var async = require('asynx');
// or be more explicit
var asynx = require('asynx');

asynx.waterfall([
    // get response and body of an url
    asynx.apply(request.get, url),
    // write body to file, but return http response from waterfall
    function (response, body, callback) {
        fs.writefile(filename, asynx.return(response, callback))
    }
], callback)

asynx.waterfall([
    // get response and body of an url
    asynx.apply(request.get, url),
    // throw away response and pass body to fs.writeFile
    asynx.shift,
    // write body to a file
    asynx.apply(fs.writeFile, filename)
], callback)

function cachedGet(url, callback) {
    var filename = __dirname + '/cache/' + url.replace(/\//g, '#');

    asynx.if(
        asynx.apply(fs.exists, filename),
        asynx.apply(fs.readFile, filename),
        asynx.apply(asynx.waterfall, [
            asynx.apply(request, url),
            function (response, body, callback) {
                fs.writeFile(filename, body, function (error) {
                    callback(error, body);
                });
            }
        ]),
        callback
    )
}

function cachedGet(url, callback) {
    var filename = __dirname + '/cache/' + url.replace(/\//g, '#');

    asynx.manual({
        // always starts from 'start' state
        start: function (next) {
            fs.exists(filename, function (exists) {
                // go to some new state
                if (exists) next.readCache()
                else next.request();
            });
        },
        request: function (next) {
            // use state transition as callback
            request(url, next.writeCache);
        },
        readCache: function (next) {
            // use next.end to leave state machine
            fs.readFile(filename, 'utf-8', next.end);
        },
        writeCache: function (response, body, next) {
            fs.writeFile(filename, body, 'utf-8', function (error) {
                next.end(error, body);
            });
        }
    }, callback);
}