From 6dbac0d3c1bdb12fc4cdf3413f86fa1f9c9834a6 Mon Sep 17 00:00:00 2001
From: sebseb7 <sebgreenbus@gmail.com>
Date: Mon, 24 Nov 2025 12:02:44 +0100
Subject: [PATCH] feat: Implement dedicated data fetchers and utilities for
 categories, products, and images, and add server compression.

---
 index.html                              | 185 ++++++++-------
 package-lock.json                       |  64 +++++
 package.json                            |   3 +-
 src/server/server.js                    |   4 +
 src/services/category-data-fetcher.js   | 141 +++++++++++
 src/services/image-data-fetcher.js      |  40 ++++
 src/services/product-data-fetcher.js    | 109 +++++++++
 src/syncers/category-products-syncer.js | 212 +++++------------
 src/syncers/category-syncer.js          | 298 ++++--------------------
 src/syncers/picture-syncer.js           | 130 +++--------
 src/utils/category-tree-utils.js        | 166 +++++++++++++
 src/utils/database-utils.js             |  58 +++++
 src/utils/file-sync-utils.js            | 134 +++++++++++
 src/utils/sync-queue-manager.js         |  76 ++++++
 14 files changed, 1022 insertions(+), 598 deletions(-)
 create mode 100644 src/services/category-data-fetcher.js
 create mode 100644 src/services/image-data-fetcher.js
 create mode 100644 src/services/product-data-fetcher.js
 create mode 100644 src/utils/category-tree-utils.js
 create mode 100644 src/utils/database-utils.js
 create mode 100644 src/utils/file-sync-utils.js
 create mode 100644 src/utils/sync-queue-manager.js

diff --git a/index.html b/index.html
index 282c276..3494a89 100644
--- a/index.html
+++ b/index.html
@@ -5,6 +5,11 @@
     <meta charset="UTF-8">
     <meta name="viewport" content="width=device-width, initial-scale=1.0">
     <title>Category Tree Viewer</title>
+
+    <!-- Resource hints to optimize loading -->
+    <link rel="preload" href="/socket.io/socket.io.js" as="script">
+    <link rel="preconnect" href="/api">
+
     <style>
         * {
             margin: 0;
@@ -421,11 +426,103 @@
     </div>
     <button id="version-reload-btn" onclick="location.reload()">New version - [reload]</button>
 
-    <script src="/socket.io/socket.io.js"></script>
+    <script src="/socket.io/socket.io.js" async></script>
     <script>
-        const socket = io({
-            transports: ['websocket']
-        });
+        // Initialize socket when io is available (async)
+        function initSocket() {
+            if (typeof io === 'undefined') {
+                // Socket.io not loaded yet, try again soon
+                setTimeout(initSocket, 50);
+                return;
+            }
+
+            const socket = io({
+                transports: ['websocket']
+            });
+
+            // Version checking
+            const clientEtag = document.querySelector('meta[name="app-version"]')?.content;
+            const reloadBtn = document.getElementById('version-reload-btn');
+
+            // Socket Events
+            socket.on('connect', () => {
+                console.log('🔌 Connected to server via WebSocket');
+                // Check version on connect and reconnect
+                if (clientEtag) {
+                    socket.emit('checkVersion', clientEtag);
+                }
+            });
+
+            socket.on('versionMismatch', ({ serverEtag }) => {
+                console.log('⚠️  New version available on server');
+                if (reloadBtn) {
+                    reloadBtn.classList.add('show');
+                }
+            });
+
+            socket.on('categoriesUpdated', () => {
+                console.log('🔄 Categories updated, reloading tree...');
+                loadCategories();
+            });
+
+            socket.on('categoryProductsUpdated', ({ id }) => {
+                console.log(`🔄 Products for category ${id} updated, reloading...`);
+                updateCategoryProducts(id);
+            });
+
+            // Debounce function
+            function debounce(func, wait) {
+                let timeout;
+                return function (...args) {
+                    clearTimeout(timeout);
+                    timeout = setTimeout(() => func.apply(this, args), wait);
+                };
+            }
+
+            const debouncedSearch = debounce((value) => {
+                socket.emit('search', value);
+            }, 300);
+
+            // Event Listeners
+            filterInput.addEventListener('input', (e) => {
+                const value = e.target.value;
+                state.filter = value;
+
+                // Toggle clear button visibility
+                if (value) {
+                    clearBtn.classList.add('visible');
+                } else {
+                    clearBtn.classList.remove('visible');
+                }
+
+                if (value.trim()) {
+                    debouncedSearch(value);
+                } else {
+                    // Clear matches and collapse all categories
+                    resetMatches(state.categories);
+                    resetExpansion(state.categories);
+                    collapseAllProducts(state.categories);
+                    render();
+                }
+            });
+
+            socket.on('searchResults', ({ query, matches }) => {
+                if (query !== state.filter) return;
+
+                const matchSet = new Set(matches);
+
+                // Reset expansion and matches
+                resetExpansion(state.categories);
+
+                // Mark matches and expand
+                markMatches(state.categories, matchSet);
+
+                render();
+            });
+        }
+
+        // Start socket initialization (async, non-blocking)
+        initSocket();
 
         // State management
         const state = {
@@ -444,72 +541,6 @@
             filterInput.focus();
         });
 
-        // Version checking
-        const clientEtag = document.querySelector('meta[name="app-version"]')?.content;
-        const reloadBtn = document.getElementById('version-reload-btn');
-
-        // Socket Events
-        socket.on('connect', () => {
-            console.log('🔌 Connected to server via WebSocket');
-            // Check version on connect and reconnect
-            if (clientEtag) {
-                socket.emit('checkVersion', clientEtag);
-            }
-        });
-
-        socket.on('versionMismatch', ({ serverEtag }) => {
-            console.log('⚠️  New version available on server');
-            if (reloadBtn) {
-                reloadBtn.classList.add('show');
-            }
-        });
-
-        socket.on('categoriesUpdated', () => {
-            console.log('🔄 Categories updated, reloading tree...');
-            loadCategories();
-        });
-
-        socket.on('categoryProductsUpdated', ({ id }) => {
-            console.log(`🔄 Products for category ${id} updated, reloading...`);
-            updateCategoryProducts(id);
-        });
-
-        // Debounce function
-        function debounce(func, wait) {
-            let timeout;
-            return function (...args) {
-                clearTimeout(timeout);
-                timeout = setTimeout(() => func.apply(this, args), wait);
-            };
-        }
-
-        const debouncedSearch = debounce((value) => {
-            socket.emit('search', value);
-        }, 300);
-
-        // Event Listeners
-        filterInput.addEventListener('input', (e) => {
-            const value = e.target.value;
-            state.filter = value;
-
-            // Toggle clear button visibility
-            if (value) {
-                clearBtn.classList.add('visible');
-            } else {
-                clearBtn.classList.remove('visible');
-            }
-
-            if (value.trim()) {
-                debouncedSearch(value);
-            } else {
-                // Clear matches and collapse all categories
-                resetMatches(state.categories);
-                resetExpansion(state.categories);
-                collapseAllProducts(state.categories);
-                render();
-            }
-        });
-
         // Clear button functionality
         clearBtn.addEventListener('click', () => {
             filterInput.value = '';
@@ -526,20 +557,6 @@
             filterInput.focus();
         });
 
