<?php
require_once __DIR__ . '/../db/config.php';
session_start();

if ($_SERVER['REQUEST_METHOD'] !== 'POST' || !isset($_SESSION['user_id']) || $_SESSION['role'] !== 'admin') {
    header('Location: /login.php');
    exit;
}

$product_id = $_POST['product_id'] ?? null;
$quantity = $_POST['quantity'] ?? null;

if (empty($product_id) || !is_numeric($quantity) || $quantity < 0) {
    $_SESSION['error_message'] = "Invalid data provided. Please enter a valid quantity.";
    header('Location: /dashboard.php?page=admin_inventory');
    exit;
}

try {
    $pdo = db();
    $stmt = $pdo->prepare("UPDATE inventory SET quantity = ? WHERE product_id = ?");
    $stmt->execute([$quantity, $product_id]);
    $_SESSION['success_message'] = "Inventory updated successfully!";
} catch (PDOException $e) {
    error_log("Inventory update failed: " . $e->getMessage());
    $_SESSION['error_message'] = "Failed to update inventory. Please try again.";
}

header('Location: /dashboard.php?page=admin_inventory');
exit;