PHP file_put_contents() make a primary key that auto_increments

Question

this is my first time asking a question since I cant find any better solutions for my problem. I got a task to make a form by website that uses file_put_contents() for book data library. My code contains:

<?php

if ($_SERVER['REQUEST_METHOD'] === 'POST') {

    $file = "dataBuku.txt";
    if (file_exists($file) && filesize($file) > 0) {
        $getContent = file_get_contents($file);
        if (preg_match_all('/Kode Buku: (\d+)/', $getContent, $matches)) {
            $kode = $matches[1];
            $kodeAkhir = max($kode);
            $kodeBuku = $kodeAkhir + 1;
        }
    } else {
        $kodeBuku = 1;
    }
    $judul = $_POST['judul'];
    $pengarang = $_POST['pengarang'];
    $tahunTerbit = $_POST['tahunTerbit'];
    $halaman = $_POST['halaman'];
    $penerbit = $_POST['penerbit'];
    $kategori = $_POST['kategori'];

    $dataBuku = "Kode Buku: $kodeBuku" . PHP_EOL;
    $dataBuku .= "Judul Buku: $judul" . PHP_EOL;
    $dataBuku .= "Pengarang Buku: $pengarang" . PHP_EOL;
    $dataBuku .= "Tahun Terbit Buku: $tahunTerbit" . PHP_EOL;
    $dataBuku .= "Halaman Buku: $halaman" . PHP_EOL;
    $dataBuku .= "Penerbit Buku: $penerbit" . PHP_EOL;
    $dataBuku .= "Kategori Buku: $kategori" . PHP_EOL;
    
    if ($_FILES['cover']['error'] === UPLOAD_ERR_OK) {
        $ekstensiFile = strtolower(pathinfo($_FILES['cover']['name'], PATHINFO_EXTENSION));
        $namaFile = $kodeBuku . "_" . $pengarang . "_" . $judul . "." . $ekstensiFile;
        $namaSementara = $_FILES['cover']['tmp_name'];
        $lokasiFile = 'cover/' . $namaFile;
        move_uploaded_file($namaSementara, $lokasiFile);
    }

    $dataBuku .= "Cover Buku: $lokasiFile" . PHP_EOL . PHP_EOL;

    if (file_put_contents($file, $dataBuku, FILE_APPEND) > 0){
        echo "<p> Data Written successfully </p>";
    }else{
        echo "<p> Data Written failed </p>";
    }

    $fileIndiv = "$kodeBuku - $judul - $pengarang.txt";

    if (file_put_contents($fileIndiv, $dataBuku) > 0){
        echo "<p> $fileIndiv Written successfully </p>";
    }else{
        echo "<p> Data Written failed </p>";
    }
}

echo "<br> <a href='tes.php'><button>Back</button></a>";
echo "<br> <a href='cek.php'><button>Cek Data</button></a>"
?>

With the expected output:

Kode Buku: 1 (auto_increment)

Judul Buku: Harga Sebuah Percaya

Pengarang Buku: Tere Liye

Tahun Terbit Buku: 2017

Halaman Buku: 302

Penerbit Buku: Mahaka Publishing

Kategori Buku: Novel

Cover Buku: cover/1_Tere Liye_Harga Sebuah Percaya.jpg

Sorry, it's all in Indonesian, but Im sure you'll get the point, tho. I wanted to make the most effective that can auto_increment the 'kodeBuku' without that long code block, reply below if you have any thoughts, will be appreciated, Thanks.

kodeBuku become auto_increment that not counting for lines but the last kodeBuku + 1