var POW_COMPUTING_TIMEOUT = 2;
var POW_HASH_LENGTH = 16;

var hasher = null;


function computeHash(iteration, guess, target, payload, timestamp, port) {
    iteration += 1;
    var hash = hasher(payload + iteration).toString();
    guess = hash.substring(0, POW_HASH_LENGTH);

    if (guess <= target) {
        //console.log("Iteration: ", iteration);
        //console.log("Guess: ", guess);
        //console.log("Target: ", target);

        var data = {
            iteration: iteration,
            timestamp: timestamp,
            guess: guess
        };
        port.postMessage(data);
    } else {
        //console.log("Iteration: ", iteration);
        //console.log("Guess: ", guess);
        //console.log("Target: ", target);

        setTimeout(function() {
            computeHash(iteration, guess, target, payload, timestamp, port);
        }, POW_COMPUTING_TIMEOUT);
    }
}

function doWork(message, difficulty, port) {
    var timestamp = Date.now();
    var iteration = 0;
    var payload = timestamp + message;

    var target = parseInt(Math.pow(2, POW_HASH_LENGTH * 3) / difficulty).toString();
    while (target.length < POW_HASH_LENGTH) {
        target = '0' + target;
    }

    var guess = target + '0';

    setTimeout(function() {
        computeHash(iteration, guess, target, payload, timestamp, port);
    }, POW_COMPUTING_TIMEOUT);
}

onconnect = function(e) {
    var port = e.ports[0];
    port.start();

    port.onmessage = function(e) {
        var difficulty = e.data.difficulty;

        if (hasher == null) {
            importScripts(e.data.hasher);
            hasher = CryptoJS.SHA256;
        }

        self.doWork(e.data.msg, difficulty, port);
    };
}