-        socket.on('searchResults', ({ query, matches }) => {
-            if (query !== state.filter) return;
-
-            const matchSet = new Set(matches);
-
-            // Reset expansion and matches
-            resetExpansion(state.categories);
-
-            // Mark matches and expand
-            markMatches(state.categories, matchSet);
-
-            render();
-        });
-
         function resetMatches(nodes) {
             nodes.forEach(node => {
                 node._hasMatch = false;
diff --git a/package-lock.json b/package-lock.json
index 108ff4a..ac72c9f 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -8,6 +8,7 @@
       "name": "category-syncer",
       "version": "1.0.0",
       "dependencies": {
+        "compression": "^1.8.1",
         "dotenv": "^17.2.3",
         "express": "^5.1.0",
         "mssql": "^12.1.0",
@@ -1093,6 +1094,60 @@
         "node": ">=16"
       }
     },
+    "node_modules/compressible": {
+      "version": "2.0.18",
+      "resolved": "https://registry.npmjs.org/compressible/-/compressible-2.0.18.tgz",
+      "integrity": "sha512-AF3r7P5dWxL8MxyITRMlORQNaOA2IkAFaTr4k7BUumjPtRpGDTZpl0Pb1XCO6JeDCBdp126Cgs9sMxqSjgYyRg==",
+      "license": "MIT",
+      "dependencies": {
+        "mime-db": ">= 1.43.0 < 2"
+      },
+      "engines": {
+        "node": ">= 0.6"
+      }
+    },
+    "node_modules/compression": {
+      "version": "1.8.1",
+      "resolved": "https://registry.npmjs.org/compression/-/compression-1.8.1.tgz",
+      "integrity": "sha512-9mAqGPHLakhCLeNyxPkK4xVo746zQ/czLH1Ky+vkitMnWfWZps8r0qXuwhwizagCRttsL4lfG4pIOvaWLpAP0w==",
+      "license": "MIT",
+      "dependencies": {
+        "bytes": "3.1.2",
+        "compressible": "~2.0.18",
+        "debug": "2.6.9",
+        "negotiator": "~0.6.4",
+        "on-headers": "~1.1.0",
+        "safe-buffer": "5.2.1",
+        "vary": "~1.1.2"
+      },
+      "engines": {
+        "node": ">= 0.8.0"
+      }
+    },
+    "node_modules/compression/node_modules/debug": {
+      "version": "2.6.9",
+      "resolved": "https://registry.npmjs.org/debug/-/debug-2.6.9.tgz",
+      "integrity": "sha512-bC7ElrdJaJnPbAP+1EotYvqZsb3ecl5wi6Bfi6BJTUcNowp6cvspg0jXznRTKDjm/E7AdgFBVeAPVMNcKGsHMA==",
+      "license": "MIT",
+      "dependencies": {
+        "ms": "2.0.0"
+      }
+    },
+    "node_modules/compression/node_modules/ms": {
+      "version": "2.0.0",
+      "resolved": "https://registry.npmjs.org/ms/-/ms-2.0.0.tgz",
+      "integrity": "sha512-Tpp60P6IUJDTuOq/5Z8cdskzJujfwqfOTkrwIwj7IRISpnkJnT6SyJ4PCPnGMoFjC9ddhal5KVIYtAt97ix05A==",
+      "license": "MIT"
+    },
+    "node_modules/compression/node_modules/negotiator": {
+      "version": "0.6.4",
+      "resolved": "https://registry.npmjs.org/negotiator/-/negotiator-0.6.4.tgz",
+      "integrity": "sha512-myRT3DiWPHqho5PrJaIRyaMv2kgYf0mUVgBNOYMuCH5Ki1yEiQaf/ZJuQ62nvpc44wL5WDbTX7yGJi1Neevw8w==",
+      "license": "MIT",
+      "engines": {
+        "node": ">= 0.6"
+      }
+    },
     "node_modules/concat-map": {
       "version": "0.0.1",
       "resolved": "https://registry.npmjs.org/concat-map/-/concat-map-0.0.1.tgz",
@@ -2136,6 +2191,15 @@
         "node": ">= 0.8"
       }
     },
+    "node_modules/on-headers": {
+      "version": "1.1.0",
+      "resolved": "https://registry.npmjs.org/on-headers/-/on-headers-1.1.0.tgz",
+      "integrity": "sha512-737ZY3yNnXy37FHkQxPzt4UZ2UWPWiCZWLvFZ4fu5cueciegX0zGPnrlY6bwRg4FdQOe9YU8MkmJwGhoMybl8A==",
+      "license": "MIT",
+      "engines": {
+        "node": ">= 0.8"
+      }
+    },
     "node_modules/once": {
       "version": "1.4.0",
       "resolved": "https://registry.npmjs.org/once/-/once-1.4.0.tgz",
diff --git a/package.json b/package.json
index 0a8bc8a..7ff3845 100644
--- a/package.json
+++ b/package.json
@@ -10,6 +10,7 @@
     "test": "node index.js"
   },
   "dependencies": {
+    "compression": "^1.8.1",
     "dotenv": "^17.2.3",
     "express": "^5.1.0",
     "mssql": "^12.1.0",
@@ -20,4 +21,4 @@
   "devDependencies": {
     "nodemon": "^3.1.11"
   }
-}
\ No newline at end of file
+}
diff --git a/src/server/server.js b/src/server/server.js
index 67cd2cf..d2b4a64 100644
--- a/src/server/server.js
+++ b/src/server/server.js
@@ -4,6 +4,7 @@ import { Server } from 'socket.io';
 import path from 'path';
 import { fileURLToPath } from 'url';
 import fs from 'fs/promises';
+import compression from 'compression';
 import { registerCategories } from './routes/categories.js';
 import { registerProducts } from './routes/products.js';
 import { registerImages } from './routes/images.js';
@@ -18,6 +19,9 @@ export function startServer(categorySyncer, categoryProductsSyncer) {
     const httpServer = createServer(app);
     const io = new Server(httpServer);
 
