feat: Refactor project structure for modularity and expandability

- Implemented the service and adapter layers instead of controllers to simplify the integration of new audio recognition and metadata fetching APIs.
- Unified code styling and practices throughout the project to ensure consistency.

src/utils/fetchFiles.js

@@ -0,0 +1,67 @@
+import fs from 'fs';
+import path from 'path';
+
+/**
+ * Fetches files from a given input path. If the path is a directory,
+ * it recursively fetches all files within it, including in subdirectories.
+ * If the path is an individual file, it returns an array with just
+ * that file path. This function handles both files and directories,
+ * making it versatile for various file fetching needs.
+ *
+ * @param {string} inputPath - The path to the file or directory to fetch files from.
+ * @returns {Promise<string[]>} A promise that resolves with an array of file paths.
+ * @throws {Error} If the inputPath does not refer to an existing file or directory.
+ */
+export default async function fetchFiles(inputPath) {
+  try {
+    const stats = await fs.promises.stat(inputPath);
+    let files = [];
+    if (stats.isDirectory()) {
+      // Recursive case: inputPath is a directory.
+      files = await fetchFilesFromDirectory(inputPath);
+    } else if (stats.isFile()) {
+      // Base case: inputPath is a file.
+      files = [inputPath];
+    } else {
+      throw new Error('Invalid path: not a file or directory');
+    }
+    return files;
+  } catch (e) {
+    console.error('Error resolving path', e);
+    throw e;
+  }
+}
+
+/**
+ * A private helper function that recursively fetches all files within a directory.
+ * It will traverse all subdirectories and return a flat array of file paths.
+ *
+ * @param {string} folderPath - The directory path to start the file search from.
+ * @returns {Promise<string[]>} A promise that resolves with an array of file paths.
+ * @throws {Error} If an error occurs while reading the directory.
+ */
+async function fetchFilesFromDirectory(folderPath) {
+  async function enumerateFilesInDirectory(dirPath) {
+    let fileList = [];
+    const entries = await fs.readdir(dirPath, { withFileTypes: true });
+    for (const entry of entries) {
+      const fullPath = path.join(dirPath, entry.name);
+      if (entry.isDirectory()) {
+        // Recurse into subdirectories.
+        fileList = fileList.concat(await enumerateFilesInDirectory(fullPath));
+      } else {
+        // Add file path to the list.
+        fileList.push(fullPath);
+      }
+    }
+    return fileList;
+  }
+
+  try {
+    // Initiate recursive file listing from the root folder path.
+    return await enumerateFilesInDirectory(folderPath);
+  } catch (e) {
+    console.error(`Error enumerating files in directory ${folderPath}:`, e);
+    throw e;
+  }
+}