Introduce Managers for readers

Some helper classes were more managers than helpers...

src/Spout/Reader/XLSX/Manager/SharedStringsCaching/InMemoryStrategy.php

@@ -0,0 +1,83 @@
+<?php
+
+namespace Box\Spout\Reader\XLSX\Manager\SharedStringsCaching;
+
+use Box\Spout\Reader\Exception\SharedStringNotFoundException;
+
+/**
+ * Class InMemoryStrategy
+ *
+ * This class implements the in-memory caching strategy for shared strings.
+ * This strategy is used when the number of unique strings is low, compared to the memory available.
+ *
+ * @package Box\Spout\Reader\XLSX\Manager\SharedStringsCaching
+ */
+class InMemoryStrategy implements CachingStrategyInterface
+{
+    /** @var \SplFixedArray Array used to cache the shared strings */
+    protected $inMemoryCache;
+
+    /** @var bool Whether the cache has been closed */
+    protected $isCacheClosed;
+
+    /**
+     * @param int $sharedStringsUniqueCount Number of unique shared strings
+     */
+    public function __construct($sharedStringsUniqueCount)
+    {
+        $this->inMemoryCache = new \SplFixedArray($sharedStringsUniqueCount);
+        $this->isCacheClosed = false;
+    }
+
+    /**
+     * Adds the given string to the cache.
+     *
+     * @param string $sharedString The string to be added to the cache
+     * @param int $sharedStringIndex Index of the shared string in the sharedStrings.xml file
+     * @return void
+     */
+    public function addStringForIndex($sharedString, $sharedStringIndex)
+    {
+        if (!$this->isCacheClosed) {
+            $this->inMemoryCache->offsetSet($sharedStringIndex, $sharedString);
+        }
+    }
+
+    /**
+     * Closes the cache after the last shared string was added.
+     * This prevents any additional string from being added to the cache.
+     *
+     * @return void
+     */
+    public function closeCache()
+    {
+        $this->isCacheClosed = true;
+    }
+
+    /**
+     * Returns the string located at the given index from the cache.
+     *
+     * @param int $sharedStringIndex Index of the shared string in the sharedStrings.xml file
+     * @return string The shared string at the given index
+     * @throws \Box\Spout\Reader\Exception\SharedStringNotFoundException If no shared string found for the given index
+     */
+    public function getStringAtIndex($sharedStringIndex)
+    {
+        try {
+            return $this->inMemoryCache->offsetGet($sharedStringIndex);
+        } catch (\RuntimeException $e) {
+            throw new SharedStringNotFoundException("Shared string not found for index: $sharedStringIndex");
+        }
+    }
+
+    /**
+     * Destroys the cache, freeing memory and removing any created artifacts
+     *
+     * @return void
+     */
+    public function clearCache()
+    {
+        unset($this->inMemoryCache);
+        $this->isCacheClosed = false;
+    }
+}