// This code is from the book JavaScript: The Definitive Guide, 5th Edition,
// by David Flanagan. Copyright 2006 O'Reilly Media, Inc. (ISBN #0596101996)
// Mar 14 08 rhw	Update to improve positioning if near right, bottom.

/**
 * Tooltip.js: simple CSS tooltips with drop shadows.
 * 
 * This module defines a Tooltip class. Create a Tooltip object with the 
 * Tooltip() constructor.  Then make it visible with the show() method.
 * When done, hide it with the hide() method.
 *
 * Note that this module must be used with appropriate CSS class definitions
 * to display correctly.  The following are examples.
 * 
 *   .tooltipShadow {
 *      background: url(shadow.png);  /* translucent shadow * /
 *   }
 *
 *   .tooltipContent {
 *      left: -4px; top: -4px;        /* how much of the shadow shows * /
 *      background-color: #ff0;       /* yellow background * /
 *      border: solid black 1px;      /* thin black border * /
 *      padding: 5px;                 /* spacing between text and border * /
 *      font: bold 10pt sans-serif;   /* small bold font * /
 *   }
 *
 * In browsers that support translucent PNG images, it is possible to display
 * translucent drop shadows. Other browsers must use a solid color or 
 * simulate transparency with a dithered GIF image that alternates solid and
 * transparent pixels.
 */
function Tooltip() {  // The constructor function for the Tooltip class
    this.tooltip = document.createElement("div"); // create div for shadow
    this.tooltip.style.position = "absolute";     // absolutely positioned
    this.tooltip.style.visibility = "hidden";     // starts off hidden
    this.tooltip.className = "tooltipShadow";     // so we can style it

    this.content = document.createElement("div"); // create div for content
    this.content.style.position = "relative";     // relatively positioned
    this.content.className = "tooltipContent";    // so we can style it

    this.tooltip.appendChild(this.content);       // add content to shadow
}

// Set the content and position of the tooltip and display it
Tooltip.prototype.show = function(text, x, y) {
    this.content.innerHTML = text;             // Set the text of the tooltip.
    this.tooltip.style.left = x + "px";        // Set the position.
    this.tooltip.style.top = y + "px";
    this.tooltip.style.visibility = "visible"; // Make it visible.

    // Add the tooltip to the document if it has not been added before
    if (this.tooltip.parentNode != document.body)
        document.body.appendChild(this.tooltip);
};

// Hide the tooltip
Tooltip.prototype.hide = function() {
    this.tooltip.style.visibility = "hidden";  // Make it invisible.
};

// The following values are used by the schedule() method below.
// They are used like constants but are writeable so that you can override
// these default values.
Tooltip.X_OFFSET = 25;  // Pixels to the right of the mouse pointer
Tooltip.Y_OFFSET = 15;  // Pixels below the mouse pointer
Tooltip.DELAY = 200;    // Milliseconds after mouseover

/**
 * This method schedules a tooltip to appear over the specified target
 * element Tooltip.DELAY milliseconds from now. The argument e should
 * be the event object of a mouseover event. This method extracts the
 * mouse coordinates from the event, converts them from window
 * coordinates to document coordinates, and adds the offsets above.
 * It determines the text to display in the tooltip by querying the
 * "tooltip" attribute of the target element. This method
 * automatically registers and unregisters an onmouseout event handler
 * to hide the tooltip or cancel its pending display.
 */
Tooltip.prototype.schedule = function(target, e) {
    // Get the text to display.  If none, we don't do anything
    var text = target.getAttribute("tooltip");
    if (!text) return;

    // The event object holds the mouse position in window coordinates
    // We convert these to document coordinates using the Geometry module
    var x = e.clientX + Geometry.getHorizontalScroll();
    var y = e.clientY + Geometry.getVerticalScroll();

    // Add the offsets so the tooltip doesn't appear right under the mouse
    x += Tooltip.X_OFFSET;
    y += Tooltip.Y_OFFSET;

    // Check to see if too far to the right/bottom, and move back left/top.
    if ( Geometry.getViewportWidth() - x < 200 ) x = 20;
    if ( Geometry.getViewportHeight() - y < 200 ) y = 10;

    // Schedule the display of the tooltip
    var self = this;  // We need this for the nested functions below
    var timer = window.setTimeout(function() { self.show(text, x, y); },
                                  Tooltip.DELAY);

    // Also, register an onmouseout handler to hide a tooltip or cancel
    // the pending display of a tooltip.
    if (target.addEventListener) target.addEventListener("mouseout", mouseout,
                                                         false);
    else if (target.attachEvent) target.attachEvent("onmouseout", mouseout);
    else target.onmouseout = mouseout;

    // Here is the implementation of the event listener
    function mouseout() {
        self.hide();                // Hide the tooltip if it is displayed,
        window.clearTimeout(timer); // cancel any pending display,
        // and remove ourselves so we're called only once
        if (target.removeEventListener) 
            target.removeEventListener("mouseout", mouseout, false);
        else if (target.detachEvent) target.detachEvent("onmouseout",mouseout);
        else target.onmouseout = null;
    }
}

// Define a single global Tooltip object for general use
Tooltip.tooltip = new Tooltip();

/*
 * This static version of the schedule() method uses the global tooltip
 * Use it like this:
 * 
 *   <a href="www.davidflanagan.com" tooltip="good Java/JavaScript blog"
 *      onmouseover="Tooltip.schedule(this, event)">David Flanagan's blog</a>
 */
Tooltip.schedule = function(target, e) { Tooltip.tooltip.schedule(target, e); }

Tooltip.writesomething = function(target, e) {alert(e.toString());}