// started on main page load
function init() {
	init_board();
}

function init_board() {
	var xhr = new XMLHttpRequest();
	
        const searchParams = (new URL(document.location)).searchParams;
        if (!searchParams.has('id')) {
                redirect_to_new_page();
                return;
        }

	// run on data received back
	xhr.onreadystatechange = function() {
				if (this.readyState == 3) {
					//set_status("Please wait while downloading " + filename + " ...");
					return;
				}
                                if (this.readyState != 4) {
					return;
				}
				if (this.status != 200) {
					//set_status("Server Error while retrieving " + filename + ", status: " + this.status + " " + this.statusText);
                                        return;
                                }

                                var file = new Blob([this.response]);
				reader = new FileReader();
				reader.onload = function() {
					var board = document.getElementById("board");
					board.innerHTML = reader.result;

					// Initialization done. Now we can start modifying.
					board.addEventListener("input", function() {on_modify(); });

					setInterval(function() {checkupdate();}, 2000);
				}
				
			        reader.readAsBinaryString(file);

				//set_status(""); // OK
	}

	var parser = new DOMParser();
	var xmlDocument = parser.parseFromString("<request></request>", "text/xml");
	
	var requestElement = xmlDocument.getElementsByTagName("request")[0];

	var commandElement = xmlDocument.createElement("command");
	commandElement.appendChild(document.createTextNode("getfile"));
	requestElement.appendChild(commandElement);

	var idElement = xmlDocument.createElement("id");
	idElement.appendChild(document.createTextNode(get_id()));
	requestElement.appendChild(idElement);

	xhr.open("POST", "whiteboard.fcgi", true);
	xhr.setRequestHeader("Content-type", "text/xml");
	xhr.responseType = 'blob';
	xhr.send(xmlDocument);

	//set_status("Please wait while server prepares " + filename + " ...");
}

function get_id()
{
        const searchParams = (new URL(document.location)).searchParams;
        return searchParams.get('id');
}

function on_new_page()
{
        redirect_to_new_page();
}

function redirect_to_new_page()
{
	var xhr = new XMLHttpRequest();
	
	// run on data received back
	xhr.onreadystatechange = function() {
				if (this.readyState == 3) {
					//set_status("Please wait while downloading " + filename + " ...");
					return;
				}
                                if (this.readyState != 4) {
					return;
				}
				if (this.status != 200) {
					//set_status("Server Error while retrieving " + filename + ", status: " + this.status + " " + this.statusText);
                                        return;
                                }

                                var id = this.responseText;
                                //alert("location=" + document.location.href);
                                var new_location = document.location.href;
                                var pos = new_location.search("\\?");
                                if (pos >= 0)
                                        new_location = new_location.substring(0, pos);
                                new_location += '?id=' + id;

                                window.location.href = new_location;
				//set_status(""); // OK
	}

	var parser = new DOMParser();
	var xmlDocument = parser.parseFromString("<request></request>", "text/xml");
	
	var requestElement = xmlDocument.getElementsByTagName("request")[0];

	var commandElement = xmlDocument.createElement("command");
	commandElement.appendChild(document.createTextNode("newid"));
	requestElement.appendChild(commandElement);

	xhr.open("POST", "whiteboard.fcgi", true);
	xhr.setRequestHeader("Content-type", "text/xml");
	xhr.send(xmlDocument);

	//set_status("Please wait while server prepares " + filename + " ...");
}

function on_modify()
{
	var xhr = new XMLHttpRequest();
	
	// run on data received back
	xhr.onreadystatechange = function() {
				if (this.readyState == 3) {
					//set_status("Please wait while downloading " + filename + " ...");
					return;
				}
                                if (this.readyState != 4) {
					return;
				}
				if (this.status != 200) {
					//set_status("Server Error while retrieving " + filename + ", status: " + this.status + " " + this.statusText);
                                        return;
                                }

				//set_status(""); // OK
	}

	var parser = new DOMParser();
	var xmlDocument = parser.parseFromString("<request></request>", "text/xml");
	
	var requestElement = xmlDocument.getElementsByTagName("request")[0];

	var commandElement = xmlDocument.createElement("command");
	commandElement.appendChild(document.createTextNode("modify"));
	requestElement.appendChild(commandElement);

	var idElement = xmlDocument.createElement("id");
	idElement.appendChild(document.createTextNode(get_id()));
	requestElement.appendChild(idElement);

	var dataElement = xmlDocument.createElement("data");
	dataElement.appendChild(document.createTextNode(document.getElementById("board").value));
	requestElement.appendChild(dataElement);

	xhr.open("POST", "whiteboard.fcgi", true);
	xhr.setRequestHeader("Content-type", "text/xml");
	xhr.responseType = 'blob';
	xhr.send(xmlDocument);

	//set_status("Please wait while server prepares " + filename + " ...");
}

// checksum of string
function checksum32(s) {
	var result = 0;
	for (var i = 0; i < s.length; i++) {
		result = ((((result >>> 1) | ((result & 1) << 31)) | 0) ^ (s.charCodeAt(i) & 0xFF)) | 0;
	}
	return (result & 0x7FFFFFFF) | 0;
}

// gets called by regular polling
function checkupdate() {
	var xhr = new XMLHttpRequest();
	
	// run on data received back
	xhr.onreadystatechange = function() {
				if (this.readyState == 3) {
					//set_status("Please wait while downloading " + filename + " ...");
					return;
				}
                                if (this.readyState != 4) {
					return;
				}
				if (this.status != 200) {
					//set_status("Server Error while retrieving " + filename + ", status: " + this.status + " " + this.statusText);
                                        return;
                                }

				// no change if response is text/plain
				if (this.getResponseHeader("Content-Type") == "application/octet-stream") {
					var file = new Blob([this.response]);
					reader = new FileReader();
					reader.onload = function() {
						var board = document.getElementById("board");
						board.value = reader.result;
					}
					
					reader.readAsBinaryString(file);
				}

				//set_status(""); // OK
	}

	var parser = new DOMParser();
	var xmlDocument = parser.parseFromString("<request></request>", "text/xml");
	
	var requestElement = xmlDocument.getElementsByTagName("request")[0];

	var commandElement = xmlDocument.createElement("command");
	commandElement.appendChild(document.createTextNode("checkupdate"));
	requestElement.appendChild(commandElement);

	var idElement = xmlDocument.createElement("id");
	idElement.appendChild(document.createTextNode(get_id()));
	requestElement.appendChild(idElement);

	var checksumElement = xmlDocument.createElement("checksum");
	checksumElement.appendChild(document.createTextNode(checksum32(document.getElementById("board").value)));
	requestElement.appendChild(checksumElement);

	xhr.open("POST", "whiteboard.fcgi", true);
	xhr.setRequestHeader("Content-type", "text/xml");
	xhr.responseType = 'blob';
	xhr.send(xmlDocument);

	//set_status("Please wait while server prepares " + filename + " ...");
}