Add Redis queue storage driver

Model/Config/Source/StorageDriver.php

@@ -0,0 +1,21 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SamJUK\CacheDebounce\Model\Config\Source;
+
+use Magento\Framework\Data\OptionSourceInterface;
+
+class StorageDriver implements OptionSourceInterface
+{
+    /**
+     * @inheritDoc
+     */
+    public function toOptionArray(): array
+    {
+        return [
+            ['value' => 'db', 'label' => __('Database (default)')],
+            ['value' => 'redis', 'label' => __('Redis')],
+        ];
+    }
+}

Model/Storage/Pool.php

@@ -0,0 +1,95 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SamJUK\CacheDebounce\Model\Storage;
+
+use Magento\Framework\App\Config\ScopeConfigInterface;
+use Magento\Framework\ObjectManagerInterface;
+
+class Pool implements QueueStorageInterface
+{
+    private const XML_PATH_STORAGE_DRIVER = 'samjuk_cache_debounce_advanced/general/storage_driver';
+    private const DEFAULT_DRIVER = 'db';
+
+    /** @var ObjectManagerInterface $objectManager */
+    private $objectManager;
+
+    /** @var ScopeConfigInterface $scopeConfig */
+    private $scopeConfig;
+
+    /** @var string[] $drivers */
+    private $drivers;
+
+    /** @var QueueStorageInterface|null $resolved */
+    private $resolved;
+
+    public function __construct(
+        ObjectManagerInterface $objectManager,
+        ScopeConfigInterface $scopeConfig,
+        array $drivers = []
+    ) {
+        $this->objectManager = $objectManager;
+        $this->scopeConfig = $scopeConfig;
+        $this->drivers = $drivers;
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function add(array $tags): void
+    {
+        $this->driver()->add($tags);
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function claim(): string
+    {
+        return $this->driver()->claim();
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function tags(string $batchId): array
+    {
+        return $this->driver()->tags($batchId);
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function clear(string $batchId): void
+    {
+        $this->driver()->clear($batchId);
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function release(string $batchId): void
+    {
+        $this->driver()->release($batchId);
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function activeBatch(): string
+    {
+        return $this->driver()->activeBatch();
+    }
+
+    private function driver(): QueueStorageInterface
+    {
+        if ($this->resolved === null) {
+            $key = (string)$this->scopeConfig->getValue(self::XML_PATH_STORAGE_DRIVER) ?: self::DEFAULT_DRIVER;
+            $class = $this->drivers[$key] ?? $this->drivers[self::DEFAULT_DRIVER];
+            $this->resolved = $this->objectManager->create($class);
+        }
+
+        return $this->resolved;
+    }
+}

Model/Storage/Redis.php

@@ -0,0 +1,99 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SamJUK\CacheDebounce\Model\Storage;
+
+use SamJUK\CacheDebounce\Model\Storage\Redis\ConnectionResolver;
+
+class Redis implements QueueStorageInterface
+{
+    private const KEY_LIVE = 'samjuk_cache_debounce:queue:live';
+    private const KEY_BATCH_PREFIX = 'samjuk_cache_debounce:queue:batch:';
+    private const ACTIVE_BATCH_ID = 'active';
+
+    /** @var ConnectionResolver $connectionResolver */
+    private $connectionResolver;
+
+    public function __construct(
+        ConnectionResolver $connectionResolver
+    ) {
+        $this->connectionResolver = $connectionResolver;
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function add(array $tags): void
+    {
+        if (!$tags) {
+            return;
+        }
+
+        $this->connectionResolver->getClient()->sAdd(self::KEY_LIVE, ...$tags);
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function claim(): string
+    {
+        if ($this->activeBatch() !== '') {
+            return '';
+        }
+
+        $client = $this->connectionResolver->getClient();
+
+        try {
+            $client->rename(self::KEY_LIVE, $this->batchKey(self::ACTIVE_BATCH_ID));
+        } catch (\CredisException $e) {
+            if (stripos($e->getMessage(), 'no such key') !== false) {
+                return '';
+            }
+            throw $e;
+        }
+
+        return self::ACTIVE_BATCH_ID;
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function tags(string $batchId): array
+    {
+        return $this->connectionResolver->getClient()->sMembers($this->batchKey($batchId));
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function clear(string $batchId): void
+    {
+        $this->connectionResolver->getClient()->del($this->batchKey($batchId));
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function release(string $batchId): void
+    {
+        $client = $this->connectionResolver->getClient();
+        $client->sUnionStore(self::KEY_LIVE, self::KEY_LIVE, $this->batchKey($batchId));
+        $client->del($this->batchKey($batchId));
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function activeBatch(): string
+    {
+        return $this->connectionResolver->getClient()->sCard($this->batchKey(self::ACTIVE_BATCH_ID)) > 0
+            ? self::ACTIVE_BATCH_ID
+            : '';
+    }
+
+    private function batchKey(string $batchId): string
+    {
+        return self::KEY_BATCH_PREFIX . $batchId;
+    }
+}