+    // Enable gzip compression for all responses
+    app.use(compression());
+
     const PORT = process.env.SERVER_PORT || 3000;
     const HOST = process.env.SERVER_HOST || '0.0.0.0';
     const CACHE_DIR = process.env.CACHE_LOCATION || './cache';
diff --git a/src/services/category-data-fetcher.js b/src/services/category-data-fetcher.js
new file mode 100644
index 0000000..9c84ede
--- /dev/null
+++ b/src/services/category-data-fetcher.js
@@ -0,0 +1,141 @@
+import { createConnection } from '../utils/database.js';
+
+/**
+ * CategoryDataFetcher - Handles all category-related database queries
+ */
+export class CategoryDataFetcher {
+    /**
+     * Fetch all categories with hierarchy information
+     * @returns {Promise<Array>} - Array of category records
+     */
+    async fetchCategories() {
+        let pool;
+        try {
+            pool = await createConnection();
+            const result = await pool.request().query(`
+                SELECT kKategorie, kOberKategorie, nSort 
+                FROM tkategorie 
+                ORDER BY nSort, kKategorie
+            `);
+            return result.recordset;
+        } finally {
+            if (pool) await pool.close();
+        }
+    }
+
+    /**
+     * Fetch category names for a specific language and shop
+     * @returns {Promise<Array>} - Array of name records
+     */
+    async fetchCategoryNames() {
+        let pool;
+        try {
+            pool = await createConnection();
+            const result = await pool.request().query(`
+                SELECT kKategorie, cName 
+                FROM tKategorieSprache 
+                WHERE kSprache = ${process.env.JTL_SPRACHE_ID} 
+                  AND kShop = ${process.env.JTL_SHOP_ID}
+            `);
+            return result.recordset;
+        } finally {
+            if (pool) await pool.close();
+        }
+    }
+
+    /**
+     * Fetch article counts per category
+     * @returns {Promise<Array>} - Array of count records
+     */
+    async fetchArticleCounts() {
+        let pool;
+        try {
+            pool = await createConnection();
+            const result = await pool.request().query(`
+                SELECT ka.kKategorie, COUNT(a.kArtikel) as count 
+                FROM tkategorieartikel ka 
+                JOIN tArtikel a ON ka.kArtikel = a.kArtikel 
+                WHERE a.cAktiv = 'Y' 
+                GROUP BY ka.kKategorie
+            `);
+            return result.recordset;
+        } finally {
+            if (pool) await pool.close();
+        }
+    }
+
+    /**
+     * Fetch category images (first image per category)
+     * @returns {Promise<Array>} - Array of image records
+     */
+    async fetchCategoryImages() {
+        let pool;
+        try {
+            pool = await createConnection();
+            const result = await pool.request().query(`
+                SELECT kKategorie, kBild
+                FROM (
+                    SELECT kKategorie, kBild, ROW_NUMBER() OVER (PARTITION BY kKategorie ORDER BY nNr ASC) as rn
+                    FROM tKategoriebildPlattform
+                    WHERE kShop = ${process.env.JTL_SHOP_ID} 
+                      AND kPlattform = ${process.env.JTL_PLATTFORM_ID}
+                ) t
+                WHERE rn = 1
+            `);
+            return result.recordset;
+        } finally {
+            if (pool) await pool.close();
+        }
+    }
+
+    /**
+     * Fetch all category data at once
+     * @returns {Promise<Object>} - Object with categories, names, articleCounts, images
+     */
+    async fetchAllCategoryData() {
+        let pool;
+        try {
+            pool = await createConnection();
+
+            const [categoriesResult, namesResult, articleCountsResult, imagesResult] = await Promise.all([
+                pool.request().query(`
+                    SELECT kKategorie, kOberKategorie, nSort 
+                    FROM tkategorie 
+                    ORDER BY nSort, kKategorie
+                `),
+                pool.request().query(`
+                    SELECT kKategorie, cName 
+                    FROM tKategorieSprache 
+                    WHERE kSprache = ${process.env.JTL_SPRACHE_ID} 
+                      AND kShop = ${process.env.JTL_SHOP_ID}
+                `),
+                pool.request().query(`
+                    SELECT ka.kKategorie, COUNT(a.kArtikel) as count 
+                    FROM tkategorieartikel ka 
+                    JOIN tArtikel a ON ka.kArtikel = a.kArtikel 
+                    WHERE a.cAktiv = 'Y' 
+                    GROUP BY ka.kKategorie
+                `),
+                pool.request().query(`
+                    SELECT kKategorie, kBild
+                    FROM (
+                        SELECT kKategorie, kBild, ROW_NUMBER() OVER (PARTITION BY kKategorie ORDER BY nNr ASC) as rn
+                        FROM tKategoriebildPlattform
+                        WHERE kShop = ${process.env.JTL_SHOP_ID} 
+                          AND kPlattform = ${process.env.JTL_PLATTFORM_ID}
+                    ) t
+                    WHERE rn = 1
+                `)
+            ]);
+
+            return {
+                categories: categoriesResult.recordset,
+                names: namesResult.recordset,
+                articleCounts: articleCountsResult.recordset,
+                images: imagesResult.recordset
+            };
+        } finally {
+            if (pool) await pool.close();
+        }
+    }
+}
diff --git a/src/services/image-data-fetcher.js b/src/services/image-data-fetcher.js
new file mode 100644
index 0000000..5fee0e1
--- /dev/null
+++ b/src/services/image-data-fetcher.js
@@ -0,0 +1,40 @@
+import { createConnection } from '../utils/database.js';
+import { processInChunks, createInClause } from '../utils/database-utils.js';
+
+/**
+ * ImageDataFetcher - Handles all image-related database queries
+ */
+export class ImageDataFetcher {
+    /**
+     * Fetch image binary data for given image IDs
+     * @param {Array<number>} imageIds - Image IDs to fetch
+     * @param {Function} imageCallback - Callback for each image (receives {kBild, bBild})
+     * @param {number} chunkSize - Size of each chunk (default: 50)
+     * @returns {Promise<void>}
+     */
+    async fetchImagesInChunks(imageIds, imageCallback, chunkSize = 50) {
+        let pool;
+        try {
+            pool = await createConnection();
+
+            await processInChunks(imageIds, chunkSize, async (chunk) => {
+                const list = createInClause(chunk);
+
+                const result = await pool.request().query(`
+                    SELECT kBild, bBild
+                    FROM tBild
+                    WHERE kBild IN (${list})
+                `);
+
+                for (const record of result.recordset) {
+                    if (record.bBild) {
+                        await imageCallback(record);
+                    }
+                }
+            }, { showProgress: true, itemName: 'images' });
+
+        } finally {
+            if (pool) await pool.close();
+        }
+    }
+}
diff --git a/src/services/product-data-fetcher.js b/src/services/product-data-fetcher.js
new file mode 100644
index 0000000..7c38a1c
--- /dev/null
+++ b/src/services/product-data-fetcher.js
@@ -0,0 +1,109 @@
+import { createConnection } from '../utils/database.js';
+import { processInChunks, createInClause } from '../utils/database-utils.js';
+
+/**
+ * ProductDataFetcher - Handles all product-related database queries
+ */
+export class ProductDataFetcher {
+    /**
+     * Fetch products for given category IDs
+     * @param {Array<number>} categoryIds - Category IDs to fetch products for
+     * @param {Object} pool - Database connection pool
+     * @returns {Promise<Array>} - Array of product records with kKategorie, kArtikel, cName
+     */
+    async fetchProductsForCategories(categoryIds, pool) {
+        const list = createInClause(categoryIds);
+
+        const result = await pool.request().query(`
+            SELECT 
+                ka.kKategorie,
+                ka.kArtikel,
+                ab.cName
+            FROM tkategorieartikel ka
+            JOIN tArtikelBeschreibung ab ON ka.kArtikel = ab.kArtikel
+            JOIN tArtikel a ON ka.kArtikel = a.kArtikel
+            WHERE ab.kSprache = ${process.env.JTL_SPRACHE_ID}
+              AND a.cAktiv = 'Y'
+              AND ab.kPlattform = ${process.env.JTL_PLATTFORM_ID}
+              AND ab.kShop = ${process.env.JTL_SHOP_ID}
+              AND ka.kKategorie IN (${list})
+            ORDER BY (
+                CASE 
+                    WHEN a.bRowversion >= ab.bRowversion AND a.bRowversion >= ka.bRowversion THEN a.bRowversion 
+                    WHEN ab.bRowversion >= a.bRowversion AND ab.bRowversion >= ka.bRowversion THEN ab.bRowversion 
+                    ELSE ka.bRowversion 
+                END
+            ) DESC
+        `);
+
+        return result.recordset;
+    }
+
+    /**
+     * Fetch product images for given article IDs
+     * @param {Array<number>} articleIds - Article IDs to fetch images for
+     * @param {Object} pool - Database connection pool
+     * @returns {Promise<Map>} - Map of kArtikel -> array of kBild
+     */
+    async fetchProductImages(articleIds, pool) {
+        const list = createInClause(articleIds);
+
+        const result = await pool.request().query(`
+            SELECT kArtikel, kBild
+            FROM tArtikelbildPlattform
+            WHERE kShop = ${process.env.JTL_SHOP_ID}
+              AND kPlattform = ${process.env.JTL_PLATTFORM_ID}
+              AND kArtikel IN (${list})
+            ORDER BY nNr ASC
+        `);
+
+        const productImages = new Map();
+        result.recordset.forEach(r => {
+            if (!productImages.has(r.kArtikel)) {
+                productImages.set(r.kArtikel, []);
+            }
+            productImages.get(r.kArtikel).push(r.kBild);
+        });
+
+        return productImages;
+    }
+
+    /**
+     * Fetch products with images for categories in chunks
+     * @param {Array<number>} categoryIds - All category IDs to process
+     * @param {Function} chunkCallback - Callback for each chunk (receives chunk data)
+     * @param {number} chunkSize - Size of each chunk (default: 50)
+     * @returns {Promise<void>}
+     */
+    async fetchProductsInChunks(categoryIds, chunkCallback, chunkSize = 50) {
+        let pool;
+        try {
+            pool = await createConnection();
+
+            await processInChunks(categoryIds, chunkSize, async (chunk) => {
+                // Fetch products for this chunk
+                const products = await this.fetchProductsForCategories(chunk, pool);
+
+                // Collect all article IDs
+                const articleIds = new Set();
+                products.forEach(p => articleIds.add(p.kArtikel));
+
+                // Fetch images for these articles
+                let productImages = new Map();
+                if (articleIds.size > 0) {
+                    productImages = await this.fetchProductImages(Array.from(articleIds), pool);
+                }
+
+                // Call the callback with chunk data
+                await chunkCallback({
+                    categoryIds: chunk,
+                    products,
+                    productImages
+                });
+            }, { showProgress: false, itemName: 'categories' });
+
+        } finally {
+            if (pool) await pool.close();
+        }
+    }
+}
diff --git a/src/syncers/category-products-syncer.js b/src/syncers/category-products-syncer.js
index c9e64a1..64f1152 100644
--- a/src/syncers/category-products-syncer.js
+++ b/src/syncers/category-products-syncer.js
@@ -1,7 +1,9 @@
 import fs from 'fs/promises';
 import path from 'path';
 import { EventEmitter } from 'events';
-import { createConnection } from '../utils/database.js';
+import { SyncQueueManager } from '../utils/sync-queue-manager.js';
+import { ProductDataFetcher } from '../services/product-data-fetcher.js';
+import { getExistingIds, deleteObsoleteFiles, writeJsonIfChanged, ensureDir } from '../utils/file-sync-utils.js';
 import pictureSyncer from './picture-syncer.js';
 
 class CategoryProductsSyncer extends EventEmitter {
@@ -10,38 +12,18 @@ class CategoryProductsSyncer extends EventEmitter {
         if (CategoryProductsSyncer.instance) {
             return CategoryProductsSyncer.instance;
         }
-        this.cacheBaseDir = process.env.CACHE_LOCATION || '.';
 
-        // Track syncing state
-        this.isSyncing = false;
-        this.queuedCategoryIds = null;
+        this.syncQueue = new SyncQueueManager();
+        this.dataFetcher = new ProductDataFetcher();
+        this.cacheBaseDir = process.env.CACHE_LOCATION || '.';
 
