//////////////////////////////////////////////
    // Backend tasks
    //////////////////////////////////////////////
    
    const appSourceDir = path.join(dir, '/app');
    const appSourceGlob = `${appSourceDir}/**/*.*`;
    const appSourceRelativeGlob = 'app/**/*.*';
    const appCodeGlob = `${appSourceDir}/**/*.ts`;
    const appCodeRelativeGlob = 'app/**/*.ts';
    const appFilesGlob = [appSourceGlob, `!${appCodeGlob}`];
    const appFilesRelativeGlob = [appSourceRelativeGlob, `!${appCodeRelativeGlob}`];
    const appBuildDir = path.join(dir, '/build');
    
    
    gulp.task('backend:symlink', [], function (done) {
      const appTargetDir = path.join(dir, '/node_modules/app');
      // symlink for app
      fs.exists(appTargetDir, function (err) {
        if (!err) {
          fs.symlinkSync(appBuildDir, appTargetDir, 'dir');
        }
      });
    
      done();
    });
    
    gulp.task('backend:clean', function (done) {
      clean([appBuildDir + '/**/*', '!.gitkeep'], done);
    });
    
    gulp.task('backend:compile', function (done) {
      tsCompile([appCodeGlob], appBuildDir, appSourceDir, done);
    });
    
    gulp.task('backend:files', function () {
      // copy fixtures and other non ts files
      // from app directory to build directory
      return gulp
        .src(appFilesGlob)
        .pipe(plugin.cached('files'))
        .pipe(gulp.dest(appBuildDir));
    });
    
    gulp.task('backend:build', function (done) {
      sequence(
        'backend:clean',
        'backend:compile',
        'backend:files',
        done
      );
    });
    
    gulp.task('backend:watch:code', function () {
      const watcher = gulp.watch([appCodeRelativeGlob], ['backend:compile']);
    
      watcher.on('change', function (event) {
        // if a file is deleted, forget about it
        if (event.type === 'deleted') {
          // gulp-cached remove api
          delete plugin.cached.caches.code[event.path];
          delete plugin.event.caches.lint[event.path];
          // delete in build
          del(getPathFromSourceToBuild(event.path, appSourceDir, appBuildDir));
        }
      });
    });
    
    gulp.task('backend:watch:files', function () {
      const watcher = gulp.watch([appFilesRelativeGlob], ['backend:files']);
    
      watcher.on('change', function (event) {
        // if a file is deleted, forget about it
        if (event.type === 'deleted') {
          // gulp-cached remove api
          delete plugin.cached.caches.files[event.path];
          delete plugin.event.caches.lint[event.path];
          // delete in build
          del(getPathFromSourceToBuild(event.path, appSourceDir, appBuildDir));
        }
      });
    });
    
    gulp.task('backend:watch', ['backend:build'], function (done) {
      // first time build all by backend:build,
      // then compile/copy by changing
      gulp
        .start([
          'backend:watch:code',
          'backend:watch:files'
        ], done);
    });
    
    //////////////////////////////////////////////
    // Helpers
    //////////////////////////////////////////////
    
    /**
     * remaps file path from source directory to destination directory
     * @param {string} file path
     * @param {string} source directory path
     * @param {string} destination directory path
     * @returns {string} new file path (remapped)
     */
    function getPathFromSourceToBuild(file, source, destination) {
      // Simulating the {base: 'src'} used with gulp.src in the scripts task
      const filePathFromSrc = path.relative(path.resolve(source), file);
      // Concatenating the 'destination' absolute
      // path used by gulp.dest in the scripts task
      return path.resolve(destination, filePathFromSrc);
    }
    
    /**
     * @param  {Array}    path - array of paths to compile
     * @param  {string}   dest - destination path for compiled js
     * @param  {string}   baseDir - base directory for files compiling
     * @param  {Function} done - callback when complete
     */
    function tsCompile(path, dest, baseDir, done) {
      const ts = plugin.typescript;
      const tsProject = ts.createProject('tsconfig.json');
    
      gulp
        .src(path, {base: baseDir})
        // used for incremental builds
        .pipe(plugin.cached('code'))
        .pipe(plugin.sourcemaps.init())
        .pipe(tsProject(ts.reporter.defaultReporter())).js
        .pipe(plugin.sourcemaps.write('.'))
        .pipe(gulp.dest(dest))
        .on('error', done)
        .on('end', done);
    }
    
    /**
     * Delete all files in a given path
     * @param  {Array}   path - array of paths to delete
     * @param  {Function} done - callback when complete
     */
    function clean(path, done) {
      log('Cleaning: ' + plugin.util.colors.blue(path));
      del(path).then(function (paths) {
        done();
      });
    }
    
    /**
     * Log a message or series of messages using chalk's blue color.
     * Can pass in a string, object or array.
     */
    function log(msg) {
      if (typeof (msg) === 'object') {
        for (let item in msg) {
          if (msg.hasOwnProperty(item)) {
            plugin.util.log(plugin.util.colors.blue(msg[item]));
          }
        }
      } else {
        plugin.util.log(plugin.util.colors.blue(msg));
      }
    }