// navbar.js
// (Global variables are declared in slide.js.)
// Display previous/next slide in sequence, or goto other slide.

// 30 July 97: rewrite to use top instead of parent so that these functions
// can be called from within index.htm and notes.htm too [enabling those
// documents to do an onload="goto_slide(1, true)" ]

// By default, filenames are relative to inside of basefile directory,
// so when loading HTML slide page files from main directory,
// we prefix "../" to the filename.  However, the onload event handler
// for documents index.htm and notes.htm must also call this function
// to load the first page; those documents are in the main directory,
// so we prefix "" to the filename.


function goto_slide(slide_num, caller_in_main_directory)
{       var filename_prefix = ""
	if (caller_in_main_directory == null) { filename_prefix = "html/" }
	if(slide_num < 1 || slide_num > top.last_slide){
		alert("Please enter number between 1 and " + top.last_slide);
	}
	else {
		top.current_slide = Math.abs(slide_num);
		top.frames["slide"].location = filename_prefix + top.filename[slide_num];
	}
}

function
prev_slide()
{
	if(top.current_slide == 1){
		alert("You are already at the first slide.\nThere is no previous slide.");
	} 
        else goto_slide(top.current_slide - 1);
}


// Display next slide in sequence.
function
next_slide()
{
	
	if (top.current_slide == top.last_slide){
		alert("You are already at the last slide.\nThere is no next slide.");
	} else goto_slide(top.current_slide + 1);
}


function
prev_slide(caller_in_main_directory)
{
	if(top.current_slide == 1){
		alert("You are already at the first slide.\nThere is no previous slide.");
	} 
        else goto_slide(top.current_slide - 1, caller_in_main_directory);
}


// Display next slide in sequence.
function
next_slide(caller_in_main_directory)
{
	
	if (top.current_slide == top.last_slide){
		alert("You are already at the last slide.\nThere is no next slide.");
	} else goto_slide(top.current_slide + 1, caller_in_main_directory);
}



// KEYBOARD CONTROL IN NAV4

// *** NOTE: SUBTLE DIFFERENCE BETWEEN THIS CODE AND CODE IN style.js ***
// Here, we do not pass parameter true to next_slide and prev_slide.

// support SPACE key codes (*not* RETURN because of Goto field!)
var nextKeys = new String("nN ")
var prevKeys = new String("pP")


function handleKeys(e) {
	var keyChar = String.fromCharCode(e.which);
	if (prevKeys.indexOf(keyChar) != -1)
	{  prev_slide(); return false  }
	else if(nextKeys.indexOf(keyChar) != -1)
	{  next_slide(); return false  }
	else return true;
}



// Workaround for Nav3.x bug in which JavaScript files
// with <SCRIPT LANGUAGE="JavaScript1.2" SRC=...> are
// loaded, even though they should be ignored.
// Make sure this code is only executed by 4.x and later.
if (parseInt(navigator.appVersion) > 3) {

   // support ESC key code  (*not* BS because of Goto field!)
   prevKeys.concat(String.fromCharCode(27))
   document.captureEvents(Event.KEYPRESS);
   document.onkeypress = handleKeys;

} // end of Nav4+ only if