index.js

'use strict';

var path = require('path'),
	fs = require('fs'),
	resolve = require('resolve');

var handledBaseFolderNames = {
	'bower_components': 'bower_components',
	'node_modules': 'node_modules'
};

function customImporter(url, prev, done) {
	if (!endsWith(url, '.scss')) {
		url += '.scss';
	}

	try {
		var resolvedNpmPath = resolveNpm(url, prev);
		if (resolvedNpmPath) {
			return complete({ file: resolvedNpmPath }, done);
		}
	} catch (e) { /* was not a node module */ }

	var baseFolderName = url.split('/')[0];

	if (handledBaseFolderNames[baseFolderName]) {
		var result = findInParentDirSync(url, prev);
		return complete(result, done);
	} else {
		return null;
	}
}

function complete(result, done) {
	if (isAsync(done)) {
		done(result);
		return;
	}
	return result;
}

function isAsync(doneCallback) {
	return typeof doneCallback === 'function';
}

function endsWith(str, suffix) {
	return str && str.indexOf(suffix, str.length - suffix.length) !== -1;
}

function resolveNpm(id, referencingFile) {
	return resolve.sync(id, {
		basedir: path.dirname(referencingFile)
	});
}

function findInParentDirSync(relativePath, startingDirPath) {
	var dirToTry = path.join(startingDirPath, '..');
	var pathToTry = path.join(dirToTry, relativePath);

	try {
		fs.accessSync(pathToTry, fs.R_OK);
		return {
			file: pathToTry
		};
	} catch (err) {
		if (pathToTry === ('/' + relativePath)) {
			return new Error('File not found: ' + relativePath);
		} else {
			return findInParentDirSync(relativePath, dirToTry);
		}
	}
}

module.exports = customImporter;