         CategoryProductsSyncer.instance = this;
     }
 
     async syncProducts(categoryIds) {
-        // Check if already syncing
-        if (this.isSyncing) {
-            console.log('⏳ CategoryProductsSyncer is busy. Queuing sync...');
-            this.queuedCategoryIds = categoryIds;
-            return;
-        }
-
-        this.isSyncing = true;
-        try {
+        await this.syncQueue.executeSync('category-products-sync', async () => {
             await this._performSync(categoryIds);
-        } catch (err) {
-            console.error('❌ Error syncing products:', err);
-        } finally {
-            this.isSyncing = false;
-            // Process queued sync if exists
-            if (this.queuedCategoryIds) {
-                const nextIds = this.queuedCategoryIds;
-                this.queuedCategoryIds = null;
-                // Use setTimeout to allow event loop to breathe
-                setTimeout(() => this.syncProducts(nextIds), 0);
-            }
-        }
+        }, categoryIds);
     }
 
     async _performSync(categoryIds) {
@@ -49,37 +31,26 @@ class CategoryProductsSyncer extends EventEmitter {
         const productsDir = path.join(this.cacheBaseDir, 'products');
 
         // Ensure directory exists
-        await fs.mkdir(productsDir, { recursive: true });
+        await ensureDir(productsDir);
 
         // Get existing files
-        let existingFiles = [];
-        try {
-            existingFiles = await fs.readdir(productsDir);
-        } catch (err) {
-            // Directory might be empty or new
-        }
-
-        // Filter for category json files (assuming we save as category_{id}.json)
-        const existingIds = existingFiles
-            .filter(f => f.startsWith('category_') && f.endsWith('.json'))
-            .map(f => parseInt(f.replace('category_', '').replace('.json', '')));
+        const existingIds = await getExistingIds(productsDir, {
+            prefix: 'category_',
+            suffix: '.json'
+        });
 
         const validIds = new Set(categoryIds.filter(id => id !== null && id !== undefined));
 
-        // 1. Delete obsolete category files
-        const toDelete = existingIds.filter(id => !validIds.has(id));
-        for (const id of toDelete) {
-            const filePath = path.join(productsDir, `category_${id}.json`);
-            await fs.unlink(filePath);
-        }
-        if (toDelete.length > 0) {
-            console.log(`🗑️  Deleted ${toDelete.length} obsolete product lists.`);
-        }
+        // Delete obsolete category files
+        await deleteObsoleteFiles(
+            productsDir,
+            existingIds,
+            validIds,
+            (id) => `category_${id}.json`
+        );
 
-        // 2. Update/Create product lists for all valid categories
-        // We update all because product assignments might have changed even if category exists
+        // Update/Create product lists for all valid categories
         if (validIds.size > 0) {
-            //console.log(`📦 Syncing products for ${validIds.size} categories...`);
             await this._fetchAndWriteProducts([...validIds], productsDir);
         } else {
             console.log(`✅ No categories to sync products for.`);
@@ -90,128 +61,49 @@ class CategoryProductsSyncer extends EventEmitter {
     }
 
     async _fetchAndWriteProducts(ids, dir) {
-        let pool;
         const globalImageIds = new Set();
 
-        try {
-            pool = await createConnection();
+        await this.dataFetcher.fetchProductsInChunks(ids, async (chunkData) => {
+            const { categoryIds, products, productImages } = chunkData;
 
-            // Process in chunks to avoid huge queries
-            const chunkSize = 50;
-            for (let i = 0; i < ids.length; i += chunkSize) {
-                const chunk = ids.slice(i, i + chunkSize);
-                const list = chunk.join(',');
+            // Group results by kKategorie
+            const productsByCategory = {};
 
-                // Fetch products for this chunk of categories
-                // We need kArtikel and cName, ordered by bRowversion descending
-                const result = await pool.request().query(`
-                    SELECT 
-                        ka.kKategorie,
-                        ka.kArtikel,
-                        ab.cName
-                    FROM tkategorieartikel ka
-                    JOIN tArtikelBeschreibung ab ON ka.kArtikel = ab.kArtikel
-                    JOIN tArtikel a ON ka.kArtikel = a.kArtikel
-                    WHERE ab.kSprache = ${process.env.JTL_SPRACHE_ID}
-                      AND a.cAktiv = 'Y'
-                      AND ab.kPlattform = ${process.env.JTL_PLATTFORM_ID}
-                      AND ab.kShop = ${process.env.JTL_SHOP_ID}
-                      AND ka.kKategorie IN (${list})
-                    ORDER BY (
-                        CASE 
-                            WHEN a.bRowversion >= ab.bRowversion AND a.bRowversion >= ka.bRowversion THEN a.bRowversion 
-                            WHEN ab.bRowversion >= a.bRowversion AND ab.bRowversion >= ka.bRowversion THEN ab.bRowversion 
-                            ELSE ka.bRowversion 
-                        END
-                    ) DESC
-                `);
+            // Initialize arrays for all requested IDs (so we create empty files for empty categories)
+            categoryIds.forEach(id => {
+                productsByCategory[id] = [];
+            });
 
-                // Collect all kArtikel IDs to fetch images
-                const artikelIds = new Set();
-                result.recordset.forEach(r => artikelIds.add(r.kArtikel));
+            for (const record of products) {
+                if (productsByCategory[record.kKategorie]) {
+                    const images = productImages.get(record.kArtikel) || [];
+                    images.forEach(imgId => globalImageIds.add(imgId));
 
-                // Fetch images for these articles
-                let productImages = new Map(); // kArtikel -> kBild[]
-                if (artikelIds.size > 0) {
-                    const artikelList = Array.from(artikelIds).join(',');
-                    const imagesResult = await pool.request().query(`
-                        SELECT kArtikel, kBild
-                        FROM tArtikelbildPlattform
-                        WHERE kShop = ${process.env.JTL_SHOP_ID}
-                          AND kPlattform = ${process.env.JTL_PLATTFORM_ID}
-                          AND kArtikel IN (${artikelList})
-                        ORDER BY nNr ASC
-                    `);
-
-                    imagesResult.recordset.forEach(r => {
-                        if (!productImages.has(r.kArtikel)) {
-                            productImages.set(r.kArtikel, []);
-                        }
-                        productImages.get(r.kArtikel).push(r.kBild);
+                    productsByCategory[record.kKategorie].push({
+                        kArtikel: record.kArtikel,
+                        cName: record.cName,
+                        images: images
                     });
                 }
-
-                // Group results by kKategorie
-                const productsByCategory = {};
-
-                // Initialize arrays for all requested IDs (so we create empty files for empty categories)
-                chunk.forEach(id => {
-                    productsByCategory[id] = [];
-                });
-
-                for (const record of result.recordset) {
-                    if (productsByCategory[record.kKategorie]) {
-                        const images = productImages.get(record.kArtikel) || [];
-                        images.forEach(imgId => globalImageIds.add(imgId));
-
-                        productsByCategory[record.kKategorie].push({
-                            kArtikel: record.kArtikel,
-                            cName: record.cName,
-                            images: images
-                        });
-                    }
-                }
-
-                // Write files
-                for (const catId of chunk) {
-                    const filePath = path.join(dir, `category_${catId}.json`);
-                    const products = productsByCategory[catId] || [];
-                    const newContent = JSON.stringify(products, null, 2);
-
-                    // Check for changes
-                    let oldContent = '';
-                    try {
-                        oldContent = await fs.readFile(filePath, 'utf-8');
-                    } catch (e) {
-                        // File doesn't exist yet
-                    }
-
-                    if (oldContent !== newContent) {
-                        await fs.writeFile(filePath, newContent);
-                        this.emit('categoryUpdated', { id: catId, products });
-                    }
-                }
-
-                const processed = Math.min(i + chunkSize, ids.length);
-                if (processed === ids.length) {
-                    //console.log(`✅ Processed products for ${processed}/${ids.length} categories.`);
-                } else {
-                    //console.log(`⏳ Processed products for ${processed}/${ids.length} categories...`);
-                }
             }
 
-            // Sync all collected images at once
-            if (globalImageIds.size > 0) {
-                //console.log(`🖼️  Syncing ${globalImageIds.size} product images...`);
-                await pictureSyncer.syncImages(Array.from(globalImageIds), 'products');
-            }
+            // Write files
+            for (const catId of categoryIds) {
+                const filePath = path.join(dir, `category_${catId}.json`);
+                const categoryProducts = productsByCategory[catId] || [];
 
