var dataURI, audio, myAudioContext, mySource, myBuffer;

if ('AudioContext' in window) {
	myAudioContext = new AudioContext();
} else if ('webkitAudioContext' in window) {
	myAudioContext = new webkitAudioContext();
} else {
	alert('Your browser does not support yet Web Audio API');
}

var chr8 = function () {
	return Array.prototype.map.call(arguments, function(a){
		return String.fromCharCode(a&0xff)
	}).join('');
}
var chr16 = function () {
	return Array.prototype.map.call(arguments, function(a){
		return String.fromCharCode(a&0xff, (a>>8)&0xff)
	}).join('');
}
var chr32 = function () {
	return Array.prototype.map.call(arguments, function(a){
		return String.fromCharCode(a&0xff, (a>>8)&0xff,(a>>16)&0xff, (a>>24)&0xff);
	}).join('');
}
var toUTF8 = function (str) {
	var utf8 = [];
	for (var i = 0; i < str.length; i++) {
		var c = str.charCodeAt(i);
		if (c <= 0x7f)
			utf8.push(c);
		else if (c <= 0x7ff) {
			utf8.push(0xc0 | (c >>> 6));
			utf8.push(0x80 | (c & 0x3f));
		} else if (c <= 0xffff) {
			utf8.push(0xe0 | (c >>> 12));
			utf8.push(0x80 | ((c >>> 6) & 0x3f));
			utf8.push(0x80 | (c & 0x3f));
		} else {
			var j = 4;
			while (c >>> (6*j)) j++;
			utf8.push(((0xff00 >>> j) & 0xff) | (c >>> (6*--j)));
			while (j--) 
				utf8[idx++] = 0x80 | ((c >>> (6*j)) & 0x3f);
		}
	}
	return utf8;
}

var fsk = {};

fsk.generate = function (str) {
	if (str.length === 0) return;
	var utf8 = toUTF8(str);
	//console.log(utf8);
	
	var sampleRate = 29400;
	var baud = 1225;
	var freqHigh = 7350;
	var freqLow  = 4900;
	var spb = sampleRate/baud; // 24 samples per bit
	var preCarrierBits = Math.ceil(sampleRate*40/1000/spb); // 49 bits
	var postCarrierBits = Math.ceil(sampleRate*5/1000/spb); // 6.125 bits => 7 bits
	var size = (preCarrierBits + postCarrierBits + 10 * utf8.length) * spb;

	var data = "RIFF" + chr32(size + 36) + "WAVE" +
			"fmt " + chr32(16, 0x00010001, sampleRate, sampleRate, 0x00080001) +
			"data" + chr32(size);
	
	var pushData = function (freq, samples) {
		for (var i = 0; i < samples; i++) {
			var v = 128 + 127 * Math.sin((2 * Math.PI) * (i / sampleRate) * freq);
			data += chr8(v);
		}
	}
	pushData(freqHigh, preCarrierBits * spb);
	for (var x in utf8) {
		var c = (utf8[x] << 1) | 0x200;
		for (var i = 0; i < 10; i++, c >>>= 1)
			pushData((c&1) ? freqHigh : freqLow, spb);
	}
	pushData(freqHigh, postCarrierBits * spb);
	
	//if (size+44 != data.length) alert("wrong size: " + size+44 + " != " + data.length);
	
	dataURI = escape(btoa(data));

	var arrayBuff = Base64Binary.decodeArrayBuffer(dataURI);
	myAudioContext.decodeAudioData(arrayBuff, function (audioData) {
		myBuffer = audioData;
	});
}

fsk.play = function () {
	mySource = myAudioContext.createBufferSource();
	mySource.buffer = myBuffer;
	mySource.connect(myAudioContext.destination);
	if ('AudioContext' in window) {
		mySource.start(0);
	} else if ('webkitAudioContext' in window) {
		mySource.noteOn(0);
	} 
};