Model/Storage/Redis/ConnectionResolver.php

@@ -0,0 +1,88 @@
+<?php
+
+declare(strict_types=1);
+
+namespace SamJUK\CacheDebounce\Model\Storage\Redis;
+
+use Magento\Framework\App\DeploymentConfig;
+use Magento\Framework\Exception\LocalizedException;
+
+class ConnectionResolver
+{
+    private const CONFIG_PATH_DEDICATED = 'cache_debounce/redis';
+    private const CONFIG_PATH_SHARED_FALLBACK = 'cache/frontend/page_cache/backend_options';
+
+    /** @var DeploymentConfig $deploymentConfig */
+    private $deploymentConfig;
+
+    /** @var \Credis_Client|null $client */
+    private $client;
+
+    public function __construct(
+        DeploymentConfig $deploymentConfig
+    ) {
+        $this->deploymentConfig = $deploymentConfig;
+    }
+
+    /**
+     * @throws LocalizedException when no usable connection can be resolved.
+     */
+    public function getClient(): \Credis_Client
+    {
+        if ($this->client !== null) {
+            return $this->client;
+        }
+
+        $dedicated = $this->deploymentConfig->get(self::CONFIG_PATH_DEDICATED);
+        $config = $dedicated ? $this->normalize($dedicated) : $this->resolveFallback();
+
+        if (!$config) {
+            throw new LocalizedException(__(
+                'SamJUK_CacheDebounce: no Redis connection could be resolved. Configure the '
+                . '"cache_debounce.redis" block in app/etc/env.php, or configure a Redis backend '
+                . 'for the "page_cache" cache frontend.'
+            ));
+        }
+
+        $this->client = new \Credis_Client(
+            $config['host'],
+            (int)$config['port'],
+            null,
+            '',
+            (int)$config['database'],
+            $config['password'] ?: null
+        );
+
+        return $this->client;
+    }
+
+    private function resolveFallback(): ?array
+    {
+        $backendOptions = $this->deploymentConfig->get(self::CONFIG_PATH_SHARED_FALLBACK);
+
+        if (!$backendOptions) {
+            return null;
+        }
+
+        return [
+            'host' => $backendOptions['server'] ?? '127.0.0.1',
+            'port' => $backendOptions['port'] ?? 6379,
+            'password' => $backendOptions['password'] ?? '',
+            'database' => $backendOptions['database'] ?? 0,
+        ];
+    }
+
+    /**
+     * Fill in defaults for whichever of host/port/database/password the
+     * "cache_debounce.redis" env.php block leaves out.
+     */
+    private function normalize(array $config): array
+    {
+        return [
+            'host' => $config['host'] ?? '127.0.0.1',
+            'port' => $config['port'] ?? 6379,
+            'password' => $config['password'] ?? '',
+            'database' => $config['database'] ?? 0,
+        ];
+    }
+}

README.md

@@ -38,6 +38,45 @@ Option | Config Path | Default | Description
 --- | --- | --- | ---
 Enabled | `samjuk_cache_debounce/general/enabled` | `0` | Feature flag to toggle functionality of the module
 Flush Schedule | `samjuk_cache_debounce/cron/flush_schedule` | `*/5 0 0 0 0` | Cron schedule to run the scheduled flush
+Storage Driver | `samjuk_cache_debounce_advanced/general/storage_driver` | `db` | Queue storage backend — `db` or `redis`. A deploy-time infra decision, not a store setting — see below
+
+This one is a deliberate exception to "Configuration can be handled via System configuration" above: it's hidden from Stores > Configuration entirely (`showInDefault`/`showInWebsite`/`showInStore` all `0`) and gated behind its own ACL resource (`SamJUK_CacheDebounce::storage_driver`) that isn't granted to any role by default. It exists only so `config:set` has a registered path to write to. Set it with:
+```sh
+php bin/magento config:set samjuk_cache_debounce_advanced/general/storage_driver redis
+```
+Add `-e` to lock it into `app/etc/env.php` instead of `core_config_data`, removing Admin overridability entirely.
+
+### Redis storage driver
+
+The `redis` driver connects via a dedicated `app/etc/env.php` block:
+```php
+'cache_debounce' => [
+    'redis' => [
+        'host' => '127.0.0.1',
+        'port' => '6379',
+        'password' => '',
+        'database' => '2',
+    ],
+],
+```
+
+If that block is absent, the module falls back to whatever Redis backend is already configured for the `page_cache` cache frontend, so it works zero-config once the driver is switched on.
+
+> **Note:** sharing the page cache's Redis instance means pending purge tags are subject to that instance's `maxmemory-policy`. If it's `allkeys-lru`/`allkeys-lfu` (common for FPC), tags can be silently evicted under memory pressure. Configure a dedicated block above to avoid this.
+
+### Adding your own storage driver
+
+Drivers are resolved from an array bound in `etc/di.xml`, keyed by the value of `storage_driver`. Any module can add an entry to extend it, without touching this module's `di.xml`:
+```xml
+<type name="SamJUK\CacheDebounce\Model\Storage\Pool">
+    <arguments>
+        <argument name="drivers" xsi:type="array">
+            <item name="my_driver" xsi:type="string">Vendor\Module\Model\Storage\MyDriver</item>
+        </argument>
+    </arguments>
+</type>
+```
+`MyDriver` just needs to implement `QueueStorageInterface`. Then `bin/magento config:set samjuk_cache_debounce_advanced/general/storage_driver my_driver`.
 
 ## Will this help my store?