterationsLeft);
+
+    expect($remainingOccurrences)->toEqual(5);
+});
+
+it('returns correct remaining occurrences for weekly frequency', function () {
+    $start = Carbon::create(2023, 1, 1);
+    $end = Carbon::create(2023, 2, 1); // 4 weeks
+    $iterationsLeft = 2;
+
+    $remainingOccurrences = Frequency::WEEKLY->getRemainingIterations($start, $end, $iterationsLeft);
+
+    expect($remainingOccurrences)->toEqual(2);
+});
+
+it('returns correct remaining occurrences for monthly frequency', function () {
+    $start = Carbon::create(2023, 1, 1);
+    $end = Carbon::create(2023, 6, 1); // 5 months
+    $iterationsLeft = 10;
+
+    $remainingOccurrences = Frequency::MONTHLY->getRemainingIterations($start, $end, $iterationsLeft);
+
+    expect($remainingOccurrences)->toEqual(5);
+});
+
+it('returns correct remaining occurrences for quarterly frequency', function () {
+    $start = Carbon::create(2023, 1, 1);
+    $end = Carbon::create(2024, 1, 1); // 4 quarters
+    $iterationsLeft = 3;
+
+    $remainingOccurrences = Frequency::QUARTERLY->getRemainingIterations($start, $end, $iterationsLeft);
+
+    expect($remainingOccurrences)->toEqual(3);
+});
+
+it('returns correct remaining occurrences for yearly frequency', function () {
+    $start = Carbon::create(2020, 1, 1);
+    $end = Carbon::create(2025, 1, 1); // 5 years
+    $iterationsLeft = 2;
+
+    $remainingOccurrences = Frequency::YEARLY->getRemainingIterations($start, $end, $iterationsLeft);
+
+    expect($remainingOccurrences)->toEqual(2);
+});
+
+it('returns one for once frequency', function () {
+    $start = Carbon::create(2023, 1, 1);
+    $end = Carbon::create(2023, 12, 31);
+    $iterationsLeft = 10;
+
+    $remainingOccurrences = Frequency::ONCE->getRemainingIterations($start, $end, $iterationsLeft);
+
+    expect($remainingOccurrences)->toEqual(1);
+});
+
+it('returns the minimum of iterations left or the differences', function () {
+    $start = Carbon::create(2023, 1, 1);
+    $end = Carbon::create(2023, 1, 5); // 4 days
+    $iterationsLeft = 2;
+
+    $remainingOccurrences = Frequency::DAILY->getRemainingIterations($start, $end, $iterationsLeft);
+
+    expect($remainingOccurrences)->toEqual(2);
+});