Rejestr wydatków miesięcznych

{
  "expenses": [
    {
      "id": 1,
      "amount": 45.50,
      "category": "jedzenie",
      "date": "2026-02-10",
      "description": "Zakupy w Biedronce",
      "created_at": "2026-02-10 18:30:00"
    },
    {
      "id": 2,
      "amount": 150.00,
      "category": "transport",
      "date": "2026-02-11",
      "description": "Bilet miesięczny",
      "created_at": "2026-02-11 08:00:00"
    },
    {
      "id": 3,
      "amount": 89.99,
      "category": "rozrywka",
      "date": "2026-02-12",
      "description": "Netflix + Spotify",
      "created_at": "2026-02-12 20:00:00"
    },
    {
      "id": 4,
      "amount": 250.00,
      "category": "rachunki",
      "date": "2026-02-15",
      "description": "Prąd",
      "created_at": "2026-02-15 10:30:00"
    }
  ]
}

$amount = filter_var($_POST['amount'] ?? '', FILTER_VALIDATE_FLOAT);
$category = $_POST['category'] ?? '';
$date = $_POST['date'] ?? date('Y-m-d');

if ($amount === false || $amount <= 0) {
    $errors[] = "Kwota musi być liczbą dodatnią";
}

if ($amount > 100000) {
    $errors[] = "Kwota wydaje się zbyt duża";
}

$validCategories = ['jedzenie', 'transport', 'rozrywka', 'rachunki', 'zakupy', 'zdrowie', 'inne'];
if (!in_array($category, $validCategories)) {
    $errors[] = "Wybierz poprawną kategorię";
}

// Walidacja daty (nie z przyszłości)
if ($date > date('Y-m-d')) {
    $errors[] = "Data nie może być z przyszłości";
}

function getCategories(): array {
    return [
        'jedzenie' => ['label' => 'Jedzenie', 'icon' => '🍕', 'color' => '#e74c3c'],
        'transport' => ['label' => 'Transport', 'icon' => '🚌', 'color' => '#3498db'],
        'rozrywka' => ['label' => 'Rozrywka', 'icon' => '🎬', 'color' => '#9b59b6'],
        'rachunki' => ['label' => 'Rachunki', 'icon' => '💡', 'color' => '#f39c12'],
        'zakupy' => ['label' => 'Zakupy', 'icon' => '🛒', 'color' => '#2ecc71'],
        'zdrowie' => ['label' => 'Zdrowie', 'icon' => '💊', 'color' => '#1abc9c'],
        'inne' => ['label' => 'Inne', 'icon' => '📦', 'color' => '#95a5a6'],
    ];
}

function getCategoryInfo(string $category): array {
    $categories = getCategories();
    return $categories[$category] ?? $categories['inne'];
}

function filterByMonth(array $expenses, int $year, int $month): array {
    return array_filter($expenses, function($expense) use ($year, $month) {
        $expenseDate = strtotime($expense['date']);
        return date('Y', $expenseDate) == $year && date('n', $expenseDate) == $month;
    });
}

function getAvailableMonths(array $expenses): array {
    $months = [];

    foreach ($expenses as $expense) {
        $yearMonth = date('Y-m', strtotime($expense['date']));
        if (!in_array($yearMonth, $months)) {
            $months[] = $yearMonth;
        }
    }

    rsort($months); // Najnowsze pierwsze
    return $months;
}

function formatMonth(string $yearMonth): string {
    $monthNames = [
        '01' => 'Styczeń', '02' => 'Luty', '03' => 'Marzec',
        '04' => 'Kwiecień', '05' => 'Maj', '06' => 'Czerwiec',
        '07' => 'Lipiec', '08' => 'Sierpień', '09' => 'Wrzesień',
        '10' => 'Październik', '11' => 'Listopad', '12' => 'Grudzień',
    ];

    list($year, $month) = explode('-', $yearMonth);
    return $monthNames[$month] . ' ' . $year;
}

function getCategoryReport(array $expenses): array {
    $report = [];
    $total = 0;

    foreach ($expenses as $expense) {
        $category = $expense['category'];
        $amount = $expense['amount'];

        if (!isset($report[$category])) {
            $report[$category] = ['amount' => 0, 'count' => 0];
        }

        $report[$category]['amount'] += $amount;
        $report[$category]['count']++;
        $total += $amount;
    }

    // Dodaj procenty
    foreach ($report as $category => &$data) {
        $data['percentage'] = $total > 0
            ? round(($data['amount'] / $total) * 100, 1)
            : 0;
    }

    // Sortuj po kwocie malejąco
    uasort($report, fn($a, $b) => $b['amount'] <=> $a['amount']);

    return [
        'categories' => $report,
        'total' => round($total, 2),
    ];
}

function compareMonths(array $expenses, int $year, int $month): array {
    $currentMonth = filterByMonth($expenses, $year, $month);
    $currentTotal = array_sum(array_column($currentMonth, 'amount'));

    // Poprzedni miesiąc
    $prevMonth = $month - 1;
    $prevYear = $year;
    if ($prevMonth < 1) {
        $prevMonth = 12;
        $prevYear--;
    }

    $previousMonth = filterByMonth($expenses, $prevYear, $prevMonth);
    $previousTotal = array_sum(array_column($previousMonth, 'amount'));

    $difference = $currentTotal - $previousTotal;
    $percentChange = $previousTotal > 0
        ? round(($difference / $previousTotal) * 100, 1)
        : 0;

    return [
        'current' => round($currentTotal, 2),
        'previous' => round($previousTotal, 2),
        'difference' => round($difference, 2),
        'percentage' => $percentChange,
        'trend' => $difference > 0 ? 'up' : ($difference < 0 ? 'down' : 'stable'),
    ];
}

function checkBudget(array $expenses, float $budgetLimit, int $year, int $month): array {
    $monthExpenses = filterByMonth($expenses, $year, $month);
    $spent = array_sum(array_column($monthExpenses, 'amount'));
    $remaining = $budgetLimit - $spent;
    $percentage = ($budgetLimit > 0) ? round(($spent / $budgetLimit) * 100, 1) : 0;

    $status = 'ok';
    $message = '';

    if ($percentage >= 100) {
        $status = 'exceeded';
        $message = 'Przekroczono budżet o ' . abs(round($remaining, 2)) . ' zł';
    } elseif ($percentage >= 80) {
        $status = 'warning';
        $message = 'Wykorzystano ' . $percentage . '% budżetu';
    }

    return [
        'budget' => $budgetLimit,
        'spent' => round($spent, 2),
        'remaining' => round($remaining, 2),
        'percentage' => $percentage,
        'status' => $status,
        'message' => $message,
    ];
}

function formatAmount(float $amount): string {
    return number_format($amount, 2, ',', ' ') . ' zł';
}