/**
 * Tooltip.js: simple CSS tool tips 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.
 */
 
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 tool tip and display it
Tooltip.prototype.show = function(text, x, y) {
    this.content.innerHTML = text;             // Set the text of the tool tip.
    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 tool tip to the document if it has not been added before
    if (this.tooltip.parentNode != document.body)
        document.body.appendChild(this.tooltip);
};

// Hide the tool tip
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 writable 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 = 50;    // Milliseconds after mouseover

/**
 * This method schedules a tool tip 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 tool tip by querying the
 * "tooltip" attribute of the target element. This method
 * automatically registers and unregisters an onmouseout event handler
 * to hide the tool tip 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 tool tip doesn't appear right under the mouse.
    x += Tooltip.X_OFFSET;
    y += Tooltip.Y_OFFSET;

    // Schedule the display of the tool tip.
    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 tool tip or cancel
    // the pending display of a tool tip.
    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 tool tip 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;
    }
}

Tooltip.tooltip = new Tooltip( );
Tooltip.schedule = function(target, e) { Tooltip.tooltip.schedule(target, e); }