Sách Giáo Khoa Việt Nam - sachgiaokhoa.org

CodeIgniter 4 website:
- Catalog 999 SGK (lớp 1-12) từ API, lọc theo lớp/môn/NXB, tìm kiếm
- Trang chủ grouped browse (bậc học -> lớp -> môn, ưu tiên môn quan trọng)
- Chi tiết sách: metadata đầy đủ, cover nghệ thuật /thumb/{W}x{H}/
- Đọc online qua gate captcha + countdown, PDF viewer pdf.js
- Download: captcha + token một lần + auto cache-bust version
- Tự đồng bộ catalog/cover khi API thay đổi (refresh:catalog)
- Legal: DMCA, miễn trừ trách nhiệm, điều khoản, bảo mật, liên hệ

app/Common.php

@@ -0,0 +1,38 @@
+<?php
+
+/**
+ * The goal of this file is to allow developers a location
+ * where they can overwrite core procedural functions and
+ * replace them with their own. This file is loaded during
+ * the bootstrap process and is called during the framework's
+ * execution.
+ *
+ * This can be looked at as a `master helper` file that is
+ * loaded early on, and may also contain additional functions
+ * that you'd like to use throughout your entire application
+ *
+ * @see: https://codeigniter.com/user_guide/extending/common.html
+ */
+
+if (! function_exists('media_version')) {
+    /**
+     * Cache-busting version for cover/thumb URLs, driven by the upstream
+     * catalog. When the API data changes (sourceUpdatedAt differs), the
+     * version bumps automatically so CDN/browser caches treat images as new.
+     * Falls back to the env override if Mongo is unavailable.
+     */
+    function media_version(): string
+    {
+        static $version = null;
+        if ($version !== null) {
+            return $version;
+        }
+        try {
+            $meta = \App\Libraries\Mongo::col('catalog')->findOne(['_id' => 'meta']);
+            $version = (string) ($meta['mediaVersion'] ?? env('media.version', '1'));
+        } catch (\Throwable $e) {
+            $version = (string) env('media.version', '1');
+        }
+        return $version;
+    }
+}