// CSV 내보내기 — 순수 PHP
public function exportCsv()
{
    $products = $db->table('products')
                   ->get()->getResultArray();

    ob_start();
    $fp = fopen('php://output', 'w');

    // UTF-8 BOM: Excel에서 한글 깨짐 방지
    fputs($fp, "\xEF\xBB\xBF");

    // 헤더 행
    fputcsv($fp, ['ID', '상품명', '카테고리', '가격', '재고']);

    // 데이터 행
    foreach ($products as $row) {
        fputcsv($fp, [
            $row['id'],
            $row['name'],
            $row['category'],
            $row['price'],
            $row['stock'],
        ]);
    }
    fclose($fp);
    $body = ob_get_clean();

    return $this->response
        ->setHeader('Content-Type', 'text/csv; charset=UTF-8')
        ->setHeader('Content-Disposition',
            'attachment; filename="products.csv"')
        ->setBody($body);
}

// CSV 가져오기 — 순수 PHP
public function importCsv()
{
    $file = $this->request->getFile('csv_file');

    // 파일 유효성 검사
    if (!$file || !$file->isValid()) {
        return redirect()->back()
            ->with('error', '파일을 선택해주세요.');
    }

    $fp = fopen($file->getTempName(), 'r');

    // UTF-8 BOM 제거
    $bom = fread($fp, 3);
    if ($bom !== "\xEF\xBB\xBF") {
        rewind($fp); // BOM 없으면 처음으로
    }

    fgetcsv($fp); // 헤더 행 스킵
    $count = 0;

    while (($row = fgetcsv($fp)) !== false) {
        if (count($row) < 5) continue;

        $db->table('products')->insert([
            'name'     => trim($row[1]),
            'category' => trim($row[2]),
            'price'    => (float) $row[3],
            'stock'    => (int)   $row[4],
        ]);
        $count++;
    }
    fclose($fp);

    return redirect()->back()
        ->with('success', "{$count}건 가져오기 완료");
}

use PhpOffice\PhpSpreadsheet\Spreadsheet;
use PhpOffice\PhpSpreadsheet\Writer\Xlsx;
use PhpOffice\PhpSpreadsheet\Style\Fill;
use PhpOffice\PhpSpreadsheet\Style\Alignment;

public function exportExcel()
{
    $products = $db->table('products')
                   ->get()->getResultArray();

    $spreadsheet = new Spreadsheet();
    $sheet = $spreadsheet->getActiveSheet();
    $sheet->setTitle('상품 목록');

    // 헤더 행 데이터
    $headers = ['ID', '상품명', '카테고리', '가격', '재고'];
    foreach ($headers as $col => $header) {
        $sheet->setCellValue(chr(65 + $col).'1', $header);
    }

    // 헤더 스타일 (파란 배경 + 흰 글자)
    $sheet->getStyle('A1:E1')->applyFromArray([
        'font' => ['bold' => true, 'color' => ['rgb' => 'FFFFFF']],
        'fill' => [
            'fillType'   => Fill::FILL_SOLID,
            'startColor' => ['rgb' => '0D6EFD'],
        ],
        'alignment' => [
            'horizontal' => Alignment::HORIZONTAL_CENTER,
        ],
    ]);

    // 데이터 입력
    foreach ($products as $i => $row) {
        $r = $i + 2;
        $sheet->setCellValue('A'.$r, $row['id']);
        $sheet->setCellValue('B'.$r, $row['name']);
        $sheet->setCellValue('C'.$r, $row['category']);
        $sheet->setCellValue('D'.$r, $row['price']);
        $sheet->setCellValue('E'.$r, $row['stock']);
    }

    // 가격 열 숫자 포맷
    $sheet->getStyle('D2:D'.($i+2))
          ->getNumberFormat()
          ->setFormatCode('#,##0');

    // 열 너비 자동
    foreach (range('A', 'E') as $col) {
        $sheet->getColumnDimension($col)->setAutoSize(true);
    }

    ob_start();
    (new Xlsx($spreadsheet))->save('php://output');
    $body = ob_get_clean();

    return $this->response
        ->setHeader('Content-Type',
            'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet')
        ->setHeader('Content-Disposition',
            'attachment; filename="products.xlsx"')
        ->setBody($body);
}

use PhpOffice\PhpSpreadsheet\Reader\Xlsx as XlsxReader;

public function importExcel()
{
    $file = $this->request->getFile('excel_file');

    $reader = new XlsxReader();
    $spreadsheet = $reader->load($file->getTempName());

    // 첫 번째 시트를 배열로 변환
    $rows = $spreadsheet->getActiveSheet()->toArray();

    $count = 0;
    foreach ($rows as $i => $row) {
        if ($i === 0) continue; // 헤더 스킵

        $db->table('products')->insert([
            'name'     => trim($row[1]),
            'category' => trim($row[2]),
            'price'    => (float) $row[3],
            'stock'    => (int)   $row[4],
        ]);
        $count++;
    }

    return redirect()->back()
        ->with('success', "{$count}건 가져오기 완료");
}

# PhpSpreadsheet 설치
composer require phpoffice/phpspreadsheet

# 지원 포맷
# 읽기: xlsx, xls, csv, ods, html ...
# 쓰기: xlsx, xls, csv, ods, html, pdf ...