feat: implement Pluggable Abstraction Layer for Data Retrieval (PALDRA) - #19

- Create ArrRetriever abstract base class defining pluggable interface
- Implement PollingSonarrRetriever and PollingRadarrRetriever with HTTP polling
- Add ArrRetrieverRegistry for managing retriever instances
- Refactor poller.js to use retriever registry instead of direct Axios calls
- Update historyFetcher.js to use retriever registry
- Preserve all cache keys, TTLs, timing logs, SSE broadcasts, error handling
- Enable future webhook listeners without touching poller logic

server/clients/PollingRadarrRetriever.js

@@ -0,0 +1,96 @@
+// Copyright (c) 2026 Gordon Bolton. MIT License.
+const axios = require('axios');
+const ArrRetriever = require('./ArrRetriever');
+const { logToFile } = require('../utils/logger');
+
+/**
+ * Polling-based Radarr data retriever.
+ * Implements the ArrRetriever interface using direct HTTP polling.
+ */
+class PollingRadarrRetriever extends ArrRetriever {
+  constructor(instanceConfig) {
+    super(instanceConfig);
+  }
+
+  getRetrieverType() {
+    return 'radarr';
+  }
+
+  /**
+   * Get tags from Radarr instance
+   * @param {Object} instanceConfig - Configuration for the instance
+   * @returns {Promise<Array>} Array of tag objects
+   */
+  async getTags(instanceConfig) {
+    try {
+      const response = await axios.get(`${instanceConfig.url}/api/v3/tag`, {
+        headers: { 'X-Api-Key': instanceConfig.apiKey }
+      });
+      return response.data;
+    } catch (error) {
+      logToFile(`[PollingRadarrRetriever] ${instanceConfig.id} tags error: ${error.message}`);
+      return [];
+    }
+  }
+
+  /**
+   * Get queue from Radarr instance
+   * @param {Object} instanceConfig - Configuration for the instance
+   * @returns {Promise<Object>} Queue object with records array
+   */
+  async getQueue(instanceConfig) {
+    try {
+      const response = await axios.get(`${instanceConfig.url}/api/v3/queue`, {
+        headers: { 'X-Api-Key': instanceConfig.apiKey },
+        params: { includeMovie: true }
+      });
+      return response.data;
+    } catch (error) {
+      logToFile(`[PollingRadarrRetriever] ${instanceConfig.id} queue error: ${error.message}`);
+      return { records: [] };
+    }
+  }
+
+  /**
+   * Get history from Radarr instance
+   * @param {Object} instanceConfig - Configuration for the instance
+   * @param {Object} options - Optional parameters for history fetch
+   * @param {number} [options.pageSize=10] - Number of records to fetch
+   * @param {string} [options.sortKey] - Field to sort by
+   * @param {string} [options.sortDir] - Sort direction ('ascending' or 'descending')
+   * @param {boolean} [options.includeMovie=true] - Include movie data
+   * @param {string} [options.startDate] - ISO date string for filtering
+   * @returns {Promise<Object>} History object with records array
+   */
+  async getHistory(instanceConfig, options = {}) {
+    const {
+      pageSize = 10,
+      sortKey,
+      sortDir,
+      includeMovie = true,
+      startDate
+    } = options;
+
+    try {
+      const params = {
+        pageSize,
+        includeMovie
+      };
+
+      if (sortKey) params.sortKey = sortKey;
+      if (sortDir) params.sortDir = sortDir;
+      if (startDate) params.startDate = startDate;
+
+      const response = await axios.get(`${instanceConfig.url}/api/v3/history`, {
+        headers: { 'X-Api-Key': instanceConfig.apiKey },
+        params
+      });
+      return response.data;
+    } catch (error) {
+      logToFile(`[PollingRadarrRetriever] ${instanceConfig.id} history error: ${error.message}`);
+      return { records: [] };
+    }
+  }
+}
+
+module.exports = PollingRadarrRetriever;