From 059e0d95d0c28bc5060e87e146eaf7411f51bf90 Mon Sep 17 00:00:00 2001
From: George Halkiadakis <gchalkiadakis@sklavenitis.co.gr>
Date: Thu, 27 Apr 2023 03:47:30 +0300
Subject: skeleton commit; based on an anom project

---
 core/classes/cache/Cache_interface.php | 34 +++++++++++++
 core/classes/cache/FileCache.php       | 93 ++++++++++++++++++++++++++++++++++
 core/classes/cache/MemcachedCache.php  | 37 ++++++++++++++
 core/classes/cache/RedisCache.php      | 69 +++++++++++++++++++++++++
 4 files changed, 233 insertions(+)
 create mode 100644 core/classes/cache/Cache_interface.php
 create mode 100644 core/classes/cache/FileCache.php
 create mode 100644 core/classes/cache/MemcachedCache.php
 create mode 100644 core/classes/cache/RedisCache.php

(limited to 'core/classes/cache')

diff --git a/core/classes/cache/Cache_interface.php b/core/classes/cache/Cache_interface.php
new file mode 100644
index 0000000..7c49789
--- /dev/null
+++ b/core/classes/cache/Cache_interface.php
@@ -0,0 +1,34 @@
+<?php
+
+/** Cache interface
+ * ---
+ * Interface to save results of expensive data-extraction proccess,
+ * in a fast-accessed medium (ussually RAM or NVME SSD units)
+ */
+interface Cache_interface
+{
+    /** Cache::set($key, $data, $ttl) : void
+     * 
+     * @param $key (string): reference label
+     * @param $data (mixed): actual data (avoid storing true|false)
+     * @param $ttl (int): time to live (seconds)
+     */
+    public function set(string $key, $data, int $ttl);
+
+
+    /** Cache::get($key) : mixed
+     *
+     * @param $key (string)
+     * @return mixed: fetched $data -or- false on failure
+     */
+    public function get(string $key);
+
+
+    /** Cache::flush( $olderThan ) : void
+     *
+     * clear cache older than $olderThan
+     * @param $olderThan (int) in seconds
+     */
+    public function flush(int $olderThan = 0);
+
+}
\ No newline at end of file
diff --git a/core/classes/cache/FileCache.php b/core/classes/cache/FileCache.php
new file mode 100644
index 0000000..fb7eee5
--- /dev/null
+++ b/core/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 $olderThan = 0)
+    {
+        return false;   // reply false until implementation
+    }
+
+}
diff --git a/core/classes/cache/MemcachedCache.php b/core/classes/cache/MemcachedCache.php
new file mode 100644
index 0000000..c89d86a
--- /dev/null
+++ b/core/classes/cache/MemcachedCache.php
@@ -0,0 +1,37 @@
+<?php 
+
+/** Memcached Implementation
+ * (implements Cache interface; extends Cache)
+ * ---
+ */
+class MemcachedCache implements Cache_interface
+{
+
+    public function set($key, $data, $ttl)
+    {
+        $hashkey = md5($key);
+
+        $mc = new Memcached();
+        $mc->addServer(\MEMCACHE_HOST, 11211);
+
+        $mc->set($hashkey, $data, $ttl);
+    }
+
+    
+    public function get($key)
+    {
+        $hashkey = md5($key);
+        
+        $mc = new Memcached();
+        $mc->addServer(\MEMCACHE_HOST, 11211);
+
+        return $mc->get($hashkey);
+
+    }
+
+    public function flush($olderThan = 0)
+    {
+        return false;
+    }
+
+}
\ No newline at end of file
diff --git a/core/classes/cache/RedisCache.php b/core/classes/cache/RedisCache.php
new file mode 100644
index 0000000..ec50f08
--- /dev/null
+++ b/core/classes/cache/RedisCache.php
@@ -0,0 +1,69 @@
+<?php 
+
+/** Redis Cache implementation
+ * ---
+ * This class uses \Predis\Redis, so do not forget require it via composer
+ * or to use the configuration options you will find into \README.md
+ */
+class RedisCache implements Cache_interface
+{
+    /** set
+     * store $data under the label $key
+     * cache expires in $ttl seconds
+     */
+    public function set($key, $data, $ttl)
+    {
+        $serialized = serialize($data);
+
+        if ($serialized = '') {
+            return false;
+        }
+
+        try {
+            $redis = new \Predis\Client([
+                'host' => \REDIS_HOST
+            ]);
+            return $redis->set($key, $serialized, 'EX', $ttl);
+
+        } catch (Exception $e) {
+            // ...
+        }
+    }
+
+
+    /** get
+     * fetch previously stored $data under label $key
+     * return $data (or false)
+     */
+    public function get($key)
+    {   
+        
+        try {
+            
+            $redis = new \Predis\Client([
+                'host' => \REDIS_HOST
+            ]);
+
+            if ($redis->exists($key)) {
+                return unserialize($redis->get($key));
+
+            } else {
+                return false;
+            }
+
+        } catch (Exception $e) {
+            // ...
+        }     
+
+    }
+
+
+    /** flush
+     * --- not umplemented yet; may not needed
+     */
+    public function flush($olderThan = 0)
+    {
+        return false; // until implementation
+    }
+
+}
\ No newline at end of file
-- 
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