-        } catch (err) {
-            console.error('❌ Error fetching products:', err);
-        } finally {
-            if (pool) {
-                await pool.close();
+                const changed = await writeJsonIfChanged(filePath, categoryProducts);
+
+                if (changed) {
+                    this.emit('categoryUpdated', { id: catId, products: categoryProducts });
+                }
             }
+        });
+
+        // Sync all collected images at once
+        if (globalImageIds.size > 0) {
+            //console.log(`🖼️  Syncing ${globalImageIds.size} product images...`);
+            await pictureSyncer.syncImages(Array.from(globalImageIds), 'products');
         }
     }
 }
diff --git a/src/syncers/category-syncer.js b/src/syncers/category-syncer.js
index 9153a56..af7daa8 100644
--- a/src/syncers/category-syncer.js
+++ b/src/syncers/category-syncer.js
@@ -1,7 +1,10 @@
 import { EventEmitter } from 'events';
 import fs from 'fs/promises';
 import path from 'path';
-import { createConnection } from '../utils/database.js';
+import { SyncQueueManager } from '../utils/sync-queue-manager.js';
+import { CategoryDataFetcher } from '../services/category-data-fetcher.js';
+import { buildTree, pruneTree, buildTranslationTemplate, formatTranslationTemplate } from '../utils/category-tree-utils.js';
+import { readTextFile } from '../utils/file-sync-utils.js';
 
 class CategorySyncer extends EventEmitter {
     constructor() {
@@ -10,8 +13,8 @@ class CategorySyncer extends EventEmitter {
             return CategorySyncer.instance;
         }
 
-        this.isSyncing = false;
-        this.queuedSync = false;
+        this.syncQueue = new SyncQueueManager();
+        this.dataFetcher = new CategoryDataFetcher();
         this.cacheDir = process.env.CACHE_LOCATION || '.';
         this.lastTreeString = null;
         this.lastTemplateString = null;
@@ -23,40 +26,21 @@ class CategorySyncer extends EventEmitter {
     }
 
     async _loadExistingTemplate() {
-        try {
-            const templatePath = path.join(this.cacheDir, 'categories_translation_template.txt');
-            this.lastTemplateString = await fs.readFile(templatePath, 'utf-8');
-        } catch (err) {
-            // File doesn't exist yet, that's fine
-        }
+        const templatePath = path.join(this.cacheDir, 'categories_translation_template.txt');
+        this.lastTemplateString = await readTextFile(templatePath);
 
-        try {
-            const treePath = path.join(this.cacheDir, 'category_tree.json');
-            const treeContent = await fs.readFile(treePath, 'utf-8');
-            this.lastTreeString = treeContent;
-        } catch (err) {
-            // File doesn't exist yet, that's fine
-        }
+        const treePath = path.join(this.cacheDir, 'category_tree.json');
+        this.lastTreeString = await readTextFile(treePath);
     }
 
     async triggerSync() {
-        if (this.isSyncing) {
-            if (this.queuedSync) {
-                console.log('🚫 Sync already in progress and next sync already queued. Ignoring.');
-                return;
-            }
-            console.log('⏳ Sync already in progress. Queuing next sync.');
-            this.queuedSync = true;
-            return;
-        }
-
-        await this._doSync();
+        await this.syncQueue.executeSync('category-sync', async () => {
+            await this._doSync();
+        });
     }
 
     async _doSync() {
-        this.isSyncing = true;
         const startTime = Date.now();
-        //console.log('🚀 Starting sync...');
 
         try {
             await this._syncFromDb();
@@ -68,247 +52,53 @@ class CategorySyncer extends EventEmitter {
             //console.log(`✅ Sync completed in ${duration}ms. Next sync in ${minutes} minute${minutes !== 1 ? 's' : ''}`);
         } catch (err) {
             console.error('❌ Sync failed:', err);
-        } finally {
-            this.isSyncing = false;
-            if (this.queuedSync) {
-                console.log('🔄 Processing queued sync...');
-                this.queuedSync = false;
-                // Use setImmediate to allow stack to clear/event loop to tick
-                setImmediate(() => this.triggerSync());
-            }
         }
     }
 
     async _syncFromDb() {
-        let pool;
-        try {
-            pool = await createConnection();
+        // Fetch all category data
+        const { categories, names, articleCounts, images } = await this.dataFetcher.fetchAllCategoryData();
 
-            // Fetch categories
-            const categoriesResult = await pool.request().query(`
-                SELECT kKategorie, kOberKategorie, nSort 
-                FROM tkategorie 
-                ORDER BY nSort, kKategorie
-            `);
+        // Build tree with ROOT_CATEGORY_ID filter (if set)
+        let tree = buildTree(categories, names, articleCounts, images, true);
 
-            // Fetch names
-            const namesResult = await pool.request().query(`
-                SELECT kKategorie, cName 
-                FROM tKategorieSprache 
-                WHERE kSprache = ${process.env.JTL_SPRACHE_ID} AND kShop = ${process.env.JTL_SHOP_ID}
-            `);
+        // Deep copy tree for unpruned version (before pruning modifies it)
+        const unprunedTree = JSON.parse(JSON.stringify(tree));
 
-            // Fetch article counts
-            const articleCountsResult = await pool.request().query(`
-                SELECT ka.kKategorie, COUNT(a.kArtikel) as count 
-                FROM tkategorieartikel ka 
-                JOIN tArtikel a ON ka.kArtikel = a.kArtikel 
-                WHERE a.cAktiv = 'Y' 
-                GROUP BY ka.kKategorie
-            `);
+        // Generate translation template BEFORE pruning (to include all categories)
+        const translationTemplate = buildTranslationTemplate(tree);
+        const templateString = formatTranslationTemplate(translationTemplate);
 
-            // Fetch images (kBild)
-            const imagesResult = await pool.request().query(`
-                SELECT kKategorie, kBild
-                FROM (
-                    SELECT kKategorie, kBild, ROW_NUMBER() OVER (PARTITION BY kKategorie ORDER BY nNr ASC) as rn
-                    FROM tKategoriebildPlattform
-                    WHERE kShop = ${process.env.JTL_SHOP_ID} AND kPlattform = ${process.env.JTL_PLATTFORM_ID}
-                ) t
-                WHERE rn = 1
-            `);
+        // Now prune for the main tree
+        tree = pruneTree(tree);
 
-            const categories = categoriesResult.recordset;
-            const names = namesResult.recordset;
-            const articleCounts = articleCountsResult.recordset;
-            const images = imagesResult.recordset;
+        // Ensure directory exists
+        await fs.mkdir(this.cacheDir, { recursive: true });
 
-            // Build tree with ROOT_CATEGORY_ID filter (if set)
-            // This gives us the subtree we're interested in
-            let tree = this._buildTree(categories, names, articleCounts, images, true);
+        // Compare pruned tree
+        const treeString = JSON.stringify(tree, null, 2);
+        const changed = this.lastTreeString !== treeString;
 
-            // Deep copy tree for unpruned version (before pruning modifies it)
-            const unprunedTree = JSON.parse(JSON.stringify(tree));
-
-            // Generate translation template BEFORE pruning (to include all categories)
-            const translationTemplate = this._buildTranslationTemplate(tree);
-            const templateString = this._formatTranslationTemplate(translationTemplate);
-
-            // Now prune for the main tree
-            tree = this._pruneTree(tree);
-
-            // Ensure directory exists
-            await fs.mkdir(this.cacheDir, { recursive: true });
-
-            // Compare pruned tree
-            const treeString = JSON.stringify(tree, null, 2);
-            const changed = this.lastTreeString !== treeString;
-
-            if (changed) {
-                // Save template if it changed
-                if (this.lastTemplateString !== templateString) {
-                    const templatePath = path.join(this.cacheDir, 'categories_translation_template.txt');
-                    await fs.writeFile(templatePath, templateString);
-                    console.log(`💾 Translation template saved to ${templatePath}`);
-                    this.lastTemplateString = templateString;
-                }
-
-                const filePath = path.join(this.cacheDir, 'category_tree.json');
-                await fs.writeFile(filePath, treeString);
-                console.log(`💾 Category tree saved to ${filePath}`);
-
-                this.lastTreeString = treeString;
-                console.log('📢 Tree updated.');
-            } else {
-                //console.log('🤷 No changes detected in category tree.');
+        if (changed) {
+            // Save template if it changed
+            if (this.lastTemplateString !== templateString) {
+                const templatePath = path.join(this.cacheDir, 'categories_translation_template.txt');
+                await fs.writeFile(templatePath, templateString);
+                console.log(`💾 Translation template saved to ${templatePath}`);
+                this.lastTemplateString = templateString;
             }
 
-            this.emit('synced', { tree, unprunedTree, changed });
+            const filePath = path.join(this.cacheDir, 'category_tree.json');
+            await fs.writeFile(filePath, treeString);
+            console.log(`💾 Category tree saved to ${filePath}`);
 
