(function() {
// D3.layout.force3d.js
// (C) 2012 ziggy.jonsson.nyc@gmail.com
// BSD license (http://opensource.org/licenses/BSD-3-Clause)

d3.layout.force3d = function() {
    var  forceXY = d3.layout.force()
        ,forceZ = d3.layout.force()
        ,zNodes = {}
        ,zLinks = {}
        ,nodeID = 1
        ,linkID = 1
        ,tickFunction = Object

    var force3d = {}
   
    Object.keys(forceXY).forEach(function(d) {
        force3d[d] = function() {
            var result = forceXY[d].apply(this,arguments)
            if (d !="nodes" && d!="links")  forceZ[d].apply(this,arguments)
            return (result == forceXY) ? force3d : result
        }
    })


    force3d.on = function(name,fn) {
        tickFunction = fn
        return force3d
    }


    forceXY.on("tick",function() {
        
        // Refresh zNodes add new, delete removed
        var _zNodes = {}
        forceXY.nodes().forEach(function(d,i) {
            if (!d.id) d.id = nodeID++
            _zNodes[d.id] = zNodes[d.id] ||  {x:d.z,px:d.z,py:d.z,y:d.z,id:d.id}
            d.z =  _zNodes[d.id].x
        })
        zNodes = _zNodes
       
        // Refresh zLinks add new, delete removed
        var _zLinks = {}
        forceXY.links().forEach(function(d) {
            var nytt = false
            if (!d.linkID) { d.linkID = linkID++;nytt=true}
            _zLinks[d.linkID] = zLinks[d.linkID]  || {target:zNodes[d.target.id],source:zNodes[d.source.id]}

        })
        zLinks = _zLinks
       
        // Update the nodes/links in forceZ        
        forceZ.nodes(d3.values(zNodes))
        forceZ.links(d3.values(zLinks))
        forceZ.start() // Need to kick forceZ so we don't lose the update mechanism

        // And run the user defined function, if defined
        tickFunction()
    })

    // Expose the sub-forces for debugging purposes
    force3d.xy = forceXY  
    force3d.z = forceZ
    
    return force3d
}
})()