/* 
 * Functions to preload/swap images
 */


// detect browser capabilities
var capable = (document.getElementById && document.getElementsByTagName);


// MenuImage constructor
function MenuImage(img_id, img_out, img_in, img_act, swapped) 
{
    this.img_id = img_id;           // the image id
    this.img_out = new Image();     // the image to use when mouseout
    this.img_out.src = imageDir + img_out;
    this.img_in = new Image();      // the image to use when mouseover
    this.img_in.src = imageDir + img_in;
    this.img_act = new Image();     // the image when page active
    if(img_act) {
        this.img_act.src = imageDir + img_act;
    } else {
        this.img_act.src = '';
    }    
    this.swapped = swapped;         // register if the image is swapped
    this.over = 0;                  // register if the image is 'over'
}

// take a full or partial path, and return it's last part
function basename(path) 
{
    var parts = path.split('/');
    return parts[parts.length-1];
}

// get an image from an image_id
function get_image(id)
{
    for(var a=0; a<=MImages.length; a++)
    {
        if(MImages[a] && MImages[a].img_id == id)
            return a;
    }
    return -1;
}

// swap in the image
function imgIn(image_id)
{
    var imgId = get_image(image_id);

    if(capable && MImages[imgId]) 
    {
        var theObj = MImages[imgId];
        var theImg = document.getElementById(theObj.img_id);
        var filename = basename(theImg.src);

        // don't swap if image is 'down' or currently active 
        if( MImages[imgId].swapped == 0 && (filename.indexOf('_ON') == -1 || filename.indexOf('_on') == -1) ) 
        {
            theImg.src = MImages[imgId].img_in.src;
            MImages[imgId].swapped = 1;
        }
    }
}

// swap out the image
function imgOut(image_id) 
{
    var imgId = get_image(image_id);

    if(capable && MImages[imgId]) 
    {
        theImg = document.getElementById(MImages[imgId].img_id);
        // only revert if "swapped" is true
        if(MImages[imgId].swapped == 1) 
        {
            theImg.src = MImages[imgId].img_out.src;
            MImages[imgId].swapped = 0;
        }
    }
}

// Set the image active and set the swapped bit (prevent reverting)
function setSwapped(image_id)
{
    var imgId = get_image(image_id);

    if(capable && MImages[imgId]) 
    {
        var theImg = document.getElementById(MImages[imgId].img_id);
        theImg.src = MImages[imgId].img_in.src;
        MImages[imgId].swapped = 2;
    }

    return;
}

// Reset all menu images to the 'OFF' state, optionally within a group
function resetMenuImages(groupname)
{
    if(groupname)
    {
        // Reset images within a group
        for(var a=0; a<=MImages.length; a++)
        {
            if(capable && MImages[a] && MImages[a].img_id) {
                // Only reset if it matches the groupname
                if( MImages[a].img_id.match(groupname) ) {
                    var theImg = document.getElementById(MImages[a].img_id);
                    theImg.src = MImages[a].img_out.src;
                    MImages[a].swapped = 0;
                }
            }
        } 
    }
    else
    {
        // Reset all images
        for(var a=0; a<=MImages.length; a++)
        {   
            if(capable && MImages[a] && MImages[a].img_id) {
                var theImg = document.getElementById(MImages[a].img_id);
                theImg.src = MImages[a].img_out.src;
                MImages[a].swapped = 0;
            }
        }
    }
    return;
}

/*
 * Functions to swap the background color of a div 
 */

var savedBG = new Array();

function changeBG(id, color)
{
    if(capable && id && color)
    {
        var objStyle = document.getElementById(id).style;
        savedBG[id] = objStyle.backgroundColor;
        objStyle.backgroundColor = "#"+color;
    }
}

function changeBackBG(id)
{
    if(capable && id && savedBG[id])
    {
        var objStyle = document.getElementById(id).style;
        objStyle.backgroundColor = savedBG[id];
        savedBG[id] = ""; 
    }
}


/*
 * Functions to open links in a new window
 */
var newwin='';

// open a popup window
function popWindow(theUrl,width,height,full) {
    // use defaults if width and height were not supplied
    var ismoz = navigator.userAgent.indexOf("Gecko");
    var isie = navigator.userAgent.indexOf("MSIE");
    var default_width = 600;
    var default_height = 450;
    var offset_width = (isie != -1) ? 4 : 0;
    var offset_height = (isie != -1) ? 0 : 0;
    var popType = (full) ? ",scrollbars=yes,resizable=yes,status=yes,toolbar=yes,menubar=yes,location=yes,directories=yes" : ",scrollbars=no,resizable=no,status=no";
    
    var popWidth = (width) ? width + offset_width : default_width + offset_width;
    var popHeight = (height) ? height + offset_height : default_height + offset_height;
    var popLeft = self.screen.availWidth/2 - popWidth/2;
    var popTop = self.screen.availHeight/2 - popHeight/2;
    
    if(theUrl) {
        if(newwin)
            newwin.close();
        newwin = window.open(theUrl,'newwin','left='+popLeft+',top='+popTop+',width='+popWidth+',height='+popHeight+popType);
    }

    return;
}


// outputs HTML for the 'random' homepage image
function writeHomeImage()
{
    var images = Array(
        "homepage_photo1.jpg",
        "homepage_photo2.jpg",
        "homepage_photo3.jpg",
        "homepage_photo4.jpg",
        "homepage_photo5.jpg",
        "homepage_photo6.jpg",
        "homepage_photo7.jpg"
    );
    var alttext = Array(
        "U.S. Department of Education's gateway to free information on preparing for and funding education beyond high school.",
        "U.S. Department of Education's gateway to free information on preparing for and funding education beyond high school.",
        "U.S. Department of Education's gateway to free information on preparing for and funding education beyond high school.",
        "U.S. Department of Education's gateway to free information on preparing for and funding education beyond high school.",
        "U.S. Department of Education's gateway to free information on preparing for and funding education beyond high school.",
        "U.S. Department of Education's gateway to free information on preparing for and funding education beyond high school.",
        "U.S. Department of Education's gateway to free information on preparing for and funding education beyond high school. (Photo copyright Jupiter Images Corporation, 2006)"
    );
    var theimage = getIncImage('homeimage', images.length); 
    var txt = '<img id="bannerimage" src="images/saotw/home/' + images[theimage] + '" alt="' + alttext[theimage] + '" />\n';
    document.write(txt);
}

// get a cookie's value
function getCookie(name)
{   
    var re = new RegExp(name + "=([^;]+)");
    var value = re.exec(document.cookie);
    return (value != null) ? unescape(value[1]) : null;
}

// set a cookie's name and value
function setCookie(name, value) 
{
    var today = new Date();
    var expiry = new Date(today.getTime() + 28 * 24 * 60 * 60 * 1000); // plus 28 days
    // no expiry = session cookie
    document.cookie = name + "=" + escape(value) + "; path=/;"; // expires=" + expiry.toGMTString();
} 


// Increment the image if they've been here before.
// Otherwise, show the first one.
function getIncImage(cookieName, arrLength)
{
    var current = getCookie(cookieName);
    if(current) {
        current++;
        if(current >= arrLength) {
            current = 0; 
        }
    } else {
        current = 0;
    }
    
    setCookie(cookieName, current);
    return current;
}