-        } finally {
-            if (pool) {
-                await pool.close();
-            }
-        }
-    }
-
-    _buildTree(categories, names, articleCounts, images, applyRootFilter = true) {
-        // Create a map for quick lookup of names
-        const nameMap = new Map();
-        names.forEach(n => nameMap.set(n.kKategorie, n.cName));
-
-        // Create a map for article counts
-        const countMap = new Map();
-        articleCounts.forEach(c => countMap.set(c.kKategorie, c.count));
-
-        // Create a map for images
-        const imageMap = new Map();
-        images.forEach(i => imageMap.set(i.kKategorie, i.kBild));
-
-        // Create a map for category nodes
-        const categoryMap = new Map();
-
-        // Initialize all nodes
-        categories.forEach(cat => {
-            categoryMap.set(cat.kKategorie, {
-                kKategorie: cat.kKategorie,
-                cName: nameMap.get(cat.kKategorie) || `Unknown (${cat.kKategorie})`, // Fallback if name missing
-                articleCount: countMap.get(cat.kKategorie) || 0,
-                kBild: imageMap.get(cat.kKategorie) || null,
-                children: [],
-                nSort: cat.nSort || 0 // Store nSort temporarily
-            });
-        });
-
-        const rootNodes = [];
-
-        // Parse excluded IDs
-        const excludedIds = new Set(
-            (process.env.EXCLUDE_CATEGORY_IDS || '')
-                .split(',')
-                .map(id => parseInt(id.trim()))
-                .filter(id => !isNaN(id))
-        );
-
-        // Build hierarchy
-        categories.forEach(cat => {
-            // Skip if excluded
-            if (excludedIds.has(cat.kKategorie)) return;
-
-            const node = categoryMap.get(cat.kKategorie);
-            if (cat.kOberKategorie === 0) {
-                rootNodes.push(node);
-            } else {
-                const parent = categoryMap.get(cat.kOberKategorie);
-                if (parent) {
-                    parent.children.push(node);
-                } else {
-                    // Handle orphan nodes if necessary, or ignore
-                    // console.warn(`Orphan category found: ${cat.kKategorie}`);
-                }
-            }
-        });
-
-        const rootId = process.env.ROOT_CATEGORY_ID ? parseInt(process.env.ROOT_CATEGORY_ID) : null;
-        let resultNodes = rootNodes;
-
-        if (rootId && applyRootFilter) {
-            if (excludedIds.has(rootId)) {
-                resultNodes = [];
-            } else {
-                const specificRoot = categoryMap.get(rootId);
-                // Return the children of the specified root, not the root itself
-                resultNodes = specificRoot ? specificRoot.children : [];
-            }
+            this.lastTreeString = treeString;
+            console.log('📢 Tree updated.');
+        } else {
+            //console.log('🤷 No changes detected in category tree.');
         }
 
-        // Sort children and remove nSort
-        for (const node of categoryMap.values()) {
-            node.children.sort((a, b) => a.nSort - b.nSort || a.kKategorie - b.kKategorie);
-        }
-
-        // Sort root nodes if returning multiple
-        resultNodes.sort((a, b) => a.nSort - b.nSort || a.kKategorie - b.kKategorie);
-
-        // Remove nSort property from all nodes
-        for (const node of categoryMap.values()) {
-            delete node.nSort;
-        }
-
-        return resultNodes;
-    }
-
-    _pruneTree(nodes) {
-        // Filter out nodes that are empty (no articles) and have no valid children
-        return nodes.filter(node => {
-            // Recursively prune children
-            if (node.children && node.children.length > 0) {
-                node.children = this._pruneTree(node.children);
-            }
-
-            // Keep node if it has articles OR has remaining children
-            const hasArticles = node.articleCount > 0;
-            const hasChildren = node.children && node.children.length > 0;
-
-            return hasArticles || hasChildren;
-        });
-    }
-
-    _buildTranslationTemplate(nodes) {
-        return nodes.map(node => {
-            const result = { name: node.cName };
-            if (node.children && node.children.length > 0) {
-                result.children = this._buildTranslationTemplate(node.children);
-            }
-            return result;
-        });
-    }
-
-    _formatTranslationTemplate(nodes, indent = 0) {
-        const spaces = '  '.repeat(indent);
-        const innerSpaces = '  '.repeat(indent + 1);
-
-        if (nodes.length === 0) return '[]';
-
-        const lines = ['['];
-
-        nodes.forEach((node, index) => {
-            const isLast = index === nodes.length - 1;
-
-            if (node.children && node.children.length > 0) {
-                // Node with children - multi-line format
-                lines.push(`${innerSpaces}{`);
-                lines.push(`${innerSpaces}  "name": "${node.name}",`);
-                lines.push(`${innerSpaces}  "children": ${this._formatTranslationTemplate(node.children, indent + 2)}`);
-                lines.push(`${innerSpaces}}${isLast ? '' : ','}`);
-            } else {
-                // Leaf node - single line format
-                lines.push(`${innerSpaces}{ "name": "${node.name}" }${isLast ? '' : ','}`);
-            }
-        });
-
-        lines.push(`${spaces}]`);
-        return lines.join('\n');
+        this.emit('synced', { tree, unprunedTree, changed });
     }
 }
 
diff --git a/src/syncers/picture-syncer.js b/src/syncers/picture-syncer.js
index 1f5fe23..61c4bef 100644
--- a/src/syncers/picture-syncer.js
+++ b/src/syncers/picture-syncer.js
@@ -1,87 +1,51 @@
 import fs from 'fs/promises';
 import path from 'path';
 import sharp from 'sharp';
-import { createConnection } from '../utils/database.js';
+import { SyncQueueManager } from '../utils/sync-queue-manager.js';
+import { ImageDataFetcher } from '../services/image-data-fetcher.js';
+import { getExistingIds, deleteObsoleteFiles, ensureDir } from '../utils/file-sync-utils.js';
 
 class PictureSyncer {
     constructor() {
         if (PictureSyncer.instance) {
             return PictureSyncer.instance;
         }
-        this.cacheBaseDir = process.env.CACHE_LOCATION || '.';
 
-        // Track syncing state per group
-        this.isSyncing = new Map(); // groupName -> boolean
-        this.queuedSyncs = new Map(); // groupName -> { imageIds, groupName }
+        this.syncQueue = new SyncQueueManager();
+        this.dataFetcher = new ImageDataFetcher();
+        this.cacheBaseDir = process.env.CACHE_LOCATION || '.';
 
         PictureSyncer.instance = this;
     }
 
     async syncImages(imageIds, groupName) {
-        // Check if already syncing this group
-        if (this.isSyncing.get(groupName)) {
-            if (this.queuedSyncs.has(groupName)) {
-                console.log(`🚫 Image sync for '${groupName}' already in progress and queued. Ignoring.`);
-                return;
-            }
-            console.log(`⏳ Image sync for '${groupName}' already in progress. Queuing.`);
-            this.queuedSyncs.set(groupName, { imageIds, groupName });
-            return;
-        }
-
-        await this._doSync(imageIds, groupName);
-    }
-
-    async _doSync(imageIds, groupName) {
-        this.isSyncing.set(groupName, true);
-
-        try {
+        await this.syncQueue.executeSync(groupName, async () => {
             await this._performSync(imageIds, groupName);
-        } finally {
-            this.isSyncing.set(groupName, false);
-
-            // Process queued sync for this group if any
-            if (this.queuedSyncs.has(groupName)) {
-                console.log(`🔄 Processing queued image sync for '${groupName}'...`);
-                const queued = this.queuedSyncs.get(groupName);
-                this.queuedSyncs.delete(groupName);
-                setImmediate(() => this.syncImages(queued.imageIds, queued.groupName));
-            }
-        }
+        }, { imageIds, groupName });
     }
 
     async _performSync(imageIds, groupName) {
         const groupDir = path.join(this.cacheBaseDir, 'img', groupName);
 
         // Ensure directory exists
-        await fs.mkdir(groupDir, { recursive: true });
+        await ensureDir(groupDir);
 
         // Get existing files
-        let existingFiles = [];
-        try {
-            existingFiles = await fs.readdir(groupDir);
-        } catch (err) {
-            // Directory might be empty or new
-        }
-
-        // Filter for image files (assuming we save as {id}.avif)
-        const existingIds = existingFiles
-            .filter(f => f.endsWith('.avif'))
-            .map(f => parseInt(f.replace('.avif', '')));
+        const existingIds = await getExistingIds(groupDir, {
+            suffix: '.avif'
+        });
 
         const validIds = new Set(imageIds.filter(id => id !== null && id !== undefined));
 
-        // 1. Delete obsolete images
-        const toDelete = existingIds.filter(id => !validIds.has(id));
-        for (const id of toDelete) {
-            const filePath = path.join(groupDir, `${id}.avif`);
-            await fs.unlink(filePath);
-        }
-        if (toDelete.length > 0) {
-            console.log(`🗑️  Deleted ${toDelete.length} obsolete images.`);
-        }
+        // Delete obsolete images
+        await deleteObsoleteFiles(
+            groupDir,
+            existingIds,
+            validIds,
+            (id) => `${id}.avif`
+        );
 
