Add FileCache driver

app/Core/Cache/FileCache.php

@@ -0,0 +1,98 @@
+<?php
+
+namespace Kanboard\Core\Cache;
+
+use Kanboard\Core\Tool;
+use LogicException;
+
+/**
+ * Class FileCache
+ *
+ * @package Kanboard\Core\Cache
+ */
+class FileCache extends BaseCache
+{
+    /**
+     * Store an item in the cache
+     *
+     * @access public
+     * @param  string $key
+     * @param  string $value
+     */
+    public function set($key, $value)
+    {
+        $this->createCacheFolder();
+        file_put_contents($this->getFilenameFromKey($key), serialize($value));
+    }
+
+    /**
+     * Retrieve an item from the cache by key
+     *
+     * @access public
+     * @param  string $key
+     * @return mixed            Null when not found, cached value otherwise
+     */
+    public function get($key)
+    {
+        $filename = $this->getFilenameFromKey($key);
+
+        if (file_exists($filename)) {
+            return unserialize(file_get_contents($filename));
+        }
+
+        return null;
+    }
+
+    /**
+     * Remove all items from the cache
+     *
+     * @access public
+     */
+    public function flush()
+    {
+        $this->createCacheFolder();
+        Tool::removeAllFiles(CACHE_DIR, false);
+    }
+
+    /**
+     * Remove an item from the cache
+     *
+     * @access public
+     * @param  string $key
+     */
+    public function remove($key)
+    {
+        $filename = $this->getFilenameFromKey($key);
+
+        if (file_exists($filename)) {
+            unlink($filename);
+        }
+    }
+
+    /**
+     * Get absolute filename from the key
+     *
+     * @access protected
+     * @param  string $key
+     * @return string
+     */
+    protected function getFilenameFromKey($key)
+    {
+        return CACHE_DIR.DIRECTORY_SEPARATOR.$key;
+    }
+
+    /**
+     * Create cache folder if missing
+     *
+     * @access protected
+     * @throws LogicException
+     */
+    protected function createCacheFolder()
+    {
+        if (! is_dir(CACHE_DIR)) {
+            if (! mkdir(CACHE_DIR, 0755)) {
+                throw new LogicException('Unable to create cache directory: '.CACHE_DIR);
+            }
+        }
+    }
+}