/* ***** BEGIN LICENSE BLOCK *****
 * Version: MPL 1.1/GPL 2.0/LGPL 2.1
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 * http://www.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is Spatial Navigation.
 *
 * The Initial Developer of the Original Code is Mozilla Corporation
 * Portions created by the Initial Developer are Copyright (C) 2008
 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 *  Doug Turner <dougt@meer.net>  (Original Author)
 *
 * Alternatively, the contents of this file may be used under the terms of
 * either the GNU General Public License Version 2 or later (the "GPL"), or
 * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
 * in which case the provisions of the GPL or the LGPL are applicable instead
 * of those above. If you wish to allow use of your version of this file only
 * under the terms of either the GPL or the LGPL, and not to allow others to
 * use your version of this file under the terms of the MPL, indicate your
 * decision by deleting the provisions above and replace them with the notice
 * and other provisions required by the GPL or the LGPL. If you do not delete
 * the provisions above, a recipient may use your version of this file under
 * the terms of any one of the MPL, the GPL or the LGPL.
 *
 * ***** END LICENSE BLOCK ***** */

/**
 * 
 * Import this module through
 *
 * Components.utils.import("resource://gre/modules/SpatialNavigation.js");
 *
 * Usage:
 *
 *
 * var snav = new SpatialNavigation(browser_element, optional_callback);
 *
 * optional_callback will be called when a new element is focused.
 *
 *    function optional_callback(element) {}
 *
 */


var EXPORTED_SYMBOLS = ["SpatialNavigation"];

function SpatialNavigation (browser, callback)
{
  browser.addEventListener("keypress", function (event) { _onInputKeyPress(event, callback) }, true);
};

SpatialNavigation.prototype = {
};


// Private stuff

const Cc = Components.classes;
const Ci = Components.interfaces;

function dump(msg)
{
    var console = Cc["@mozilla.org/consoleservice;1"].getService(Ci.nsIConsoleService);
    console.logStringMessage("*** SNAV: " + msg);
}

var gDirectionalBias = 10;
var gRectFudge = 1;

function _onInputKeyPress (event, callback) {
    
    // If it isn't an arrow key, bail.
    if (event.keyCode != event.DOM_VK_LEFT  &&
        event.keyCode != event.DOM_VK_RIGHT &&
        event.keyCode != event.DOM_VK_UP    &&
        event.keyCode != event.DOM_VK_DOWN  )
        return;
    
    function snavfilter(node) {
             
        if (node instanceof Ci.nsIDOMHTMLLinkElement ||
            node instanceof Ci.nsIDOMHTMLAnchorElement) {
            // if a anchor doesn't have a href, don't target it.
            if (node.href == "")
                return Ci.nsIDOMNodeFilter.FILTER_SKIP;
            return  Ci.nsIDOMNodeFilter.FILTER_ACCEPT;
        }
        
        if (node instanceof Ci.nsIDOMHTMLInputElement  ||
            node instanceof Ci.nsIDOMHTMLSelectElement ||
            node instanceof Ci.nsIDOMHTMLOptionElement)
            return Ci.nsIDOMNodeFilter.FILTER_ACCEPT;
        return Ci.nsIDOMNodeFilter.FILTER_SKIP;
    }
    var bestElementToFocus = null;
    var distanceToBestElement = Infinity;
    var focusedRect = _inflateRect(event.target.getBoundingClientRect(),
                                   - gRectFudge);
    var doc = event.target.ownerDocument;
    
    var treeWalker = doc.createTreeWalker(doc, Ci.nsIDOMNodeFilter.SHOW_ELEMENT, snavfilter, false);
    var nextNode;
    
    while ((nextNode = treeWalker.nextNode())) {
        
        if (nextNode == event.target)
            continue;
        
        var nextRect = _inflateRect(nextNode.getBoundingClientRect(),
                                    - gRectFudge);
        
        if (! _isRectInDirection(event, focusedRect, nextRect))
            continue;
        
        var distance = _spatialDistance(event, focusedRect, nextRect);
        
        if (distance <= distanceToBestElement && distance > 0) {
            distanceToBestElement = distance;
            bestElementToFocus = nextNode;
        }
    }
    
    if (bestElementToFocus != null) {
        //        dump("focusing element  " + bestElementToFocus.nodeName + " " + bestElementToFocus);
        // Wishing we could do element.focus()
        doc.defaultView.QueryInterface(Ci.nsIInterfaceRequestor).getInterface(Ci.nsIDOMWindowUtils).focus(bestElementToFocus);

        if (callback != undefined)
           callback(bestElementToFocus);

