index.js

var Q = require('q');
var _ = require('lodash');
var path = require('path');
var fs = require('fs');
var sass = require('node-sass');

// Compile a SASS file into a css
function renderSASS(input, output) {
    var d = Q.defer();

    sass.render({
        file: input
    }, function (e, out) {
        if (e) return d.reject(e);

        fs.writeFileSync(output, out.css);
        d.resolve();
    });

    return d.promise;
}

module.exports = {
    hooks: {
        // Compile sass as CSS
        init: function() {
            var book = this;

            var styles = book.config.get('styles');

            return _.reduce(styles, function(prev, filename, type) {
                return prev.then(function() {
                    var extension = path.extname(filename).toLowerCase();
                    if (extension != '.sass' && extension != '.scss') return;

                    book.log.info.ln('compile sass file: ', filename);

                    // Temporary CSS file
                    var tmpfile = type+'-'+Date.now()+'.css';

                    // Replace config
                    book.config.set('styles.'+type, tmpfile);

                    return renderSASS(
                        book.resolve(filename),
                        path.resolve(book.options.output, tmpfile)
                    );
                });
            }, Q());
        }
    }
};