-        // 2. Download missing images
+        // Download missing images
         const toDownload = imageIds.filter(id => id !== null && id !== undefined && !existingIds.includes(id));
 
         if (toDownload.length > 0) {
@@ -93,49 +57,17 @@ class PictureSyncer {
     }
 
     async _downloadImages(ids, dir) {
-        let pool;
-        try {
-            pool = await createConnection();
-
-            // Process in chunks to avoid huge queries
-            const chunkSize = 50;
-            for (let i = 0; i < ids.length; i += chunkSize) {
-                const chunk = ids.slice(i, i + chunkSize);
-                const list = chunk.join(',');
-
-                const result = await pool.request().query(`
-                    SELECT kBild, bBild
-                    FROM tBild
-                    WHERE kBild IN (${list})
-                `);
-
-                for (const record of result.recordset) {
-                    if (record.bBild) {
-                        const filePath = path.join(dir, `${record.kBild}.avif`);
-                        // Resize to 130x130 and convert to AVIF using sharp
-                        await sharp(record.bBild)
-                            .resize(130, 130, {
-                                fit: 'cover',
-                                position: 'center'
-                            })
-                            .avif({ quality: 80 })
-                            .toFile(filePath);
-                    }
-                }
-                const processed = Math.min(i + chunkSize, ids.length);
-                if (processed === ids.length) {
-                    console.log(`✅ Processed ${processed}/${ids.length} images.`);
-                } else {
-                    console.log(`⏳ Processed ${processed}/${ids.length} images...`);
-                }
-            }
-        } catch (err) {
-            console.error('❌ Error downloading images:', err);
-        } finally {
-            if (pool) {
-                await pool.close();
-            }
-        }
+        await this.dataFetcher.fetchImagesInChunks(ids, async (record) => {
+            const filePath = path.join(dir, `${record.kBild}.avif`);
+            // Resize to 130x130 and convert to AVIF using sharp
+            await sharp(record.bBild)
+                .resize(130, 130, {
+                    fit: 'cover',
+                    position: 'center'
+                })
+                .avif({ quality: 80 })
+                .toFile(filePath);
+        });
     }
 }
 
