Refactor: Extract tag functions to TagMatcher service

- Extract six pure tag-related functions from dashboard.js into new server/services/TagMatcher.js
- Functions: sanitizeTagLabel, tagMatchesUser, extractAllTags, extractUserTag, getEmbyUsers, buildTagBadges
- Update dashboard.js to import TagMatcher and replace all inline function calls
- Add comprehensive unit tests in tests/unit/services/TagMatcher.test.js (26 tests passing for 5 pure functions)
- Note: getEmbyUsers tests excluded due to CommonJS mocking complexity

server/services/TagMatcher.js

@@ -0,0 +1,86 @@
+// Copyright (c) 2026 Gordon Bolton. MIT License.
+const axios = require('axios');
+const cache = require('../utils/cache');
+
+// Return all resolved tag labels for a series/movie.
+// For Radarr: tags is array of IDs, tagMap is id -> label mapping.
+// For Sonarr: tags are objects with a label property.
+function extractAllTags(tags, tagMap) {
+  if (!tags || tags.length === 0) return [];
+  if (tagMap) {
+    return tags.map(id => tagMap.get(id)).filter(Boolean);
+  }
+  return tags.map(t => t && t.label).filter(Boolean);
+}
+
+// Return the tag label that matches the current username, or null.
+function extractUserTag(tags, tagMap, username) {
+  const allLabels = extractAllTags(tags, tagMap);
+  if (!allLabels.length) return null;
+  if (username) {
+    const match = allLabels.find(label => tagMatchesUser(label, username));
+    if (match) return match;
+  }
+  return null;
+}
+
+// Replicate Ombi's StringHelper.SanitizeTagLabel: lowercase, replace non-alphanumeric with hyphen, collapse, trim
+function sanitizeTagLabel(input) {
+  if (!input) return '';
+  return input.toLowerCase().replace(/[^a-z0-9]+/g, '-').replace(/-+/g, '-').replace(/^-|-$/g, '');
+}
+
+// Check if a tag matches the username: exact match first, then sanitized match
+function tagMatchesUser(tag, username) {
+  if (!tag || !username) return false;
+  const tagLower = tag.toLowerCase();
+  // Exact match (handles users whose tags weren't mangled)
+  if (tagLower === username) return true;
+  // Sanitized match (handles Ombi-mangled tags for email-style usernames)
+  if (tagLower === sanitizeTagLabel(username)) return true;
+  return false;
+}
+
+// Fetch all Emby users and return a Map<lowerName -> displayName> (and sanitized variants).
+// Result is cached for 60s to avoid hammering Emby on every dashboard poll.
+async function getEmbyUsers() {
+  const cached = cache.get('emby:users');
+  if (cached) return cached;
+  try {
+    const response = await axios.get(`${process.env.EMBY_URL}/Users`, {
+      headers: { 'X-MediaBrowser-Token': process.env.EMBY_API_KEY }
+    });
+    // Build map: both raw lowercase and sanitized form -> display name
+    const map = new Map();
+    for (const u of response.data) {
+      const name = u.Name || '';
+      map.set(name.toLowerCase(), name);
+      map.set(sanitizeTagLabel(name), name);
+    }
+    cache.set('emby:users', map, 60000);
+    return map;
+  } catch (err) {
+    console.error('[Dashboard] Failed to fetch Emby users:', err.message);
+    return new Map();
+  }
+}
+
+// Classify each tag label: matched to a known Emby user, or unmatched.
+// Returns array of { label, matchedUser: string|null }
+function buildTagBadges(allTags, embyUserMap) {
+  return allTags.map(label => {
+    const lower = label.toLowerCase();
+    const sanitized = sanitizeTagLabel(label);
+    const displayName = embyUserMap.get(lower) || embyUserMap.get(sanitized) || null;
+    return { label, matchedUser: displayName };
+  });
+}
+
+module.exports = {
+  extractAllTags,
+  extractUserTag,
+  sanitizeTagLabel,
+  tagMatchesUser,
+  getEmbyUsers,
+  buildTagBadges
+};