Feature: Add locking via .withLock

package.json

@@ -79,6 +79,9 @@
   },
   "dependencies": {
     "bluebird": "^3.4.7",
+    "fs-ext": "^0.5.0",
+    "fs-extra": "^2.0.0",
+    "lockfile": "^1.0.3",
     "minimatch": "^3.0.3"
   }
 }

src/file.js

@@ -3,6 +3,8 @@ import fs from 'fs';
 import path from 'path';
 import fileGlob from 'minimatch';
 
+import lock from './lock';
+
 const fsp = Promise.promisifyAll(fs);
 
 function joinWith(dir) {
@@ -156,6 +158,16 @@ class File {
   delete() {
     return fsp.unlinkAsync(this._pathname);
   }
+
+  withLock(fn) {
+    return lock.lockAsync(this._pathname)
+      .then(() => {
+        fn();
+      })
+      .finally(() => {
+        return lock.unlockAsync(this._pathname);
+      });
+  }
 }
 
 module.exports.create = (filename) => {

src/lock.js

@@ -0,0 +1,4 @@
+import lockfile from 'lockfile';
+import Promise from 'bluebird';
+
+module.exports = Promise.promisifyAll(lockfile);

test/file.js

@@ -4,6 +4,9 @@ import path from 'path';
 import File from '../lib/file';
 import moment from 'moment';
 import sinon from 'sinon';
+import Promise from 'bluebird';
+
+import lockfile from '../lib/lock';
 
 const sandbox = sinon.sandbox.create();
 
@@ -525,4 +528,25 @@ describe('File', () => {
       assert.equal(file.getName(), getFixturePath('dates/a.txt'));
     });
   });
+
+  describe('.withLock', () => {
+    beforeEach(() => {
+      sandbox.stub(lockfile, 'lockAsync').returns(Promise.resolve());
+      sandbox.stub(lockfile, 'unlockAsync').returns(Promise.resolve());
+    });
+
+    afterEach(() => {
+      sandbox.restore();
+    });
+
+    it('executes a given function whilst managing a file lock', () => {
+      const fn = sinon.spy();
+      const file = File.create('justFiles/a.json');
+
+      file.withLock(fn)
+        .then(() => {
+          sinon.assert.callOrder(lockfile.lockAsync, fn, lockfile.unlockAsync);
+        });
+    });
+  });
 });