diff --git a/src/utils/category-tree-utils.js b/src/utils/category-tree-utils.js
new file mode 100644
index 0000000..c2b16b6
--- /dev/null
+++ b/src/utils/category-tree-utils.js
@@ -0,0 +1,166 @@
+/**
+ * Category tree manipulation utilities
+ */
+
+/**
+ * Parse excluded category IDs from environment variable
+ * @returns {Set<number>} - Set of excluded category IDs
+ */
+export function parseExcludedIds() {
+    return new Set(
+        (process.env.EXCLUDE_CATEGORY_IDS || '')
+            .split(',')
+            .map(id => parseInt(id.trim()))
+            .filter(id => !isNaN(id))
+    );
+}
+
+/**
+ * Build a hierarchical category tree from flat data
+ * @param {Array} categories - Category records with kKategorie, kOberKategorie, nSort
+ * @param {Array} names - Name records with kKategorie, cName
+ * @param {Array} articleCounts - Article count records with kKategorie, count
+ * @param {Array} images - Image records with kKategorie, kBild
+ * @param {boolean} applyRootFilter - Whether to apply ROOT_CATEGORY_ID filter
+ * @returns {Array} - Array of root category nodes
+ */
+export function buildTree(categories, names, articleCounts, images, applyRootFilter = true) {
+    // Create maps for quick lookup
+    const nameMap = new Map();
+    names.forEach(n => nameMap.set(n.kKategorie, n.cName));
+
+    const countMap = new Map();
+    articleCounts.forEach(c => countMap.set(c.kKategorie, c.count));
+
+    const imageMap = new Map();
+    images.forEach(i => imageMap.set(i.kKategorie, i.kBild));
+
+    const categoryMap = new Map();
+
+    // Initialize all nodes
+    categories.forEach(cat => {
+        categoryMap.set(cat.kKategorie, {
+            kKategorie: cat.kKategorie,
+            cName: nameMap.get(cat.kKategorie) || `Unknown (${cat.kKategorie})`,
+            articleCount: countMap.get(cat.kKategorie) || 0,
+            kBild: imageMap.get(cat.kKategorie) || null,
+            children: [],
+            nSort: cat.nSort || 0
+        });
+    });
+
+    const rootNodes = [];
+    const excludedIds = parseExcludedIds();
+
+    // Build hierarchy
+    categories.forEach(cat => {
+        // Skip if excluded
+        if (excludedIds.has(cat.kKategorie)) return;
+
+        const node = categoryMap.get(cat.kKategorie);
+        if (cat.kOberKategorie === 0) {
+            rootNodes.push(node);
+        } else {
+            const parent = categoryMap.get(cat.kOberKategorie);
+            if (parent) {
+                parent.children.push(node);
+            }
+        }
+    });
+
+    const rootId = process.env.ROOT_CATEGORY_ID ? parseInt(process.env.ROOT_CATEGORY_ID) : null;
+    let resultNodes = rootNodes;
+
+    if (rootId && applyRootFilter) {
+        if (excludedIds.has(rootId)) {
+            resultNodes = [];
+        } else {
+            const specificRoot = categoryMap.get(rootId);
+            // Return the children of the specified root, not the root itself
+            resultNodes = specificRoot ? specificRoot.children : [];
+        }
+    }
+
+    // Sort children and remove nSort
+    for (const node of categoryMap.values()) {
+        node.children.sort((a, b) => a.nSort - b.nSort || a.kKategorie - b.kKategorie);
+    }
+
+    // Sort root nodes
+    resultNodes.sort((a, b) => a.nSort - b.nSort || a.kKategorie - b.kKategorie);
+
+    // Remove nSort property from all nodes
+    for (const node of categoryMap.values()) {
+        delete node.nSort;
+    }
+
+    return resultNodes;
+}
+
+/**
+ * Prune tree to remove empty categories with no children
+ * @param {Array} nodes - Array of category nodes
+ * @returns {Array} - Filtered array of nodes
+ */
+export function pruneTree(nodes) {
+    return nodes.filter(node => {
+        // Recursively prune children
+        if (node.children && node.children.length > 0) {
+            node.children = pruneTree(node.children);
+        }
+
+        // Keep node if it has articles OR has remaining children
+        const hasArticles = node.articleCount > 0;
+        const hasChildren = node.children && node.children.length > 0;
+
+        return hasArticles || hasChildren;
+    });
+}
+
+/**
+ * Build translation template structure from tree
+ * @param {Array} nodes - Array of category nodes
+ * @returns {Array} - Simplified structure with only names and children
+ */
+export function buildTranslationTemplate(nodes) {
+    return nodes.map(node => {
+        const result = { name: node.cName };
+        if (node.children && node.children.length > 0) {
+            result.children = buildTranslationTemplate(node.children);
+        }
+        return result;
+    });
+}
+
+/**
+ * Format translation template as formatted JSON string
+ * @param {Array} nodes - Translation template nodes
+ * @param {number} indent - Current indentation level
+ * @returns {string} - Formatted JSON string
+ */
+export function formatTranslationTemplate(nodes, indent = 0) {
+    const spaces = '  '.repeat(indent);
+    const innerSpaces = '  '.repeat(indent + 1);
+
+    if (nodes.length === 0) return '[]';
+
+    const lines = ['['];
+
+    nodes.forEach((node, index) => {
+        const isLast = index === nodes.length - 1;
+
+        if (node.children && node.children.length > 0) {
+            // Node with children - multi-line format
+            lines.push(`${innerSpaces}{`);
+            lines.push(`${innerSpaces}  "name": "${node.name}",`);
+            lines.push(`${innerSpaces}  "children": ${formatTranslationTemplate(node.children, indent + 2)}`);
+            lines.push(`${innerSpaces}}${isLast ? '' : ','}`);
+        } else {
+            // Leaf node - single line format
+            lines.push(`${innerSpaces}{ "name": "${node.name}" }${isLast ? '' : ','}`);
+        }
+    });
+
+    lines.push(`${spaces}]`);
+    return lines.join('\n');
+}
diff --git a/src/utils/database-utils.js b/src/utils/database-utils.js
new file mode 100644
index 0000000..70761ac
--- /dev/null
+++ b/src/utils/database-utils.js
@@ -0,0 +1,58 @@
+/**
+ * Database utility functions for common operations
+ */
+
+/**
+ * Process items in chunks with a callback function
+ * @param {Array} items - Items to process
+ * @param {number} chunkSize - Size of each chunk
+ * @param {Function} processFn - Async function to process each chunk (receives chunk array)
+ * @param {Object} options - Optional configuration
+ * @param {boolean} options.showProgress - Whether to log progress (default: true)
+ * @param {string} options.itemName - Name of items for logging (default: 'items')
+ * @returns {Promise<void>}
+ */
+export async function processInChunks(items, chunkSize, processFn, options = {}) {
+    const { showProgress = true, itemName = 'items' } = options;
+
+    for (let i = 0; i < items.length; i += chunkSize) {
+        const chunk = items.slice(i, i + chunkSize);
+        await processFn(chunk, i);
+
+        if (showProgress) {
+            const processed = Math.min(i + chunkSize, items.length);
+            if (processed === items.length) {
+                console.log(`✅ Processed ${processed}/${items.length} ${itemName}.`);
+            } else {
+                console.log(`⏳ Processed ${processed}/${items.length} ${itemName}...`);
+            }
+        }
+    }
+}
+
+/**
+ * Create a SQL IN clause from an array of IDs
+ * @param {Array<number>} ids - Array of numeric IDs
+ * @returns {string} - Comma-separated string of IDs
+ */
+export function createInClause(ids) {
+    return ids.join(',');
+}
+
+/**
+ * Execute a database query with automatic connection management
+ * @param {Function} queryFn - Async function that receives pool and executes queries
+ * @param {Function} createConnection - Function to create database connection
+ * @returns {Promise<*>} - Result from queryFn
+ */
+export async function withConnection(queryFn, createConnection) {
+    let pool;
+    try {
+        pool = await createConnection();
+        return await queryFn(pool);
+    } finally {
+        if (pool) {
+            await pool.close();
+        }
+    }
+}
diff --git a/src/utils/file-sync-utils.js b/src/utils/file-sync-utils.js
new file mode 100644
index 0000000..2551a20
--- /dev/null
+++ b/src/utils/file-sync-utils.js
@@ -0,0 +1,134 @@
+import fs from 'fs/promises';
+import path from 'path';
+
+/**
+ * File synchronization utility functions
+ */
+
+/**
+ * Get existing IDs from files in a directory
+ * @param {string} dir - Directory path
+ * @param {Object} options - Configuration options
+ * @param {string} options.prefix - File prefix to filter (e.g., 'category_')
+ * @param {string} options.suffix - File suffix to filter (e.g., '.json')
+ * @param {RegExp} options.pattern - Custom regex pattern to extract ID
+ * @returns {Promise<number[]>} - Array of numeric IDs
+ */
+export async function getExistingIds(dir, options = {}) {
+    const { prefix = '', suffix = '', pattern = null } = options;
+
+    let existingFiles = [];
+    try {
+        existingFiles = await fs.readdir(dir);
+    } catch (err) {
+        // Directory might be empty or new
+        return [];
+    }
+
+    if (pattern) {
+        return existingFiles
+            .map(f => {
+                const match = f.match(pattern);
+                return match ? parseInt(match[1]) : null;
+            })
+            .filter(id => id !== null && !isNaN(id));
+    }
+
+    return existingFiles
+        .filter(f => {
+            if (prefix && !f.startsWith(prefix)) return false;
+            if (suffix && !f.endsWith(suffix)) return false;
+            return true;
+        })
+        .map(f => {
+            let id = f;
+            if (prefix) id = id.replace(prefix, '');
+            if (suffix) id = id.replace(suffix, '');
+            return parseInt(id);
+        })
+        .filter(id => !isNaN(id));
+}
+
+/**
+ * Delete obsolete files based on valid IDs
+ * @param {string} dir - Directory path
+ * @param {number[]} existingIds - IDs of existing files
+ * @param {Set<number>} validIds - Set of valid IDs to keep
+ * @param {Function} filenameFn - Function to generate filename from ID
+ * @returns {Promise<number>} - Number of files deleted
+ */
+export async function deleteObsoleteFiles(dir, existingIds, validIds, filenameFn) {
+    const toDelete = existingIds.filter(id => !validIds.has(id));
+
+    for (const id of toDelete) {
+        const filePath = path.join(dir, filenameFn(id));
+        await fs.unlink(filePath);
+    }
+
+    if (toDelete.length > 0) {
+        console.log(`🗑️  Deleted ${toDelete.length} obsolete files.`);
+    }
+
+    return toDelete.length;
+}
+
+/**
+ * Write JSON to file only if content has changed
+ * @param {string} filePath - Full path to file
+ * @param {*} data - Data to write (will be JSON.stringify'd)
+ * @param {number} indent - JSON indentation (default: 2)
+ * @returns {Promise<boolean>} - True if file was written, false if unchanged
+ */
+export async function writeJsonIfChanged(filePath, data, indent = 2) {
+    const newContent = JSON.stringify(data, null, indent);
+
+    let oldContent = '';
+    try {
+        oldContent = await fs.readFile(filePath, 'utf-8');
+    } catch (e) {
+        // File doesn't exist yet
+    }
+
+    if (oldContent !== newContent) {
+        await fs.writeFile(filePath, newContent);
+        return true;
+    }
+
+    return false;
+}
+
+/**
+ * Ensure directory exists, create if it doesn't
+ * @param {string} dir - Directory path
+ * @returns {Promise<void>}
+ */
+export async function ensureDir(dir) {
+    await fs.mkdir(dir, { recursive: true });
+}
+
+/**
+ * Read JSON file safely
+ * @param {string} filePath - Full path to file
+ * @returns {Promise<*|null>} - Parsed JSON or null if file doesn't exist
+ */
+export async function readJsonFile(filePath) {
+    try {
+        const content = await fs.readFile(filePath, 'utf-8');
+        return JSON.parse(content);
+    } catch (err) {
+        return null;
+    }
+}
+
+/**
+ * Read text file safely
+ * @param {string} filePath - Full path to file
+ * @returns {Promise<string|null>} - File content or null if file doesn't exist
+ */
+export async function readTextFile(filePath) {
+    try {
+        return await fs.readFile(filePath, 'utf-8');
+    } catch (err) {
+        return null;
+    }
+}
diff --git a/src/utils/sync-queue-manager.js b/src/utils/sync-queue-manager.js
new file mode 100644
index 0000000..2a560c6
--- /dev/null
+++ b/src/utils/sync-queue-manager.js
@@ -0,0 +1,76 @@
+/**
+ * SyncQueueManager - Manages sync operations with queuing support
+ * 
+ * Prevents concurrent syncs for the same key and queues subsequent requests.
+ * Supports both global syncing (single key) and per-group syncing (multiple keys).
+ */
+export class SyncQueueManager {
+    constructor() {
+        this.isSyncing = new Map(); // key -> boolean
+        this.queuedSyncs = new Map(); // key -> queuedData
+    }
+
+    /**
+     * Execute a sync operation with automatic queuing
+     * @param {string} key - Unique identifier for this sync operation
+     * @param {Function} syncFn - Async function to execute
+     * @param {*} queuedData - Data to pass to queued sync (optional)
+     * @returns {Promise<void>}
+     */
+    async executeSync(key, syncFn, queuedData = null) {
+        // Check if already syncing this key
+        if (this.isSyncing.get(key)) {
+            if (this.queuedSyncs.has(key)) {
+                console.log(`🚫 Sync for '${key}' already in progress and queued. Ignoring.`);
+                return;
+            }
+            console.log(`⏳ Sync for '${key}' already in progress. Queuing.`);
+            this.queuedSyncs.set(key, queuedData);
+            return;
+        }
+
+        await this._doSync(key, syncFn);
+    }
+
+    async _doSync(key, syncFn) {
+        this.isSyncing.set(key, true);
+
+        try {
+            await syncFn();
+        } finally {
+            this.isSyncing.set(key, false);
+
+            // Process queued sync for this key if any
+            if (this.queuedSyncs.has(key)) {
+                const queuedData = this.queuedSyncs.get(key);
+                this.queuedSyncs.delete(key);
+
+                // Log only if we have meaningful data to show
+                if (queuedData !== null && queuedData !== undefined) {
+                    console.log(`🔄 Processing queued sync for '${key}'...`);
+                }
+
+                // Use setImmediate to allow stack to clear/event loop to tick
+                setImmediate(() => this.executeSync(key, syncFn, queuedData));
+            }
+        }
+    }
+
+    /**
+     * Check if a sync is currently in progress for a key
+     * @param {string} key - Unique identifier
+     * @returns {boolean}
+     */
+    isSyncInProgress(key) {
+        return this.isSyncing.get(key) || false;
+    }
+
+    /**
+     * Check if a sync is queued for a key
+     * @param {string} key - Unique identifier
+     * @returns {boolean}
+     */
+    isSyncQueued(key) {
+        return this.queuedSyncs.has(key);
+    }
+}