diff --git a/.eslintrc.yaml b/.eslintrc.yaml
index 1475d78..888dd18 100644
--- a/.eslintrc.yaml
+++ b/.eslintrc.yaml
@@ -1,5 +1,5 @@
 parserOptions:
-  ecmaVersion: 2017
+  ecmaVersion: 2018
   sourceType: module
 env:
   node: true
diff --git a/src/cli.js b/src/cli.js
index 558c5ea..05d4a83 100644
--- a/src/cli.js
+++ b/src/cli.js
@@ -39,8 +39,8 @@ program
     }
     fs.ensureDirSync(args.target);
     const files = scan.findFilesSync(source);
-    const filesWithTags = await scan.readTags(files);
-    const organisedFiles = await organise.byAlbum(target, filesWithTags);
+    const taggedFiles = await scan.readTags(files);
+    const organisedFiles = await organise.byAlbum(target, taggedFiles);
     const releaseInfo = generate.releaseInfo(organisedFiles);
     fs.writeFileSync(path.resolve(target, 'releases.yml'), releaseInfo);
   });
diff --git a/src/generate.js b/src/generate.js
index b245c1d..73b4df8 100644
--- a/src/generate.js
+++ b/src/generate.js
@@ -2,17 +2,15 @@ const path = require('path');
 const _ = require('lodash');
 const yaml = require('js-yaml');
 const debug = require('debug')('publikator:generate');
-
-const getTags = (track, tags) =>
-  tags.reduce((all, tag) => {
-    all[tag] = track[tag]; // eslint-disable-line
-    return all;
-  }, {});
+const tags = require('./tags');
 
 module.exports = {
-  releaseInfo: files => {
-    debug(`generating release info for ${files.length} file(s)`);
-    const albums = _.groupBy(files, file => path.dirname(file.path));
+  /**
+   * Generates a release YAML with data
+   */
+  releaseInfo: taggedFiles => {
+    debug(`generating release info for ${taggedFiles.length} file(s)`);
+    const albums = _.groupBy(taggedFiles, file => path.dirname(file.path));
     return yaml.safeDump(
       Object.keys(albums).map(key => {
         const tracks = albums[key];
@@ -22,7 +20,7 @@ module.exports = {
             path: track.path,
             size: track.size,
             position: i,
-            tags: getTags(track.tags, [
+            ...tags.getTags(track, [
               'title',
               'artist',
               'album',
diff --git a/src/organise.js b/src/organise.js
index 9e6786c..fee68ad 100644
--- a/src/organise.js
+++ b/src/organise.js
@@ -3,31 +3,27 @@ const path = require('path');
 const _ = require('lodash');
 const sanitize = require('sanitize-filename');
 const debug = require('debug')('publikator:organise');
-
-const ensureTags = (files, tags) => {
-  return files.filter(file => {
-    if (tags.some(tag => file.tags[tag] === undefined)) {
-      debug(
-        `ignored '${file.path}' because it is missing one or more required tags`
-      );
-      return false;
-    }
-    return true;
-  });
-};
+const tags = require('./tags');
 
 const getFolderName = file => `${file.tags.artist} - ${file.tags.album}`;
 const getFileName = file =>
   `${file.tags.track} - ${file.tags.title}${path.extname(file.path)}`;
 
 module.exports = {
-  byAlbum: async (root, filesWithTags) => {
-    const files = ensureTags(filesWithTags, [
-      'artist',
-      'album',
-      'track',
-      'title',
-    ]);
+  /**
+   * Organises tracks into a new folder structure in `root`, as follows:
+   *
+   * {artist} - {album}/
+   *   {track} - {title}.{ext}
+   *   {track} - {title}.{ext}
+   *   ...
+   *
+   * Returns `taggedFiles` with the paths changed to the new paths.
+   */
+  byAlbum: async (root, taggedFiles) => {
+    const files = taggedFiles.filter(file =>
+      tags.hasTags(file, ['artist', 'album', 'track', 'title'])
+    );
 
     debug(`grouping tracks by album`);
     const folders = _.uniq(files.map(file => getFolderName(file)));
@@ -41,13 +37,13 @@ module.exports = {
 
     debug(`copying tracks`);
     return Promise.all(
-      files.map(file => {
+      files.map(async file => {
         const newPath = path.resolve(
           root,
           getFolderName(file),
           getFileName(file)
         );
-        fs.copyFileSync(file.path, newPath);
+        await fs.copyFile(file.path, newPath);
         return _.assign({}, file, { path: newPath });
       })
     );
diff --git a/src/scan.js b/src/scan.js
index 002544d..00bf14c 100644
--- a/src/scan.js
+++ b/src/scan.js
@@ -1,8 +1,11 @@
 const debug = require('debug')('publikator:scan');
-const jsmediatags = require('jsmediatags');
 const walk = require('walkdir');
+const tags = require('./tags');
 
 module.exports = {
+  /**
+   * Recursively searches for files.
+   */
   findFilesSync: (root, extension = '.mp3') => {
     debug(
       `scanning directory '${root}' for files with extension '${extension}'`
@@ -17,28 +20,21 @@ module.exports = {
     return files;
   },
 
+  /**
+   * Reads ID3 tags from all files and returns an array in the form of:
+   * [{ path, size, tags }, ...]
+   */
   readTags: files => {
-    debug(`reading tags for ${files.length} file(s)`);
+    debug(`reading tags from ${files.length} file(s)`);
     return Promise.all(
-      files.map(
-        file =>
-          new Promise((resolve, reject) => {
-            jsmediatags.read(file, {
-              onSuccess: info => {
-                resolve({
-                  path: file,
-                  size: info.size,
-                  tags: info.tags,
-                });
-              },
-              onError: error => {
-                debug(error.type);
-                debug(error.info);
-                reject(error);
-              },
-            });
-          })
-      )
+      files.map(async file => {
+        const info = await tags.readTags(file);
+        return {
+          path: file,
+          size: info.size,
+          tags: info.tags,
+        };
+      })
     );
   },
 };
diff --git a/src/tags.js b/src/tags.js
new file mode 100644
index 0000000..b4292c8
--- /dev/null
+++ b/src/tags.js
@@ -0,0 +1,43 @@
+const jsmediatags = require('jsmediatags');
+const debug = require('debug')('publikator:tags');
+
+module.exports = {
+  /**
+   * Reads tags from a track.
+   */
+  readTags: file =>
+    new Promise((resolve, reject) => {
+      jsmediatags.read(file, {
+        onSuccess: info => {
+          resolve(info);
+        },
+        onError: error => {
+          debug(error.type);
+          debug(error.info);
+          reject(error);
+        },
+      });
+    }),
+
+  /**
+   * Returns true if a file has all required tags.
+   */
+  hasTags: (taggedFile, tags) => {
+    if (tags.some(tag => taggedFile.tags[tag] === undefined)) {
+      debug(`track'${taggedFile.path}' is missing one or more required tags`);
+      return false;
+    }
+    return true;
+  },
+
+  /**
+   * Extracts tags from a file into an object, ignoring missing tags.
+   */
+  getTags: (taggedFile, tags) =>
+    tags.reduce((all, tag) => {
+      if (taggedFile.tags[tag] !== undefined) {
+        all[tag] = taggedFile.tags[tag]; // eslint-disable-line
+      }
+      return all;
+    }, {}),
+};