From 47cbb529f5723b246125ae083a193e11481b89ef Mon Sep 17 00:00:00 2001
From: George Halkiadakis <gchalkiadakis@sklavenitis.co.gr>
Date: Sun, 12 Mar 2023 07:01:30 +0200
Subject: initializing classroom structure using anom framework

---
 classes/cache/FileCache.php | 93 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 93 insertions(+)
 create mode 100644 classes/cache/FileCache.php

(limited to 'classes/cache/FileCache.php')

diff --git a/classes/cache/FileCache.php b/classes/cache/FileCache.php
new file mode 100644
index 0000000..fb7eee5
--- /dev/null
+++ b/classes/cache/FileCache.php
@@ -0,0 +1,93 @@
+<?php
+
+/* FileCache
+ * ---
+ * Saves serialized data into filesystem.
+ * Use it for expensive database-queries.
+ * Performanve on a NVMe-SSD drive is really great;
+ * (even better than MemCached and Redis)
+ * performance on a typical HDD is just fair.
+ *
+ * NOTE:
+ * Memcached and Redis are much faster cache-technologies
+ * and generally recommended; but they are not always available;
+ * FileCache is (almost) always available;
+ * 
+ * Before tou decide on your caching technology
+ * run some benchmarks.
+ */
+class FileCache implements Cache_interface
+{
+
+    /** store
+     * ---
+     * serializes and saves data in a file
+     * along with TTL (time-to-live)
+     */
+    public function set(string $key, $data, int $ttl)
+    {
+        // filename is a hashed 48-hex-digit string
+        // probability of collision = exp( (-k*(k-1)) / 2N )
+        // ex: for 10tril.samples P(collision) = 1.5E-11%
+        $filename = FILECACHE_PATH . sha1($key);
+
+        // Opening file for write
+        $h = fopen($filename, 'w');
+        if (!$h) throw new Exception('Can not write to cache');
+
+        // Serialize along with the TTL
+        $data = serialize( array(
+            time() + $ttl,      // array[0] holds expiration time
+            $data)              // array[1] holds the actual data
+        );
+
+        if (fwrite($h,$data) === false) {
+          throw new Exception('Can not write to cache');
+        }
+        fclose($h);
+    }
+
+
+    /** fetch
+     * ---
+     * feth data for certain key
+     * @param $key (string)
+     * @return fetched $data -or- false on failure
+     */
+    public function get(string $key)
+    {
+        $filename = FILECACHE_PATH . sha1($key);
+
+        // can not read the cache-file? return false
+        if (!file_exists($filename) || !is_readable($filename)) return false;
+
+        $data = file_get_contents($filename);   // get cache-file contents
+        $data = @unserialize($data);            // unserialize
+
+        if (!$data) {
+
+           // Unlinking the file when unserializing failed
+           unlink($filename);
+           return false;
+
+        }
+
+        // checking if the data was expired
+        if (time() > $data[0]) {
+
+           // Unlinking
+           unlink($filename);
+           return false;
+
+        }
+
+        return $data[1];
+    }
+
+
+    public function flush(int $olderThan = 0)
+    {
+        return false;   // reply false until implementation
+    }
+
+}
-- 
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