chore: refactor cleanup to be easier to read & test

src/steps/step-cleanup.js

@@ -6,28 +6,30 @@ const path = require('path')
 const readdir = require('fs-readdir-recursive')
 
 exports.run = function (fileCollection, outputRoot, dryRun) {
+  const obsolete = findObsolete(fileCollection, outputRoot)
   return new Observable(observer => {
-    const mediaRoot = path.join(outputRoot, 'media')
-    const diskFiles = readdir(mediaRoot).map(f => path.join(mediaRoot, f))
-    const requiredFiles = []
-    fileCollection.forEach(f => {
-      Object.keys(f.output).forEach(out => {
-        const dest = path.join(outputRoot, f.output[out].path)
-        requiredFiles.push(dest)
-      })
+    obsolete.forEach(f => {
+      const relativePath = path.relative(outputRoot, f)
+      if (dryRun) {
+        debug(`Dry run, would delete: ${relativePath}`)
+      } else {
+        observer.next(relativePath)
+        fs.unlinkSync(f)
+      }
     })
-    const useless = _.difference(diskFiles, requiredFiles)
-    if (useless.length) {
-      useless.forEach(f => {
-        const relativePath = path.relative(outputRoot, f)
-        if (dryRun) {
-          debug(`Dry run, would delete: ${relativePath}`)
-        } else {
-          observer.next(relativePath)
-          fs.unlinkSync(f)
-        }
-      })
-    }
     observer.complete()
   })
 }
+
+function findObsolete (fileCollection, outputRoot) {
+  const mediaRoot = path.join(outputRoot, 'media')
+  const diskFiles = readdir(mediaRoot).map(f => path.join(mediaRoot, f))
+  const requiredFiles = []
+  fileCollection.forEach(f => {
+    Object.keys(f.output).forEach(out => {
+      const dest = path.join(outputRoot, f.output[out].path)
+      requiredFiles.push(dest)
+    })
+  })
+  return _.difference(diskFiles, requiredFiles)
+}