Improve files_decorator performance

**How?**
Previously the files_decorator inserted parent folders inefficiently.
It started at the first part and ensured each was inserted.

Since the file entries are given to use in alphabetical order, we can
start at the last part of the blob's parents. If this exists, we can
short circuit and be done inserting parents.

**What else?**
- Improve performance of decorateData. The object spread operator is
not needed because the object is brand new.

1 files changed, 113 insertions, 0 deletions

diff --git a/app/assets/javascripts/ide/lib/files.js b/app/assets/javascripts/ide/lib/files.js
new file mode 100644
index 00000000000..5dfba8fe531
--- /dev/null
+++ b/app/assets/javascripts/ide/lib/files.js
@@ -0,0 +1,113 @@
+import { viewerInformationForPath } from '~/vue_shared/components/content_viewer/lib/viewer_utils';
+import { decorateData, sortTree } from '../stores/utils';
+
+export const splitParent = path => {
+  const idx = path.lastIndexOf('/');
+
+  return {
+    parent: idx >= 0 ? path.substring(0, idx) : null,
+    name: idx >= 0 ? path.substring(idx + 1) : path,
+  };
+};
+
+/**
+ * Create file objects from a list of file paths.
+ */
+export const decorateFiles = ({
+  data,
+  projectId,
+  branchId,
+  tempFile = false,
+  content = '',
+  base64 = false,
+}) => {
+  const treeList = [];
+  const entries = {};
+
+  // These mutable variable references end up being exported and used by `createTempEntry`
+  let file;
+  let parentPath;
+
+  const insertParent = path => {
+    if (!path) {
+      return null;
+    } else if (entries[path]) {
+      return entries[path];
+    }
+
+    const { parent, name } = splitParent(path);
+    const parentFolder = parent && insertParent(parent);
+    parentPath = parentFolder && parentFolder.path;
+
+    const tree = decorateData({
+      projectId,
+      branchId,
+      id: path,
+      name,
+      path,
+      url: `/${projectId}/tree/${branchId}/-/${path}/`,
+      type: 'tree',
+      parentTreeUrl: parentFolder ? parentFolder.url : `/${projectId}/tree/${branchId}/`,
+      tempFile,
+      changed: tempFile,
+      opened: tempFile,
+      parentPath,
+    });
+
+    Object.assign(entries, {
+      [path]: tree,
+    });
+
+    if (parentFolder) {
+      parentFolder.tree.push(tree);
+    } else {
+      treeList.push(tree);
+    }
+
+    return tree;
+  };
+
+  data.forEach(path => {
+    const { parent, name } = splitParent(path);
+
+    const fileFolder = parent && insertParent(parent);
+
+    if (name) {
+      parentPath = fileFolder && fileFolder.path;
+
+      file = decorateData({
+        projectId,
+        branchId,
+        id: path,
+        name,
+        path,
+        url: `/${projectId}/blob/${branchId}/-/${path}`,
+        type: 'blob',
+        parentTreeUrl: fileFolder ? fileFolder.url : `/${projectId}/blob/${branchId}`,
+        tempFile,
+        changed: tempFile,
+        content,
+        base64,
+        previewMode: viewerInformationForPath(name),
+        parentPath,
+      });
+
+      Object.assign(entries, {
+        [path]: file,
+      });
+
+      if (fileFolder) {
+        fileFolder.tree.push(file);
+      } else {
+        treeList.push(file);
+      }
+    }
+  });
+
+  return {
+    entries,
+    treeList: sortTree(treeList),
+    file,
+    parentPath,
+  };
+};