    } else {
        // couldn't find anything.  just advance and hope.
        //        dump("advancing focus");
        var windowMediator = Cc['@mozilla.org/appshell/window-mediator;1'].getService(Ci.nsIWindowMediator);
        var window = windowMediator.getMostRecentWindow("navigator:browser");
        window.document.commandDispatcher.advanceFocus();

        if (callback != undefined)
           callback(null);
    }
    
    event.preventDefault();
    event.stopPropagation();
}

function _isRectInDirection(event, focusedRect, anotherRect)
{
    if (event.keyCode == event.DOM_VK_LEFT) {  
        return (anotherRect.left < focusedRect.left);
    }
    
    if (event.keyCode == event.DOM_VK_RIGHT) {
        return (anotherRect.right > focusedRect.right);
    }
    
    if (event.keyCode == event.DOM_VK_UP) {
        return (anotherRect.top < focusedRect.top);
    }
    
    if (event.keyCode == event.DOM_VK_DOWN) {
        return (anotherRect.bottom > focusedRect.bottom);
    }
    return false;
}

function _inflateRect(rect, value)
{
    var newRect = new Object();
    
    newRect.left   = rect.left - value;
    newRect.top    = rect.top - value;
    newRect.right  = rect.right  + value;
    newRect.bottom = rect.bottom + value;
    return newRect;
}

function _containsRect(a, b)
{
    return ( (b.left  <= a.right) &&
             (b.right >= a.left)  &&
             (b.top  <= a.bottom) &&
             (b.bottom >= a.top) );
}

function _spatialDistance(event, a, b)
{
    var inlineNavigation = false;
    var mx, my, nx, ny;
    
    if (event.keyCode == event.DOM_VK_LEFT) {
        
        //  |---|
        //  |---|
        //
        //  |---|  |---|
        //  |---|  |---|
        //
        //  |---|
        //  |---|
        //
        
        if (a.top > b.bottom) {
            // the b rect is above a.
            mx = a.left;
            my = a.top;
            nx = b.right;
            ny = b.bottom;
        }
        else if (a.bottom < b.top) {
            // the b rect is below a.
            mx = a.left;
            my = a.bottom;
            nx = b.right;
            ny = b.top;       
        }
        else {
            mx = a.left;
            my = 0;
            nx = b.right; 
            ny = 0;    
        }
    } else if (event.keyCode == event.DOM_VK_RIGHT) {
        
        //         |---|
        //         |---|
        //
        //  |---|  |---|
        //  |---|  |---|
        //
        //         |---|
        //         |---|
        //
        
        if (a.top > b.bottom) {
            // the b rect is above a.
            mx = a.right;
            my = a.top;
            nx = b.left;
            ny = b.bottom;
        }
        else if (a.bottom < b.top) {
            // the b rect is below a.
            mx = a.right;
            my = a.bottom;
            nx = b.left;
            ny = b.top;       
        } else {
            mx = a.right;
            my = 0;
            nx = b.left; 
            ny = 0;	    
        }
    } else if (event.keyCode == event.DOM_VK_UP) {
        
        //  |---|  |---|  |---|
        //  |---|  |---|  |---|
        //
        //         |---|
        //         |---|
        //
        
        if (a.left > b.right) {
            // the b rect is to the left of a.
            mx = a.left;
            my = a.top;
            nx = b.right;
            ny = b.bottom;
        } else if (a.right < b.left) {
            // the b rect is to the right of a
            mx = a.right;
            my = a.top;
            nx = b.left;
            ny = b.bottom;       
        } else {
            // both b and a share some common x's.
            mx = 0;
            my = a.top;
            nx = 0;
            ny = b.bottom;
        }
    } else if (event.keyCode == event.DOM_VK_DOWN) {
        
        //         |---|
        //         |---|
        //
        //  |---|  |---|  |---|
        //  |---|  |---|  |---|
        //
        
        if (a.left > b.right) {
            // the b rect is to the left of a.
            mx = a.left;
            my = a.bottom;
            nx = b.right;
            ny = b.top;
        } else if (a.right < b.left) {
            // the b rect is to the right of a
            mx = a.right;
            my = a.bottom;
            nx = b.left;
            ny = b.top;      
        } else {
            // both b and a share some common x's.
            mx = 0;
            my = a.bottom;
            nx = 0;
            ny = b.top;
        }
    }
    
    var scopedRect = _inflateRect(a, gRectFudge);
    
    if (event.keyCode == event.DOM_VK_LEFT || 
        event.keyCode == event.DOM_VK_RIGHT) {
        scopedRect.left = 0;
        scopedRect.right = Infinity;
        inlineNavigation = _containsRect(scopedRect, b);
    }
    else if (event.keyCode == event.DOM_VK_UP ||
             event.keyCode == event.DOM_VK_DOWN) {
        scopedRect.top = 0;
        scopedRect.bottom = Infinity;
        inlineNavigation = _containsRect(scopedRect, b);
    }
    
    var d = Math.pow((mx-nx), 2) + Math.pow((my-ny), 2);
    
    // prefer elements directly aligned with the focused element
    if (inlineNavigation)
        d /= gDirectionalBias;
    
    return d;
}