Add ArrayCache engine

This cache engine gives us a cache implementation that is ideal for
application test suites. Previously folks would have to use peristent
data stores that could leave artifacts behind requiring manual cleanup
or use NullEngine which provides none of the benefits that caching
offers. Now folks can use this in memory cache that offers expiration
and group support.

src/Cache/Engine/ArrayEngine.php

@@ -0,0 +1,183 @@
+<?php
+/**
+ * CakePHP(tm) : Rapid Development Framework (https://cakephp.org)
+ * Copyright (c) Cake Software Foundation, Inc. (https://cakefoundation.org)
+ *
+ * Licensed under The MIT License
+ * For full copyright and license information, please see the LICENSE.txt
+ * Redistributions of files must retain the above copyright notice.
+ *
+ * @copyright     Copyright (c) Cake Software Foundation, Inc. (https://cakefoundation.org)
+ * @link          https://cakephp.org CakePHP(tm) Project
+ * @since         3.7.0
+ * @license       https://opensource.org/licenses/mit-license.php MIT License
+ */
+namespace Cake\Cache\Engine;
+
+use Cake\Cache\CacheEngine;
+
+/**
+ * Array storage engine for cache.
+ *
+ * Not actually a persistent cache engine. All data is only
+ * stored in memory for the duration of a single process. While not
+ * useful in production settings this engine can be useful in tests
+ * or console tools where you don't want the overhead of interacting
+ * with a cache servers, but want the work saving properties a cache
+ * provides.
+ */
+class ArrayEngine extends CacheEngine
+{
+    /**
+     * Cached data.
+     *
+     * Structured as [key => [expiration, value]]
+     *
+     * @var aray
+     */
+    protected $data = [];
+
+    /**
+     * Write data for key into cache
+     *
+     * @param string $key Identifier for the data
+     * @param mixed $value Data to be cached
+     * @return bool True if the data was successfully cached, false on failure
+     */
+    public function write($key, $value)
+    {
+        $key = $this->_key($key);
+        $expires = time() + $this->_config['duration'];
+        $this->data[$key] = [$expires, $value];
+
+        return true;
+    }
+
+    /**
+     * Read a key from the cache
+     *
+     * @param string $key Identifier for the data
+     * @return mixed The cached data, or false if the data doesn't exist,
+     *   has expired, or if there was an error fetching it
+     */
+    public function read($key)
+    {
+        $key = $this->_key($key);
+        if (!isset($this->data[$key])) {
+            return false;
+        }
+        $data = $this->data[$key];
+
+        // Check expiration
+        $now = time();
+        if ($data[0] <= $now) {
+            unset($this->data[$key]);
+
+            return false;
+        }
+
+        return $data[1];
+    }
+
+    /**
+     * Increments the value of an integer cached key
+     *
+     * @param string $key Identifier for the data
+     * @param int $offset How much to increment
+     * @return bool|int New incremented value, false otherwise
+     */
+    public function increment($key, $offset = 1)
+    {
+        if (!$this->read($key)) {
+            $this->write($key, 0);
+        }
+        $key = $this->_key($key);
+        $this->data[$key][1] += $offset;
+
+        return true;
+    }
+
+    /**
+     * Decrements the value of an integer cached key
+     *
+     * @param string $key Identifier for the data
+     * @param int $offset How much to subtract
+     * @return bool|int New decremented value, false otherwise
+     */
+    public function decrement($key, $offset = 1)
+    {
+        if (!$this->read($key)) {
+            $this->write($key, 0);
+        }
+        $key = $this->_key($key);
+        $this->data[$key][1] -= $offset;
+
+        return true;
+    }
+
+    /**
+     * Delete a key from the cache
+     *
+     * @param string $key Identifier for the data
+     * @return bool True if the value was successfully deleted, false if it didn't exist or couldn't be removed
+     */
+    public function delete($key)
+    {
+        $key = $this->_key($key);
+        unset($this->data[$key]);
+
+        return true;
+    }
+
+    /**
+     * Delete all keys from the cache. This will clear every cache config using APC.
+     *
+     * @param bool $check Unused argument required by interface.
+     * @return bool True Returns true.
+     */
+    public function clear($check)
+    {
+        $this->data = [];
+
+        return true;
+    }
+
+    /**
+     * Returns the `group value` for each of the configured groups
+     * If the group initial value was not found, then it initializes
+     * the group accordingly.
+     *
+     * @return array
+     */
+    public function groups()
+    {
+        $result = [];
+        foreach ($this->_config['groups'] as $group) {
+            $key = $this->_config['prefix'] . $group;
+            if (!isset($this->data[$key])) {
+                $this->data[$key] = [PHP_INT_MAX, 1];
+            }
+            $value = $this->data[$key][1];
+            $result[] = $group . $value;
+        }
+
+        return $result;
+    }
+
+    /**
+     * Increments the group value to simulate deletion of all keys under a group
+     * old values will remain in storage until they expire.
+     *
+     * @param string $group The group to clear.
+     * @return bool success
+     */
+    public function clearGroup($group)
+    {
+        $key = $this->_config['prefix'] . $group;
+        if (isset($this->data[$key])) {
+            $this->data[$key][1] += 1;
+        }
+
+        return true;
+    }
+}