refactoring the code by extracting some functionalities out of extension.js

src/extension.js

@@ -0,0 +1,78 @@
+// The module 'vscode' contains the VS Code extensibility API
+// Import the module and reference it with the alias vscode in your code below
+var vscode = require('vscode');
+var file = require('./file')
+var _ = require('lodash');
+
+var list = [];
+var buffer = ""; // to store current file;
+// this method is called when your extension is activated
+// your extension is activated the very first time the command is executed
+function activate(context) {
+
+  // Use the console to output diagnostic information (console.log) and errors (console.error)
+
+  //add current active tab to list, check if there is an active tab
+  if (!!vscode.window.activeTextEditor && !!vscode.window.activeTextEditor._documentData) {
+    buffer = vscode.window.activeTextEditor._documentData._uri.path;
+  }
+
+  // The command has been defined in the package.json file
+  // Now provide the implementation of the command with  registerCommand
+  // The commandId parameter must match the command field in package.json
+  var disposable = vscode.commands.registerCommand('extension.openRecentFiles', function () {
+    // The code you place here will be executed every time your command is executed
+    vscode.window.showQuickPick(file.mapUriToDisplayName(list)).then((item) => {
+      handleUserInput(item);
+    });
+  });
+
+  context.subscriptions.push(disposable);
+  context.subscriptions.push(vscode.window.onDidChangeActiveTextEditor(handleChangeActiveWindow));
+
+  // This line of code will only be executed once when your extension is activated
+  console.log('"recent-files" is now active!');
+}
+exports.activate = activate;
+
+
+// this method is called when your extension is deactivated
+function deactivate() {
+  list = [];
+  buffer = ''
+}
+
+exports.deactivate = deactivate;
+
+function handleUserInput(item) {
+  if (!item || item.trim === '') return;
+  let targetUri = _.findLast(list, (uri) => {
+    return uri.indexOf(item) !== -1;
+  })
+  if (!targetUri) {
+    vscode.window.showWarningMessage("Can't find the file you selected.")
+    return;
+  }
+  let targetDocument = vscode.workspace.openTextDocument(targetUri);
+  targetDocument.then(function (document) {
+    vscode.window.showTextDocument(document);
+  });
+}
+
+function handleChangeActiveWindow(e) {
+  if (!e) return;
+  //ignore invalid item
+  if (!e._documentData || !e._documentData._uri) return;
+  let uri = e._documentData._uri.path
+  if (!uri || uri.trim() === '') return
+  //only allow to show 20 files.
+  if (list.length === 20) list = _.tail(list);
+  if (file.isFileNameExist(list, uri)) _.remove(list, (item) => {
+    return item === uri
+  });
+
+  if (!!buffer) list.push(buffer);
+  buffer = uri; //update buffer
+
+  list = _.uniq(list);
+}

src/file.js

@@ -0,0 +1,25 @@
+var vscode = require('vscode');
+var _ = require('lodash');
+
+const mapUriToDisplayName = (list) => {
+  return _.chain(list.slice()).uniq().reverse().remove(item => {
+    return item.split(vscode.workspace.rootPath).length != 1;
+  }).map((item) => {
+    return item.substring(vscode.workspace.rootPath.length + 1);
+  }).filter((item) => {
+    //ignore the system iles which starts with .
+    return !!item && (item.trim() !== "") && !(item.startsWith("."));
+  }).value();
+}
+
+const isFileNameExist = (list, fileName) => {
+  return _.some(list, (item) => {
+    return item === fileName;
+  })
+}
+
+
+module.exports = {
+  mapUriToDisplayName,
+  isFileNameExist
+}