Form Bibliografi dengan upload Cover

<!-- pages/bibliografi.php -->
<div class="container-fluid">
          <!-- Page Heading -->
          <div class="d-sm-flex align-items-center justify-content-between mb-4">
            <h1 class="h3 mb-0 text-gray-800">Bibliografi Buku</h1>
          </div>
             <?php tampilPesan(); ?>
          <!-- Content Row -->
          <div class="row">
            <div class="col-xl-3 col-md-6 mb-4">
              <div class="card shadow mb-4">
                <!-- Card Header - Dropdown -->
                <div class="card-header py-3 d-flex flex-row align-items-center justify-content-between">
                  <h6 class="m-0 font-weight-bold text-primary">Entry Data Bibliografi</h6>
                </div>
                  <?php // mengambil baris data untuk diedit, jika terdeteksi parameter URL id
                  $data = false;
                  if (isset($_GET["id"])) {
                      $id = $_GET["id"];
                      $stmt = $conn->prepare("SELECT * FROM buku
                                                WHERE Kode_Buku = ?");
                      $stmt->execute([$id]);
                      $data = $stmt->fetch(PDO::FETCH_OBJ);
                  }
                  ?>
                <!-- Card Body -->
                <div class="card-body">
                   <!-- PERHATIKAN bagian atribut pada form, harus ada enctype... tsb untuk bisa upload file -->
                   <form action="proses/biblio-proses.php" method="post" enctype="multipart/form-data">
                    <div class="form-group">
                        <label>Judul Buku</label>
                        <input type="text" name="judul_buku" class="form-control"
                        value="<?= ($data) ? $data->Bk_Judul_Buku : ''; ?>">
                    </div>
                    <div class="form-group">
                        <label>Penulis</label>
                        <input type="text" name="penulis" class="form-control"
                        value="<?= ($data) ? $data->Bk_Penulis : ''; ?>">
                    </div>
                    <div class="form-group">
                        <label>Peberbit</label>
                        <input type="text" name="penerbit" class="form-control"
                        value="<?= ($data) ? $data->Bk_Penerbit : ''; ?>">
                    </div>
                    <div class="form-group">
                        <label>Tahun Terbit</label>
                        <input type="text" name="th_terbit" class="form-control"
                        value="<?= ($data) ? $data->Bk_Th_Terbit : ''; ?>">
                    </div>
                    <div class="form-group">
                        <label>Kategori</label>

                        <select name="kode_kategori" class="form-control" id="select_kategori">
                        <?php
                        $sql = "SELECT * FROM kategori_buku
                                ORDER BY Nama_Kategori ASC";
                        $stmt = $conn->query($sql);
                        while ($row = $stmt->fetch(PDO::FETCH_OBJ)):
                        ?>
                            <option value="<?= $row->Kode_Kategori; ?>"
                             <?= ($data && ($data->Bk_Kode_Kategori == $row->Kode_Kategori)) ?
                                 "selected" : ''; ?>>
                                <?= $row->Nama_Kategori; ?></option>
                        <?php endwhile; ?>
                        </select>
                    </div>
                   <div class="form-group">
                       <label>Cover (jika ada)</label>
                       <input type="file" name="file_cover" class="form-control">
                   </div>
                    <input type="hidden" name="kode_buku"
                           value="<?= ($data) ? $data->Kode_Buku : 0; ?>">
                    <input type="hidden" name="cover_existing"
                           value="<?= ($data) ? $data->Bk_Foto : ''; ?>">
                    <input type="submit" class="btn btn-success" value="Simpan">
                   </form>
                </div>
              </div>
           </div>
          </div> <!-- end row untuk form -->

          <div class="row"> <!-- start row untuk tabel -->
            <div class="col-xl-12 col-md-12 mb-12">
                <table class="table table-striped" id="tabel_biblio">
                    <thead>
                    <tr>
                        <th>Kode</th>
                        <th>Judul Buku</th>
                        <th>Tahun Terbit</th>
                        <th>Kategori</th>
                        <th>Aksi</th>
                    </tr>
                    </thead>
                    <tbody>
                    <?php
                        $sql = "SELECT * FROM buku
                                LEFT JOIN kategori_buku
                                ON Kode_Kategori = Bk_Kode_Kategori
                                ORDER BY Kode_Buku DESC";
                        $stmt = $conn->query($sql);
                        while ($row = $stmt->fetch(PDO::FETCH_OBJ)):
                    ?>
                    <tr>
                        <td><?= $row->Kode_Buku; ?></td>
                        <td><?= $row->Bk_Judul_Buku; ?>
                            <?php if ($row->Bk_Foto != "") { ?>
                                <br>
                                <img src="img/coverbuku/<?= $row->Bk_Foto ?>" width="80">
                            <?php  } ?>
                        </td>
                        <td><?= $row->Bk_Th_Terbit; ?></td>
                        <td><?= $row->Nama_Kategori; ?></td>
                        <td>
                            <a href="?p=bibliografi&id=<?= $row->Kode_Buku; ?>" class="btn btn-sm btn-warning">Edit</a>
                            <a href="proses/biblio-proses.php?id=<?= $row->Kode_Buku; ?>"
                               class="btn btn-sm btn-danger"
                               onclick="return confirm('Apakah Anda yakin untuk menghapus ?')">Hapus</a>
                        </td>
                    </tr>
                        <?php endwhile; ?>
                    </tbody>
                </table>
            </div>
          </div> <!-- end row untuk tabel -->
        <!-- /.container-fluid -->
</div>
<script>
    $(document).ready(function() {
       $('#select_kategori').select2();
       $('#tabel_biblio').DataTable({
           "language": {
               "url": "http://localhost/pwd2019/perpustakaan/vendor/datatables/Indonesian.json"
           }
       });
    });
</script>