process.php

<?php
// Catch all output (suppress any whitespace from includes)
ob_start();

// Show all errors for debugging
error_reporting(E_ALL);
ini_set('display_errors', 1);

require_once("includes/config.php");

// Clean any output from includes before sending our response
ob_clean();

// Always return plain text
header('Content-Type: text/plain');

$username   = isset($_POST['username'])   ? trim($_POST['username'])   : '';
$tool_id    = isset($_POST['id'])         ? trim($_POST['id'])         : '';
$marks      = isset($_POST['totalMarks']) ? trim($_POST['totalMarks']) : '';

if ($username === '' || $tool_id === '' || $marks === '') {
    echo "Data Missing! Username: " . htmlspecialchars($username) . ", Tool: " . htmlspecialchars($tool_id) . ", Marks: " . htmlspecialchars($marks);
    exit;
}

// Check file upload
if (!isset($_FILES['pdfFile'])) {
    echo "No file received by server!";
    exit;
}

$uploadError = $_FILES['pdfFile']['error'];
if ($uploadError !== UPLOAD_ERR_OK) {
    $uploadErrors = [
        UPLOAD_ERR_INI_SIZE   => 'File exceeds server upload limit (upload_max_filesize).',
        UPLOAD_ERR_FORM_SIZE  => 'File exceeds form upload limit.',
        UPLOAD_ERR_PARTIAL    => 'File was only partially uploaded.',
        UPLOAD_ERR_NO_FILE    => 'No file was uploaded.',
        UPLOAD_ERR_NO_TMP_DIR => 'Missing a temporary folder.',
        UPLOAD_ERR_CANT_WRITE => 'Failed to write file to disk.',
        UPLOAD_ERR_EXTENSION  => 'File upload stopped by extension.',
    ];
    echo isset($uploadErrors[$uploadError]) ? $uploadErrors[$uploadError] : "Upload error code: $uploadError";
    exit;
}

$file = $_FILES['pdfFile'];

// Validate extension (avoid finfo dependency issues)
$ext = strtolower(pathinfo($file['name'], PATHINFO_EXTENSION));
if ($ext !== 'pdf') {
    echo "Only PDF files are allowed! Uploaded: .$ext";
    exit;
}

// Check file size (max 10 MB)
if ($file['size'] > 10 * 1024 * 1024) {
    echo "File size must be 10 MB or less!";
    exit;
}

// Check if already submitted
$query = $con->prepare("SELECT id FROM tools_assignment_filelink WHERE username=:username AND tool_id=:tool_id");
$query->bindValue(":username", $username);
$query->bindValue(":tool_id",  $tool_id);
$query->execute();

if ($query->rowCount() > 0) {
    echo "File already submitted!";
    exit;
}

// Build unique filename and save
$uploadDir = __DIR__ . '/uploads/assignments/';
if (!is_dir($uploadDir)) {
    if (!mkdir($uploadDir, 0755, true)) {
        echo "Could not create uploads directory.";
        exit;
    }
}

$safeBase    = preg_replace('/[^a-zA-Z0-9_-]/', '_', pathinfo($file['name'], PATHINFO_FILENAME));
$newFilename = $username . '_' . $tool_id . '_' . time() . '_' . $safeBase . '.pdf';
$destination = $uploadDir . $newFilename;

if (!move_uploaded_file($file['tmp_name'], $destination)) {
    echo "Failed to save file to server. Check folder permissions.";
    exit;
}

$filePath = 'uploads/assignments/' . $newFilename;

// Insert into DB
$insert = $con->prepare(
    "INSERT INTO tools_assignment_filelink (username, tool_id, fileLink, filePath, totalMarks)
     VALUES(:username, :tool_id, :fileLink, :filePath, :totalMarks)"
);
$insert->bindValue(":username",   $username);
$insert->bindValue(":tool_id",    $tool_id);
$insert->bindValue(":fileLink",   $file['name']);
$insert->bindValue(":filePath",   $filePath);
$insert->bindValue(":totalMarks", $marks);

if ($insert->execute()) {
    echo "File submitted Successfully!";
} else {
    $err = $insert->errorInfo();
    echo "Database error. Please try again. " . $err[2];
}
?>