var CryptoUtils = {
    cypher: "AES-GCM",
    key: null,
    urlSafeKey: null,
  
    initialize: function(key = null) {
	if(key === null) {
	    return this.generateKey();
	}
	else {
	    this.urlSafeKey = key;
	    return this.importKey(this.base64ToArrayBuffer(key));
	}	    
    },
    
    generateKey: function() {
	var self = this;
	return window.crypto.subtle.generateKey(
	    {
		name: this.cypher,
		length: 256,
	    },
	    true,
	    ["encrypt", "decrypt"]
	).then(function(k){
	    self.key = k;
	    return window.crypto.subtle.exportKey("raw", k)
	}).then(function(keydata) {
	    console.log(keydata);
	    self.urlSafeKey = self.arrayBufferToBase64(keydata);
	}).catch(function(err){
	    console.error(err)
	});	    
    },
    
    encrypt: function(data) {
	var self = this;
	var iv = window.crypto.getRandomValues(new Uint8Array(12));
	return window.crypto.subtle.encrypt(
	    {		
		name: this.cypher,
		iv: iv,
	    },
	    this.key,
	    data
	).then(function(encrypted){
	    return new Blob([iv, encrypted], {type: 'application/octet-binary'});  
    	});
    },
    
    decrypt: function(data) {
	var self = this;
	return window.crypto.subtle.decrypt(
	    {
		name: this.cypher,
		iv: data.slice(0,12),
	    },
	    this.key,
	    data.slice(12)
	);
    },
    
    importKey: function(key) {
	var self = this;
	return window.crypto.subtle.importKey(
	    "raw",
	    key,
	    {
		name: self.cypher
	    },
	    true,
	    ["encrypt", "decrypt"]
	).then(function(k){
	    self.key = k;
	});
    },

    arrayBufferToBase64: function(a) {
	return btoa(String.fromCharCode(...new Uint8Array(a)))
    },

    base64ToArrayBuffer: function(b) {
	var str = atob(b);
	var buf = new ArrayBuffer(str.length);
	var bufView = new Uint8Array(buf);
	for (var i=0, strLen=str.length; i<strLen; i++) {
	    bufView[i] = str.charCodeAt(i);
	}
	return buf;
    }
}